Thread: Pin holes/bubbles in NC lacquer

Originally Posted by malb

Not trying to take sides in this, but thought I had seen it and went back to check. Third line in the first post "A problem I have occasionally is pin holes/bubbles in the finish, and I am looking for a solution. Right now I spray on 2-3 diluted coats of lacquer, sanding with wet and dry between coats. That usually does the trick, but it is time consuming."

Just hoping that this may produce a more fruitful answer for riverbuilder.

Thanks, malb.

I did a search for the word, but did not think to go back to the first page.

Yes, I dilute lacquer with GP thinners.

Yesterday I had a chat with my Mirotone sales rep.

He confirmed NG Rosewood as one of the worst timbers for producing bubbles in lacquer. Apparently the stuff is notorious for this problem. He also mentioned cedar as a regular troublemaker, although my experience is that surian cedar is a breeze compared to NG Rosewood. Don't know about Red cedar.

His solution was to apply several very thin coats to begin with, in an attempt to seal up the holes that produce the bubbles. Given that the problem only occurs on horizontal surfaces, I think I'll keep using the Solarez to seal the surface before applying sanding sealer and lacquer.

It's nice to know that I'm not the problem ... that NG Rosewood does produce bubbles in lacquer.

Originally Posted by John Samuel

It's nice to know that I'm not the problem ... that NG Rosewood does produce bubbles in lacquer.

NG Rosewood can be difficult to get a satisfactory finish on due to its porosity. I make a lot of inlay banding to use in small turnings, mostly pens, and have issues with the "extractives" from NGR transferring across into almost all woods used in the banding. It seems that no matter what is used to pore fill / seal the NGR that subsequent coats of finish will draw the "extractives" out. Any wipe on finish and even some sprayed coats can be affected.

Originally Posted by Mobyturns

NG Rosewood can be difficult to get a satisfactory finish on due to its porosity. I make a lot of inlay banding to use in small turnings, mostly pens, and have issues with the "extractives" from NGR transferring across into almost all woods used in the banding. It seems that no matter what is used to pore fill / seal the NGR that subsequent coats of finish will draw the "extractives" out. Any wipe on finish and even some sprayed coats can be affected.

I think I'm beginning to understand why one can sometimes buy NG Rosewood "on special". It can be very difficult to maddening during finishing. My only real problems with this timber were pin holes and bubbling on horizontal surfaces. Thank goodness the Solarez seems to stop that.

Silica and lacquer do not mix happily. Bubbles are the result. Many timbers have it naturally (NG rosewood being one.) Silica may also be introduced when using silicon based sprays and waxes as a lubricant on woodworking machine tables. Drying lacquer in direct sunlight can also exacerbate the problem.

Agh! Rustynail beat me to it.

Its silica.

Happens in car finishes. Fisheyes are the bane of car refinishers and introducing silica into a shop can result in someone being shot.

Simple solution is to wipe down with prepsol and a cloth. One can also put this goop in the NC/lacquer/poly: 804 ANTI SILICONE - Bodyshop Paint Supplies Bayswater

Originally Posted by rustynail

Silica and lacquer do not mix happily. Bubbles are the result. Many timbers have it naturally (NG rosewood being one.) Silica may also be introduced when using silicon based sprays and waxes as a lubricant on woodworking machine tables. Drying lacquer in direct sunlight can also exacerbate the problem.

I have been careful not to get silicone in my shop. I only use lubricants declared safe with finishes like lacquer. The only timber used that routinely gives me bubbles is NG Rosewood, and even then only on horizontal surfaces ... not on vertical surfaces. The Mirotone rep said that was his experience, too.

The NGR has silica in it naturally. I never lacquer it, I only use an oil. As for red cedar, I use a lot of it and have never had a problem with lacquer or any other polish for that matter.
I mill my own timber except for NGR, which I buy in against order. The big question is; What has the timber been exposed to prior?
Even if the timber is rough sawn when you get it, that is not to say silica has not been introduced. If the timber has been dressed, the possibility increases. Machine surfaces can become pretty bunged up with gum from milling green timber, a quick "fix" is a squirt of silicon between runs. Solves the problem for the machinist, makes a problem for the polisher.

Just seeking a bit of clarification - are we talking silica as in the mineral in beach sand; or silicone used in some polishes, spray lubricants etc?

Silicone is one of the causes of "fish eye" in painted finishes. The fish eye is formed because the silicone modifies the surface tension f the paint.

"Popping" or "solvent popping" can be caused by a number of factors, but is basically the paint solvent; or moisture in the timber; or another solvent / thinner; moisture from the air line; or even the compressed air being trapped under the paint usually by the fast drying paint forming a skin.

PPG state this may be due to:

• Poor quality or too fast thinner.
• Excessive film thickness, or insufficient drying time between coats.
• Compressed air pressure too low.
• Drying temperature too high, heat source too close to the film, too hot, or applied too soon.

The bubbles structure will give some clues to identify "fish eye" or "solvent popping."

NGR has many quite large vessels and capillaries in its structure - and my theory for what causes them for me is moisture in those vessels mobilizes while spraying or the compressed air is trapped by a fast drying or heavy coat.

"Fish eye" is typically a shallow crater where as "solvent popping" is characterized by bubbles trapped in the finish as well as popped bubbles.

I am building a chest of drawers in NG rosewood.

Usually, I'd finish the top with Solarez before using sanding sealer and lacquer. This time I went directly to the sanding sealer.

I got heaps of bubbles ... but only on the top which was horizontal. No bubbles on the cedar drawers and no bubbles on the sides or the framework ... only on the horizontal top.

So, as an experiment I sanded it back with an orbital sander. Then I rolled it onto it's back, so that the top of the cabinet was now vertical, and I applied three coats of sanding sealer allowing it to flash off between coats.

No bubbles.

Once it had dried I rolled it back onto its feet, sanded it off again and applied another coat of sanding sealer to fill the wood grain.

I have used a wide variety of timber in my shop over 20 years. The only timber that gives me bubbles is NG Rosewood, and then only when the panel is sprayed in the horizontal position.

I guess I stop grizzling and roll cabinets onto their back to spray the top whilst it is in the vertical position, then roll it back onto its feet and spray the remainder of the cabinet.

This morning I put a thin coat of lacquer on the chest of drawers.

No bubbles.

So then I put on a very full coat of lacquer, On my return an hour later the top was full of bubbles. The heavy coat had melted through and opened up the pin holes so bubbles were created.

ENOUGH!

I used nuclear grade carcinogenic paint stripper to go back to bare wood. I'm going back to using Solarez as a sealer.

Maybe a swipe or two of Shellac first?

Originally Posted by woodPixel

Maybe a swipe or two of Shellac first?

That's worth thinking about woodPixel.

What I still struggle with is the fact that I only get the problem with NG Rosewood (although my lacquer supplier did say bubbles were a common problem with this timber) and only when the panel is horizontal.

I stripped it yesterday, re-sanded and re-routed it and applied two coats of Solarez (to be sure ... to be sure ... like the Irishman who wore two condoms ... then two coats of sanding sealer followed by two coats of lacquer.

Once everything is dry and hard I'll rub it back with 400 grit wet and dry and apply a final, thin flash coat.

The Solarez works.

I was using some Solarez today. I was filling/flooding some cracks. Put the timber in the sun to cure which is instant and I put a finger on the curing solarez to fine it gets extremely HOT whilst curing.