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MG Midget and Sprite Technical - Cellulose paint quality

Before I start, I've looked at the archive but can't spot anything relevant. I think I've discussed this here before but I can't find the thread now.

I restored the steel bonnet a few years ago. It was of course bright steel, and prepared with etch primer then high build. Colour coat was Colorado Red cellulose from Rainbow Paints in Ferndown, not far from home. Degreased with panel wipe before each layer of course. Within a year it had faded badly, the gloss went off, and tiny blisters appeared all over it. These were in the colour coat not the primer. So I bought another lot of colour, this time from Simply Coatings in Luton, plus UV stable clear coat to stave off the fading. Big problems - there were white specks in both, and I had to re-do sections affected. I have never used any light colour in this spray gun. It was all done in a great rush as I had to get the car ready for my son's wedding using wedding cars sevenoaks! Hence I ended up with a thicker coat of colour in some places, and this eventually cracked under the clear coat.

So I stripped the bad areas back to metal and redid them. I now find that the colour has cracked again under the clear. I had waited about 2 weeks before flatting and applying the clear coat, although the received wisdom is that you can either apply it the same day, or after 24 hours. When I did do it, the colour was hard and flatted OK.

Today I sanded off the clear coat, aiming to get rid of the soft stuff. And is it soft! The colour underneath, which was hard when coated, is now soft enough to peel off with a finger nail. Some other areas which have not actually cracked are still soft, even after more than a year. I should say that I used the correct fast thinner for the colour, and the clear was already thinned. I can't see what I could have done wrong.

I have been spraying cellulose since 1965 and think I know what I am doing. In the old days I didn't, I never bothered with such refinements as panel wipe or tack cloths, and always got great results. Here's a pic of my first Sprite taken in 1977, 6 years after spraying with post office red cellulose. I never noticed any fading (the 35mm slide has though). I am now at my wits' end and this seems to be like painting the Forth Bridge.

I know there are some who will say don't bother with all this and give it to the professionals. Sadly I have had bad experience with one of those who repaired accident damage to the rear some years ago. Some day I will have to deal with the blisters. The fact is, I know I can do this, I have done it before, but now the paint behaves quite differently. So before I re-do this yet again, does anyone have any advice?

BTW I just noticed that you can now get non-isocyanate 2-pack. Does anyone have experience of this?

Les


L B Rose

If you speak to Ken Burdekin of car restoration paints he will tell you that most cellulose suppliers use a modern type of base for the paint and so it tends to give poor results. It also means that using the same mixing ratios as say a 1960's colour might give a different shade.
Apparently Ken uses the original type of base for his paints and so it should work as it did years ago.
I can't fully vouch for that but I have used a little of his cellulose on my motorbike and it worked well and the Ice Blue I bought from him was a much better match to the original than the Ice blue I got from another supplier.
He also recommends a certain thinners as he reckons a lot of the other 'quality' thinners are crap. He does 'sell' his stuff and gives fairly robust advice but he seems to use quality products and if you've got a spare half hour or so it's worth giving him a call.
John Payne

clear coat on top of cellulose? That might be an issue.

The cellulose can take up to a fwe months to properly go off, up till then it's still not able to be covered as it's soft (might feel hard, but not finished evaporating)

If you've clear coated on top before the colour coat has finished gassing then there will be blooming and oddness.

I've never used a clear coat on cellulose, just polished it back once it's hardened. The P6 has had 3 years no bother (dark blue). The midget's paint is fine but the application was pants...
Rob Armstrong

Thanks guys. I took advice from the supplier about the fading and they recommended the clear coat. The problem is that the red fades in a matter of months so I need to protect it quickly. As I've said, the other problem is that the red is hard when coated, and then softens under the clear. I'll try to contact Ken Burdekin.

Les
L B Rose

Les,

About the red fading I was told that was due to a switch from lead based pigments to non lead based pigments which were much more prone to fading due to UV exposure hence the need for a clear coat. Regarding clear coat over celly I have only done that with base and clear and not recently but had no problem spraying the clear almost immediately over the base coat with no problems and I have never suffered blister in paint and have always painted coat on coat with no further prep in between but this was not recently so maybe a modern celly paint formulation issue. I did most of my celly spraying with International and PPG paints and they haven't been in the auto paint market for quite some years as mainly celly couldn't be back by a VBRA guarantee IIRC. I still have some celly stock that may be 30 - 40 years old or more and still good but its noticeable that the old celly seems to have a much more pungent solvent than the current stuff.
David Billington

I have just had a long chat with Ken Burdekin. He doesn't need a lot of winding up! The basic problem he says is that almost all the so-called 'automotive' celly sold today is actually industrial. In the small print it says 'for professional use only' so that gets the suppliers off the hook if it doesn't work for an amateur. He also says most problems stem from the thinner. The cracking is caused by solvent trapping, because most of the thinner these days is reclaimed. Even for primer/filler you should use fast thinner of good quality. Poor thinner also causes micro-blisters, which I had on the original coat.

I used ready-mixed clear coat, but the problem is that you don't know what thinner is in it. In any case it was never intended for other than small patch repairs.

He doesn't recommend non-isocyanate 2-pack. It doesn't give a good finish, and in any case isn't dramatically safer. There was a long lecture about masks, which made me think! I really need to replace those charcoal canisters.

Basically there is no option but to strip back to bare steel and start again, with the right materials which he can of course supply. He suggests 2K etch primer which can be sprayed at home with a good mask, not necessarily air fed. This isn't hygroscopic so there's no rush to top coat once it's on.

I will have to plan this carefully, doing it panel by panel. Overall, from the start of this saga I have been misled by paint suppliers. The first lot 15 years ago supplied trade enamel when I ordered 1k acrylic. Nightmare. Most of that has gone now apart from the interior. The fibreglass bonnet looked crap after a few years but was sold when I restored the steel one. Then started all this anguish with celly. I'm getting too old for this.

Les
L B Rose

I just dug out the receipt from Rainbow Paints. It says "Ind Cellulose". I didn't know what that meant at the time, but now I do.

Les
L B Rose

LB Rose. . . . i have recently sprayed cellulose, and have used paints form colourweld.co.uk and found them to be fine, and at reasonable cost to. I also use Automotive Paints in Aldershot, and can recommend them as well.
Like all things the quality is reflected in the price per litre, and i can assure you that there is a difference in how Max Meyer paints spray over that of a stock shelf brand like HMG. So you may want to look at the quality of the product you start with too.
P Bentley

Well the industrial celly from Rainbow wasn't cheap - 56 for 2.5L. Colourweld wants 39.80 mixed for HMG.
L B Rose

This thread was discussed between 29/03/2018 and 17/04/2018

MG Midget and Sprite Technical index

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