Polyurethane Blending Techniques

[Jeff Perkins]

I'm curoius about what techniques you guys use to blend the "ghost lines" when doing a touchup repair on a polyurethane finish. Third Coast Guitar Service posted the following:

 

POLYURETHANE: Poly presents another beast. Poly doesn’t let other finishes “melt” into it......We have been experimenting with different ways of blending these lines and have had very promising results using a process that we have to keep under wraps. The poly color touchups we’ve done lately have been coming out tremendously well and I think it’s just another way we can keep a hand up on the competition.

 

I'm curious what you guys out there are doing to make the ghost lines as invisible as possible. Let's get this "secret" of T.C.G.S. out in the air! Any info is appreciated!!!

[Chris Rochow]

If we all kept 'secrets' here... then we all lose!  And, what good is this forum? Isn't it so we all share and learn for the sake of the art?

[Pierre-Antoine Roiron]

As far as I know, there's no way to do it. I usually do the following :

- sand to provide grip

- clean with alcohol

- touch-up with either very thin CA glue (for little cracks or little holes) either with nitro

- let dry

- sand and polish

Nitro has the advantage of letting no obvious witness lines. You can still see under some light conditions, but it's very good.

If you want the touchup to be "as new", you'll have to spray a complete coat of PU.

[Mark A. Kane]

Rob Magargal at Taylor and others (Pat Diburro for one) are using UV cured poly for touch up with good results. You can use it over nitro as well. The equipment is not exactly cheap (lamp, protective gear etc) but the real expense is the poly itself. The speed, according to Rob, is where this technique really shines. It takes only a minute or so to go from wet finish to fully cured, ready to sand etc.

[Jeff Perkins]

Yeah, I've also heard of the good results of UV cured poly. I just can't yet justify the setup cost for it. Thanks for the reply's guys, keep 'em coming.

[Frank Ford]

One technique we've used with reasonable success is to "dish out" the area (with 1200 grit abrasive paper) a couple of thousandths and then fill with CA.  To be sure of adhesion, we typically don't fill past the sanded area,  We'll apply a very thin coat of thin CA and then mist the layer with the regular catalyst (accelerator) sprayed from an airbrush.  The airbrush is important to avoid using any more than the least possible catalyst - to avoid white spots, you know.  Then repeating until the area is filled, leveling with a hard sanding block and buffing gives us a pretty decent fill.

[Jeff Perkins]

I should have been a bit more specific about the type of repair. Basically, I have a student who's tried to "fix" a ding in his black tele with epoxy. He used the wrong epoxy and we had to dig it all out. He also sanded through a large area (about the size of a quarter). I've airbrushed black poly on the spot, but am trying to figure out what the next step is... spraying it with clear poly (airbrushed as well) with as minimal ghost lines as possible. How do I minimize the ghost lines when airbrushing is more what I'm asking. Thanks for your help Frank.

[FRANK]

jeff you may never eliminate the fine cracks unless cleaned out properly before the thin S Glue this is good for tight places and thicker S glue for the larger gappier areas sand flat apply black top coat a few coats of clear top coat and wet sand and buff it out . you were right to dig out the epoxy uv sounds good but supper glue works also and you would be able to build up a gap with it which is the way it sounds ? good luck 

[Jeff Perkins]

Oh, I've already got the dent filled in and done. And I've already airbrushed color on it. It looks good so far. It's the clear coats I haven't put on yet because I know I'm going to get ghost lines. I think I'm just going to try to fade the poly out with the airbrush then wet sand and buff. I'll get a picture up soon.