Introduction and question

[Jim De Bressac]

Hi everyone. Thanks adding me. My daughter and I are building a double neck guitar ( probably a bit ambitious to start with !! ). We sanded the necks and body through to 800 grit. We undercoated with auto body primer and lightly sanded. We sprayed with a red metallic auto spray ( same brand as the primer) and left the paint to harden. We then gave the neck and body ( of the guitar ) multiple clear coats of auto spray ( again, same brand) and left them to cure for a week. We sanded the necks with 1200 then 2000 wet and dry ( with water ) , cut and polished and then wax and polished. They came up great. When we tried the same process on the body, we found bubbling around the holes for the dials and screws etc. . I have sanded the clear coat off the body and will repeat the painting and clear coat process. Is there a way to stop the bubbling happening again ? Thanks. Sorry the post is quite wordy

[RocknRolf]

Hi Jim welcome, and how exciting to be undertaking the double neck together with your daughter!

Regarding the bubbling, could it be you have been spraying on an inclining temperature? More porous and lighter wood can breathe and when sealing them on an inclining temp, they talk bubble at you. If this is not the case, I am keen to know what it could be...

[Rabbit]

When putting on the first coat of epoxy on my canoe I had bubbles. This from the timber heating up and "breathing". I've never had it happen with paint (gotta make sure that each coat has finished outgassing as it dries). What some people do with the epoxy is warm the timber before putting on that first coat. As the timber cools the first coat of epoxy gets drawn into the pores of the timber and seals it for subsequent coats.

[McCreed]

Welcome Jim.
Unfortunately I don't have any clear-cut answers for you as it could be a myriad of things that are the cause. Sometimes things like bubbling, wrinkling happen inexplicably. I experienced this with two allegedly compatible products from the same manufacturer.

This may not explain your bubbling, but sanding timber to 800 is way too fine, and can cause issues with adhesion. Fine grits like 600, 800 begin to polish the surface instead of abrading. The primer needs the microscopic abrasions for "mechanical bonding" (in simple terms "stick to"!). Again, this does not account for the bubbling, it would be more likely that you'd experience the paint lifting or peeling. It's recommended to not go finer than P240 (or 220 if in the US) for preparation before painting timber.

Did you clean the bare wood with metho or naptha before applying the primer? There may have been traces of machine oil or other contaminant on the wood from the manufacture. Hard to say, I'm just throwing things out there.

As for "Sorry the post is quite wordy"... you obviously haven't looked around the forum much (or read some of mine )... your post is brief by comparison!

[Jim De Bressac]

Hi RnR

It seems to have happened only after we lightly sprayed the clear coat with water. It looks as though moisture may have crept underneath the clear, paint or primer coat ???

[Jim De Bressac]

Thanks Rabbit

I think I left plenty of time between coats and cure time for the clear coat ( as I was delaying the terrifying proposition of actually putting the whole guitar together !!)

[Jim De Bressac]

Thanks McCreed

I feel better about being verbose !!

We didn't put any metho or such on as the grain hadn't raised. Good point about too fine a grit and I'll note that for next time.

The bubbling only happenend after the wet and dry process and only around the penetrations so I am assuming water has crept under one or some of the layers of primer, paint or clear coat. I have sanded the clear coat off and starting again. I have sealed the small screw holes with pva glue and coated the insides of the large holes with pva as well ( and crossed my fingers ).

I'll let the group kmow how this goes.

Thanks for the support

[RocknRolf]

Hi Jim,
It could be that the coats didn't cover in the holes where it was able to take up the water.
In smaller holes, I put surf wax with a cocktail pick before wet sanding, but this isn't a guarantee but it helps and doesn't affect the finishing.

Good luck finishing the guitar, looking forward to the result!

[Jim De Bressac]

surf wax !! Brilliant. Cheers mate. I will definitely try that

[McCreed]

The bubbling only happenend after the wet and dry process and only around the penetrations so I am assuming water has crept under one or some of the layers of primer, paint or clear coat. I have sanded the clear coat off and starting again. I have sealed the small screw holes with pva glue and coated the insides of the large holes with pva as well ( and crossed my fingers ).

Ahhh, I see... I was thinking a reaction with base and clear coat kind of bubbling. I'd say the water absorption sounds like the probable cause now. The PVA is a good idea and might work, but similar to RnR, I plug mine with bee's wax. A bonus is it lubricates the screw holes when it comes time to put them in.

In cases where I have any unpainted exposed wood in control or pickup cavities, I brush on a few coats of shellac just to seal them before undertaking any wet sanding. Shellac is really handy in guitar building. I use it for lots of things.