Epoxy finish

[Jack Wood]

I am doing an inlay that I am using epoxy to seal. For the most part the stuff is clear but there are some small areas of bubbles on the surface that I want to remove, how do I do that and not ruin it?

[Earl Kelly]

Jack, are you talking about bubbles that popped to the surface and then stayed while the epoxy hardened? If that 's the case, you should sand the piece down flat and smooth, making sure to remove enough to get rid of the bubbles and then recoat. If it's bubbles down in the epoxy not much you can do about that.

The way to prevent bubbles, use a very good brush to tip off the finish. Your first coat is almost impossible to stop the bubbles, just prick them as you see them, provided the finish is not gelled already.

[Jack Wood]

Thanks Earl. Yes these are those little bubbles at the surface that happened when I mixed the the parts together. So sand it down and then top coat with another layer of epoxy using a brush. The epoxy I used has a 30 minute set time, should I look at getting a slower type in order to let the bubbles pop the surface? I used the twin tube type from the hardware store, better recommendation on a brand? I appreciate your help!

[Doug Shepard]

System 3 makes something called Clear Coat that I think would go on thinner and without the bubble problem. Quite a few luthiers are using it as a sealing/filler coat before putting clear finish on. The only other suggestion if you're able to do it - can you hold it by the edges and lightly slap it on a flat surface after applying the epoxy? Or tap it from underneath? I think if you could agitate it somewhat before it sets, you might be able to get the bubbles to raise to the surface and pop.

[Frank Hagan]

A scraper works better than sandpaper to remove the bubbles ... epoxy tends to soften with the heat of sanding and gets gummy. For small projects you can use a single edged razor blade held vertically to scrape away the excess.

Bubbles can be caused by the mixing process ... be careful to stir the components together gently rather than whipping or beating them together.

But bubbles can also be caused by the wood outgassing. I'm unclear as to why this happens; perhaps its because the epoxy generates heat as it cures, and heating wood can cause gasses to be released. Following this theory, some boat builders warm up their shops to over 100 degrees F before applying epoxy, then allow the shop to cool, with the belief that the cooling wood will tend to suck the epoxy in rather than allowing the heat from the epoxy process to create outgassing. Not sure I buy that!

I don't see it when I add something like wood flour, talc or silica to the epoxy, but that does color the epoxy which isn't always desireable.

[Jack Wood]

Doug it is a large half of a 100 year old cedar log, won't be able to tap that sucker:D Frank I have read where some people take smaller pieces and warm them in the oven before applying the epoxy, might work for those small projects of mine. The scrapper makes sense, I tried sanding the stuff and it did gum up like you wrote, I'll try a scrapper next time. On another angle how well will epoxy hold up in the elements? This bench is going to be outside. Thanks for y'alls help:)

PS Doug what is a Luthier?

[Doug Shepard]

Doug it is a large half of a 100 year old cedar log, won't be able to tap that sucker:D....


Not without a big deadblow mallet anyway:D



PS Doug what is a Luthier?


Lex Luthier:- arch-nemisis of Superman.:D
Seriously, the word comes from Lute, but means stringed instrument maker. Guitar finishing is an art unto itself, and quite a few of those folks are using epoxy as a sealer/pore-filler.

[Earl Kelly]

Jack, you must sand the epoxy to recoat. The second coat will only stick good if the surface is sanded, you can still scrape initially, but finish up with 180-280 sandpaper. If your using this outside use some west sytem epoxy with the 207 hardener and sand and top coat with a good exterior varnish with a uv blocker. I was told Epoxy does not hold up good to uv.

[Frank Hagan]

Doug it is a large half of a 100 year old cedar log, won't be able to tap that sucker:D Frank I have read where some people take smaller pieces and warm them in the oven before applying the epoxy, might work for those small projects of mine. The scrapper makes sense, I tried sanding the stuff and it did gum up like you wrote, I'll try a scrapper next time. On another angle how well will epoxy hold up in the elements? This bench is going to be outside. Thanks for y'alls help:)

PS Doug what is a Luthier?

Epoxy is water resistant, and makes a very good outdoor adhesive, but is affected by both UV in sunlight and heat. For outdoor installations in the sunlight, you should provide a barrier to keep it from deteriorating (paint, varnish, etc.) System Three mentions that in the tropical sun of Florida, an epoxy finish will last most of a single season, then will start clouding up and deteriorating. The heat thing will get you if you use dark colors as a topcoat, and live in a very hot area anyway (Phoenix or Las Vegas, for instance).

Varnish will work to keep UV away from the epoxy, but has to be reapplied periodically.

[Frank Hagan]

Jack, you must sand the epoxy to recoat. The second coat will only stick good if the surface is sanded, you can still scrape initially, but finish up with 180-280 sandpaper. If your using this outside use some west sytem epoxy with the 207 hardener and sand and top coat with a good exterior varnish with a uv blocker. I was told Epoxy does not hold up good to uv.

Earl ... you really don't have to sand to get epoxy to bond to epoxy. You have to remove any amine blush that forms, but washing it will remove that. Scraping will do exactly what sanding does ... remove the surface material that might have some amine blush on it.

The epoxy bond is so strong that the difference between a bond to a smooth-but-scraped surface of epoxy and one that has been sanded to 280 grit is miniscule. To get the strongest bond, you should recoat within 24 hours to take advantage of a chemical bond rather than just a mechanical one ... but again, the epoxy bond is so strong that the difference seen in woodworking makes all the extra effort hardly worth it. Its going to stick and stay stuck.

But UV will cause it to turn chalky, and deteriorate rapidly.

[Earl Kelly]

Frank, I have always worked under the assumption, that no catalyzed finish has a chemical bond. Sure if you apply another coat before complete curing has occured it will bond, but otherwise it only attaches by grabbing onto a rough surface. If it had a chemical bond there would be no demarkation between the layers, no halos around a repair or sand thru to the first coat. Laquer and shellac have a chemical bond, each sucessive coat becomes one with the first. Meaning, no matter how many coats you apply, you still basically have only one.