Sealers Behave Differently, Why?
Question:
On a recent stained concrete project, some areas of the floor were sealed with a two-part polyurethane sealer, while other areas of the same floor where sealed with a solvent-based acrylic sealer. Why did the two-part polyurethane peel off, while the one-part solvent-based acrylic is still down and performing great? The surface has a hard-troweled machine finish, and no additional surface prep was completed prior to staining or sealing.
Answer:This is a case of chemical versus mechanical bonding and solids content. Two-part polyurethane sealers form only a mechanical bond with concrete. This is why profiling the surface – creating more surface roughness – is always called for when working with two-part polyurethane sealers.
The same reason two-part polyurethane sealers don’t chemically bond to concrete is also what makes them such good sealers. They don’t chemically stick to anything, and nothing chemically sticks to them, including oil, gas, solvents, water, dirt, and graffiti.
The other major factor is solids content. Most two-part polyurethane sealers are high in solids, above 55%. The higher solids content makes them less able to penetrate the concrete surface, thus requiring additional surface profiling to promote adhesion.
Conversely, one-part acrylics bond both mechanically and chemically with concrete and are lower in solids – typically 20% to 30%. They tend to wet out faster, even on hard-troweled surfaces. As illustrated by the case in question, an acrylic sealer may chemically bond to a hard-troweled surface, but the surface won’t have sufficient profile, or roughness, to mechanically bond with a high-solids polyurethane sealer.
Most manufacturers of high-solids sealers require a well-defined profile before application of their products. The use of a primer or diluting the first coat of sealer are also common methods for promoting sealer adhesion on denser surfaces. Before applying a high-solids sealer, be sure to consult with the manufacturer and perform an on-site adhesion test. Find out more about two-part and one-part sealer technology and application methods from Surtec Inc.
On a recent stained concrete project, some areas of the floor were sealed with a two-part polyurethane sealer, while other areas of the same floor where sealed with a solvent-based acrylic sealer. Why did the two-part polyurethane peel off, while the one-part solvent-based acrylic is still down and performing great? The surface has a hard-troweled machine finish, and no additional surface prep was completed prior to staining or sealing.
Answer:This is a case of chemical versus mechanical bonding and solids content. Two-part polyurethane sealers form only a mechanical bond with concrete. This is why profiling the surface – creating more surface roughness – is always called for when working with two-part polyurethane sealers.
The same reason two-part polyurethane sealers don’t chemically bond to concrete is also what makes them such good sealers. They don’t chemically stick to anything, and nothing chemically sticks to them, including oil, gas, solvents, water, dirt, and graffiti.
The other major factor is solids content. Most two-part polyurethane sealers are high in solids, above 55%. The higher solids content makes them less able to penetrate the concrete surface, thus requiring additional surface profiling to promote adhesion.
Conversely, one-part acrylics bond both mechanically and chemically with concrete and are lower in solids – typically 20% to 30%. They tend to wet out faster, even on hard-troweled surfaces. As illustrated by the case in question, an acrylic sealer may chemically bond to a hard-troweled surface, but the surface won’t have sufficient profile, or roughness, to mechanically bond with a high-solids polyurethane sealer.
Most manufacturers of high-solids sealers require a well-defined profile before application of their products. The use of a primer or diluting the first coat of sealer are also common methods for promoting sealer adhesion on denser surfaces. Before applying a high-solids sealer, be sure to consult with the manufacturer and perform an on-site adhesion test. Find out more about two-part and one-part sealer technology and application methods from Surtec Inc.
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