I reached the stage where I was ready to apply the colour on the exterior surfaces having spent a lot of time ensuring everything was clean and prepared
I am using cellulose paint in Forrest / sambesi green
I applied 2 light coats at 40/60 paint to thinners and noticed some yellow particles in the surface of the paint.
I initially though it was contamination from the paint gun / paint pot and it was remnants of the etch primer.
I flatted the paint back with 800 grit and cleaned everything thoroughly and applied another coat at 40/60, once again the particles could be seen. I tried to apply another coat with a filter in place but the gun was not happy and despite adjusting air pressure up and down the paint wouldnt spray consistently, the air flow was uneven and low volume of paint was coming through as though the filter was preventing supply.
When I cleaned everything down I put the washed out paint through a filter and found yellow and black particles in the paint

Particles in paint
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I will speak to my paint supplier in the morning and see what he advises
Any thoughts?
thanks
David

Looks like it may not be mixed enough, and maybe you don't have a good strainer screen. How old is the paint, and where's it been stored?

Not sure about that ,reason for this is when I did my last repaint of a Golf GTI in Alpine White I had the same issue,it turned out the gun was dirty and it was silver from a previous paint touch up.
Soaked the gun overnight in acetone and all sorts of shit came out,put the gun back together and blasted half a pot of reducer through it and all was good.
Was my own silly fault and to make matters worse I had to repaint the whole panel before applying clear coat.

I don’t think it’s residue in the gun
I can thin some paint down and filter it with out putting it through the gun to show the particles
I have had the paint about 6 months, it’s been stored in the garage and will have been down to 0 degrees C over winter
I’ll check the effect of temp with the supplier tomorrow
Thanks for giving me some pointers to consider

You say paint pot? Do you have feed hoses to the pot and gun? How old is this set up?

If so I am pretty sure that you have old paint from previous jobs that are visiting you as the solvent in the paint is softening them up and spraying them out.

I would just buy a new set up. For sure you have crap coming out. Also double up on your straining filters


Bob B

fascinating - cellulose paint

- we have not seen that in USA for a LONG time - (nor in UK per link below)

fwiw per other comments - high quality "slow" lacquer thinner" which would be used in cellulose paint is extremely aggressive in dissolving "other stuff"

- could be attacking the undercoat or dislodging stuff in the painting apparatus

https://www.jawel.co.uk/jawel_pdf_data/pain...se_paint%20.pdf

we can use cellulose on vehicles that were of the period where cellulose may have been used
its a classic car scene cop out that suits us and enables the amateur to DIY

I have proved to my self that its in the paint, I mixed up some paint and filtered it without putting it through the gun. I was then able to dissolve it in thinners with the exception of some minute black particles, I then put it through a 400 micron strainer and it pulled all the particles out

so I need to mix much more thoroughly and strain the paint at least once before spraying

I will point this out for you one more time. If you rig was used for paint jobs before, there is a chance that there is paint in the feed hose if you have that kind of set up with a paint pot and feed hose.

I have had this problem before shooting lacquer. My company used to shoot a lot of lacquer and as I said I had this problem. I fixed it by putting on new feed hoses and made sure that the rig was super cleaned.

So, what is your set up for painting? Paint pot, hoses and a paint gun?


Bob B

Hi Bob
the paint gun is a high volume low pressure devilbiss with the paint pot on top.

I think it's just a regular paint gun, in North America a paint pot set up has an external 2-5 gallon "pot" with lines running to the gun.
Where as on a regular paint gun we don't call it a pot, we call it a cup.

thanks Mark, its a cup type then

I paint with different things but have painted a bit of lacquer in industrial use for different parts we made at my plastic factory. I remember spraying a 68 MGB that was painted with some cheap Earl Scribe paint job (In the states in the early 70s you could get a car painted for $29.95)


Anyway, my buddie came up with a 5-gallon pail of Red Lacquer used to paint Fire Trucks in So CA. I removed the crap white enamel paint and went to town on the red lacquer paint.

It worked great right in my garage and a color sand with 600 then a buff back then, and it looked like a fresh red jag. Shiny as hell and it dried fast.

Or you could color sand and clean and spray with Clear instrument lacquer with some retarder if it dry’s too fast. I take it that it is colder there than in L.A. where things dry too fast a lot of the time.

The Guitar shown I have not buffed yet but I used clear lacquer as shown with a super cheap Harbor Freight gun. It worked well. I tinted the clear with alcohol base tints that I use in my cast plastic for color.

If I cannot get a gun clean I use acetone as a clean-up. These chemicals I have had around my shop for 46 years.

Good luck I do not know if this will help but for what it is worth.

Best, Bob B

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Years ago, I bought paint from Dupont to paint a set of Flames on my bike. Shot the flames and the paint changed color. How much, I'm color blind and could tell. I repainted the Flames 3 times, same problem.

Took the paint back. Dupont tells me, they'd bought a bunch of empty paint cans that were Contaminated. Sorry about that. Got a refund for the paint, nothing for the lost time and work. I switched to PPG.

Could be contaminated paint cans. Especially with the crap you found.

from another forum
Make sure you give it a good stir, use a spatula or similar dont just shake the tin as what happens is in cellulose paint the component colour used to formulate the final colour tends to settle out after a long time hence the need to stir.