Painting issue - primer bleed?

[joesbox]

I painted my chassis over the weekend. All in all the process has gone like this:

1. Bare metal
2. POR15 rust preventative paint (left to fully cure, several weeks)
3. POR15 Etch primer (left to dry for about 45 minutes)
4. Solvent basecoat from Jawel paints (1:1 with 2K thinners and left to dry for about 45 minutes)
5. UPOL 1K smart clear

The reason I left the basecoat for 45 minutes was because the tech sheet for the lacquer says that solvent basecoats should be coated within 1 hour. Problem is in some areas where the lacquer went on fairly thick I got this problem:

The UPOL clear kind of "sagged" (not sure if that's the correct term). The red basecoat kind of fell away a bit and exposed primer beneath.

Fortunately it's not a massive issue given that it's the chassis but I want to avoid this when it comes to the rest of the bodywork.

Any ideas guys? Any tips greatly appreciated!

 

[PSweeney]

I'd say the issue is in the basecoat re-activated and pickling when the 1k clear went on. 1k has a high thinners content to dry as opposed to 2k.

 

[joesbox]

Any ideas how to avoid it?

 

[711jrp]

My guess is the problem is in the Etch primer stage, what are the application specs for that?

 

[joesbox]

POR15 claim that it "can be topcoated in 15 - 30 minutes". I did have some suspicions that it was a problem with the primer though. I've got more suspension parts to paint in the next week or so. I was going to prime these a day or two before applying the basecoat and clear to see if the issue creeps up again but I'm not sure.

 

[joesbox]

The POR15 etch uses a Xylene based thinners too by the way.

 

[Flapdisk]

What happened is exactly what PSweeny said, I have done it myself. It's nothing to do with the primer, it's just you can now see bits of the primer. I had it happen when epoxy primer had been used. Where the clear went on thick the thinners in it re activated the colour coat and it moved, the trick is always when spraying the clear do a very light coat first, it will look patchy and grotty but that's ok, let it flash off for 20 minutes or so but it will now protect the base, then you can spray a couple of heavier coats, but not too heavy

 

[joesbox]

Cool OK. Thanks for the help guys.

 

[MG David]

You also need to understand that the waiting times on the data sheets generally are a bit on the short side. This is because a) productivity is important to commercial bodyshops making short waiting times attractive and b) us home sprayers probably put the paint on a bit thicker than the trade so it needs to be left longer to get to the same level of dryness.

So leave the solvent basecoat longer and only use a very light coat of the 1k clear to start with as Flapdisk says. I say this having had the same problem in a much bigger way on the bonnet of my MGB. I was rushing.

An alternative to consider is using water born basecoat. I used it after a scrape on the side of my MG ZT. It was much easier than I feared to get an even, flat, mat coat. The 1k clear went over it with no problem. So I have now ordered some to try on the next job on the MGB.

 

[ajlelectronics]

I painted my chassis over the weekend. All in all the process has gone like this:

1. Bare metal
2. POR15 rust preventative paint (left to fully cure, several weeks)
3. POR15 Etch primer (left to dry for about 45 minutes)
4. Solvent basecoat from Jawel paints (1:1 with 2K thinners and left to dry for about 45 minutes)
5. UPOL 1K smart clear

Too many stages of paint. POR-15 is a self priming paint. You can topcoat it before it has fully gone off with no aditional prep, or wait until full cure, flat and topcoat. Yes, they suggest etch priming it, but not really required. All those coats, plus high solvents are a recipe for the problem you see.

My chassis has POR-15 only. Nothing else is required on top unless regularly exposed to UV.

 

[anjum]

The etch primer IIRC was only for fully hardened POR-15.
I guess the OPs paint would have fully hardened in several weeks. The alternative is to lightly scuff the POR-15 but that may cause finish problems unless careful.