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So I am still having pinholes issue on ash.
I have followed advice here and got a AAA pump. less pinholes but they are still there.
I have read a lot of threads here and followed many advices but got mixed results. what has helped so far:
-leaving the wood unfilled as the cv would sink into them rather than bridging and trapping air/solvent.
What did not help:
-grain filing. tried proper oil or water based filler and also using very thin timbermate putty. maybe made them more visible since the surface was more smooth.
- spraying thinner coats may help at first but eventually they beging appearing on the last coats.
I am now looking for causes rather than cure/solution. right now I have these:
-I have read that blowing dust with compressed air could be a cause as it loads the pore with air. it seems logic in theory but how would I remove dust efficiently then. I am unsure about tack cloth and stuf that could contaminate wood
-Using a tip wich output too much cv. I use a graco m211. I sure have to move the gun fast(3-4' per sec.).would using a smaller tip help or worsen the problem
also added some pics to help. Keep in mind that I am going for a semi filled look so visible pores are ok to me
Oh forgot to ask if multiple application or grain filler and sanding could help.
I was looking at an older project and noticed :
They almost Always seem to appear on larger surface. The ones you have to make multiple passes in order to spray. When I shoot narrow pieces that only need one pass(2 inch or less) I almost never get pinholes.
Could they come from the air the AAA use to blend the tails. I mean can it make the finish skin too fast. I generally need about 10-12 psi to blend the tails correctly.
Maybe I am holding the gun to close to the surface. I come from a hvlp background and am used to hold the gun 6-8 inches from the surface. Maybe this is to close and the overlapping passes act like I was blowing a air drier on the piece?
(I once used a air drier to speed up the drying of a test piece an got the WORST case of pinholes and solvent pop ever…teenage pimples everywhere)
Light coats are what I do on oak. So I end up doing one extra coat to make up for the thinner coats. Use retarder instead of thinner. This will give more time for the finish to flow. A more thinned finish might help with the flowing. Once you get a solid finished coat you won't get anymore pinholes.
I too tried retarder/reducer (Mohawk only seem to make one product for this). This works but I often have to go up to 30% thinning to get significant results and it makes the varnish very prone to sag and run.
Instead of thinning that much could I Use a smaller tip and thin less. Would that end up in the same results.
and have you ever heard that tacking with compressed air can cause trapped bubbles?
Maybe next time I will just leave the ash unfilles as it seems to have pinholed a lot less
graco makes a fine finish, reversible tip which you might want to consider, made for wb which have tendency to pin hole, just their nature, the difference between the tips is that there is a pre atomizing plate, a disc that disturbs the laminar flow of the fluid before it hits the tips that does the final atomization of the fluid,, the fine finish tip also is available ifyou don't use a rac or reversible tip. i would strongly recommend you try one. the cost a little more. also you might have to increase your pump pressure as the pre atomization plate or disc whatever you choose to call it creates a bit of pressure drop so that would be the need for bumping the pump air pressure "hydraulic atomization pressure" looking at your pictures and the pin holing, this i believe would be a good investment for you
Well I use solvent base.
But would using a smaller tip help in reducing this problem. I am using a .011 tip and boy I have to move fast with it
Or maybe spray farther away. I am generally within 6-8 inch form the surface
sorry i misread your post.....
and yes you would be moving slower with a smaller tip
No problem herb I tend to ask a lot of questions in the same post.
Right now my AAM211 is laying a serious amout of material. These small 10" x 15" are coated in less than 5 sec. Any slower and the CV is pooling.
The one I spray is Mohawk 550voc. They specify no spray tips size. I had to guess reading here sand there and i'm left with general guideline like .009 to .011.
But would using a smaller tip help with this problem. I mean this could help in laying down a thinner coat thus limiting trapping solvent
Your coats look really heavy to me for oak. I echo the advice of thinner coats, dial your fluid settings down. You can also experiment with different coatings. Some are formulated for open pore definition, some for closed pore, a lot of data sheets will tell you.
Did not know some CV where more suited for open pore woods.
But how do you dial down the fluid amout on an AAA pump. As asked before do a smaller tip will reduce the problem.
Most manufacturer recommend from .009 to .011 tip size. That makes 3 size possible. How big of a difference does a .001" gap makes between tips.
I have ordered a .009 tip that I should receive in a few weeks (nearest distributor hundred miles away)
Just wanted to point out what your seeing is not the industry standard "Pinholes". What your seeing is the in between coating thickness stage of open pore versus closed pore... The "pinholes" your seeing is areas of grain structure that is more open than the other pores around it... Always an issue with wood species that have large grain pores. I generally keep an open pore low film build look on those species or fully fill them... The true "pinholes" term is when a coating has some contamination issues and pin holes develop in the coating.. not a surface tension issue surrounding an open pore on your substrate. Get yourself a pocket microscope that goes from 60-120X power and start eyeballing some of your issues and you will start to understand how some of them are happening...
you may also be right since this is ot the first time this problem happenned to me and curiously always happen on the 3rd coat.
this may be the unecessary coat that ends up being too much
I know noting about Mohawk .
Campbell is the the way to go with a pump , ask a rep you'll get expert advice .
Also when I switched to the pump I redid my air made a dryer out of 2 air conditioning rad from cars it on youtube how to do it .Happy to report the air so dry not a drop of moisture
would using a smaller tip result in a thinner film applied as long as I dont slow the gun speed.
I mean I am already at 300-400 psi fluid pressure and going lower begin to result in atomisation problem with my .011 tip.
Yes, smaller tip size, constant everything else (gun speed) will result in a thinner film up to a point.
Depending on the flowout/etc of the CV, at some point it will result in dry spray because it will be too little to form a consistent film.
But as someone else says, what you are seeing is really the inability to flow, wet, and stay in the open pores. That is a much more complex issue.
The mohawk 550 and 275 CV, while very thin in viscosity, are pretty high solids (44%). That means it's gonna be harder to spray thin coats that look like a coat, because there is less solvent/etc to help it flow.
All chemistry being equal (and it's not, but again, it would be a really long post to go into this), the higher solids content CV is going to have more issues getting into, and staying, in the pores of open pore woods.
You would be almost certainly be better off with a lower solids (25-30%) content CV and spraying two coats of it.
I will definitly try the smaller tip as thinner coat will surely help.
and nice explaination of the problem I always thought it was pinholes but you re right that when I sprayed lacquer, vinyl etc with half or les solid I never had this sort of issue even with WET coats.
oh and i suppose it means that going for a full grain filled look rather than a partial fill should (hopefully) deal with most of the problem?
Yeah, if you sprayed a grain filler or vinyl sealer or something that filled in the pores as a first coat, and sanded it back, i expect you'd see no issue here.
Looking through mohawk's stuff, it looks like the duracoat ii post-cat is much lower solids (26%), so i expect it would work better here to flow into the pores.
as of now I was using waterbased grain fillers but they always seemed to fill the grain poorly leaving lots of small holes that you only seem when you get my problem.
I will use their oil based grain filler even if drying time is longer. It very easy to thin I use varsol paint it on bare wood then sand back. much easier than applying after staining and sealcoat.
as for the duracoat I have sprayed it. easy and very forgiving but alwqys found irs resistance well...meh...can scratch it with my nails if I push hard enough. its more brittle than cv.
Use a rubber squeegee to work in grain filler. It forces the product into the pores compared to just painting it on.
I have always found using anything water based like a grain filler will not only fill the grain you want filled but also open up some other 'holes' as it is water and that is what it does to wood.
Yeah. i've never used duracoat, i was just looking through the product lines you have access to. Mohawk does not have a ton of options for coatings.
Unless you are out of the US, i would just have krystal or something shipped to you - i know plenty of distributors who will happily ship it to you freight no matter where you are, and the shelf life is 3+ years, so as long as you can store a few cans, it works out fine.
As an aside- Mohawk reintroduced their iso-free 2k urethane, which is going to be your best bet in ultimate scratch/etc resistance in their line.
I spray conversion varnish with a Graco G40 air-assisted airless. I use the M409 and the M509 tips. You use an M211? Too narrow a fan width and too much material being pumped onto your surface. A wider fan, suvh as the M409 will allow you to move slower but also to get more coverage.
30% thinner? Too much thinner itself can contribute to pinholes. At such a thin coating, your film has trouble bridging the pores. Lay down vinyl sealer for your sealer coat and forget that your coating is self-sealing. Most coatings are self-sealing but that doesn't mean for better finishing. Vinyl sealer, as a first coat, might help. It has a better "wrap" on the wood than your CV does. It gives you a better foundation on which to build your topcoats. It's a thin product, put it on thin, sand it right before topcoating it so the tooth doesn't close up.
Thin your CV with no more than 15% thinner - and 15% is a lot. I thin up to 10% thinner, and I think that amount seems thin to me.
Lately I'm shooting with an M411 tip and an M611 tip. On large panels, especially, I like the quicker speed in laying down the finish, lots of square footage to cover while maintaining a wet edge.
I have ordered a m209 lately and be able to try it in 2 weeks when I receive It.
is generally use narrow pattern since I generaly spray narrow but long piece so I did not want to waste material sprayin a 1 - 2" wide piece with a 8 inch fan. largest panels I sprayed in last 3 months are maybe 12" by 18"
I also have a m207 wich came with my gun but never tried it. I may has well give it a try next job.
oh and btw thanks everyone for your input I have so much to try next time
It is hard to see what is happening from a picture taken after your material is dry.
It sounds to me like you are ending up with a lot of solvent pop, Google solvent pop and you will find some good information.
Like others Have said you are going to get some holes or indents with open grain material as a couple coats of finish coat won’t fill those holes.
If your spray is like little air bubbles that are popping you are having solvent pop. By what you were saying and I would agree with Daniel, you have to much thinner, and the other thing is it sounds like you are laying down to much material.
The other thing to consider is the temperature and humidity, finishes have a design temperature that they should be applied at, if you are spraying where it is super hot or cold you may have to get an additive to either speed up or slow down the flash time . Your supplier can help you with this.
The other important thing to consider that has already been mentioned is you need clean, dry air. (so very important.) Contaminants in your air can cause you a multitude of problems. An air dryer is important, but also the type of airlines you are using is important, black pipe is terrible for airlines as an example.