Large chunk of poly peeled off the headstock

surge98

Senior Member
Joined
May 14, 2013
Messages
145
Reaction score
38
I have some experience with finishing, enough that I've been able to get good results with oil-based wipe-on poly and nitrocellulose lacquer. Each piece I do seems to end up a little better than the last, but last night I had something bizarre happen as I was finishing up a build. I put a piece of masking tape on the face of the headstock so I could mark the position of the holes for the string retainer bar. When I pulled the tape up, a huge chunk of poly came off with it, all the way down to the bare wood. I was shocked to see how easily it came off, I'm used to thinking of wipe-on poly as thin but very durable. Has anyone seen something like this with a poly finish before? There are two things I can think of that may have caused this:

1. I had originally planned on spraying due to having a waterslide decal on the headstock. I've sprayed lacquer before, but not poly, and not knowing any better I bought a 2X clear instead of a 2K clear. I kept getting an orange peel texture, so I sanded it back as far as I could without damaging the decal and did the rest of the coats with wipe-on poly. Both were oil-based, could there have been some incompatibility between different products, and could it have caused something like this?

2. In working with poly, I've run into issues where I see sanding scratches between layers of finish if I scuff sand with too aggressive of a grit. I started using something less abrasive, which solved that problem. Everything looked great when I was done, but now I'm wondering if I sanded too smooth between coats, leaving nothing for the subsequent coats to stick to. The Minwax instructions say to sand with 220 grit between coats, but that seems way too coarse for wipe-on poly. Still, I don't understand how it came up all the way down to the bare wood, it seems like the initial few coats should've at least adhered properly. What grit does everyone recommend for sanding poly between coats, and how do you avoid visible scratches between layers of finish?

Thanks.

finish.jpg
 

ARandall

Senior Member
Joined
Apr 16, 2012
Messages
14,819
Reaction score
11,209
The only time I've had the same sort of thing happen was when the wood/filler/sealer wasn't fully cured before finish application.....so the bond to lower substrate was at fault.
 

Michael Matyas

Senior Member
Joined
Oct 24, 2020
Messages
137
Reaction score
101
Sorry to see all that work marred when you were almost done. Did you sand your wood, before finishing, finer than about 220? If you sand the wood too fine it can end up too smooth for finish coats to adhere properly. If you use the wrong kind of tape or pull it off too quickly it can remove finish as well. Dan Erlewine recommends using a low-tack draftsman' tape and removing it slowly and at an angle. Draftsman' tape can usually be bought at an art supply store.
 

surge98

Senior Member
Joined
May 14, 2013
Messages
145
Reaction score
38
Sorry to see all that work marred when you were almost done. Did you sand your wood, before finishing, finer than about 220? If you sand the wood too fine it can end up too smooth for finish coats to adhere properly. If you use the wrong kind of tape or pull it off too quickly it can remove finish as well. Dan Erlewine recommends using a low-tack draftsman' tape and removing it slowly and at an angle. Draftsman' tape can usually be bought at an art supply store.
I do have some of the low tack tape, not sure why it didn't occur to me to use it in this situation. Removing poly is always a huge hassle, so the thought of it coming off in a huge chunk without a heat gun never crossed my mind. The neck came from Warmoth, I gave it a light tint using ColorTone dye diluted in denatured alcohol before I started applying the finish. I didn't do any additional sanding, but I did give it a good wipedown with naphtha before starting and between each coat.
 


Latest Threads



Top