Spray painting outside

Baldytyke88

I am repairing a few dents in my van. I have read that primer and P38 filler are porous and so if it gets wet it can cause the metal underneath to rust.

Forty years ago, I was aware of this, when I painted cars etc. we used wet n dry paper etc.

How worried should I be when painting my van outside and leaving it overnight? What I need is some dry weather :)

paul_c123

Just wait for some decent weather.

Baldytyke88

https://forums.moneysavingexpert.com/discussion/comment/82109427#Comment_82109427

I have started on one door, but put a coat of paint on it to let it dry. For another door, I am filling a dent, I have covered it up because we were due rain. I will see what the forecast is like tomorrow.

QrizB

I have read that primer and P38 filler are porous and so if it gets wet it can cause the metal underneath to rust.

What brand of primer are you using?

Dulux for example say their red oxide primer is "water resistant when dry":

https://www.duluxdecoratorcentre.co.uk/blackfriar-red-oxide-metal-primer

Goudy

Normal body grade filler like P38 tends to create pin holes and tiny air pockets.

No matter how well you mix it and try and squeeze all the air out of it, you still end up with them. If you leave the filler exposed to the atmosphere too long moisture tends to form as the filler is exothermic ie it heats as it sets and can attract condensation in a humid atmosphere. Then when you paint over it, the moisture becomes trapped.

It get a reliable finish it's best not to leave the filler exposed too long after curing. If it's really humid where you are working, a fan will help. Then use something to fill all those tiny exposed holes, like coats of high build primer or a stopper (a thick paint like fine filler) before finishing it with a finer primer, colour coat and lacquer.

If you've left it overnight, you could try gentle heat with a hair dryer on the area to try and rid yourself of any excess moisture before painting over it, just enough to drive the moisture off but let it cool a little before painting.

Baldytyke88

https://forums.moneysavingexpert.com/discussion/comment/82109474#Comment_82109474

I am using red primer, Auto Extreme, but it does not mention being water-resistant. I have a break in the rain this morning, so I will try and get it covered with a coat of final paint.

Baldytyke88

I ended up painting the repaired door before I was finished, I thought it might be ok. I need another tub of P38, so I will need to remove some paint before I reapply.

I have also brush-painted the side door; the finish is terrible. I asked AI, and it stated that the temperature on that day could have been too high and that could have been the cause for the paint not spreading properly. So that needs leveling and another coat applied.