Classic cars forum & vehicle restoration.

[buzzy bee]

Hi

Obvious question maybe.

When painting over an existing colour, say a darker blue over a lighter blue, am I meant to undercoat it, or can I rub the existing colour down and put first coat of topcoat on, using the old colour which is similar as an undercoat?

In addition, if some area's have been greasy/oily, what is best to use to degrease it prior to paint?

Cheers

Dave

[ukdave2002]

Hi Dave

Yes its ok to paint straight over existing paint as long as the paints are compatible, if they are not you will have to use a barrier coat, but if you are using 2K it seems to work over everything. De-grease everything with panel wipe (don't use thinners or other solvents as you can find it dissolves the paint and creates more work!), rub it down de-grease again and before you put paint on go over with a tack cloth.

I can sort you out with some panel wipe and tack cloths, have loads of both!

Cheers

Dave

[peppiB]

2K does not work over everything. Paint shop I used last year, having asked them to use bar coat and primer first, simply rubbed down the existing coach paint and sprayed 2K on top. There were many areas of reaction all over the body.

I have just finished sanding out those areas, giving the whole car 3 coats of bar coat (there were still reactions after only 1 coat) high build then normal primer and finally the top coat - which is still waiting for me to be well enough to flatten and mop (so far only managed 1 wing )

Panel wipe is the only way I have found to effectively remove all grease and wax

[buzzy bee]

I am to use a Coach Enamel over an ordinary gloss paint, as that you buy from Johnstones etc, is it an alkyd based paint?

[ukdave2002]

[Bitumen Boy]

Enamel over gloss should be fine, but as Dave says, try a small area to be sure.

[baconsdozen]

Someone used Barcoat on my taxi during one of its myriad resprays at least.
Trying to touch up or respray and part of it turns into a nightmare as the paint used to do any repairs reacts with the stuff underneath and it bubbles or cracks sometimes days later.
I think I can either take it down to bare metal and start again (or rather bare metal and filler) or try some sort of enamel.
_________________
Thirty years selling imperial hand tools for old machinery(Now happily retired).

[ukdave2002]

[baconsdozen]

Thanks,I think thats what's happening,when rubbing down to repaint after a rust or dent repair the sanding removes the barcoat and the new paint then reacts. On the last repair I used a red oxide paint as a primer/undercoat and its held rust at bay (it brke through conventional primer quickly) and has not reacted with the paint underneath.
_________________
Thirty years selling imperial hand tools for old machinery(Now happily retired).

[kevin2306]

just reviving this topic and a question i need to ask.
when using cellulose, you read so many nightmares about the primer absorbing moisture prior to the topcoat and causing blisters.
so, a few questions please.
when using cellulose, how long can the primer be left safely without absorbing moisture (is a couple of days ok?)
when prepping between coats, do you rub each layer with wet n dry using water or do you use the paper dry?

some conflicting info out there hence my questions to those of you who have experience.

kev