DIY painting

[Heathg]

Another question I have been mulling over. My car has been dried stored for 5 years in primer and has faired OK but will need stripping back to bare metal to ensure all rust is gone before repainting. I have read plenty of horror stories of paint jobs going wrong due to moisture and tiny rust pores working away under the surface so want to kill it all before I repaint.
I would like to do as much as I can but without a nice heated garage or paint booth am concerned that once I get to bare metal the rust will beat me. I spoke to a technical expert at Frost who suggested I painted the whole body work in POR15 which was a surprise to me as he said that it can be painted over. The thought of painting the whole car in this very tough black paint that is vitually impossible to remove concerns me a lot. I may be a slightly unusual etype owner in that I am broke so when i eventually get to a paint shop I need to make sure they do not have to start again but I can reduce costs as much as possible. So there you have it! Any suggestions!

[christopher storey]

I am not a painter but I have had some recent experience of this sort of problem . Under no circumstances would I use use POR 15 . I think that if you did this, no reputable painter will even look at the job because the stuff is difficult to get off, and there is no knowing what adverse reactions will take place with proper paints . Take the primer off by sanding back to bare metal, and then (as you do it) immediately coat the body with a 10% solution of phosphoric acid. This is available from agricultural merchants. The body should then be sprayed with etch primer ( which is actually an acid based primer) as soon as possible. It will then last reasonably well until a proper spray job can be undertaken

[e-bygum]

Chris
When the phosphoric acid has been applied do you rub it off before it has dried and then spray the etch primer or do you let the acid dry completely and then spray the primer straight over it without any cleaning off?

[christopher storey]

Well, I have done both and have not found it to make much difference. If put on dilute, and left to dry , it tends to form a primable phophate surface which gives lasting protection. If you rub it off with eg wet and dry , you gain the reassurance that it is unlikely to cause any reaction with paints applied, but you lose the phosphate protection

[38E]

[quote="Heathg"I spoke to a technical expert at Frost who suggested I painted the whole body work in POR15 ....[/quote]

OK, Stop right there. That guy is no expert.

I'm not a painter either but I worked for 30 years in the OEM automotive finishing industry, designing the equipment that prepares products for painting. Two things need to be done to steel to ensure a successful and lasting paint job. Much simplified, it needs to be thoroughly cleaned of all microscopic rust and impurities and then it needs to have a zinc phosphate conversion coat applied.

Zinc phosphate reacts with the surface to form a chemically bonded christaline coating that provides the very best mechanical key for the paint and will also prevent future rust creep under the film from a stone chip. (Where you commonly saw cars in the 80s with rosettes of rust on the doors etc, it was because the shell was improperly phosphate treated during the painting process.)

Once the surface has been treated, rinsed and dried, an epoxy primer should be applied. It should not be an etching primer. Etching primers are for use only in cases where phoshpatizing was omitted. Not together with it.

People like PPG supply these products to the automotive re-finish trade although you won't find many so-called professionals who use them or even know about them. (After all, how long is an average refinish collision job expected to last?)

PPG's metal cleaner for steel would be DX579 and the conversion coat or conditioner, DX520. These would be applied with a Scotchbrite pad and then thoroughly rinsed and dried, followed by say PPG DP40 epoxy primer, then a hi-build urethane primer surfacer over that. In the case of DSP40 epoxy, it must be re-coated within a few days to ensure a chemical bond with the following coat.

[Heathg]

Thanks Chris and Clive it did not feel right using POR15 for anything on the top side. On using phosphoric acid or zinc phosphate does this kill the rust or do I need to us a rust killer before. I have used metal ready which seems to apply a zinc phosphate coating and so just wanted to check.

Clive if I could pick your brains a bit more is it possible to brish paint any of the products your suggest? If not can the low cost DIY spray options be used or is this a professionaljob. Last question can I actually purchase any of these products or are they trade supplied only.

Thanks again for the advice, much appreciated

[christopher storey]

The phosphoric acid, or indeed the Zinc phosphate primer, will kill the rust. I prefer the acid because it more certainly converts any rust to ferrous phosphate thus killing it. You can then use zinc primer on top

You should be able to spray any of the primers yourself reasonably successfully , but a decent gun with a small compressor is best - rubber inner tubes and home made sprayers never give good results . It is a good way to learn the techniques and the mistakes which arise ( runs etc) without doing any irremediable harm because it can all be rubbed down easily and without having to wait weeks for it to harden which is a problem with modern finishing paints

[e-bygum]

Heath
I use Clarkes Rust Remover from Machine Mart. In my opinion it works considerably better than Metal Ready and is a lot cheaper. Both products are phosphoric acid based but the Clarkes seems to be less dilute.

[e-bygum]

Heath
I use Clarkes Rust Remover from Machine Mart. In my opinion it works considerably better than Metal Ready and is a lot cheaper. Both products are phosphoric acid based but the Clarkes seems to be less dilute and more aggressive.
Clarkes Rust Remover ? 4.69 per litre, Metal Ready ?14 per litre from Frost's (plus p&p).

[38E]

Clive if I could pick your brains a bit more is it possible to brish paint any of the products your suggest? If not can the low cost DIY spray options be used or is this a professionaljob. Last question can I actually purchase any of these products or are they trade supplied only.

Heath, Actually obtaining these products is something else again and probably depends a lot on your local laws. I do know that companies like PPG and DuPont used to provide excellent re-finish books which you could just pick up at the supplier but they don't do that any more. They want only professionally trained operators to use their products. Even the containers have no application data, just safety information.

Regarding application, there are times when brushing may be suitable, eg for when you are restoring a lot of dismantled components etc and I generally keep a jam jar of ready mixed epoxy in the shop fridge just for that, using say a 1/2" squirrel hair brush to flow it on. You can also brush urethane surfacer if you don't mind the extra sanding you'll need to do, but it only lasts 1/2 hour or so once mixed..

But to obtain professional results with a modest outlay, I'd suggest getting one of the knock-offs of the Binks Model 115 top lever touch-up guns currently available everywhere. The pattern and volume can be readily adjusted, just like on a full size gun.

http://www.machinemart.co.uk/shop/produ ... ir-brushes

I have such a gun and use it much more than any of my full size guns. It is just large enough to paint say a wing or a door and ideal for painting components. You could probably get away with a small compressor although it's always better to have plenty of air available in any shop.

[christopher storey]

Like Clive, I have had one of those touch up guns for many years and have nothing but praise for it. The only thing I would say is that it perhaps needs a little more practice than a full size gun because the use of the thumb trigger takes a bit more practice than a squeeze type. Mine works very well with a small portable compressor

[38E]

.... the use of the thumb trigger takes a bit more practice than a squeeze type. ...

My version works best with the index finger, giving very precise control.