Understanding and Caution in their Usage

By Girish C Dubey

The use of additives in sealcoating coincides with the very introduction of sealcoatings in the 60’s. Additives based on specialty latex/rubber polymers have been a part of the FAA Specification since early 1970’s. Considering the myriad of additives available today, it is imperative to understand the basic chemistries of such additives and select the ones that will truly enhance the performance of the sealcoating in terms of better flexibility, toughness, fuel & chemical resistance and overall longevity. Sealcoating specifications, delineating the proper ratios of various components in the mix design are of critical importance for the optimum performance of sealcoating systems.

The use of additives has enabled sealcoating professionals to use sealcoatings even in unfavorable ambient application conditions and still accomplish the optimum performance out of sealcoatings. Although it may appear that most of the additives are supplied to make the sealer dry fast and yet faster but that is only a part of the benefits provided by additives.
Now some basics; sealcoatings are mostly supplied in a concentrated form, which must be mixed with.

  • Water to obtain a workable consistency.
  • Sand/ aggregate to improve the skid resistance, abrasion resistance, cover minor surface defects and impart a uniform textured surface.
  • Additives to improve the overall performance properties.

The topic of sealcoating additives is quite exhaustive; therefore, we will attempt to confine our discussion to only those substances that are added to sealcoatings to accomplish the following main objectives:

  1. Fast Drying: Even under “not-so-ideal” drying/ weather conditions.
  2. Uniform Dry Color: Under shade or direct sun light.
  3. Sand/ Aggregate Suspension.
    Large amounts of sand/aggregate are used in the sealcoating mix to improve skid resistance, produce uniform texture and fill minor surface defects. Additives keep sand/ aggregate uniformly suspended in the mix, thus eliminating settling in the bottom of the tank. Additionally, additives help distribute sand/ aggregate evenly throughout the sealcoating and produce a uniform and streak free appearance of the completed job.
  4. Performance Improvement: Sealcoatings modified with properly selected additives improve:
    a. Resistance to chemicals, deicing salts, oil, jet fuel etc.
    b. Resistance to water and elements of weather (UV etc.),
    c. Toughness, Flexibility and Elongation.
  5. Thickening of the excessively diluted sealer.
    It is not recommended by sealer suppliers, still some contractors do it primarily to save money. Doing so, they are simply putting down an inferior product, which most likely will show premature wear. The excessive amount of water literally “waters down” the mix, thus reducing cured film thickness of sealcoating dry film, which drives the performance.

Additives are used to enhance sealcoatings properties. They should be selected with the proper understanding of their properties and overall contribution to sealcoating longevity. All additives are not made equal, some may actually degrade the properties of the sealer if the polymers in them are not resistant to the destructive elements and chemicals. Additionally, additives are not “cure all”. They will not compensate for poor mix designs, e.g., the ones using excessive water or sand/aggregate. The advice is to follow manufacturers’ recommendations.

Highly Crucial – Do not intermix additives from different suppliers in a mix design.

Additives are specialty products, which are formulated with compounds having complex chemistries. Although recommended for the same end use, they may be materially different in their formulation from one manufacturer to another. It is, therefore, imperative to follow manufacturer’s instructions to the letter and never intermix different brands of additives in the same mix design.

If you are going to try a new additive it is a good practice to make a small test batch to see what happens when you combine the two different chemistries. Fill a 5-gallon pail with 4 gallons of your sealer mix (with water and sand), add the required percentage of the additive you want to test. For checking compatibility, observe the mixture over a period of 12 hours for any adverse change in texture or the viscosity of the mix. In some cases, incompatibilities may manifest as excessive thickening, coagulation of the mix (like cottage cheese) or excessive settling and separation which cannot be re-dispersed.

Too much of a good thing? Using additives beyond the recommended amounts is commonly considered as a waste of money, e.g., using more of a fast-drying additive may not necessarily make your sealer dry even faster. Not only for cost considerations, but chemically speaking, the components in an additive may begin to negate amongst themselves or worse yet, interfere with chemicals or surfactant components in the sealer concentrate. Following this thinking, it is advisable to discuss options with your supplier if you should buy additives for post adding or use their premium grade sealers which have additives and specialty chemicals “built-in” their sealcoatings. All the guess work (type, amount, mixing, etc.) is eliminated when you buy premium grade sealers, where the precision, performance and accuracy are assured.

Additives are specialty products. They have to be used in sealcoating with proper understanding, following manufactures’ guidelines and instructions.