More paint palaver

[newm4npb]

Now on my third respray of my Spit bonnet top panel after paint has "micro-bubbled" yet again (see picture}.  I've stripped back to metal and used club-bought etch primer and top coat.  The primer flatted back fine and I used a guide coat to make sure no pinholes, but as soon as the top coat is sprayed on it "fizzes" - you can actually see tiny bubbles bursting on the surface.  The weird thing is that when I flat back again it's the primer coat that looks like it has pimpled up (see other picture with 8mm spanner for scale).

This is doing my head in!  I've checked everything; the pressure is set right (compressor and paint gun), all the paint and thinners are new, there are two water separators in the air line, the paint is filtered, weather couldn't be better.  I've successfully sprayed all the other panels, even the front wings, without any problem.  What have I missed?

I have read somewhere that too thin a primer coat might cause problems and wonder if I've flatted the primer back too much.

Help!

[Colin Lindsay]

The photos have not attached - can you try again?

Are you sure the primer has fully dried? I know there can be issues if the primer is not completely cured, and the top coat reactivates it with the thinners when applied. It's normally too thick a coat, rather than too thin, that causes problems.

Microblistering is usually moisture under the paint, but fizzing seems like some kind of chemical reaction - are your primer and top coat incompatible?

[newm4npb]

I hope the pictures attached this time!

The primer was left for a day in the sunshine we had recently to cure, then wet and dry sanded and then dried again in the sunshine for a couple of days before spraying some test patches this time.

Prime and paint bought via the Club Shop - so hopefully compatible.

[Neil Clark]

I am not at all experienced but I've been reading the Haynes restoration guide and other paint guides a lot lately and it seems the paints etc can be incompatible, so worth talking through with your supplier.

[Graham C]

Looking at the picture the bubbles actually look like pin holes in the top coat, as if the primer is contaminated/ reacting and the top coat can't attach to small areas of the primer. Not a paint expert but I agree with Neil. You talk about leaving the bonnet outside was this the same for all other panels, at the same time. You can still get moisture on panels due to temp changes and condensation forming.

Graham

[poppyman]

You also get that reaction if you have traces of polish or silicon sprays such as WD40. When this starts happening, it's back to bare metal i'm afraid   Some paint suppliers might have a barrier sealer coat that can be sprayed on first. Have a chat with these guy's  https://www.yell.com/biz/b-s-supplies-stoke-on-trent-900570331/ they are very helpful.

Tony.

[newm4npb]

Thanks everyone.  I'm wondering if there is a chemical reaction and whether it is something to do with the original reason for the first respray which was corrosion caused by salt spray getting through cracked paint.  I stripped back the paint to metal and treated the corrosion with Bilt Hamber Hydrate 80 (I think), which I'd had good results with before.  The patterns of blisters look suspiciously like where I applied it with a brush.  Add in any remaining salt contamination and there's a whole chemistry set there! Anybody used Rustbuster's ChlorX salt remover and/or Custom 421 epoxy primer?

[SpitFire6]

Silicone?

[poppyman]

12 hours ago, SpitFire6 said:

Silicone?

That as well Mate  

Tony.

[poppyman]

16 hours ago, newm4npb said:

Thanks everyone.  I'm wondering if there is a chemical reaction and whether it is something to do with the original reason for the first respray which was corrosion caused by salt spray getting through cracked paint.  I stripped back the paint to metal and treated the corrosion with Bilt Hamber Hydrate 80 (I think), which I'd had good results with before.  The patterns of blisters look suspiciously like where I applied it with a brush.  Add in any remaining salt contamination and there's a whole chemistry set there! Anybody used Rustbuster's ChlorX salt remover and/or Custom 421 epoxy primer?

https://www.ebay.co.uk/itm/U-POL-Barcoat-1L/402070702133?epid=1723388673&hash=item5d9d480835:g:U30AAOSwJhZeOtG8 I have had good results with this in the past.

Tony.