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by **gwlreno** on Thu Mar 14, 2013 6:48 am

Dave's right-Cast aluminum needs to be pre-baked prior to coating to make the metal out-gas. Also, there is a special primer powder called appropriately enough, "Outgas killer primer". I haven't been able to try it yet, but once I get back into powder coating that will be one of the first things I'll be trying.

by **vaughn** on Thu Mar 14, 2013 8:41 pm

This is good to know about the out-gas prebake in the process of powder coating. Looks like if it's not prebaked it'll turn out like Easy's part with bubbles in the paint. Thanks for the heads up.

by **somuchtoseeanddo** on Fri Mar 15, 2013 12:35 am

This happens all the time with concrete out-gassing. One way to prevent this is to avoid the "heat sink," which occurs when it is warm and definitely during rising temperatures.

The item should be primed/painted when the temperature on the surface is falling. Don't rely on the ambient temperature, because the substrate may hold heat for a while even when the air temperature is dropping. When the temperature on the substrate and the pores is falling, the primer will suck inwardly and this should eliminate pin-holing and bubbling.

We often have to prime at night because of this very issue, prior to priming and coating with the elastomeric coatings I sell. I have seen a pin-hole/bubble go all the way through 1/2" of urethane.

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