How can I fill this cavity with a clear "epoxy" ?

[Mark Gibney]

The cavity in this piece of walnut is 3/4" deep (to zero) and about 1" across.

421917

I'd like to fill it with a clear epoxy type filler. Problem is that if I use West Systems slow setting epoxy or a similar product I know I'll get air bubbles, even if I use a heat gun, and I'll also probably get hazy areas.

I'm not familiar with other products out there, so any suggestions are welcome.

Thanks, Mark

[Richard Coers]

You can go to Hobby Lobby and buy clear casting resin. Auto parts stores sell Fiberglass repair kits that have resin. And a ton of places to buy on-line. Shop for resin, not epoxy.

[Mark Gibney]

Thanks Richard, I will do that.

[johnny means]

Careful when doing a fill that size. Epoxy curing is an exothermic reaction and can very hot. In my experience a fill like that will gradually heat up with the wood acting as an insulator. Eventually, it will start to bubble and burn. You can pour it in stages, but that brings about it's own set of problems.

[Jacob Reverb]

You can go to Hobby Lobby and buy clear casting resin. Auto parts stores sell Fiberglass repair kits that have resin. And a ton of places to buy on-line. Shop for resin, not epoxy.

+1 Acrylic casting resin or polyester...you'll want a wax in the resin if you use polyester, so it will cure at the surface.

[Pat Barry]

If you search you tube for river tables you will find hundreds of videos on this topic. By the way, never heard of 'burning'. I don't think epoxy gets anywhere near hot enough to cause burning although it can get too hot to touch in some circumstances such as a very deep cavity but 3/4 inch is not that deep.

[Jim Becker]

There are resins specifically made for this kind of thing. Total Boat has a nice one that I plan on trying for some intended projects. So do others. Some resins require multiple pours for deep situations; some are rated for pours up to an inch and a half or so. That may also require long cure times, as much as 72 hours. Some are water clear; some are not. It's a normal practice to use a heat source (typically a torch but a hot heat gun "may" work, but it's always a quick flash-pass over the pour to help relieve the bubbles.

[Jacob Reverb]

By the way, never heard of 'burning'. I don't think epoxy gets anywhere near hot enough to cause burning

A large enough volume mixed together will start a fire, if it's warm enough and humid enough – particularly after you add fillers that bulk it up. The main thing to avoid is having it all together in one mass -- IOW, better to spread it out on a cookie tray than to have it in a cup, so the heat can dissipate. When it's all in one mass, the heat created goes back into the curing epoxy, rather than out into the air, causing it to cure faster and create heat faster. Think: Critical mass.

It's kind of like a forest fire in that it creates a feedback loop -- the hotter it gets, the faster it reacts, and the faster it reacts, the more heat it liberates, making it hotter.

I've never started an actual fire with the stuff, but I've seen it melt plastic mixing cups.

[Jim Becker]

Yes, one of the limits of how deep the pour can be is the exothermic factors for the particular resin formula. Thicker would most likely cure with no problem, but the heat generated by the chemical reaction during the curing could be above the manufacturer's recommendation for safety. The stuff really does get major hot!

[eugene thomas]

Maybe am just lucky I dont burn shop down but I fill areas bigger than the knot area regularly with system 3.

[andy bessette]

...it will start to bubble and burn...


A large enough volume mixed together will start a fire...


...never heard of 'burning'...

Now you have. I have had it cause a small fire.

[Roger Feeley]

You can use vibration to get the bubbles out. My dad was a dentist and when he made the molds for casting gold crowns there could be no bubbles. He used a combination of vacuum and vibration. When he mixed the refractory, he did it in a little vacuum chamber. Then, when he poured it he had this magnetic vibrator that helped the stuff flow and worked the bubbles out.

some years ago, I needed some bubble free plaster. What worked for me was one of those vibrator eggs they sell for...gratification. I simply held the egg and mold in the same hand and poured with the other hand.

i also made vibrating table once using a small motor and an eccentric to make it off balance. You have to fiddle with it a bit to get the amplitude right but it works. My wife makes soap and I’ve been thinking about making her workbench vibrate.

[Jacob Reverb]

You can use vibration to get the bubbles out. My dad was a dentist and when he made the molds for casting gold crowns there could be no bubbles. He used a combination of vacuum and vibration. ..

There's an article in West System's free "Epoxy Works" magazine this month that talks about pulling a vacuum and using vibration to get bubbles out...I think it's online (though it sometimes isn't online for a while until after the hard copy has been circulating)...

Yep, here it is:

https://www.epoxyworks.com/index.php/casting-epoxy/

[Prashun Patel]

'clear' epoxy is not necessarily the best choice here. That's a pretty thick void. It will be a challenge to keep microbubbles from turning the hardened product hazy, and at worst, a phlegmy shade of yellow. Given that the bottom of the void is black, you may save yourself a ton of effort by just tinting your 'normal' slow setting epoxy black. A few drops of transtint will turn it black - and more to the point, opaque. Bubbles would then be a non issue (aesthetically). I would still fill in stages. Doing it in one big go, you may find that it stays soft for a long time, and gradually sinks below the surface (DAMHIKT).

In fact, if *I* had a void this large, I'd tape the open end, wipe a coat of sealcoat on the surface, and fill the bottom 2/3 first with a sawdust/epoxy slurry, letting it dry for a day or two. Then I'd do the top 1/3 with black epoxy.