Frequently Asked Questions About Pavement Sealer and Its Performance

Question 1: Why are two thin coats better than one thick coat?

Answer 1: 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.

Q2: What causes white streaks in the sealer?

A2: Possibly incomplete mixing of clays and fillers in the manufacturing process of the sealer. Your sealcoating manufacturer should be contacted to rectify this problem.

Q3: Why does the sealer dry gray?

A3: The graying is caused by sealer drying under less-than-ideal conditions, for example in shaded areas, cooler temperatures, or high humidity. The problem is mostly temporary; after a few days in full sun it will cure to its normal color. Temporary graying can be eliminated through the use of a specialty additive that helps sealer dry faster and at a uniform rate. If the problem persists and the sealer does not dry to its characteristic charcoal black color, the manufacturer should be consulted.

Q4: Why does sealer wear out faster in traffic lanes, entrances, and exits?

A4: Aside from the obvious reason of more traffic in those areas, it could be an adhesion problem. If the wear is excessive, surface aggregates in these areas become smooth (polished) over the years of usage. For any sealer to bond properly the surface should be sufficiently rough. To improve adhesion use a specialty primer that penetrates the polished aggregates and allows the sealcoating to bond effectively.

Q5: How soon can I sealcoat a freshly laid asphalt pavement?

A5: As soon as the surface rids of light oils through oxidation. It usually takes about four to six weeks, depending on geographical locations. To ensure that the asphalt surface is ready for sealcoating, spread some water on the surface. If the water spreads evenly without beading, you are ready. It is also called "water break test."

Q6: While spraying how do I know if I am applying at the recommended coverage rate, say 0.12 gal./sq. yd.?

A6: Coverage rate dictates film thickness, which can be measured by a film thickness gauge, available at most paint stores. Select a 10-ft. x 10-ft. area of the pavement and place a 3-in. x 6-in. metal plate in the center. Spray sealer in this area and lift the metal plate before the sealer 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 gal./sq. yd. coverage which is 21 mils.

Q7: Can you explain sieve size, percent retained, and percent passing?

A7: Sand or the other aggregates added to a sealer must fall within a range of particle sizes, neither too coarse nor too fine. This is ascertained by a sieve analysis in which sand is sifted through a set of screens with varying mesh sizes (openings in the screen). Percent retained means how much of 100 grams of sand was retained on the screen and percent passing is how much passed through the screen. Use your manufacturer's recommended grades.

Q8: Why should we use sand?

A8: Sand is used for traction, skid resistance, and also to provide a uniform texture to the surface.

Q9: Why use latex?

A9: The use of latex additives is very common. There are many latex additives to impart all types of performance advantages. For example:

  • Rubberizing additives improve flexibility, durability, toughness, etc.
  • Faster drying additives help sealers dry fast
  • Thickening additives build the viscosity of sealcoatings diluted with large amounts of water

Q10: Why apply two coats when one coat looks good enough?

A10: 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 will wear out in less than half the time. You will have to sealcoat more frequently if you used only one coat.

Q11: How much water can I use?

A11: Follow the manufacturers' recommendations. Normally 25 to 30 gal. per 100 gal. of concentrated sealer is recommended. Higher percentages are recommended for mix designs that use additives and larger amounts of sand.

Q12: What happens when you use different additives (different suppliers) in the same tank? Why does the viscosity go haywire?

A12: 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 manufacturer's warranty may be void if you use other additives.

Q13: Why does sealer fail or peel?

A13: Peeling is caused by sealer not bonding to oil spots or any other surface containments like dirt, grease, etc. or oxidized pavements . All the areas shall be thoroughly cleaned; oil spots must be primed with specialty primers. Oxidized pavements should be treated with a diluted coat of sealer, specialty product, or asphalt emulsion.

Girish Dubey is president of STAR Inc., Columbus, OH.