Epoxy discoloration with heat

I was in the second of three epoxy colors on some coasters tonight and when I applied heat from my torch to clear the bubbles the first one discolored badly. Initially it was all over the surface and since it was messed up I gave a little more heat and it chased the color to the edges.

I have used this same epoxy, dye and torch before and not had issues. The only thing Incan think of is some chemical reaction with the tape I am using to dam an area for a different color.

I had 11 more of these to do and had customers for some of them so I didn’t want to try again. I resorted to popping bubbles with an xacto knife. Hopefully they will not be too bad and clear when I flatten back out.

Ever seen this before?

Did you have a sealer on the board beforehand? It might have a different boiling point than the epoxy. It’s a lot more noticeable in white, but I’ve seen the oily mark of oops in black before too. Try a heat gun instead, the temp is lower.

I have a propane torch and always had trouble with it going out when I tilted it over to pop bubbles. I bought a heat gun. It works fine and pops the bubbles. As @dustmite asked did you seal the wood before epoxy. Air escapes from the wood and rises. I use Zinsser Universal sanding sealer (Dewaxed Shellac) to seal my projects before applying epoxy. You could also mix up a small batch of your epoxy and coat the inside of the project and wait for it to dry or almost cure and apply your epoxy to fill.

Air bubbles are just a face of life for epoxy. I use MAS table top epoxy and it gets very hot in the pot an gets lots of air bubbles. I also use Magic Resin for deep pours and it does not get hot in the pot and has very few bubbles in it. Both types still need the heat gun run over it to pop the inevitable bubbles. The heat gun is hot enough to pop air bubbles but not nearly as hot as a torch. I have a lot of dewalt 20v batteries and tools so I bought a dewalt clone on amazon for the heat gun. It works very well and does not over heat the epoxy.

If your epoxy gets very hot in the mixing pot with the additional heat from the torch may be the problem and you may need to get a different epoxy. Heat is caused by the chemical reaction of the epoxy and with warm weather and the torch it may just have over heated your epoxy.

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My assumption is the wood was not sealed first.
A clear coat of epoxy brushed on the surface first is good practice with any wood. Takes more time, but leaves less issues perhaps.
Resin is a chemical reaction producing heat. It can act like a ‘stripper’ during its initial contact and setting.

In my experience a heat gun has been better but that can change with materials.

It appears that the tape burnt and discoloured your epoxy. I would suggest either a heat gun or a butane torch. I use a butane torch as it is a constant flame. Also, I would suggest never using tape to prevent epoxy flowing over as it is highly flammable and doesn’t seal well against it. Hot glue or silicone is far more effective.

I did not seal this time but I usually do put a coat of shellac on first. I can’t say that I have always done that though but maybe.

As I mentioned, I have used this same epoxy, dye and torch combo before and even the same wood. But maybe I always used shellac as well. I can do some experimenting on a test piece later.

EDIT: I just looked at the pieces and the bubbles don’t seem to be an issue, will find out for sure when I flatten. However, the painters tape dam was an unmitigated failure this time. There was really only a tiny portion where the prior black epoxy layer looked like it would allow the white to come over but I covered a larger area and it failed. I guess I will have to recut the beak portion before putting in the yellow and hope that things line up well enough.

Next time I should cut the pockets for the feathers and beak first and then come back with the V Bit for the black outlines and text.

I don’t think the tape burned. Yeah, see my edit to that post about the tape dam. Used it once before but on a smaller scale.

I do use a butane kitchen torch. I got that instead of the heat gun based on lots of online comments but I guess I can try a heat gun next time. Not sure what wattage I would need.

And yes I should have used hot glue or silicone. I think I can change the order of operations next time to prevent having to do that. It will take some redesign of my file and toolpaths.

I am trying to get a process that is not too painful as this is for coasters for teachers at the kids school. I made some last year and have been asked for some more. I made spares this time but it is still a painfully slow process. I expect I will get asked for more.

Depending on how much you get into this but a nice flat board of HDPE is very handy. Resin does not stick to it.
If doing a bunch of coaters you could make a circular barrier or ‘ring’ to place on the surface to contain the pour. If you can picture what im trying to suggest.
You could make an HDPE board with 12 circles and do 12 coasters at a time. No messy glue, no tape and the HDPE is heat resistant and cleans easily. The HDPE can be cut in any way to make plenty of barriers for resin.

Thanks. I sort of do that already by cutting multiple in a single piece of walnut and start by creating a circular pocket to create the damn.

The reason I needed the tape is that I cut the recess for the black and then after it hardened I cut the recessed for both the white and yellow at the same time which leaves a very this black separator that is some cases was too low.

Ultimately they should look like this:

If I do the black after the colors it will probably work better and use a lot less black epoxy.

I do want to build the jig you are talking about though so that I can cut and pre do the eagle since that is the largest part of work and then come back later to add the customization. I was hoping that could be done with black CA glue but I have not had good success with that.