Paint blisters

[Mark Wilson]

I'm not a happy bunny I've been restoring my Traveller for several years, most of which it has been in the garage, where I sprayed the shell. I had all the removeable panels media blasted and ecoated elsewhere. Over the last few months I've varnished the new wood and I've sprayed the rear panels and wings ready for fitting. Huge learning curve on achieving a satisfactory finish (should never have decided on Maroon) but I'm getting there with a lot of flatting and compounding.

Earlier this week I left the painted ally panels outside overnight - forgot I'd put them outside, and they got wet. Today I found that the three side panels and two door panels I'd left outside are covered in microblisters, actually some not all that micro. The door panels were blasted and coated, but the side panels were new and I etch primed these before primer filler and top coats.

From what I've read the problem would seem to be trapped moisture, but as the panels have been inside since painting I assume that the problem is with my spraygun set-up - I've got a small cheap water trap on the outlet from the compressor, but I now know that it would be better to have something more effective as far away from the compressor as possible.

Can anyone advise on the best course of action with the affected panels - do I strip all the paint off, or will a bar coat be sufficient? I'm just hoping that I don't get this on the main body of the car if it ever gets to see outdoors again.

Mark

[les]

Sorry to hear that Mark, most annoying. I think I'd be inclined to strip the panels again, mainly to remove all doubt of leaving something to react again. Sounds like trapped water, not sure why getting wet external caused the blisters to appear, I presume the paint had been dry for some time, prior to leaving outside. It might be prudent to allow each coat, etch/ primer to dry for a few days before top coat, of course you may have done this last time. Other than that, a more knowledgeable member may be more helpful.

[amgrave]

Your problem "might" stem from leaving the panels covered in primer for a time before top coating. Most primer paints that have a flat finish will absorb moisture and so it will get trapped by the top coat. When painting you should always coat primer with at least one top coat soon after applying the primer and definitely the same day.

[les]

Cant argue with that Andy but if the primer is kept away from damp conditions, letting it harden before top coat, would likely be favourable.

[amgrave]

One way round the problem would be to sand the top coat off down to the primer, then go over the panel with a hot air gun before applying top coats. That should remove any moisture trapped under the paint.

[amgrave]

Les. If you think about it a paint shop would do a bare metal panel spray in a day, drop it off in the morning and collect the next morning and that's prep, primer and top coat. there is no need to let a primer coat cure (for want of a description) before applying top coat. The important thing to remember is primer is porous and therefore can hold moisture so if there is a delay between coats it is important to dry the panel off with a hot air gun before a further coat. Also a paint shop is always heated with indirect heating and therefore tends to be a dry environment.

[kennatt]

the problem is exactly as described,even in a warm dry garage primer will absorb moisture.if you take the panels inside and direct a decent infrared heater onto them the blisters may go,but you risk them coming back,since they are off the car I would strip the lot back to bare metal and start again.You haven't by chance been using a cover over the stored car/panels ,because even inside these covers are a 100% sure way of causing micro blisters.How have you been heating the garage ,if at all ,over the years, gas heaters put a lot of moisture into the air?? If you know a friendly paint shop,they may let you put the panels in their drying booth when they have it on to dry one of their repaints,if so that should cure the blisters and drive the moisture out,eliminating repainting. GOOD LUCK,been where you are several times,with fibre bodied cars,lotus and scimitar,they are notorious for microblistering.Don't think it's your water trap,because if it was supplying damp air it usually shows up straight away with water spotting as the damp air condenses in the gun and deposits water onto the panel,you would see it straight after painting.

[Mark Wilson]

Thanks all. All the panels have been sprayed and stored in a warmish garage (built into the house and with the central heating boiler in there). They were sprayed very soon after priming, within a day or so. I do remember that I was trying to avoid my usual pebbledash like orange peel and possibly over- thinned the top coats. Could overenthusiastic flatting (through to primer in a couple of places) have caused the problem? I've had a scrape at the blisters and it looks as though the primer may be lifting as well, but surprisingly difficult to tell.

I'm resigned to bare metalling these panels, but really worried about the rest of the car. I've put the painted steel rear wings and valance outside to see if they go the same way. Fingers crossed!

[les]

I've had primer on my pickup roof for six months, I look forward to micro blisters next year.