Painting a garage door

Just a quick question.

Is the steel, zinc galvanizing ?

If so, that changes the nature of the question.

It's a lot harder to get paint to stick to zinc, and that's why that question has a different answer.

If the material is just plain shiny flat steel, with excessive rust capability as a side effect, then the paint question is a different one. Where the paint has come off, would have rusted, if it was plain steel. With a galvanized layer, it won't rust (at least not right away), but on the other hand, ordinary paint will not adhere well.

If you don't select the right materials, what happens is the paint peels off in about a year. I have a galvanized flashing here, which won't take regular paint. You can tell by the way the paint film doesn't set up on it, what's going to happen. Your paint brush can "tell you a story" sometimes, predicting what's going to happen to the attempt to get paint to stick. Like, run a paint brush over surface mildew some time, and see how the paint "beads" instead of "spreads". And the price you pay in that case, is early finish failure, if it even covers at all.

Each material needs more or less prep or process. The mildew problem is why we clean paint surfaces (or try to). Like washing with trisodium phosphate, to get a tooth on the paint (remove enough biological film so the paint will spread over the real surface).

Applying the paint, is the last and easiest step. Any joker can paint. Prep requires a genius. There are plenty of people in this world who will slap paint on stuff, and then "act surprised" when it falls off. You can even pay them to do that.

Paul

Is there any rust? If yes then some of that rust inhibitor sealer stuff is good. I think prime it all myself, if you cannot get down to base metal, then its not going to come off. Brian

I think it's galvanized. There is no sign of any rust.

This was why I thought about primer.

I washed with sugar soap then rinsed with a jet wash.

I think that is what happened when it was done last time by contractors appointed by the managing agents.

Try keywords like "wash primer".

I've not used any, because I'm the guy with the galvanized surfaces with no paint on them :-) I can tell you with authority, that regular paint lasts around a year, before the lack of adhesion makes it come off again.

Something is required to get a "tooth" on the material. Otherwise, with regular paint, the zinc reacts with the organic content a bit. The purpose of the primer, is to not allow that reaction, and provide some isolation.

The wash can be acidic, as one means of building a primer. And a concern would be if the acid part bleeds through the next layer of paint or not. And the primer has to cover the metal part, as you don't want to be seeing any metal where the regular paint goes on top.

Paul

Hmmm... we had new railings put up around 4 years ago. They were galvanised and spray painted before fitting. Nothing special about the paint other than it being thinned to be able to spray it. Apart from weathering of the paint its still sound. They are ready for a paint next year though.

Did you see them spraying? Or is it in fact powder coat? Mordant solution is sposed to prep new zinc for paint. I've had mixed results tho...

Zinsser Bulls Eye 123 primer.

I've used this successfully with a variety of undercoats/gloss both water and solvent base.

technical details

I would spot prime the patches first with 123 then when dry in 1 hour apply a coat of 123 over the whole door. This paint will stick well to previous gloss, providing that the old paint is sound, and give a somewhat mat keyed finish for the next coat of paint. At both points check if the old paint was feathered enough at the edges and/or if the finish so far is acceptable to you. The paint is not a filler and any sharp raised edges between the sanded areas and existing paint is likely to show in the final cot of paint.

If you have sanded through the galvanisation 123 is also claimed to be a rust inhibiter.

Oh - and wear disposable gloves as 123 can be a PITA to get off skin once dried (and it dries fast). A green pan scrubber lubricated with plenty of washing up liquid will held remove it from skin.

I take it red oxide would be a mistake then, on a metal that seems not to be prone to corrosion (presumably because it's galvanised)?

Get a primer for zinc it is almost certainly zinc plated and clean with acetone or similar before applying.

Its definitely *not* powder coat and yes I saw them spraying it. The chap who made them is only a few miles from us so easy to drop in to watch progress or have a brew.

Oh good, when you're next passing ask him what he painted your fresh galvanised steel with?

It would be worth it if you can get hold of a hot air gun, it will strip easily. Then use Hammerite Special metals primer and a couple of coats of gloss. It will last for years.

Thanks for the suggestions to use Zinsser. The job finally started this morning. At first I thought the Zinsser was a bit thin. However, when I discovered how difficult it is to remove from my hands, I am now reassured that the grip is impressive.