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MG Midget and Sprite Technical - Perplexing paint

Some have a mental block over the fairly straightforward electrics of our cars. I have a similar problem in making sense of simple paintwork!I

I had what I thought was a sound sequence of using an epoxy primer from Bilt Hamber to establish an inert and waterproof 'skin' over the varied surfaces of my car - steel, lead, filler and paint of various ages. The intention was then to flat it off, make good any remaining minor imperfections and finish with a colour coat. Sounds simple.

Today I painted the offside inner wing, footwell side and sill with the epoxy primer. It went on ok but as it cured it has already reacted with something, puckering the surface in places. I don't know if I now need to remove this completely or if I can just sand it smooth and progress.

Should I have used some sort of barrier coat first, before the primer? And if so, what?
GuyW

Guy,
I haven’t used BH epoxy but many use a ‘strong’ thinners similar to celly and has likely reacted with an old paint. Similar to applying Hammerite over old paint.
For a good coating system I would remove the crinkled areas as there will be unbonded areas.

Again a call to BH might be worthwhile ?

R.
richard b

I think you have been a bit unlucy Guy, its the same approach I used to paint my midget and I didnt have any problems.

Agree with Richard, you need to remove the crinkled areas otherwise its just going to bite back later unfortunately.
Chris Madge

The wrinkled areas are quite limited so I can easily strip those off again, though when I realised there was a reaction I stopped applying the epoxy stuff over any more paintwork. Although there are other areas over paint that haven't apparently reacted. I wonder if it may have been reacting with some other contaminant, not the paint?

There is a bit of history to the paint as it is. I did a full back to bare metal restoration in the 1990's. I borrowed an industrial compressor and pot blaster and took the whole shell back to bright steel then within 20 minutes sprayed with an etch primer. I then used celly in lots of very fine coats with good results.

Despite my heavy use and abuse of the car in all sorts of conditions this lasted pretty well for 20 years or so by when it was beginning to look a bit tired. Someone convinced me then that he could do a freshen up with 2K which would be quick and longer lasting. As he was a professional crash damage restorer I agreed but was never that happy with the end result and it hasn't lasted anything like as well as my earlier amateur efforts!

So, upshot of this is that there is cellulose paint largely overcoated with 2k, though only on the exterior body panels. Other parts of the tub are still cellulose but will also have areas of rattle can paint (acrylic?). This varied surface plus areas of new or stripped to bare metal and some filler (and who knows what other contaminants!) is why I had hoped to give the whole thing a coat of waterproof epoxy primer ending up, I hoped, with a single uniform base for the colour coats.

Anyway Rain Stops Play as it is now set in to rain for the next 10 days or so. Grrr!
GuyW

That's a real bummer Guy
Your new primer, is that 1K or 2K
If it's 2K did you happen to tip any extra thinners in it
It sounds a bit like the thinners has soaked through into whatever was under there
Maybe use just a dusting coat to start with and plenty of time to flash off before you do another dust coat
Unfortunately if you put a decent coat on the thinners creeps into whatever's under there so lightly lightly and plenty of drying time between should stop it frying up--
willy
William Revit

Yes its a 2k epoxy primer. No thinners added as I am brush painting the primer just dealing with sections of the car as I work around it. Another reason for using the epoxy primer! It needs to withstand a mild wet UK winter ready for proper painting, I hope, next spring!
GuyW

I'm thinking that brushing it on, you're probably getting a lot more on in one go than you would spraying it and the thinners part of the 2 pack is getting into it---If you're going to brush it, it's probably going to happen unfortunately when it finds something to attack----Following on from Richards advice, now's the time to fix it before it hardens up and makes a real nuisance of itself later on.
William Revit

I'm confused now. Is it the thinners in the epoxy primer that is reacting? Or is it the old (cellulose) paint reacting to the new thinners?
GuyW

It'd be the thinners in the epoxy reacting with something, not necesarily the celly, it might be going back into the primer underneath--? If you haven't bought a heap of primer it might be worth changing brands with hopefully a different less agressive base-
Or contact whoever you got what you've got off and see what they have to offer as a cause---
William Revit

Its Bilt Hamber stuff. A very well respected producer. I'll give them a call and see what they say.
GuyW

You could ask them about additives, If your conditions are a bit cold and the 2K is taking too long to dry it 'could' be letting the thinners creep through into .the paint underneath. Any good primer will get into what's underneath, it's a part of getting good adhesion.
There's an additive here called 2K Rocket Fuel for speeding up the drying process--good for cold weather.
William Revit

During a break between showers I had a better look at my paint problems. The epoxy primer has in fact gone on very well for a brushed application. Brushing, not spraying, is what is recommended for this product and I must say the resulting surface is very smooth.

The only areas of crazing of the surface are a couple of small areas on the inner wing. This I know is where the cellulose remains that I applied in 1994. The engine bay area wasn't sprayed with 2k when the outer body panels were done.

So on that basis I think I will carry on as planned, other than within the engine bay where I will use a standard celly compatible primer.
GuyW

onwards and upwards
William Revit

Still seems odd though. You say you didn't add thinners to the epoxy so I'm surprised it reacted with old celly whose own thinners must have evaporated years ago I.e. you'd think no thinners was present! There must be another constituent in the epoxy that's reacting with the old cellulose.
Bill Bretherton

Bill, the product is designed for brush painting. I think if it was to be sprayed it would need thinning but there's no information about that. I didn't add any thinners. The paint had a clear fluid on the top and needed thorough stirring. Maybe that is thinners? When stirred in it had an oily appearance until fully incorporated. I then added the 2nd part (liquid hardener?) At 1:4 ratio. As you say, there must be some volatile component though, to cause it to react.

It may seem irrelevant but I assume the process is the cellulose paint reacting to the sudden addition of newly applied 2k. Rather than the 2k reacting to the cellulose. Or do I have that the wrong way round?
GuyW

Some 2K paints are really potent brews, I suspect yours is one that's fairly aggressive. It's in the design of the paint itself to get into whatever you're painting to promote good adhesion, specially if it's an etch primer---I can remember painting a m/bike fuel tank with some black gloss 2K---On the tin it said it could be recoated after 10 mins or after 24 hours. About 2 hours after painting it, it had dried out fairly well so I got into it with some 2400 paper and soapy water to get the perfect finish and mixed up another pot full and gave it a really light dust coat just for luck--exactly the same paint out of the same tin and it stood up and crinkled up like sawdust
The rep said read the tin, recoat straight away or tomorrow, not 2hours-------------weird
William Revit

This thread was discussed between 14/11/2022 and 16/11/2022

MG Midget and Sprite Technical index

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