The first application of polyurethane finally dried on my red oak
baseboard. I sanded the baseboard and used a tacky cloth to remove the
dust. Should I wipe down the baseboard with a rag dipped in mineral
spirits before I apply the next coat of polyurethane?
No. Poly uses a mechanical bond between coats, you want as little as
possible between coats so as to get the best bond. Just make sure you
get the dust off, that's all.
And I hope by "finally dried" you mean "I waited as long as the can
said to wait". If you don't recoat in the time specified, you need to
wait at least a week or two (to fully cure) and sand before recoating.
If you recoat in the time specified, you only need a light sanding (to
remove raised grain and such) as the poly hasn't fully cured so it
will bond with the next layer whether you sand or not.
Cure time depends on the poly. The stuff I use isn't cured until at
least a week passes. After 8 hours it's only dry, but not cured.
Well, nobody is going to stop you if you want to sand whenever you
feel like it. I'm assuming the OP wants as good a finish as is
I've noticed that before the recoat time, I can sand lightly, and only
to remove raised grain. The poly is still soft enough that if I try
to sand into it, it just rolls up into lumps (like a pencil eraser).
Only after it's fully cured is it hard enough to actually sand into
When fully cured, sanding poly should result in a fine, light, dusty
powder. Like what you usually see with sanding sealer.
I'm saying that if you recoat outside of the recommended times, the
coat won't hold as well. Why? Because of how the poly layers join.
During the cure time, the poly molecules go from loose to tight, so if
you recoat during that time you can still hook into the uncured
molecules for a mechanical join at the molecular level. Once they're
cured too much, this is no longer an option for a reliable join, so
you wait until it's cured enough (i.e. hard) to sand it to make a
mechanical joint at the macro level.
Sure. There is nothing wrong with doing this. As long as you wait long
enough for the poly to cure sufficiently (varies by temperature/humidity).
If you were able to sand successfully, than your poly was cured
sufficiently. There is no danger in wiping sufficiently cured poly with
mineral spirits. I have done this NUMEROUS times.
After all, most people use mineral spirits as a solvent to dilute
polyurethane. How could this same solvent be counter indicated for wiping
cured poly? :)
Go right ahead!
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