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Wetsanding/glue Joint Anomaly


Xanthus

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I'm really frustrated :D <-- That is my angry face.

My project might have to go in for its third "round" of paint.

Round 1-Paint and wetsand. Looking pretty decent.

Round 2-Paint and wetsand. Looking pissa.

Wait... Why the !*$& are the glue joints coming through???

VERY disappointed. We are so close to finishing this.

My dad and I brainstormed and are thinking that maybe when we were wetsanding, too much water seeped through and got into the wood, swelling it.

Well, poly is plastic, if I'm not mistaken. And between two rounds of painting, there is a LOT of paint on this guitar. How could it be that enough paint mysteriously soaked through that much paint to make the glue joints appear? I don't know if I'm buying it.

Another explanation could be a problem with the glue. I used Elmer's carpenter glue. Couldn't find Titebond, which I'd have liked to use, and a carpenter's glue (read: for gluing together wood) would be exactly what I needed.

Is the glue receding, and taking the paint with it? Is the paint being soaked into the glue joint? I'm really confused about this, but I don't really want to have to put more paint on this.

Also, we left the guitar alone for a good 3 or 4 days before wetsanding it, and there wasn't even a hint of a shadow of a glue line. So I honestly don't know what's up at all.

Any ideas, oh those-who-have-done-many-a-guitar-build?

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Joints have to be so tight that you shouldn't be able to see any glue. Its happened to me over the long haul with poly and lacquer. I know when cured poly becomes very rigid and if there is any contraction and expansion in the opposing woods it can form hairline cracks along the joint. Shrinkback in the curing process happens over a very long time. I have guitars that weren't initially grain filled, I just filled with poly from the get go years ago. The finish at the time was like glass but now I see grain pattern showing through all over. Its no big deal, one day I'll just scuff over and reshoot. :D

I only wetsand the final coat of poly unless there are some serious anomalies in the finish, like drips, sags, runs etc. along the way. Otherwise its just a dry scuffing and quick wash with a clean damp cloth between shooting sessions. There is no need to remove material via wetsanding in the middle stages.

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Thanks a lot guys, here're some answers to your questions:

Jon - yeah, I filled the grain of BOTH the mahogany and the maple with grain filler, then primed the body with white Krylon primer.

Southpa - the reason we decided to wetsand the black is becasue there were some specks of dust that settled in the paint as it was drying; I have to admit, we cleaned the garage out as best we could :D apparently not well enough. Would wiping the body down with a wet rag pick up the dust that hasn't had time to stick? I'm assuming I'd have to wait about a half hour after shooting the paint to do so. What grit paper do you scuff your poly with before clearing? The clear coats fill in the scratches from the sandpaper, I assume, bearing that the grit isn't too aggressive.

I'll probably end up using your method, Southpa, when I RE-RE-spray the body. I mean, the finish was flawless aside from the specks of dirt. It's a shame, really.

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Hello Xanthus, My name is Mike Navarro and I own a guitar custom shop it's name is Guitar Zone, when you glue, depends the kind of glue, you should seal with an activate primer, sometimes glue liberate quimical fumes, and those fumes try to scape through the finish and thats why the joint marks, if you paint in solid color, as I said, you can use an active primer, this kind of primer blocks any quimical reaction, but when you glue you should let it cure at list 48 hours. If you'll paint a translucent color, sunburst, clear etc, apply first coats, and let it dry 48 to 36 hours to verify if theres no reaction problem, sand, and repeat the coats.

Any cuestion you can write me Guitarzonepr.com, will be my pleasure help you, you can also have a tour inside my shop! Mike Navarro---- Guitarzonepr.com

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Would wiping the body down with a wet rag pick up the dust that hasn't had time to stick? I'm assuming I'd have to wait about a half hour after shooting the paint to do so.

nonono, I use a damp rag after scuffing an already cured surface. I generally wait a couple or 3 days between shooting sessions. Do not touch the finish with anything until the finish is reasonably dry. That also goes for laying the guitar down on things for a long time after 3 days drying. It may be dry to the touch but overall still soft, fingernail will dent it. I've seen some nice towel fabric imprints on a few of my clearcoats after I left the guitar for a couple hours. :D

What grit paper do you scuff your poly with before clearing? The clear coats fill in the scratches from the sandpaper, I assume, bearing that the grit isn't too aggressive.

My initial coats are thick so I don't accidentally sand thru, makes sense. But I don't use any coarser than 320 and thats with light pressure. Corners and edges are sanded with finer grits, up to 600. All you are doing is roughening the surface so following coats will adhere better. But it must be very clean after scuffing. A clean damp/wet rag and then wipe with paper towels immediately after. You don't want any water soaking in anywhere.

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So I think I know what the deal was.

It's this goddamn New England weather.

For anyone who lives up here, they know what our weather's been like. At the current, it's 45F. two days ago, it didn't pass 30F. It's the most horrible roller-coaster weather.

I'm thinking that the weather caused the wood to expand and contract, pushing a bit of glue out of the crack, therefore pushing up a tiny ridge of paint. The guitar is hanging up in the basement, which is heated, but can be drafty, seeing as the house is so old.

So in other news, I'm painting another coat on it again, and this WILL be the final coat. No dust, no runs, no sanding necessary. Just tape the bevels, spray the red, unmask and clear.

On a side note: Does anyone know a cheap way to make a paint booth? I really want to keep this thing as clean as possible. I was thinking of calling the body shop, but they are REALLY good, and the offchance that I could tie up their paint booth for an hour would cost quite a penny.

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