Avoiding Common Problems With Sealers and Coatings for Concrete Applications
Part 3 of a 3 part article covering coatings for concrete surfaces
Managers can avoid common problems with sealers and coatings by proper selection and by carefully re-reading and following surface-preparation and application directions. Among the problems workers encounter are: bleeding, discoloration, color variation, uneven gloss, and blushing; poor adhesion, lifting, or wrinkling between coats; soft, tacky, slow-drying film, or low film thickness; and poor surface integrity, including pinholes, caters, cracks, crazing, and alligatoring.
Questions for managers to consider to avoid problems include these:
- What are the aesthetic considerations? Is a color effect needed? Same color? Different color?
- Will workers perform periodic maintenance, such as cleaning and resealing, or is a low-maintenance, seal-and-forget solution desired?
- Does the application require better wearability or easier application?
- How is the coating applied — roller, spray, brush, float?
- What are the proper surface-preparation and methods?
- Are temperature and humidity OK?
- What environmental exposure will there be? Moisture? Acid? Alkaline?
- Will the coating match the film build specifications for the job?
- Will enough air movement exist at the job site?
- Is odor a concern?
- How long will off-gassing continue?
- What is the life-cycle cost in dollars per mil thickness, per square foot, and per year of life?
The coating should match performance requirements for the surface and the environment. Managers should check the product specification sheet and material safety data sheet should be checked for suitability.
For example, what is the product’s VOC content? As measured by American Society of Testing Materials ASTM 6886, a low-VOC product releases fewer than 50 grams of VOCs per liter of coating as it dries. Less is better. In the case of solids content, more is better and, though more costly, it covers better. If yellowing is a concern, managers can specify an anti-yellowing formula.
Epoxies are excellent thick-film-surface hardeners. A polyamide hardener provides the best film flexibility, adhesion, color stability, and water and corrosion resistance. Aromatic amine provides the best acid resistance. Aliphatic amine provides the best solvent resistance. Phenalkamine provides the best low-temperature stability. Cycloaliphatic offers the best viscosity characteristics.
In making a specification decision, managers can turn to selection aids in order to get the best performance from concrete sealers. Managers calculate life expectancy based on testing on various products, substrates, environmental conditions, surface preparation, and application methods. Managers can use the information to specify the most appropriate product for the substrate and conditions, the best surface preparation, and proper application methods. While some products might have lower first costs, they might fail sooner. The real test is whether it offers a balance of optimum performance and low life-cycle cost.
Thomas A. Westerkamp is a maintenance and engineering management consultant and president of the work management division of Westerkamp Group LLC.