Fixing Pinholes

[thirdstone]

Okay guys , I have sprayed clear nitro over a sunburst and the clear has got some pin hole problems. I know the cause , being that I let it dry under a heat lamp ( so i'm learning as I go) I have sanded back with 400 wet and dry and most of the holes are gone but there is still quite a few left showing.I sprayed another coat , this time with body layed flat ,result is a small improvement.

Now my question is , other than drop filling every hole to fix it, is it possible to spray a clear filler / sealer like sanding sealer or schallac to fill the pin holes?

kev

[chunkielad]

The only way to do this properly is to drop fill or keep sanding and spraying until they level out. The latter being a poor way of doing it really but should work just as well in the end. Ensure that there is no sanding swarf in anything before you spray and you should be OK.

[mammoth guitars]

What kind of wood is it?

[thirdstone]

What kind of wood is it?

Grain filled Mahogany

[mammoth guitars]

Sounds like the grain is not completely filled.

[thirdstone]

Sounds like the grain is not completely filled.

Your dead right. I have to be honest and admit that after thinking about this quite a bit I realised that after grain filling I should have sand sealed to completely fill the grain. After the initial post I drop filled and resprayed , what a complete disaster , hundreds of airbubbles appeared as it was drying. I think that after wet sanding the lacquor I must have been a bit slack in drying the body befor respraying. I have now completely sanded off the finish and am in the process of filling and sealing the grain. Before I spray againg its gonna be flat as glass.And dry as .........., well you know!!

[thirdstone]

okay the progress so far , and its not good. After grain filling and sand sealing flat still getting bubbles forming in the lacquor as it drys

I thought it might have been a reaction to the chemicals used in the bleach that was used to bleach the mahogany so I neutralised it the 3 different ways that rustins recommends. That didn't help.

Next I went and bought a different acrylic lacquor and prewash but again that didn't help.

Next I suspected that the Compressor was blowing out oil (water trap was clean) so I sprayed air on to a sheet of white paper , clean as a whistle. I am running out of ideas with no progress in sight.

[thirdstone]

Is it possible that bubbles in the lacquor in the gun pot go through the gun in the spray??

[thirdstone]

I think I may have the answer. I will add this for referance for other people.

from http://www.woodweb.com/knowledge_base/Bubb...er_topcoat.html

woodweb.com

Bubbles in lacquer topcoat

What causes bubbles in lacquer topcoats? September 26, 2000

Q.

I run a medium-size refinishing shop and from time to time we get small bubbles in our final coats. We use regular sanding sealer with two or more coats of various nitrocellulose lacquer.

Retarder, different dry times, stripped pieces or virgin woods don't seem to have a connection.

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Bubbles in the final topcoat can be caused by many things. Wood species also plays a part in this problem. More porous woods, such as oak, mahogany, and walnut, for example, will tend to bubble more than less porous woods or woods with tighter grain patterns.

Most causes for bubbles can be directly related to stain not being properly dried prior to applying sealer and topcoat. What happens is that the stain is still releasing solvent after the sealer and topcoat have been applied, thus causing bubbles. The solution, of course, is assuring the stain has had sufficient time to dry before topcoating.

Another cause is using a sealer and/or topcoat that is too high in viscosity. A lacquer or sealer works much better at 17-18 seconds viscosity in a No. 2 Vahn viscosity cup. Add a good grade of lacquer thinner and retarder in the right proportions to achieve the proper viscosity. You want just enough retarder to keep the lacquer open long enough to flow and rewet overspray when spraying a piece, but trying to achieve this with lacquer retader alone will not fix the problem, and will sometimes make it worse. Your ratios for thinner and retarder will vary depending on weather factors including humidity and temperature. This will be a trial-and-error process on your part to make it work.

I will add that a nitrocellulose lacquer and sealer finish is more forgiving than a conversion varnish or similar finish. Bear in mind also that your stripped pieces may still retain some of the wash solvents down in the pores of the wood if you are not letting them dry long enough.

There are many things to consider with this problem. Look closely at what I mentioned above and see if any of these causes may at the root of your problems.

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From the original questioner:

Thanks for the quick responses and advice. I have tried all the solutions in the past but without any consistent results.

I know that as temperature and humidity go up it seems to happen more frequently. You're right that retarder alone increases the problem. I have had to re-strip many a piece before giving up on that as a solution.

If any of you have any more advice, I would like to hear it. If it makes any difference, sometimes I can get satisfactory results from spraying the tops on their sides (only happens on horizontal surfaces) letting them de-gas easier.

I'll try some retarder in with my regular thinner on the next tops and see if I can get the right combo.

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Make sure that you are using a reducer that is of the same brand as your finish. You didn't say if you were stripping or not; if so, make sure all of the methylene chloride is out of the wood.

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I often find that thinners and reducers can cause the problem you have described. A "hot" or fast-drying thinner with the incorrect air flow (fast or excessive) can cause the thinner to flash off too fast, leaving solvents under the dried film with nowhere to go, thus causing bubbles or pinholes. Viscocity means everything in situations with minimal air flow.

Not knowing what products you're using other than nitrocellulose, I would suggest that you keep your lacquer warm and off the concrete to lower the viscosity, and if any reducer or thinner is needed, I suggest you use it sparingly.

Also, while spraying, make sure you apply a wet coat, and check the air coming out of your gun. Too much can cause air to get trapped under your finish.

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May I ask if you are using a lacquer that has lot of acetone in it? I did new and refinsh work for over 20 years and know what you are talking about.

What are you using for a retarder? Also, what is your brand of finish (if you want to tell us), or are you in a state that requires low VOC's and you have one of "those" lacquer formulas that are a little temperamental?

Bob Niemeyer, forum moderator

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Since you said you have the problem on just the tops and not the sides, what I am about to recommend should help a lot.

When spraying the top of a piece, many people have a tendency to apply too much material. Lighten up on the top some, don't cross-coat it or overload it with material. Just spray a medium wet to wet coat and that's it. Allow all coats to flash off or dry in between and also take the advice mentioned previously about reducing your material. Hope this is of some help.

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You say that you see it more when it is humid; are you sure that it is not fiber stand you are seeing?

There is bubble relaxer out on the market. Contact your supplier or look for more suppliers on the 'Net. I have used acetone to get rid of the bubbles and that seems to work.

Finally, check the air pressure of your gun; too much will often cause bubbles.

[thirdstone]

Still having problems, bought a new gun but no improvement.

This is a pic of the problem.

[chunkielad]

That looks like a setup problem to me. Either your mix isn't right or the air pressure is wrong. Try dropping the air pressure so it JUST sprays and then up it just a click or so. What mix of retarder/hardner//thinner/clear are you using?

[thirdstone]

After spending a small fortune on prep wash , different brand lacquor and matching thinners, and a new spray gun i did'nt get anywhere. Next I played around with spray gun settings and I foud I could reduce the problem by droping the pressure to 18 psi and spraying very dry ,but not a very nice finish. I guess that this allowed the solvent to escape before the lacquor set. This is the crux of the problem I think, being that the solvent is still trying to evaporate but the lacquor is curing blocking the release hence the bumps. I increased the thinners ratio from 50/50 to 1 part lacquor to 1 . 5 parts thinners and it is spraying better but a bit too early to be confident that I have resolved the problem as I am still spraying a bit dry.Next is to spray a wet coat and see what happens.

The weird thing is that I have used the same lacquor/ thinners set up before with no problem.

Chunkylad what mix ratios do you use for your lacquor?

[chunkielad]

I never use nitro - I use 2 Pack car paint and my mix has very little thinner in it at all really. Maybe 25% and then a small splash of hardner/activator. It may be worth playing around with the mix on scrap and the pressure drop was always going to help but you may have gone a little too low. Try upping it a little and messing with the mix. It's a wierd one if you have used the mix before but spraying is an art not a science!

[thirdstone]

The latest drama , I was still having problems so I rang up the producer of the lacquor and was told that to keep the lacquor open for longer, to allow the thinners to get out I should increase the lacquor content. This I did the a reatio of one part thinners two parts lacquor. This reduced the amount of bubbles but still not good enough.Next was to use acetone as the thinners and spray from a further distance than normal with low pressure. The idea put to me was that this would make the majority of the thinners evaporate before it reached the wood. It works but the result is realy bad. I think even the lacquor was going off in the air as well resulting in very dry finish.

In despiration I rang a renown guitar builder in Aus I know, I know I should have done this earlier but...........

Guess what ; some pieces of mahogany react badly with nitro and thinners and you just have to go very slowly and be very careful with the sealing. Its so unique that the back of my piece of wood is not affected just the front. Back to square one ( for the 8th time)

[oz tradie]

Thirdstone, Is there any chance of shooting a clearer pic?

I wouldn't mind a looksee but with better focus.( b.t.w the tarp looks great)

[thirdstone]

Thirdstone, Is there any chance of shooting a clearer pic?

I wouldn't mind a looksee but with better focus.( b.t.w the tarp looks great)

Sorry about the photo I took it with my phone , it looked ok on the small screen. Hopefully i won't see them again but if I do I will take a photo then burn the wood.

What happens is that I spray a wet coat and as it drys these bubbles appear . When sanded flat the void that is under the bubble goes all the way down to the wood base so you can't sand them out . when sanded they resemble white rings.It only happens on the front of the wood not the back, same piece of wood

At the moment I have sprayed about 6 coats of wood sealer and i am wondering if I should chance another

attempt with the lacquor or buy some rustins clear coat.

[oz tradie]

With your sealer coats already on, is the surface pitted or open pored in any way or does it resemble a flat,

totally sealed off surface? You will obviously have a better shot at it if there is a totally sealed smooth surface with no irregularities. ( probably stating the obvious)

Have you tried applying lighter coats, but with more time between each to allow the solvents to pop?

But maintaining your psi rating around 30 ? (It'll atomise the particles more evenly) Shooting at 15 psi wont improve anything, just give you more orange peel. Are you putting much heat into the body? using lamps, booth ?

If you need a hand, I'm only down the big road..................... in Melbourne.

[thirdstone]

With your sealer coats already on, is the surface pitted or open pored in any way or does it resemble a flat,

totally sealed off surface? You will obviously have a better shot at it if there is a totally sealed smooth surface with no irregularities. ( probably stating the obvious)

Have you tried applying lighter coats, but with more time between each to allow the solvents to pop?

But maintaining your psi rating around 30 ? (It'll atomise the particles more evenly) Shooting at 15 psi wont improve anything, just give you more orange peel. Are you putting much heat into the body? using lamps, booth ?

If you need a hand, I'm only down the big road..................... in Melbourne.

The first time I just grain filled and then sprayed a coat of clear. The intention was to sand that flat. That was a disaster.

second attempt was to grain fill then sand seal using feast watson sanding sealer. This was also terrible but thinking about it I realise that in sanding it flat I have sanded down to the wood surface. At the time I thought the idea was to have a flat surface only ie just the grain pores filled.

The next attemp was to use schallac as the sealer. This improved things quite a bit but I was still getting bubbles around the edges dispite all the other settings I was also trying.

Now i am poring on the feast watson proof seal. I have used this product before although not with acrylic lacquor so I am doing a test piece as well to try the compatability.

With this I hope to get it mirror flat and 100% coverage of the surface before I go any further.

To answer you questions; I have used low temp heat lamps at various stages. I stoped using them after realising that they may have exaspirated the problem although in hindsite I don't think they played a big part in the bubbles as the bubbles start to form before the heat lamps were turned on.

I did try lighter coats but It had to be so light that there was hardly any lacquor going on and it was a very dry flaky result.

Thanks for your comments.

[thirdstone]

haha looks like I fixed the problem. I just needed to seal the thing better to stop the lacquor from making contact with the wood.Doh

[chunkielad]

No way, I've never seen that before but hey, if it worked, wicked!

[oz tradie]

haha looks like I fixed the problem. I just needed to seal the thing better to stop the lacquor from making contact with the wood.Doh

A happy ending after all.

Any new pic updates in the pipeline for this one? Is it the LP jr?

[thirdstone]

Well yes happy ending of sorts as I have solved the problem but.............Not that happy with my burst so Its coming off Again. Don't laugh , I have a 4 day plan to get me out of strife

Day 1 ,strip,Bleach,Grainfill

Day 2,seal 3 coats

Day 3 Clear lacquor wait two hours , Spray yellow

Day 4 Spray burst and Clear on top.

For pics check out my other post of the build

http://projectguitar.ibforums.com/index.ph...24927&st=30.

Thats where I started the LP Jr post so I'll keep it going there.

Thanks for your input.Kev