EDUCATION & FAQ'S

STAR SEAL, Inc. is a recognized leader in the pavement maintenance industry. We provide professionals in this business with the best products and technology.

STAR (Specialty Technology And Research), Inc. is one of the largest manufacturers of sealcoatings and a comprehensive range of products used in the pavement maintenance industry. Sealcoatings are specialty coatings that've been used in the U.S. since late 1950’s for the protection and preservation of asphalt surfaces; commercial parking lots, home driveways, schools, airports, gas stations, fast food restaurants, etc.

Introduction to STAR

 Understanding Sealcoatings

Sealcoatings have been an indispensable part of asphalt pavement maintenance programs for the past 6 decades; therefore, it is logical for the sealcoating professionals to have an insight into the basics of their composition, manufacturing, and properties. Sealcoatings are specialty coatings, which are used for the protection and preservation of asphalt surfaces. They act as a true “Barrier coat” between asphalt surfaces and the destructive elements that attack those surfaces (mainly the sun’s ultraviolet rays, gasoline, oils, salts, grease/fats, etc.). The very term “sealcoating” means keeping the redeeming properties of asphalt (like waterproofing and flexibility) sealed in so as to prolong the pavement life and preserve its functional properties. After all, your pavement is a sizable investment and it has been technically acknowledged that Sealcoating extends the life of a sound pavement by more than 300%, at 1/3rd the cost of pavement replacement.

In appearance, sealcoatings are thick semi-fluid (like house paints), dark-chocolate brown colored, water-based coatings. They are essentially fine dispersions of binders (commonly refined tar or asphalt), clays, fillers, and specialty chemicals in a medium of water. The four major components in sealcoatings are described below:

Binder – It is the backbone of sealcoating compositions, the component that is responsible for imparting protection, preservation, and beauty while bonding tenaciously to the asphalt pavement.

Clay and Fillers – impart tensile strength, hardness, and abrasion resistance. Selection of the right clays and also regulating the amount of those fillers are imperative to maintain the proper balance between the toughness and flexibility of the sealcoating for its proper functioning.

Water – is the medium in which all the ingredients stay stably dispersed and is the reason for a sealcoatings ease in handling, application, and storage.

Specialty Chemicals – are added to perform specific functions e.g. water repellency, flexibility, specific resistance to salts and petrochemicals, while also maintaining the physical stability of the sealcoating.

There are two major types of sealcoatings:

Refined Tar-Based sealcoatings (RTS) are based on RT-12, a highly refined grade of coal tar, which, inturn is generated during the conversion of coal into coke for steel metallurgy. RT-12 is composed of numerous very stable chemicals that are not affected by the destructive elements of weather, sun’s ultraviolet rays (UV), salts, gasoline, oils, fats and other petrochemicals. RTS has been the workhorse of the industry for several decades and their properties and compositions are fully delineated in many specifications.

Asphalt Emulsion-Based Sealcoatings (AE), are based on asphalt and are formulated either using hot asphalt (AC) or pre-emulsified asphalt. AE coatings originated on the west coast, primarily this was due to the unavailability of refined tar in that area. Coal and steel mills were primarily located east of the Rockies. Although the AE based sealcoatings generally lack resistance to petrochemicals (gasoline, oils, fats, etc.), they work very well in maintaining the surface integrity of asphalt pavements and keep cracks from appearing. Over the years, the performance of AE coatings has been fortified with chemicals and specialty rubber polymers to enhance their overall performance.

How are the sealcoatings made?

There are two commonly used methods for manufacturing sealcoatings, both methods yield sealcoatings with comparable performance properties.

The Batch Process involves adding formula ingredients individually in the right sequence and grinding them into a fine dispersion in a high-speed disperser (HSD). The major benefit of this process is the excellent control over the processing and the quality of the sealer.

The Continuous Process or Colloid Mill Process involves feeding a continuous stream of materials into the mill where they are subjected to a grinding action much like a flour mill. This process requires highly skilled batch operators to achieve batch-to-batch consistency. The major benefit of the Colloid Mill process is the high production rate.

Important Notes:

Sealcoatings shall be applied to sound, properly constructed asphalt pavements that are free from defects, according to manufacturers or project engineers detailed instructions. Meet all applicable specifications; FAA, ASMA, ASTM D-5727-00 (Formerly Federal Specification RP-355e), and commercial specifications.

The Applicator must read the safety data sheet on the products and observe all precautions for both personal and environmental safety. NEVER allow the uncured sealer to be washed into the bodies of water. Washings from all tools and equipment shall be collected and disposed of according to applicable local, state and federal regulations.

Site Survey, Surface Preparation, Cleaning and Priming

Why Surface Preparation and Priming Is Important

Why bother cleaning the asphalt…?  Because a sealcoating application will NOT stick if the surface is not properly prepared and YOUR reputation will likely suffer if the job doesn’t perform as promised!  It doesn’t matter what type of coating or mix design – If the asphalt surface isn’t clean – It isn't going to bond.

Why Asphalt Sealer Does or Does Not Bond to a Surface

Knowing when NOT to sealcoat could be one of the keys to your success. A good understanding of asphalt surfaces themselves, sealcoatings and why they work, the effects climate has on the curing process, and generally, best practices for preparing the surface to accept the sealcoating will help you know when, and when not to do an application.

You should understand how to do a “water break free” test on newer asphalt pavement surfaces. Conversely, you should know when an asphalt pavement surface is too old and badly oxidized, or the aggregate is too polished, to allow the coating to properly adhere to the surface.

Climate will play a big role in the success of the final product and a good applicator will be able to communicate the impact that inclement weather will have on a job.

Know Your Site and Potential Obstacles That May Cause Problems

Being a manufacturer ourselves, we have the unique position of being the sounding board for applicators who are complaining about a job or telling stories about something that they had to do to overcome while facing a bad situation. We have heard all kinds of horror stories about things that have tripped up applicators. Some of the more obvious are:

 •  Forgetting to have the sprinklers shut down on the property – Have it understood with your client that sprinklers on the property should be SHUT-OFF two (2) days prior to the application & they should be kept OFF for two (2) additional days AFTER you are done with the Job. We STRONGLY recommend that you address the sprinkler issue in the contract! Consider something along the lines that if this does not get addressed, additional mobilization charges may apply and let them know how much those charges are. That additional expense above & beyond the contract may just be the thing that clicks in their mind that this Is IMPORTANT!

 •  Proper Site Survey – Not doing a proper site survey and finding a lot more work than you intended when you get there can kill your profits or could influence your judgment and lead you down a path that cuts corners and could hurt your reputation. With today’s technology, many people sit back in their office and use Google Earth to assess a property for a proposal – remember Google Earth's maps may be several years old and may not show the true, current condition, of the site. Proper planning is yet another key to your success.

 •  Not paying close attention to the weather and the potential for rain – There are more horror stories pertaining to weather than about anything else we get to hear. A rain event within a few minutes or even a few hours can lead to disastrous results. Environmental concerns, sealer splashing up onto buildings and cars, and ultimately premature failure of the coating itself are some of the bigger issues a rain event can cause. Pay extra attention to the day's weather forecast, and get an app for your smartphone that has a weather radar feature, that way you can see what’s coming in real time.

•  Landscaping and edging issues – If you go to the site (which you all should be doing) check the asphalt edge on the lot for overgrown grass or any serious amount of sand, dirt, or muck built-up. Bring these issues to the attention of your client and ask them to have their lawn maintenance service address this issue before you arrive to do the job. Talking to the customer about the issue prior to performing any services will help to avoid any unnecessary surprises should there be an issue the day you show up to do the application.

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•  Tree sap – Yes, tree sap. If the lot is lined with trees or there are trees hanging over the asphalt surface then you might see problems down the road that are unexpected. Things like the sealcoating flaking off and general adhesion problems that are uncharacteristic of your normal applications. Tree sap is one of those things that gets overlooked. Trees like olive, maples or pines on the site can cause sap problems. Trees can leave a fine mist of tiny sap particles onto the asphalt surface. This one has baffled more than a few people. Sap will cause the sealer to release from the asphalt surface. If you have visible tree sap on the lot it will have to be power washed off, or primed much like an oil spot.

The Mechanics of Site Preparation

Let us get into the mechanics of preparing your site now that we have laid the proper foundations for a successful job site survey.

SURVEY – Take a good look around and assess the work to be done vs. the instructions you have from the job costing bid. If you see something that is unexpected and will likely cause a problem – deal with that immediately. Call the dispatcher or your office and tell them immediately that something is not as it was supposed to be. If you are an independent – then immediately contact the client and tell them that things are not as initially quoted and an adjustment will need to be made.

MOISTURE – Is the pavement properly dry? You might show up while sprinklers were just on or maybe right after a rain event, and there is visible water on the asphalt surface. You are going to need a good blower and a squeegee or brush to move the water around and then allow the asphalt surface sufficient time to dry as much as possible. You need to wait until the surface is visibly dry and there is no water ponding on the surface. Too much moisture held in the surface will DEFINITELY interfere with your coating being able to cure & maintain it’s longevity and this will likely result in tracking or a failure of the coating to bind properly!

ASSESS – Think about where you will start the work and where you will end up when you are finished. No sense moving around too many times and wasting time and energy. Beware of working yourself into a corner, don’t laugh, it has happened to some people! Spend a minute planning your movements with your crew and make sure they are all on the same page. DON’T OVERLOOK SAFETY for your crew – Before any work begins you should make sure they ALL have the necessary protective gear available to them and that they are using that gear. Lastly, make sure the site is secured, traffic is properly controlled, and no one can mistake that the area is actually closed off to car and foot traffic.

REPAIR – Address the cracks and potholes. Cleaning and treating the cracks can be accomplished while the rest of the lot's surface is being cleaned and swept. Hitting these areas right away will allow the crack filler proper time to cure before you begin the process of sealcoating. Having sufficient people in your crew to do these kinds of things simultaneously will make the time on the property much more efficient.

TREAT – Oil-Spot Primer – A seal coaters best friend. You should always have a ready-to-use oil spot primer on your truck. This stuff can cure all sorts of pavement surface issues. Of course, the main purpose of a primer is for oil spots, but it works wonders on other issues. After the pavement around a spot has been properly cleaned (broomed & blown off) apply primer on any oil spots or other areas that have been discolored or stained. Cut in entrances, exits and cul-de-sac’s with primer to ensure the sealcoating properly bonds to the polished aggregates in that area.

CLEAN, CLEAN, CLEAN – Get a hand-held edger, a weed eater, good high powered blower and go to work! You have got to spend the time to broom & blow off ALL of the dirt, sand, and debris on the asphalt. Not just the stuff you can see on the top of the surface, you got to get down into the profile of the asphalt where the dirt is stubborn and hides between the stone in the asphalt. Be sure have every inch of the asphalt hit by a brush and the blower. You may have to get a wire broom out & hit the difficult spots. And, don’t forget the corners & behind the car stops. If you have the manpower you should have one guy brooming and brushing and the other guy operating the blower & blowing the debris out of the way. This is also where you might have to do the landscape edging where the grass meets the lot. Nothing looks worse then what happens after the coating is applied over grass that has been edged AFTER you leave.

Yes, we know it is HARD work, but it has to be done! Failing to do this step properly can lead to disastrous results. Any sealcoating you lay down will stick to whatever it is applied to, and if that material is dust and dirt, not the asphalt surface itself, then it will lift right up as soon as it is disturbed.

READY FOR APPLICATION – After all this preparation work your crew will welcome the opportunity to finally get to the sealcoating step! Even though the reason you are on the lot is to apply a sealcoating, it is the preparation that makes or breaks the final success of the job you are doing. Skimp on any of the preparation steps and you will likely pay a price for it after you are done and gone. The companies who have been around for years, the ones with the best reputations, know this well and their work reflects it… So does their customer loyalty for that matter!

If you chose not to do these things properly then you can expect a decrease in longevity of the coating you just applied. You will likely have an unhappy customer, potentially a call back to the site – which ultimately will come out of the bottom line – and that means less money in YOUR pocket.  For the extra few minutes you spend doing it right – doing it wrong can cost you a lot more.

The list of positive results is much shorter, however, positive results make you more money in the long run. A quality job with a happy customer, in this current economical climate, is tremendously important. Do these things to stay financially viable for your family and the families your company supports. Be known in your area as the BEST! Never forget, keeping an existing customer is a heck of a lot cheaper than trying to get a new one!

Adhesion of Sealcoatings to Polished Aggregates in Asphalt Pavements

The very basic requirement for a sealcoating to bond firmly to an asphalt surface is that the surface shall be sound, dry, clean, and have an acceptable degree of surface profile.

What is Surface Profile?

Surface profile simply means if the surface is smooth, rough or in between. The surface profile of a pavement depends on the pavement mix design, type and quantity of the asphalt binder (AC type), and the type of the aggregate used in the mix design. Coarse aggregates produce a rough profile and finer aggregates produce a denser and smoother profile.

The paving method and the time of the year may influence the profile as well. For example, the surface may look too coarse or irregular if the roller compaction were inadequate or the weather was too cold for the proper knitting of the aggregates under the roller compaction.

Previous sealcoatings and the frequency of sealcoating. Sealcoatings fill the surface profile of the asphalt pavement and make them uniform. The use of sand in sealcoating mix designs is a common practice to impart a uniform textured appearance to the surface.

Why does the sealer fail prematurely, in some areas?

It is understandable that sealer will not last as long in high traffic areas as in low traffic areas. It has, however, been noticed that sealcoatings may wear out prematurely in some areas that handle steady traffic (i.e. traffic lanes, exits, entrances, etc.). If this is the case on your property, the sealcoating may be gone from such areas, in a matter of months.

If the overall surface profile was also proper at the time of the application then what caused the failure?

In most instances, the failure is due to the loss of adhesion of the sealcoating from the top of the aggregates that become polished (smooth as glass) on the top. Such aggregates are called “Polished Aggregates” and they are too smooth on the surface to bond to the sealcoating. It is just like painting a mirror. All coatings need a certain degree of surface profile of the substrates to establish bonds.

In addition to traffic frequency, some aggregates are easily polished under normal traffic and are generally not used for paving. Their use in paving can potentially increase slipperiness. That is the reason why only “non-polishing aggregates” are used for road paving. It would be a good idea to check if the right type of aggregate was used on the problematic asphalt surface.

What to do for polished aggregates?

Roughen the surface by sandblasting, grinding or extensive wire brushing. These may be too expensive and time-consuming.

Prime the areas of high traffic (drive lanes, exits, entrances, etc) with a specialty primer that will soak into the aggregate and bond to the surface. Priming provides a new surface for the sealcoating to bond. Primers are generally water-based coatings, with built-in polymers and surfactants that help them to penetrate into the polished aggregates to create the adhesive surface for the sealcoating. Priming is a very cost-effective method to ensure adhesion and they are safe to handle and easy to apply.

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CONCLUSION

For proper adhesion, it is essential that the asphalt surface be dry, clean, free of contaminants, and have an adequate surface profile. The premature sealer failure has been observed to be essentially adhesion failure of the sealer from the top of the “Polished Aggregate”. Such aggregates are created either by the nature of the aggregate or traffic volume. In either case, the aggregate surface is too smooth to bond. The surface of such aggregates has to be rendered rough or suitable for bonding through priming. Priming provides a highly cost-effective solution to the premature sealer failure problem.

Sand or Aggregate in Sealcoatings

Select grades of clean angular, quartz sand or aggregate are commonly added to sealcoatings for the following benefits. Boiler slag or coal slag, which is an amorphous mixture of iron, aluminum and calcium silicates, is available under the brand name Black Beauty is also commonly used with sealcoatings.  In the following paragraphs, the descriptions mentioning sand, largely apply to Black Beauty as well.

• Improved traction and skid resistance.

• Improved longevity.

• Hiding minor surface defects and filling hairline cracks,

• Uniform textured appearance, reduction in sun glare and streak-free appearance.

Sand has a certain degree of porosity, therefore, its own need to absorb liquids. When added to the sealer in a mix design, it absorbs the binder (refined tar or asphalt) and water from the sealer. The amount of sand in the sealer must be limited to the extent where it does not absorb excessive amounts of the binder from the sealer, otherwise, the binder will not be available to bond to the pavement and form a continuous film. The limit is reached at about 5 lbs. of sand per gallon of sealer. At this level, binder and filler in the sealer system are still in balance to expect optimum performance. Sand loading exceeding 5 lbs. will rob the binder from the sealer, thus rendering the sealer film, porous, brittle, poor in adhesion and resistance to chemicals, salts, fuel, etc.

Recommended Sand Amounts

For normal textured pavements:  2 to 2.5 lbs. per gallon of undiluted sealer.
For rougher pavements:  Sand loading of 4 to 4.5 lbs. per gallon of undiluted sealer is used to accomplish proper texturing and filling of the surface profile. Sand shall be used in recommended quantities, per sealer manufacture’s recommendations.

Sand Musts:  Clean, water-washed, pure silica type, with an angular and irregular particle shape. Free of contaminants, metals, clay, trash and organic matter. Of fineness 50-75 MESH AFS (American Foundrymen Specification).

Too Little Sand or No Sand:  You will not have above-mentioned benefits.

Too Much Sand:  The sealer may become brittle, lose flexibility and its resistance to chemicals, fuel, salts, etc.

Sand Gradation (size) – Why is it so important?

In selecting sand, it is imperative that the average particle size be very close to the cured film thickness of the sealer. The sand particles should be at least 2/3 embedded in the cured sealer film. For example, a sealer applied in two coats (at 25% dilution) will dry to approximately 11-13 mils, therefore, the AFS of the sand shall be around 50-70.

One of the most common ways of measuring and specifying particle size of sand is by the use of sieves, often called meshes or screens.

How do they work? Particle sizes are separated industrially or in the laboratory by passing material over sieves that have an opening of specified sizes.

These sieves can range from extremely coarse devices that look like sewer grates for large size separations [range of inches] to sieves that look very much like window screens for middle separations [millimeter], to very fine woven screens for fine separations [~50 micrometers]. Separation can be either dry or wet. Wet screening is more efficient, but drying of the product adds cost.

What do the numbers mean?

Each sieve has a number, such as 20 mesh, 50 mesh, 200 mesh, 325 mesh. This number relates to the number of openings in the screen per inch.

Lower the sieve number, larger is the screen opening and coarser the particles passing through it, e.g. a 20 mesh sieve has a screen opening of 33.5 mils, whereas a 50 mesh sieve has screen opening of 11.7 mils. Modern practice is to refer to the screen by the size of the opening in microns, but for our purpose mil unit suits better because we denote the cured film thickness in mils.
 

Some Units:
1 millimeter (mm) = 1000 microns
1 millimeter  =  39.37 mils.
1 mil = 1/1000 of an inch
1 micron = 0.03937 mils.

Sand/Aggregate Selection

Sand is supplied in different grades, classified according to their average particle size and denoted as AFS (American Foundrymen Specifications) numbers. For example, AFS 60 grade has the majority of the particles passing through a 60-mesh screen. Sieve analysis of one of the recommended grades, No 1, dry sand from central silica follows:

U.S. SIEVE        Screen Openings            % RETAINED    % Cumulative retained
 

( mm)              (mils)
20 Mesh         0.850              33.46              –                                       –
30 Mesh         0.600              23.62            1.50                                   1.5
40 Mesh         0.425              16.73             7.00                                  8.5
50 Mesh         0.30                11.81               22.0                                 30.5
70 Mesh         0.212                8.35             23.0                                 53.5
100 Mesh       0.15                  5.91               22.5                                76.0
140 Mesh       0.106                4.17               14.5                                 90.5
200 Mesh      0.075               2.95              6.50                                97.0
PAN                                                               3.0                                  100

Sand/Aggregate shall not have too many fines (i.e. finer than 200 mesh) 

Sand particles absorb water and binder from the sealer and the degree of absorbency increases with the surface area. The surface area increases with the number of particles, for the same weight of sand. For example, one pound of 200-mesh sand has 4 times the surface area of Sand at 50 mesh. Sand with too many fines will soak up excessive binder amounts from the sealer, thus resulting in poor performance of the sealer.

Too many coarse particles, coarser than 30 mesh.

Too many coarse particles will not have enough fines to effectively interlock, knit and reinforce the cured sealer film. Additionally, they will not be properly anchored in the cured sealer film and are likely to be dislodged from the cured film under traffic. The loose sand thus dislodged, acts as a sandpaper on the cured sealer film and may cause premature failure.
Ideally, the major proportion of sand particles in a particular grade should fall within 40 to 100 mesh to properly interlock without placing excessive demands on the binder (for surface absorption and saturation of the sand particles). Sand with medium fineness between 50 to 70 AFS rating produces the best results.

Do NOT use these types of Sand or Aggregate

1.  Recycled sand from steel sandblasting. It has lots of iron and will cause brown rust streaking of the sealer.

2. Foundry spent sand. It may contain various metals that may interfere with the stability of the sealer and its performance. Additionally, foundry Sand becomes very fine and has excessive absorbance for the sealer. Sealer thus absorbed by the foundry sand may not be sufficient to bond to the pavement and adhesion failure may result.

3. Beach sand, (unwashed) because of the very high salt content that will make the sealer film water sensitive, which may lead to premature wear and tracking.

4. Any recycled sand which may contain harmful metals and organic compounds.

Use only water washed, clean, angular silica sand or aggregate.

Use washed dry silica sand /aggregate that shall be angular, free of dust, trash, clay, organic matter or other contaminants and meet the gradation requirements per sealcoat manufacturers specifications.

TECHNICAL NOTE:
SAND ROLL-OUT IN SEALCOATING

The term sand roll-out generally describes all situations where sand/aggregate does not stay in uniform suspension, especially during the application or in cured films. They may appear as unsightly streaks or as free sand released from the cured coating.
Sandroll out may be caused by the deficiencies in the sealcoating mix, the application conditions or a combination of both. Let us consider two broad categories.

Mix design deficiencies:

The mix may be too thin to support the sand suspension, resulting in a streaky appearance of the cured film.

An excessive amount of water in the mix will produce a thinner dry film that will be too thin to hold the sand and keep them properly anchored in the cured film. Under such conditions,  sand particles will be sticking out of the cured film of the sealer and liable to be knocked off by traffic. It results in premature wear of the sealer.

The sand aggregate quantity may be too high to be suspended by the mix. It results in bunching of the sand during application and an uneven appearance after full cure. These deficiencies will be will be aggravated due to a thin viscosity of the sealer.

Sand/Aggregate may be too coarse. The average fineness of the sand/aggregate is recommended to be within 50-70 mesh AFS. Sand particles that are too large will be sticking out of the cured film of the sealer and are very liable to be knocked off by traffic. It results into premature wear of the sealer.

Remedy:

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• Use the mix design recommendations from your manufacturer

• Avoid excessive amounts of water

• Apply at the recommended coverage rates

• Understand the components of the various terms (ratios, dilution rates, etc.) in the mix design

Ambient and curing conditions

Under hot (over 100 º F) pavement and ambient conditions, the water may flash off the sealer film too fast to allow the film to coalesce properly. In visual terms, it means egg on a frying pan.

The water evaporates instantly, immobilizing the film.  It results in:

• Poor film formation. The film formed under such conditions is full of voids and has poor resistance to the elements of destruction.
  Sand release from the cured film due to the lack of opportunity for sand particles to interlock and reinforce the cured film. The way sand particles work in the sealcoating is that during the initial drying process they (sand particles) move around in the wet film and interlock. By interlocking they strengthen the film.  If the film dries too quickly they do not get this opportunity to interlock and are liable to be released.

Remedy:  

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• Fogging the pavement (without puddling) is the preferred method to cool down the pavement.

• If fogging is not possible add an additional 3-5% of water to the mix. The amount of water shall always be calculated on the amount of sealer in the tank. For example, if you have 100 gallons of sealer, 25 gallons of water and 200 lbs. of sand in your tank,

• 3-5 % additional water will mean adding 3-5 gallons of water.

Film Formation Mechanism and the Importance of Proper Cure Conditions

The majority sealcoatings are water-based coatings, based on refined coal tar or asphalt cement (AC). Such coatings are safe to handle, store, and provide years of projection to asphalt surfaces when applied properly and allowed to cure under the right ambient conditions. In this article, we will discuss the film formation mechanism and the desired ambient conditions for the initial and final cure of sealcoatings.

Water is the major component of sealcoating (i.e. the sealer supplied as a concentrate contains typically 60% water by volume). After adding 30% water to 100 gallons of the concentrated sealer, the water proportion increases to nearly 70%, by volume. Sealcoatings, like other water-based coatings, cure by releasing water into the atmosphere and reach their full strength after the release of all the water. It is beneficial to understand how the water is released from the film and the influence of the pavement and ambient conditions on the release of water and cure of the sealcoating films.

Sealcoating professionals are well versed in these details and all make possible efforts to comply, recognizing that deviations may result in poor performance and premature failure. Even the very best of the coatings if applied and cured improperly is liable to fail.

For the optimum performance, sealcoatings should be;

Mixed accurately per the mix design as agreed for the project (i.e. proper dilution with water, sand loading, additive content, etc.). Applied at the proper coverage rate, (expressed either in gallons/sq. yard or sq.ft./gallon), on a properly cleaned and repaired surface. Allowed to cure “thoroughly” or “sufficiently” under a set of pavement and ambient weather conditions that will allow the coating to attain its optimal firmness.  These “ideal” conditions are simply the ambient and pavement conditions that are specified by the manufacturers and accepted by the industry under which the sealcoatings shall be applied and allowed to cure.

Some Sealcoating Basics

Sealcoating, based on either asphalt or refined coal tar, is stable dispersions of various ingredients in water.

The major ingredients are:

Binder.  The refined coal tar or asphalt cement (AC) is called the binder in sealcoatings. As you may know, both asphalt and coal tar are thermoplastic materials, meaning that they soften and melt at higher temperatures (about 100°F to 180°F) and become hard and brittle to cooler temperatures (below 60°).

The binder is the backbone of sealcoating. It is the ingredient that protects the asphalt pavement. In the wet state (uncured), sealer contains a fine dispersion of binder particles in the range of 2 to 5 microns (human hair is approx. 25 microns or 1 mil), in either spherical or elongated cigar shapes. Upon full cure the binder forms the continuous film, tightly holding all the fillers and sand/aggregate.

Clay. Clay fillers and aggregates. To impart proper toughness to the sealcoating film and counteract the tackiness of the binder at elevated surface temperatures.

Specialty chemicals. Such as surfactants and emulsifiers to stabilize the sealcoating systems.

Water. As the medium. In most sealcoatings, water constitutes the major component, more than 60% by volume.

The Film Formation Mechanism

Sealcoatings, like all water-based coatings, attain full cure through the loss of all the water from the wet film. As the water leaves, the volume of the wet film shrinks. The shrinkage in volume is directly proportional to the amount of water (by volume) in the mix.  For example, if the mix design has 70% water by volume, the wet film will shrink by 70%, or down to the 30% of the original volume.

The evaporation of water from the wet film produces a steady turbulence in the film and forces the suspended particles into a closer proximity. The film becomes progressively denser, thus forcing the binder particles to touch one another and fuse into a continuous film, encapsulating the filler particles in the process. Simultaneously, the excess binder in the matrix allows the film to effectively bond to the pavement surface.

Descriptions such as the full cure, final set or optimum strength convey the message that sealcoating has reached its full strength and is capable of performing its task, as a protective coating. During the curing process, all water-based coatings, including sealcoatings, pass through various stages of water evaporation from the applied film. 

Properly cured sealcoating form a continuous film, free of voids or imperfections, which stop water, chemicals, salts, etc. from penetrating and damaging the asphalt pavement underneath. Understandably, any deficiency in the curing process will not allow the binder to fuse properly and leave voids in the film, thus resulting in inferior performance or failure. First, it attains initial drying when the film becomes “tack free” to the light touch, then it becomes firmer (about 90% cured) to take light pedestrian traffic, and finally, full firmness to withstand light vehicular traffic, when all the water (99%) is lost through evaporation.

The wet sealcoating film is not one solid film but a composite of several layers of very thin films (imagine a sheet of plywood). Like most water-based coatings, sealcoating dries, in successive layers, from top to bottom. As each layer dries, it shrinks in volume, becomes tight and relatively impervious to water vapor, therefore, impeding the evaporation of water from the bottom layers.
 

The first 80% to 85% of the film dries relatively fast, but the release of the last 10% to 15% of water becomes difficult and requires the right set of ambient and pavement conditions. It’s a fact that the release of water from the bottom layers of most water-based coatings becomes progressively difficult as the film cures. For optimum performance, all water must leave the film: 80% to 90% is not good enough. The uncured 10% to 15% of the coating will be torn or dislodged if traffic is allowed on it too soon. The percentages are mentioned here only to explain the phenomenon. They will, of course, vary with material and mix designs (i.e. mix designs with fillers and/or aggregates will dry faster than sealcoatings coatings without them).

The Cure Conditions

The conditions described below play the decisive role in determining the thoroughness of the overall cure process, therefore, sealcoating performance. These conditions are the recommendations of the industry and its research association, Pavement Coatings Technology Center (PCTC), the University of Nevada at Reno. 

These factors are important in obtaining the optimum cure of sealcoatings.

1. Temperatures: Both Ambient and Pavement

Sealer should not be applied unless the pavement temperature is at least 50°F and the air temperature is 50°F and rising. As described in the foregoing sections, the fusion of the binder particles (in the sealcoating) to form a uniform and continuous film depends on their ability to soften under the ambient and pavement temperatures. The process of fusion is greatly enhanced at higher temperatures; say 75°F to 85°F. Conversely, it is significantly reduced at temperatures below 50°F. Let us review the extremes; cold and hot temperature applications

Cold Application and Cure Conditions

When sealcoating is applied below 50°F, tar (or asphalt particles do not soften and form a continuous film, thus leaving clay and filler particles uncoated. The color of the sealcoating cured under such conditions usually turns out grey and blotchy in appearance and never returns to its normal slate black appearance even at higher pavement temperatures, at a later date, because the temperature of the pavement normally does not reach high enough to re-melt the binder particles and force them to flow and form a continuous film. Even if the pavement temperatures reach high enough, still it will not assure proper fusion. The binder particles will melt but will not have the capability to flow and envelope the clay and filler particles already set in a rigid matrix. Needless to say, sealcoating cured under cold weather conditions lack the integrity and sealcoating properties that are normally expected.

Hot Applications and Cure Conditions

Sealcoating applications under hot temperatures can be equally problematic. Sealcoatings should not be applied under the summer sun (90°F ambient) without first cooling the surface with a fine mist of water, also called “fogging”. Water should only dampen the pavement, without leaving puddles.

If applied to a hot pavement without “fogging” it, the sealcoating film almost gets “baked” as soon as it hits the pavement.  The sudden loss of fluidity of the film, due to flashing of water, immobilizes binder particles and prevents them from fusing and forming a continuous film. Devoid of the proper fusion process, binder particles do not effectively envelop the clay and filler particles in the sealer film. Additionally, binder particles under such conditions do not reach the hardness imparted by the clay and fillers and continue to stay sticky and soft which could lead to lead to a problem called “tracking”, where the sealer is tracked on the floors or carpets, etc.

2. Humidity or Relative Humidity (R.H.)
 

Humidity or Relative Humidity (R.H.) of the atmosphere plays a significant role in the cure mechanism. It directly influences the rate of water loss from the sealcoating film.
Relative humidity (R.H.) is the ratio of the actual moisture content of the air, at a specified temperature, to its total capacity. For example, 50% R.H. means that only half of the air’s total capacity to hold water has been used and it is capable of absorbing another 50% of moisture or vapor from the surroundings.
Conversely, 90% means that it has very little capacity left (only 10%) to absorb additional moisture, thus drastically slowing down the release of water. from the sealcoating film. The sealer film will release only that much amount of water that can be accommodated by the atmosphere. The atmosphere and the surrounding environment can be thought of as a sheet of paper towel:  when dry it will soak up the spill but will not mop up if the towel is too wet.
Sealcoatings, understandably, will cure faster at a lower humidity than at higher humidity. Under highly humid conditions, sealcoatings shall be allowed longer drying time before the application of the subsequent coats and finally opening to traffic.

3. Wind Velocity
 

The drying and cure times specifications do not take wind velocity or air movement under consideration, however, it is a known fact that air movement, especially under highly humid conditions, helps sealer dry faster than without any air movement. A light breeze assists in the dissipation of the water and volatiles from the immediate vicinity. Conversely, under low humidity conditions (below 20-25%), the air movement may cause the sealcoat to dry a bit too fast.

SEALCOATING MIX DESIGNS

 Sealcoatings, both refined tar (RTS) and asphalt emulsion (AE) based, are supplied as concentrates (undiluted). Prior to application, sealcoatings must be mixed with water, silica sand and additives (as recommended) for proper application consistency according to the manufacturer’s recommendation. Mix designs are simply the proportions in which the ingredients are mixed in the sealer for the desired performance properties. The sealcoating contractor must read and understand the product literature, Material Safety Data Sheet (MSDS) and Detailed Application Specifications, prior to the sealer application. Let us review the relevance and qualifications of various ingredients in the sealcoating mix design.

1. WATER:  Water is added to give proper fluidity to the mix. It should have the right flow and leveling characteristics to evenly spread and coat the pavement surface. The water used in the mix shall be;

• Clean, potable (drinkable), low in hardness and iron. Hard water and high iron content may produce an uneven cure and also streaky appearance.

• Free of suspended solids and metal contaminants. May interfere with the proper cure and uniform appearance.

• Between 7-8 pH. Low pH water may thicken the mix. Conversely, high pH may have a thinning effect.

Test data of water can be obtained from the city water treatment department.

Use the right amount of water recommended by the manufacturer

Too little water:  The mix will be too heavy, will not spread uniformly and may deposit a heavy film. It may result in wasted material and cause tracking under hot ambient conditions. Uneven appearance; ridges and brush marks with squeegee and brush applications, and orange peel type of appearance with a sprayed application.

Too much water:  The mix will result in a thin cured sealer film that will wear out prematurely.  Inferior performance.

Sealer not covering the aggregates properly and have a tendency to flow into the valleys of the profile.

2.  SAND/AGGREGATE: Sand and/or aggregate is commonly added to the sealer for the following benefits.
 

APPEARANCE: Uniform textured appearance, reduced sun glare, streak-free appearance.

• Hides minor surface defects.

• Improves traction. Be cautious in making claims about the skid resistance of the sealcoatings, it is generally not recommended for inclined surfaces.

• Improved wearability.

Too little sand or no sand:  You will not have the above-mentioned benefits.

Too much sand:  The sealer loses flexibility with increased sand loadings. Commonly recommended amounts are 2-4 lbs. of sand per gallon of undiluted sealer. Do not exceed 5 lbs. of sand.

Sand must be quartz, angular, clean and washed. Free of contaminants, metals, clay, and trash. Of fineness 50-75 MESH AFS (American Foundry Standard). Do not use recycled sand from steel sand blasting, or foundry.

It is recommended that you purchase bagged sand. This ensures that the sand is dry and it is measured in units that can be used in developing your mix design.

Safety Aspects. The use of sand in sealcoatings improves surface traction. Sealer without sand may become slippery under wet surface conditions and cause cars and people to slip and slide. Property owners and contractors have encountered lawsuits where injuries are claimed from falling on sealcoated surfaces.

Do not sealcoat steeply inclined surfaces.

• Never claim that sealcoatings with sand will stop slipperiness

• Seek sealcoating manufacturer’s advice on such matters

3.  ADDITIVES:

Today, there is a myriad of additives available to sealcoaters. As a matter of fact the major work in the sealcoating industry has been attributed to additive, during the last 20-25 years. It is imperative to understand the types of the additives and their benefits. The additives are primarily based on:

Rubber/Polymers Latices; Acrylonitrile/Butadiene (AB) have been used since the late 60’s, as a part of the FAA specifications. They have been the workhorses of the sealcoating industry. It has been established that the additives based on Acrylonitrile/Butadiene.

Meet FAA Specifications

• Improves toughness, flexibility and durability of the sealer.

• Increases sand/aggregate suspension and skid resistance.

• Improved gasoline, oil and chemical resistance.

• Improves color uniformity

• Improves drying time, especially under unfavorable weather condition

Over the years additives based on 100% acrylics, poly/vinyl acrylic, nitrile, styrene butadiene, etc. have been developed and used in sealcoatings. 

Non-Polymer Additives, based on chemicals and surfactant are more recent introductions. They contain specialty chemicals, surfactants, and pH adjusting chemical. These additives have limited performance record and the only aspect of their property that can be seen in sealcoatings is their thickening effect, which is a very common property of most of the additives, anyhow. 

It is imperative to follow the manufacturer’s instructions for selecting additives for a specific purpose, and their blending procedure, into the batch.

Pre-mix the additive with an equal volume of water, prior to adding into the mixing tank. It reduces the “shocking” effect. For pre-dilution, it is a good practice to add water into the latex additive, not vice-versa, in order to avoid latex destabilization in the additive.

Do not use additives with premium grade sealers, which have built-in rubbers and specialty chemicals. Do not mix various additives together, even from the same manufacturer. Seek their permission if you intend to use several additives in the same mix.

Highly crucial – Do not use additives from a different supplier. It may cause destabilization of the mix, meaning a severe gelling (thickening, destabilization) problem due to reactions between the additives.

General purpose additives can be used in most refined tar-based sealer (RTS), because of the similarity in composition of various brands of RTS, which, in turn, is guided by the applicable specification, e.g. ASTM 5727-00.

You cannot take the same liberty with asphalt-based sealers due to the fact that there are various types of asphalt emulsion (AE) based sealers available on the market, which are made in different ways using various types of chemicals, fillers and, specialty chemicals.

There are two main types of AE products, one commonly is made using pre-emulsified asphalt, called soap emulsions: tack coat SS-1-H (negatively charged particles, anionic), and CSS-1-H, (positively charged particles, cationic).

The other type of AE is made from scratch, using hot asphalt, emulsifier, clays, fillers and specialty chemicals. It is out of the scope of this article to draw comparisons between different type of AE, or between RTS and AE, but one point is worth mentioning and that is AEs are not covered by ASTM, but only by the industry specifications.

It is strongly recommended that you let your additive supplier know that your sealer is made with SS-1-H, CSS-1-H or is clay stabilized. A negatively (anionic) charged additive may destabilize a sealer that made with positively (cationic) chemicals.

GENERAL RECOMMENDATIONS FOR QUANTITIES OF WATER, SAND & ADDITIVES

Proper mix design is very important to achieve the desired sealcoating performance.
For mix design calculations, the quality of the sealer is always considered at 100 base points and the quantities of other ingredients are expressed as a percentage of the sealer base, for example:

Water dilution at 30% means, adding 30 gallons of water into 100 gallons of sealer. Some contractors make the mistake of thinking 30% dilution as 30 gallons of water and 70 gallons of sealer.

Sand at 3 lbs. per gallon of sealer means adding 300 lbs. of sand to 100 gallons of sealer.

Additive at 3% on the sealer volume means adding 3 gallons of additive added to 100 gallons of sealer. For pre-dilute with water, mix 3 gallons of water into 3 gallons of additive and add 6 gallons of the mixture into the sealer. Remember to deduct the amount of water used for pre-dilution from the water of dilution.

SEALCOATINGS - RTS & AE MIX DESIGNS – The following proportions serve as a guideline in determining your mix design.  Please follow the recommendations detailed in the manufacturer’s literature.

Components                                    Sealcoating     Water           Sand        Additive

                                                                          (Gals.)             (Gals.)               (Lb.)              (Gals.)
SEALECOATING (No sand)                               100               25-30                  –                     –
SEALECOATING + ADDITIVE (No sand)          100               30-40                  –                   2-4
SEALECOATING (with sand)                             100               30-40          200 – 400              –
SEALECOATING+ ADDITIVE (with sand)         100               40-50          300 – 600           3-5

MIXING PROCEDURE: Sequence of Material Addition;

• Sealcoating

• Water

• Additive (if needed). Dilute 1:1 with water. Very Important - Water must be added to the additive not vice-versa. Add the pre-mix slowly into the mix with agitation.

• Sand – Add slowly, about 100 lbs./minute, with agitation.
  Start with undiluted sealer in your mixing tank.  Whenever mixing, it is imperative that the agitation is running at all times.

• Add water and continue mixing.

• Slowly add the Additive/water premix.

• Add sand slowly, approx. @ 100 lb. bag per minute.

• Let the agitation run for 5 to 10 minutes mixer after all the ingredients have been added. During application, the agitator should continue to turn.

Summary – Sealcoatings are commonly supplied as concentrates, which have to be mixed with water, sand, and additives, in recommended proportions, prior to the application. Additives, when considered for use shall be selected at manufactures recommendations and all the details shall be shared with the manufacturer about the type of sealcoating used, to assure proper compatibility. Water, sand and the additives have to meet all the purity, gradation and chemical requirements to achieve the desired performance properties.