The Fundamentals of Asphalt Sealer Mix Design

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 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 on 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 into;

• 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 spray application.

Too much water: The mix will result into;

• 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 and/or 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 recommend for inclined surfaces.
• Improved wear ability.

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.

Additional comments:

• It is recommended that you purchase bagged sand.  This insures 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:

1. 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 workhorse 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 conditions.

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

2. 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.

Additional comments

It is imperative to follow 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 manufacture. 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.

The very basic fact in the mix design is that sealer is always used at 100 base. The quantities and the percentages of other ingredients are always expressed at sealer being at the 100 base. For example:

1. Water dilution at 30% means, adding 30 gal of water into 100 gal of sealer. Some contractors make the mistake of thinking 30% dilution as 30 gal of water and 70 gals of sealer.
2. Sand at 3 lb. per gallon of sealer means adding 300 lb of sand to 100 gal of sealer.
3. Additive at 3% on the sealer volume means adding 3 gal of additive added to 100 gal of sealer. For pre-dilute with water, mix 3 gal of water into 3 gal of additive and add 6 gal. of the mixture into the sealer. Remember to deduct the amount of water used for pre-dilution from the water of dilution.

Presented below are common mix designs.

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.

 

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 lb./minute, with agitation.

1. Start with undiluted sealer in your mixing tank.  Whenever mixing, it is imperative that the agitation is running at all times.
2. Add water and continue mixing.
3. Slowly add the Additive/water premix.
4. Add sand slowly, approx. @ 100 lb. bag per minute.
5. 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

Sealcoating are commonly supplied as concentrates which have to be mixed with water, sand and additives, prior to application, in recommended proportions. 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.