# Pin hole causes



## sayn3ver (Jan 9, 2010)

I've been shooting breakthrough 50 thinned 3oz distilled water/3oz bm512 per gallon through a 410FF.

I also have been final sanding only to 220. 

Chasing perfection I final sanded some new crown today to 320 grit and thinned 4oz/4oz to hopefully help eliminate a slight egg shell/molting in the final film. 

While spraying it definitely flowed nicer and dried down close to perfect but was getting some small pin holes that didn't seem to want to flow together. I'd have to back track and dust the section to get them to merge together. (Obviously I missed a few which is prompting the post.)

Was the little additional water/extender to blame (increased surface tension?) Or the finer grit (increased surface tension?) 

My clean/tack schedule wasn't changed and I haven't had this issue prior to today.

I suppose I should have only tried one variable. The finer final grit was to hopefully eliminate any visible scratching which I occasionally can still see with 220.


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## PremierPaintingMa (Nov 30, 2014)

It could be few think, solvents trapped in the film, unclean surfaces, or if you put heavy coats or to many coats before the solvents have off-gassed, or check the room temperature. 
Hope this helps Dan.


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## sayn3ver (Jan 9, 2010)

The surfaces we're prepped as usual for me which is why I'm ruling out contamination. Sanded. Vac'd. Damp miro fiber. Dry microfiber. Shoot it. 

These didn't develop during drying. I'd hit a run and then check coverage and they were appearing during the wet out...first coat. Primer was SW wall wood and was dry and sanded for a few days before this room. 

Room temp was around 68-70 about 40% relative humidity. 



PremierPaintingMa said:


> It could be few think, solvents trapped in the film, unclean surfaces, or if you put heavy coats or to many coats before the solvents have off-gassed, or check the room temperature.
> Hope this helps Dan.


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## Tprice2193 (Oct 3, 2017)

Of the two variables you have proposed I am betting on the extra thinner. I am not a big Breakthrough guy but I have seen this before with General Finishes white poly. Keep your sanding the same and back down to 3.5 oz. I have sanded to 600 without problems with products that adhere well. It is surface tension....sometimes the bubble wont break.


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## CApainter (Jun 29, 2007)

What about the sand paper? Could silicone carbide residue interfere with film formation? I've read in a metallurgy book that certain emery cloths shouldn't be used to prep steel for welding because they contain traces of oil.


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## PACman (Oct 24, 2014)

Are you absolutely sure they are pinholes and not perfectly round "grit"? I've been fooled quite a few times the last couple of years by what appear to be pinholes but are actually tiny perfectly round and somewhat transparent spheres. It has happened so many times i have posted on here about it. (a year or two ago.) If you can look at them through at least a 10x magnifying glass (i use the jewelers loupes from Harbor Freight. $4.99 for a set) and use tiny probe or needle to see if they are hard. If it is a pinhole you will be able to collapse the edges. If it is a microsphere it will be hard and you won't be able to smash it at all. I have found this in many different paints from multiple manufacturers so it is in my opinion somewhat industry wide. Knowing the difference will help you fix the problem easier. In fact this all came about in my hillbilly test lab because a customer couldn't get rid of what he thought was "pinholes" in his paint and i tested it and found out it was a microsphere problem. He had to switch products to eliminate it.


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## sayn3ver (Jan 9, 2010)

3m paper paper different grit only. 

I'm always Leary of ordering bulk hook and loop paper online because I'm unsure if the coating that they sterate with will be an issue. 



CApainter said:


> What about the sand paper? Could silicone carbide residue interfere with film formation? I've read in a metallurgy book that certain emery cloths shouldn't be used to prep steel for welding because they contain traces of oil.


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## CApainter (Jun 29, 2007)

sayn3ver said:


> 3m paper paper different grit only.
> 
> I'm always Leary of ordering bulk hook and loop paper online because I'm unsure if the coating that they sterate with will be an issue.


It seems that the finer the sand paper, the more area is affected in terms of film penetration and possible contaminate release from the paper. Do you follow up with a wipe of some sort?


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## Tprice2193 (Oct 3, 2017)

Once you identify the "pinhole" can it be popped with a pin or stroke from small brush? if so its a bubble and likely a surface tension issue. Like you I was in the pursuit of perfection when this problem came up. I believe most of mine appeared during drying about 0.5-2 minutes. They did not appear to be coming from gun. I was doing cabinet doors horizonnally one at a time so I could watch them form and pop them. Some did form a little later. I was using HVLP so the next quart backed down a little on the thinner (distilled water) and they disappeared just as quickly as they had shown up. The micro orange peel disappeared as well! One step closer to perfection....


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