AVOID SURFACE CONTAMINATION BEFORE EPOXY APPLICATION

By The West System Technical Staff

The old saying “cleanliness is next to godliness” is certainly true when preparing a surface for an epoxy application. If a surface isn’t clean, there may be adhesion problems. But well-intentioned cleaning often results in contaminants being deposited on the surface. Knowing how to identify potential contaminants, how to avoid them and how to determine if a surface is clean will ensure that your next epoxy application will be problem free.

OIL, GREASE, WAX

Unless there’s good evidence an organic contaminant is present, there’s no reason to wipe the surface with an organic solvent. Acetone, lacquer thinner and proprietary mixtures are solvents that remove organic contaminants such as oil, grease and wax.

But, cleaning with solvents may do more harm than good. Solvents are capable of dissolving contaminants found in rags and depositing them on the work surface. For example, silicone, a mold release, is an ingredient in many fabric softeners. A surface can be contaminated by silicone from using a supposedly clean rag straight from the laundry.

In addition, many solvents dissolve man-made fibers found in rags. A wipe down with acetone can deposit plastic on the very surface you are trying to clean.

If you need to use a solvent to remove oil, grease or wax, employ plain white or unbleached paper towels. Wipe the solvent on with fresh paper towels. Remove the solvent while it’s still wet and change paper towels frequently to avoid re-depositing the contaminants on the surface.

SANDING DUST

Besides the dust, a freshly sanded surface is about as clean as it can get. Refrain from rubbing your hand over it to check for smoothness. Unless you are wearing a clean glove, the naturally occurring oil that helps protect your skin has just been spread all over the surface. Not only does this contaminate surfaces, but the salt on your skin also speeds corrosion of metal surfaces, which may cause adhesion problems.

Every last particle of sanding dust does not need to be removed to have good adhesion. Simply remove the bulk of it and consider the remaining dust epoxy filler. Excellent methods for getting rid of sanding dust include vacuuming, sweeping with a non-contaminated bench brush or washing it off with water.

The manufacturers of sticky tack rags maintain that wiping a surface with their products won’t leave a residue. It’s likely the rags actually do leave a residue, it just is dissolved by solvents in most paints and varnishes. Epoxy, in contrast, contains none of these aggressive solvents. The residue from tack rags can cause adhesion difficulties and fisheyes in subsequent coats. An effective alternative, dry static wipes, leave no residue.

Although it’s common practice to use compressed air to remove sanding dust, it is not recommended. Aside from the mess created by blowing dust, it’s possible that blowing compressed air on the surface will contaminate it with compressor oil or water.

HOW CLEAN IS CLEAN?

An easy way to tell if the prepared surface is truly clean is to wash it with water. This unsophisticated water break test works on the principle that most contaminants repel water. Apply water using a clean pad. If it sheets off the surface evenly, that part is clean. If the water channels or beads on certain areas, the surface will need additional cleaning.

This test is simple to perform on both large and small areas. To be effective, the water must be free of debris, contaminants and surfactants. The water break test will not indicate soap residue or other water-soluble films, but it will help remove them.

Some materials don’t allow good epoxy adhesion, no matter how well you clean the surface. However, most adhesion problems can be traced back to some form of surface contamination. For the best possible results make sure the substrate is clean.