How To: TRADE SECRET Why keeping surfaces clean makes for a strong epoxy bond
When it comes to preparing a surface for epoxy application, the best advice is to follow the mantra cleanliness is next to godliness. If your surface isn’t clean before you begin, you’ll be making life harder for yourself in the long run as contamination actually reduces the adhesive power of epoxy.
To ensure your epoxy bond is strong and durable, your surface must be clean, dry and thoroughly abraded. This is because the strength of the bond relies on the ability of the epoxy to mechanically ‘key’ into the surface.
But don’t worry, there are a few simple precautions you can take to guard against putting contaminates onto the surface.
What should I watch out for?
You – Your body creates oils to protect your skin. Even though you’ll feel like running your hand across the surface to test the smoothness, don’t unless you’re wearing a clean glove. If you do, you’ll just contaminate the clean surface.
Sanding Dust – The best methods to clear sanding dust are: use a vacuum, sweep it off with an uncontaminated bench brush or wash it off with water.
Organic Solvents – These can react with other elements and leave deposits on the surface that can affect adhesion. If you need to use a solvent, use plain white or unbleached paper towels to wipe the solvent on. Then use fresh paper towels to wipe it off while it’s still wet. Change paper towels regularly. Do not use rags.
Compressed Air – These cans can contain their own oils and water that can contaminate your surface.
Heaters – Some heaters, such as Salamander heaters, do not burn cleanly and can actually produce lots of moisture that may accumulate on your surface.
Zinc Stearate – This is a chemical that can be found in some types of sand paper. You can contaminate a surface just by using it. We suggest that you use aluminium oxide or non-stearate treated, waterproof wet/dry sandpaper instead.
Amine Blush – Many organic solvents will not help you remove blush. Instead, wash with clean water with a Scotch Brite pad and dry with paper towels.
How do I know the surface is clean enough?
Wash it with water. If the water channels or beads in certain areas then you need to get back to cleaning – you’re not done yet! However, if it sheets off the surface evenly then the part is ‘clean’ and ready for use.
Why not keep a list of these causes of contamination to hand when preparing your next surface? And if you’re still after more, head over to West System International where you can find plenty more surface preparation techniques.
Our thanks to Brian Knight for his great ideas on how to avoid surface contamination.