Can anyone with experience spraying Cellulose help me out.
I have resprayed my MGB in celly, Tahiti blue mixed with High Gloss thinners at 50:50 then getting thinner for the last few coats. Total of 8 coats, then colour sanded and polished to a mirror finish.
However... most of the panels have a mottled effect, it looks a bit like patchy blooming of the layers below that are now showing through after the flatting process. Panels that I have not flatted do not have the problem, but they have orange peel of course.

Any ideas on the cause is most welcome.

MGB Celly paint issue

[Edited on 12/8/15 by captainwilkie]

Certainly looks like blooming. Was it wet outside or raining when you painted it. Steve.

No, didnt paint when it was wet outside, but I did spray my workshop floor with water to keep the dust down, perhaps that got airbourne?

Do you have a good water seperator in your airline? wetting the floor is fine for keeping the dust down but it does increase moisture in the air which the compressor picks up......

Second the water trap.

That doesn't look unlike normal celly paint after flatting. Try polishing up with rubbing compound before you do anything drastic. You need to flat to an even, matt finish first but that looks like it will polish up.

HTH,
Craig.

The photo I took was after the complete process, so sanded by hand wet with 2000 grit to a matte finish, then 3000 wet on a DA, then compound with G3 and then G10, its only after the G10 that you start to see the mottling effect, if you then polish it with Autoglym Resin Polish the mottling is masked somewhat, but it comes back again after a day of so, some panels are worse than others.

I have one water trap near the compressor and a disposable one on the end of the gun, I remember that when I took the hose off the end of the gun between coats, you get a a few spits of water in the air that escapes from the end of the hose.

what thinners did you use? were they premium thinners or just general purpose thinners? where did you buy the paint? ebay? most of the ebay stuff it complete crap.

If you're getting water droplets at the gun end of the hose, I think that is your problem.

I built a water trap similar to the pictures below, but mine only has 2 x 3 metre verticals with the supply and output points about 300mm from the bottom, those bowl type traps are of limited effectiveness, I tried my Sealy trap before the copper pipes, and there was still water in the copper....

After spraying a gun full of paint its surprising how much water comes out of the valves at the bottom of each vertical.


Air trap

Thanks for all your replies, most helpful.
It looks like my problem is moisture in the finish. I will put an extra water trap in the system and then I am going to re-flat the paint and put 2 more coats on to cover the problem.

I am also considering putting a clear coat on of 1k acrylic, so I will be flatting the clear coat and not the colour, it also gives it some uv protection etc.

I know that Acrylic clear will go onto cellulose, I have seen it done, and Jawel Paints even sell a kit which includes both.

My next question is this:

Do you apply the clear coat like a normal clear over base system, ie apply the clear just after the colour base coat has flashed off. Or as this is cellulose, do you need to wait until the colour has 'cured' for a few weeks before applying the clear.

I have looked on the U-pol website but cannot find a definitive answer. Their data sheet says you apply the clear withing 1hr of applying any solvent base coats, but I am not sure if this applies to normal cellulose colour.

I've had great results with 1 pack clear over cellulose, see pic...

As cellulose dries by evaporation you need to give it a few weeks, I usually give it a couple of weeks, then a really light flat with 2000, followed by the clear...


t250