Heat-Setting Acrylics

[Eric Roach]

I wanted to finish a needle in a pollock-like color scheme because there are hordes of the little brown bombers up my way this year. To do this I figured I'd skip over the rattle-cans and break out the airbrush.

After, I thought I'd heat-set the acrylic. My oven's lowest setting is 170, and I had it in there for 8 minutes. Unfortunately, in several spots bubbles appeared from gas escaping from the wood (yellow birch sealed with 100% Tung).

I think I just learned another building lesson (#13 of 1,000,000+).

What do some of you do to heat-set your acrylics? Clearly my problem was too hot / too long.

Thank you,

Eric

[The Dad Fisherman]

Just let it Air Dry......Patience is a Virtue

Nice looking Needle by the way

[numbskull]

Actually your problem is unhardened sealer and or sap (probably the former with birch) that is driven out of larger pores as the heat expands the moisture in the wood. Even tiny areas that seem innocuous will discolor the epoxy gradually after the plug is done.

You can try heating your sealed plug @ 180 for 20" before priming, let it cool then sand lightly. That will stop most of it. Don't try this unless the sealer is already dried by normal means.

[Eric Roach]

Thank you, TDF. RM knock-off.

I think you're right about the unhardened sealer, numbskull...I don't think I let the birch dry long enough; I had submerged it in Tung for 30minutes and let it dry for 2 days in the basement, but I think the birch absorbed more than I expected (I didn't do any absorption testing) and it was pretty humid when I did this.

Question: If you get really deep sealer penetration, is it possible the outer layers will dry and never give the inner portion enough oxygen to finish the job (assuming the sealer used required O2)?

[numbskull]

You can let it dry a year and heat will still drive unhardened oil out. Wood pores are little tubes. Oil sealers goes in, harden on each end, and stay soft in between. You heat it, gas/water vapor inside pushes it out. So heat it first to get it all out, then clean it and prime.

PS I soak hardwood for hours and adjust my weighting to account for the weight the unsealed wood gains.

[Eric Roach]

Thank you again. This explains why I have had some plugs discolor over the years when they are left in Plano boxes in the truck on hot days.

I'll try that suggestion next time to drive some out.