Water is a critical material in sealcoatings, both in manufacturing as well as their application. We, the manufacturers of sealcoatings use processed water, clean, potable, and free of contaminants. The following article is written expressly for you, the sealcoating professional, to impart a basic understanding of water, criticality of its selection and its role in the overall sealcoating performance.

Why is water a critical material?

Water is the major component of sealcoatings, one (1) gallon of ASTM (old Fed. Std. RP 355e) contains about;

• 60% water (0.6 gallon).
• By the time you add  30 gallons of water to 100 gallons of concentrated sealer to overall % goes up to 70% by volume.

Please note that when the manufactures tell you that the sealer is 50% solids, it is by weight not volume, and that is a big difference which is due to the differences in the densities of water and sealer.

What type of water should be used?

The question about the suitability of the water to be used for mixing with sealer is best answered in our specifications, which state that; Water shall be clean and potable, free of harmful soluble salts, within a temperature range of 50-80 º F.

What do you mean, water is water?

No! Absolutely not. Water may be good or bad.  Water is available everywhere, however, it should not be used from just any source. The water should be;

a. Clean- Meaning free of suspended solids, turbidity, etc.
b. Potable- drinkable.
c. Free from harmful soluble salts- It should be of low hardness, which refers directly to the soluble carbonates and bicarbonates of calcium and magnesium (see section on hardness).
d. Free from metal contaminants, mainly iron.
e. Low in Total Dissolved Solids (TDS).

Water shall have:

Hardness:  Below  20
pH:  7-8*
Total Dissolved Solids (TDS) as low as possible

 * Local municipal water may be over pH 8. We have seen pH as high as 9 in some cities.

Water: Its role in sealcoatings

a. In manufacturing: Water is the ‘carrier phase’ or the medium for refined tar, clay and other ingredients. Sealer is a dispersion of refined coal tar, in a water slurry of clay and fillers. Emulsifiers and other specialty chemicals are added to achieve the dispersion and stabilize the sealer. Water plays the pivotal role in developing the clay structure, which is responsible for the proper dispersion of coal tar.

b. In application: Water imparts fluidity to the sealer so the sealer can be uniformly applied at the specified coverage rate.

c. In the drying and curing process: After application the sealer dries and cures by water evaporation. Proper fluidly in the film is essential for the particles of tar to flow and fuse properly to form a continuous film. Clay and filler particles are encapsulated by tar in the film formation process.

Water must be of suitable quality to form a good clay slurry during the manufacturing process. The contaminants, if any, shall not interfere with the proper sealer film formation.

Impurities in Water – Their Sources & Effect on Sealer Properties 

Contaminants in water are either picked up in the normal course of the flow of water, or added as part of the municipal water treatment methods. The contaminants in water are primarily dissolved or suspended solids in water. They are measured as Hardness, Total Dissolved Solids (TSD),  iron content, etc.  What are the factors that must be considered?

a. Hardness of water 

Water hardness is a layman’s term for the sudsing properties of water with soap. If soap lathers up properly , water is called “soft” and “hard” if it does not.  When we wash with soap, organic matters (oil, grime, etc.)are emulsified by soap into water. If soap does not lather up, it is because the contaminants (calcium, magnesium, metals,) in water interfere with the emulsification process.

These contaminants also interfere with the emulsification of refined tar (organic matter) in the clay slurry, during the manufacturing process of sealcoatings.

The hardness in water is the result of the dissolved carbonate and bicarbonates of calcium and magnesium picked up by water from inorganic matter, on its course.  Hardness, though expressed as concentration of calcium carbonate in parts per million parts (ppm), of water, actually denotes the sum of both calcium and magnesium, present in water.

– Water with low concentrations (less than 15 p.p.m.) is termed ‘soft’.
– Water with high concentrations (100-200, sometimes even more than 200 p.p.m.) is called ‘hard’.

Hardness is also denoted in degrees.  One degree is one grain of calcium carbonate per gallon of water.  It is equivalent to .017 gram per liter or 17 parts per million (ppm).

Patterns of hardness in the United States vary according to geographic region.

– The Softest waters are common in parts of  New England, the South Atlantic-Gulf, Pacific Northwest, and Hawaii regions.
– Moderately hard waters are common in many of the rivers of  Tennessee, the Great Lakes, Pacific Northwest, and Alaska regions.
– Hard and very hard waters are found in some of the streams in most of the regions throughout the country. Hardest waters (greater than 1,000 mg/L) are measured in streams in Texas, New Mexico, Kansas, Arizona, and southern California.

Total Dissolved and suspended Solids (TDS) e.g. clay, sand, silt etc.  

How TDS is going to affect the sealer properties?

The dissolved salts in the water with high TDS may have a tendency to precipitate out and deposit on the sealer film, producing a grayish finish, which will not be easily washed away by rain. That means that sealer may never turn to its characteristic slate black color. The problem may be aggravated under hot humid conditions. Hot temperature of the pavement will accelerate the precipitation of the salts, which may spread over the sealer film. The problem may be aggravated by high humidity which slows down the cure of the sealer.

c.   Dissolved gases; Oxygen, nitrogen, carbon-dioxide, hydrogen-sulfide, ammonia, etc.
d.   Dissolved organic matter from the decay of vegetable and animal matter.
e.   Contaminants as part of municipal water-purification process are;

– Alums (alum. sulfate) and lime are added before the filtration process and they promote settling of the suspended impurities and bacteria.  A1 (OH) 3 formed as the result of chemical reaction between Alum and Lime is a gelatinous mass which carries down the impurities with it, upon settling.  Lime also helps neutralize bicarbonate in water.
–  Chlorine is added to kill microorganisms.
– Soda ash is added to remove chlorine and sulfate but these contaminants are not easily removed.  Sulfate can be removed as Barium Sulfate, by adding water-soluble Barium Chloride.  Chlorides are generally very soluble and can be removed by deionizing the water.

Water treatment and its effects on pH of the water should be recognized.

– The alkalinity (high pH) of natural water arises from soluble salts of calcium and magnesium, particularly bicarbonates.  Water treatment introduces carbonate and hydroxy1 ions, which also, elevate the alkalinity.

– The acidity (low pH) is elevated by chlorides, sulfates, etc. Sulfates and chloride ions significantly increase the viscosities of the clay slurries.  Sulfates can be removed by adding Barium Chloride to a batch of sealer.  The Barium Sulfate, thus formed will not interfere and at the very least act as a filler.  The critical level for sulfate ions is 100 p.p.m. Chloride ions cannot be removed through precipitation due to the fact that they form highly soluble salts and stay ionized, in the sealer. The only practical way to eliminate chloride is to deionize the process water.

How is Sealer affected by acidity or alkalinity of the water?

The effect of the pH is augmented by other ions present in water and the best results are obtained between the 7 to 8 pH range.

– The higher pH, beyond 8.0 introduces water sensitivity and a tendency for re-emulsification of the cured sealer film. The pH of water can be easily adjusted by using minor amounts of weak acids, in the clay slurry of sealer batches.
– Lower pH may cause slight gelling and minor destabilizing of the sealer.

Do the properties of municipal or well water change?

Yes! Definitely. Water properties vary from day-to-day, month-to-month, season-to-season and region to region. They may be natural or water-processing contaminants. Water processing plants use different chemicals all the time to address the contaminants in the water being processed.


This article attempts to deliver a clear and detailed understanding about the qualities of water used in sealcoat manufacturing and application. It also reinforces the appreciation and need for compliance to our specifications, which are based on technical facts and numerous years of professional experience. In conclusion, I would like to repeat that the;

Water used in sealcoat manufacturing and application shall be clean and potable, free of harmful soluble salts, within a temperature range of 50-80 º F.

Read our Asphalt Sealcoating Guide for more information.