Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) One for the paint guys - cellulose over cellulose

I have some areas to repaint on a panel which has otherwise sound paint. I'm not happy with the transition between new and old paint so am considering painting the whole panel. Do I need to use primer on the flatted back original coat or can I put gloss onto gloss?

I am not a paint expert, and there are others here who are so take my comments as such.

So much depends upon the finish you are trying to achieve , if you really want an undetectable super smooth join , then I would go right back to bare metal and start afresh every time. If a less than perfect result is acceptable then you may be pleased with the finish that results from your proposed primer over top coat method.
However i will say that as ever preparation is the key, time spent on this will pay dividends down the line. A perfectly flat surface with no imperfection to eye or feel is almost essential.

There is one thing in your favour though. Cellulose is a solvent based paint , and so the new topcoat will etch into the underlying paint film much better than modern acrylics or epoxy based systems. However it will etch differently into different substrates and this might show on the final result, I would therefore be prepared to prime the whole surface rather than the repair area.

Also NOT an expert but you may not be painting on top of cellulose, given the possible age of the paint and perhaps layers of polish it may have enjoyed as well as tree sap and perhaps other chemicals such as silicone which rubbing down may not remove completely, only to be discovered when the paint is applied drying or even some time later..? As best I can remember I used to give a suspect panel a rub down with T Cut in an attempt to neutralise whatever may be lying in wait, I also used to but some sort of flurite (?) or similar which came in a small eye drop type of container to which I added a frew drops in the top coat... I suspect my old processes have been consigned to history by now...

Good luck with the task at hand, hope I have not muddied the water..err..paint... (-:

I've done a bare metal respray before. Took me 18 months! Your comment on the various surfaces is certainly very valid. It's probably prudent to prime the whole panel. I've already done the rear wings in this way. Easily done as they just unbolt. Not so easy on the "boot' panel as it's attached to the car and not so easily transported to my makeshift paint booth!

I've messed around with cellulose paint all my adult life. Not much to add really, except as Andy says, if you feather the edge you may see a tide mark as different layers interact, and even when it looks OK just done, it can sink with time.

The most consistent approach is full panel with meticulous prep.

Don't expect one topcoat straight onto another to last. It can chip and lift very easily.

I'd recommend a good rub down with a Scotchbrite pad and then spot priming where you have rubbed through with a high build etch primer.

Two or three coats of a good primer filler, then a speckle guide coat to get the levels right

Then the top coats, wet flatted between coats.

Arwyn

A friend of has problems to erspart his HARLEY. HARLEYalso uses an „oldstyle“ colourcoat.

He sanded and clean it and does the respray. With no success. After a lot of tries it always looks that there is some grease
on the surface. At last he use a fluid „silicone remover“ and it works.

Keep also attention about the filler, some filler works very well on the old paint, but when you spray the final color you get a more or less nice wrinkle finish. An bad expierence at my old VESPA scooter.

Greets René

The issue here lies not with the Paint (Paint over Paint) but with the Thinner used, Cellulose Thinner
is the most volatile, Thinner used in the Automotive Refinishing process.

It is well renowned for a workshop to have a can of C/T lying around, this is because it is versatile for
lots of uses, mainly cleaning Paint from your Paint Spray guns and your hands.

The key is to use as minimal Thinner as possible on the application, keep in mind the Thinner's only
purpose is to thin the Paint so you can spray it through a very fine nozzle (of the Gun) once the Paint mix
is applied to the Panel the Thinner then has to evaporate which allows the Paint to then dry and harden.

Cellulose used to be 1:1 mix so when you were throwing a ltr of Paint at the Panel you were also throwing a ltr
of Thinner at it too, the Thinner is that potent it melts its way through any old substrates on the panel and its
like a Volcano irrupting under the layers.

advisory:-

a) try and add as little Thinner to the mix as possible, heat up the Paint Can to heat up the Paint this will thin it
rather than the Thinner, i could actually Spray Cellulose with out Thinner if it was warm enough and this eradicated
lots of the reaction issues.

b) do not attempt to try and obtain a full gloss by spraying lots of Paint on at once, Cellulose is a Polish finish and
can (with a Polishing Machine or by hand) be brought to life, so thin layers, dry coating, so you billed up the thickness,
once dry bring the Gloss in by polishing.

Thanks for that advise. I have had to add thinner. Keeping a "wet" edge can be difficult with temperatures recently. I'm planning on 6 to 8 coats (gives me sufficient for flatting back before polish). How long will I need to leave the final piece before polishing? Thinking a few weeks. It's been a while since I repainted the MGB and I've forgotten some of the details.

The longer the better, leave the vehicle somewhere where the heat (sunshine) can stay on it, 4 weeks minimum
Would be good, that will give ample time for all the Thinner to evaporate and the Paint to harden.