The National Pavement Contractors Association's
FREQUENTLY ASKED SEALCOATING QUESTIONS

From the Pavement Pro's at the N.P.C.A.

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Consumers: Please note that some of these questions and answers apply to contractor issues (such as mixing, burning, etc.).

  1. Sealer performance F.A.Q.
  1. 1. Why are two thin coats better than one thick coat?
  1. 2. Why did the sealer fail or peel?
  1. 3. What causes white streaks in the sealer?
  1. 4. Why does the sealer dry gray?
  1. 5. Why does brand "X" burn more than brand "Y"? What conditions aggravate burning? What precautions shall be taken to avoid burning? What is the industry doing about it?
  1. 6. Why does the sealer wear out faster in traffic lanes, entrances and exits?
  1. Application F.A.Q.
  1. 7. How soon I can sealcoat a freshly laid asphalt?
  1. 8. While spraying how do I know if I am applying at the recommended coverage rate such as 0.12 gallon/sq. yard per coat?
  1. 9. What type of striping paints to use and how soon can the lot be striped?
  1. Mix designs F.A.Q.
  1. 10. Can you explain sieve size, % retained, % passing, etc.?
  1. 11. Why should we use sand?
  1. 12. Why use latex?
  1. 13. Why apply two coats, when one coat looks good enough?
  1. 14. How much water can I use?
  1. 15. What happens when you use different additives (different suppliers) in the same tank. The viscosity went haywire?
  1. 16. What is the deal with specifications using excessive amounts of sand, e.g. 18 lb. of sand in one of the FAA Specifications?

 

 

ANSWERS

 

 

 

bulletMuch like paint, sealer applied in two coats dries and cures much better than one thick coat application. Remember sealers are water-based coatings, which cure through the process of water release (evaporation). A thin coat will release water much faster than a thick coat. If applied in one thick coat, sealer will have a tendency to hold water and stay soft for a longer period of time, possibly causing tracking.  back to top

 

 

bulletPeeling problems may be caused by sealer not bonding to oil spots or any other surface contaminants like dirt, grease, etc. or oxidized pavements. All the areas should be thoroughly cleaned, oil spots shall be primed with specialty primers. Oxidized pavements should be treated with a specialized primer or a diluted coat of sealer or asphalt emulsion (this treatment does not count as a "coat" in two-coat application).  back to top

 

 

bulletPossibly due to incomplete mixing of clays and fillers in the manufacturing process of the sealer. Your sealcoating manufacturer should be contacted to rectify this problem.  back to top

 

 

bulletIf the problem persists and the sealer does not cure to its normal charcoal black dried color, the manufacturer should be consulted. It is possibly due to higher clay and filler content in the sealer itself.  If the problem is temporary i.e. after a few days in full sun it will cure to its normal color, the initial graying is due to either sealer curing under shaded areas or the surface containing too much moisture. Temporary graying can also be eliminated through the use of specialty additive that helps sealer dry faster and at a uniform rate.  back to top

 

 

bulletSealcoatings based on coal tar are manufactured using refined coal tar within a very narrow range of properties. Coal tar suppliers remove most of the lighter components (potential irritants), quite effectively.

In our opinion the ambient conditions or improper skin protection causes the skin irritation and burning sensation. On hot humid days the vapors coming out of the sealer do not dissipate fast enough and have a tendency to deposit on the skin, causing the irritation. People with lighter skin are, therefore, affected more than people with darker pigmentation. Protective clothing and equipment are a must for safe handling of sealcoatings. Wear long sleeved shirts, pants, impervious boots and gloves and use safety goggles. Use a skin barrier cream and a sun screen with a high SPF factor on face and other exposed body parts. Read the Material Safety Data Sheet (M.S.D.S.) supplied by the manufacturer.

The industry professionals association, Pavement Coatings Technology Center (PCTC) at the University of Nevada at Reno is currently researching into the components in the refined coal tar that cause skin irritation and the possibility of reducing those components, without jeopardizing the sealcoating properties.  back to top

 

 

bulletIt is usually an adhesion problem. The surface aggregates in these areas become smooth (polished) over the years of usage. For any coating, including sealcoatings, to bond properly, it is imperative that surface should by sufficiently rough. Our recommendation is to use a specialty primer to prime faster traffic lanes, exits and entrances. These primers penetrate the smooth polished aggregates and allow the sealcoating to bond effectively.  In very high-traffic locations a third coat may be required on the main drive lanes to equalize wear. back to top

 

 

bullet7. As soon as the surface rids of light oils, through oxidation. To ensure spread some water on the surface. It the water spreads evenly without beading, and shows no "rainbows" from surface oils you are ready. This is also called "water break test". It usually takes about 4-8 weeks, depending on geographical locations.  back to top

 

 

bullet8. The coverage rate dictates the film thickness which can be measured by a simple film thickness gauge, available at most paint stores. Select a 10’ x 10’ area of the pavement and place a 3"x 6" metal plate in the center. Spray sealcoating in this area and lift the metal plate before the sealcoating dries. Use the film thickness gauge to determine the wet film thickness. The reading will be in mils (1/1000 of an inch). Compare this reading with the desired film thickness for 0.12 gallon/ sq. yard coverage which is 21 mils.  back to top

 

 

bullet9. Water-based  acrylic or latex traffic paints. Allow at least 24 hr. after the application of the final coat of sealer.  back to top

 

 

bullet10. Sand or the other aggregates added to sealer must fall within a set of particle sizes, neither too coarse nor too fine. This is ascertained by the sieve analysis which means that sand has been sifted through a set of screens with varying mesh sizes meaning the openings in the screen. Percent retained means how much of 100 grams of sand was retained on the screen and % passing is how much passed through the screen. Use your manufacturers recommended grades.  back to top

 

 

bullet11. Sand is used for traction, skid resistance and also to provide a uniform texture to the surface. Sealcoatings with sand wear longer and are much safer to walk and drive on.  back to top

 

 

bullet12. The use of latex additives is very common. There are many latex additives to impart all types of performance advantages. For example;
bulletRubberizing additives improve flexibility, durability, toughness, etc.
bulletFaster drying additives help sealers dry fast.
bulletThickening additives build the viscosity of sealcoating diluted with large amounts of water.  back to top

 

 

bullet13. Appearance is only part of the benefits. The sole purpose of sealcoating is to protect and preserve the asphalt. One coat will possibly provide only half of the protection and wear out in less than half the time. You will have to sealcoat more frequently if you use only one coat. This would be more costly since labor costs for cleaning and surface-prep do not change for a two-coat application.  back to top

 

 

bullet14. Follow the manufacturers’ recommendations. Normally 25-30 gallons per 100 gallons of concentrated sealer are recommended. Higher percentages are usually recommended for mix designs that use additives and extra amounts of sand.  back to top

 

 

bullet15. The viscosity went haywire because the additives were not compatible with each other. Do not mix different additives and stick to manufacturer recommendations. Also the manufacturers’ warranty may be void if you use other additives.  back to top

 

 

bullet16. Those are special sand slurry specifications and not used commonly for sealcoating specifications. The industry recommends a maximum of 8 lb. of sand per gallon. Very high sand loading (18 lb. for example) will result in a coating that will be poor in flexibility, adhesion and chemical resistance.  back to top
 

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Revised: February 07, 2006 .