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Hi Folks...

Currently spraying my 10th guitar in nitro and i noticed that there are many little poc holes that i just cant seem to fill with the build-coats / sand back / build coats process.

The guitar is mahogany, and had two sessions of grain filling - all as i normally do with no trouble - but these holes just dont seem to be getting filled up... Its now about 8-9 build coats of 50/50 lacquer/thinner, sanded back every 3. They are more or less all over the back and sides.

Never seen this before!!??

Hope you can see from the photo and i hope someone can help me solve this.

Thanks a lot!!

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www.leddingtonguitars.com

Are you spraying in the cold and then moving the guitar into the warmth to dry? It could be that cold air trapped in the pores is expanding as it warms and pushing the lacquer back out of the pores. I would suspect this if all the holes are above pores. If the spots move around it might be solvent vapor bubbles getting trapped in the film.

Just guesses, but I have run into both situations while spraying in the winter.

Kent

From the picture it looks like incomplete pore fill.

That would be my guess too. Looks from the pic that the holes are in the black grain.

I agree... any tips on how to procede considering i already sprayed some lacquer.

G.

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www.leddingtonguitars.com

You can spend some quality time drop filling them, or sand back and apply some additional filler.
If you do drop fill them let them sink back for quite awhile (as long as your patience will allow) before leveling and proceeding.

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Jim Watts
http://jameswattsguitars.com

Looks like unfilled pores to me as well. I've never had to deal with this situation as I make sure all pores are completely
filled before starting nitro application. The good thing about your situation is that the pores are now very easy to see. I
would use an epoxy finishing resin, z-poxy/ west/ or system 3 to fill them. Using a hard applicator, something like a credit card
I would apply a couple coats with the end result of getting epoxy only in the pores. Should be fairly straight forward with a smooth
substrate to apply to. The goal would be to scrape off, as you go, any unneeded epoxy leaving only in the pores. A light sanding
if necessary and proceed with nitro application. If done correctly I wouldn't think there would be any finish bond issues.

I seal fill seal I use the vinyl sealer or what the manufacturer suggests. Learned a long time ago do what they say on the can.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Well thanks to those who came with solutions.... i never had this before and i did inspect the pore fill, i think these holes were so small i didn't notice them until lacquer built up around the edges and amplified them.

G.

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www.leddingtonguitars.com

Solvent pop..... I see holes where there are no pores so it can't be filler problems...

Here is my handy spray problem solving chart, see the section on pinholes and solvent pop. https://howardguitars.blogspot.com/2015/05/spray-finish-problem-solving-chart_18.html

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Thats interesting Brain... but your chart is ore like a 'how to avoid in the future' ... which is actually great... but what would you do now it has happened?

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www.leddingtonguitars.com

Drop fill with full strength lacquer. Let it cure at least 2 weeks. It’ll shrink back a fair amount. Use a toothpick and literally put a drop on each hole.
3 weeks would be better but you should be able to sand back after 2. Inspect and repeat if needed.

I suspect that the 50/50 mix is your issue as that’s a lot of thinner, which would have caused the solvent pop as Brian mentioned (as others did too).

Also, I’ve never sanded between sessions of lacquer, why waste the paper? Every coat burns into the last with nitro, so as long as my prep work is as close to perfect as possible I don’t have to level sand between sessions. That was my choice anyway.


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Just took a zoomed in look of your picture. You’d be better off sanding it fully back and restarting. That’s a lot of pin holes to fill.


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My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

What is happening now is a function of surface tension. Liquid will build at an edge due to ST and the little holes are all edge with nothing basically to flow into....

What you can do now? sand back and start over as mentioned is one option. The other is to carefully re-wet the nitro with solvent. Keep spraying it with a slow reducer or reducer/retarder mix wetting the surface and as soon as it flashes spray it again. Eventually all the nitro you have applied will become a liquid again and when the viscosity drops enough it will flow and the holes will come out. This can however allow the coating to run and sag and may take 2-3 weeks before it hardens back up enough to prep sand and re-coat.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Well thanks for all the tips folks.. i tried epoxy to no avail... ended up sanding back and starting the process again... quite the bummer.

Many thanks though.

G.

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www.leddingtonguitars.com

It happens, wait till you have to re-top a guitar after you've finished the entire thing...

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My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

For what it is worth, mahogany and similar woods seem to require at least three coats of epoxy and 4 on very curly stock. System 3 SilverTip may be recoated without sanding provided the timeline in the instructions is observed, and that makes a single-day fill possible, although it usually requires more cleanup work versus a multi-day schedule with sanding between coats.

Paste wood fillers provide a single coat fill, with any opaque filler giving a different look versus a clear, higher index-of-refraction material like epoxy. We've trialed some of the latex fillers such as TimberTech and Saman, but have found that solvent-based Behlens paste wood filler is preferable for those times when we need an older school look.

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