nitro problem help needed!

[Hobbyist]

Hello all
I am using nitro (Nitorlack brand) for the first time and I have this white fleck problem really bad and urgently need some expert input if possible please.I sprayed and left for 3 weeks. Wet sanded with my Festool 800/1200 and 1500 paper but keep getting this white fleck problem each time! I had previously used a different brand and thought it was old and that's why I was getting the fleck so I sanded down, resprayed black and then the nitorlack but still the same problem. Has anyone any ideas or have you seen this before??? All help appreciated. Dave

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[Grez]

Those may be pin holes. If the lacquer isn't thinned enough this can happen.  If you spray too thick of a coat this can happen and if the lacquer isn't thinned you have to spray a thick coat to get it to layout properly.  What happens is that it skins over while the middle and bottom layer of a coat are still gassing out and the gas pushes through the top layer creating a little hole.  Adding a little retarder can also help.  If it's super hot when you spray this is also more likely. Say over 95 deg. F.  If they are pin holes, you have to sand them out and if they were in the first coat you will sand through and have respray.  I use Cardinal lacquer and it says on the label that it's ready to spray, but it needs at least 4:1 thinning to work properly so get it to the right viscosity for your equipment and technique regardless of what the can says.

[Doug Shaker]

I would love to help, but I’ve never used nitro. If it were me I think I would send a copy of that photo to the makers of your nitro and ask their advice. 

Doug Shaker

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[René B. Peña]

Just a thought, could you be having adhesion problems due to poor surface prep and sealing or incompatibility issues, also can the product be defective? I think I might start over and use a different lacquer like StewMac’s.

Right is right, and wrong ain't right!
But,
close enuf is good enuf!

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[Michael Minton]

Adhesion problems from (surface or air line contamination) usually cause fish eyes, not pin holes.  I think Grez nailed it.  If the pin holes weren't there immediately after spraying, but showed up later, it is almost certainly gas that got trapped because the coat applied was too thick for the conditions.  There are a number of key variables you have to dial in correctly, including the viscosity of the material you are spraying (which you can test with a Zahn cup), the orifice of your gun, the pressure at the gun, the flow you have set on the gun, the shape of the pattern you have dialed in to spray, the overlap you apply to that pattern, and how quickly you move the gun over the surface.

I saved myself years on the self-learning curve by going to my local auto paint distributor and getting a lesson on gun techniques from their technical guy (who teaches the guys at the body shops how to spray their materials).  

I always spray a test pattern on paper before I ever spray a guitar to make sure everything is dialed in correctly.

[Colorado Clem]

What they are describing is called "solvent pop". I would wager that is what you have.  

[Hobbyist]

solvent pop...! That actually makes more sense because it just doesn't look like sanding slurry. So if it is that issue ( I certainly did spray too thick at the start but ended up diluting with 20% thinners but just couldn't seem to get the same flow as I was able to get with either water based or AC lacquer and that's what's puzzling me. i have sent the images to the supplier (Nitorlack) as I feel sure it is something that I am doing and not the product so hopefully they can explain it to me. Normally with sanding slurry you would see the low spots before sanding but there was none on this before sanding..what a puzzle !! It seems that either way I will have to sand back (2 guitars and 2 necks!!) to bare wood or at least to primer! All thoughts welcome here!!

[Colorado Clem]

You only need to sand back until they are gone. Unfortunately that may be all the way back to primer. It's usually caused by too heavy a coat which traps the solvent, not allowing them to gas off at the surface. A slower (higher temp) reducer, and or, adding some retarder will normally take care of it. 

[DR DR]

Thanks Robert

That seems to be the problem alright.. I have been researching and it’s called “solvent pop” and as you said due to one layer not gassing off in time before the next layer went on or too heavy a coat.. will update you all when the company comes back to me( if they do!) 

What seems

Strange to me is that companies say the product is ready to spray direct from the can but everyone else seems to say that they need to be thinned down with at least 15 or 20% Thinners..spraying direct from the can is what I did and that seems to be the best way to cause this problem it seems. Wil let you all know 

Dave 

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[Gill Brewster]

I would try to put some pure lacquer thinner in your spray gun and spray over the area.  You have to spray with a faster pattern than when you have lacquer in your gun.  Make sure and move your gun quickly. It’s worth a try before you sand it  back down.

Gill Brewster Sent from my iPhone

On Sep 24, 2023, at 11:26, DR DR <davidaft...@gmail.com> wrote:



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[Hobbyist]

I would love to think that would work but what is the thinking behind it?? that the thinners would allow movement in the lacquer and hopefully pop the lacquer without having to sand it back ???

[Gill Brewster]

Because it is pure lacquer thinner and “hot” it can melt the coats and allow the trapped solvent gas to escape.  I’m not saying it’s 100% that it will work, but I’ve been spraying lacquer for more than 30 years and I have had success with similar situations.  I can’t emphasize enough that you need to really be fast with your spray pattern when going back over your area.  

Gill Brewster Sent from my iPhone

On Sep 24, 2023, at 12:13, Hobbyist <davidaft...@gmail.com> wrote:

I would love to think that would work but what is the thinking behind it?? that the thinners would allow movement in the lacquer and hopefully pop the lacquer without having to sand it back ???

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[Hobbyist]

Thanks for that and I will defo try it

I am a newbie to nitro as I have always done either water based or AC so 2 quick questions for those more used to nitro...

Percentage thinner used??? (I understand this could all be based on which product but they do all seem to say they are ok to spray as they come in the can,,)

Time between coats??

[Robert Erdman]

I agree with Gill, try a fast pass with thinner.    This finishing stuff is so complicated, sigh, I just wanna build guitars…..

Sent from my iPhone

On Sep 24, 2023, at 1:42 PM, Hobbyist <davidaft...@gmail.com> wrote:

Thanks for that and I will defo try it

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[Hobbyist]

as promised here is the response from the suppliers...

Hi David,

You are using spray or nitro in can with spraygun?

nitrocellulose is a product that is greatly affected by temperature and humidity.
The stains you indicate are moisture trapped inside the finish.

The solution is to make the application in very thin layers and try to do it in days of low humidity and medium temperature.

We recommend 10 to 20% thinner. The exact amount depends on your application equipment and your application method.

24 hours between coats and apply thin coats.

I have said that that doesn't sound quite right to me as I have seen bloom from damp conditions but this is pin spots etc. I am hoping they will come back with something better and will keep you guys informed. Your thoughts on their response are welcome!

[Colorado Clem]

Moisture trapped causes blushing. This is not blushing. it's solvent pop, but the cure is the same. Thin reduced coats, although 24 hours is a bit overkill. I would also add a little retarder as well. 

[DR DR]

Clem

So how would you say solvent pop is caused ?? I have told the suppliers that workshop is kept between 45/50 humidity and that’s why I didn’t see moisture as the problem .. if I read everyone right solvent pop is caused by the first coat skinning over (drying) before the gas has had time To be released. Is that your understanding? 

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[Colorado Clem]

Yes, that's exactly what causes it. Painters talk in terms of "flashing off". If the surface flashes too quick, the surface hardens over and traps the solvents. Car and motor cycle painters tend to see it in clear coats, which by nature are applied thicker. It happens to most all of us over time. 

[DR DR]

Thanks clem

So it is the nitro being applied to thick and made worse by not allowing sufficient time between coats…not humidity.   So solution is to thin out about say 20% and allow more time between coats ?? Thanks again for all the helpful input here

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[Colorado Clem]

That's the cure. A little retarder can't hurt. Also, many coating manufactures sell different reducers based on the temperature you are spraying at. A high temp reducer acts the same as adding retarder by slowing the flash time. 

[Hobbyist]

All
latest response from supplier
There can obviously be a translation issue going on (spanish company) but you get the idea. So it is solvent pop or needle points as they call it and not normal bloom from high humidity
I will just sand back these 2 guitars now and have to start again..this nitro is defo more tricky than AC or water based but I want to relic it so needs must!
I assume I can thin 20% and leave good time between coats so that I don't have to use retarder?? I would prefer to solve the problem without more products if possible so I can really get a handle on the product as I assume all luthiers would just learn to use the product and not be introducing retarder??

Excuse me, we had a mistake and its other problem i was thinking.
I konw this problem as “needle points”
Its easy to solve with retard solvent and thin coats
This happens because the varnish gets trapped and when it comes out it makes this little bubble.
Use solvent retard and this coats and will work ok.

[Colorado Clem]

That time he got it close to correct. First off it's solvent, not varnish. Second, he says, the bubble comes out. Technically it doesn't come out of the coating. That's the problem, it stays trapped. When you level the surface, you cut into the bubble. Get's lost a bit in the translation.