Sorry but very basic questions

[sixtwoeight]

Ok, i've made my apology, the more i read the more confused i get, but you all seem easy going enough to be asked simple questions again.

I'm about to start some work on my bmw m535i, it needs several patches of welding done which I should be fine with.
My questions are.

After welding the patch in what primer do you recommend (rattle can will be used) keep reading about epoxy, zinc and etch...does it depend on what paint the paintshop will use? (dont know who will do it yet and wont be for a while)

Does any filler that will be required to the patches go over the bare metal or over the primer? Can filler be left uncovered or does it need primer over top to protect it straight away.

What would you protect the back of a patch with prior to welding in if there is no access to the back of it?

Finally..for now, what product would you use to give a close to factory finish on any patches which are on the underside of the floor? primer then stonechip?

Any makes of primer and filler that you recommend would also be helpful.

Hope you can help,
Cheers

 

[GeorgiePorgie]

What would you protect the back of a patch with prior to welding in if there is no access to the back of it?

Grease or oil.

 

[Chipper]

This isn't (thankfully) one of those forums where folk get told to 'use the search' so no-ones going to worry about more qq's

Best would be 2k epoxy primer. Unless it's got to be rattle cans, in which case a dose of primer & colour to seal out moisture and oils etc. The shop can whizz that off, or wipe off with thinners if there's not huge areas.

Filler on clean, degreased and keyed steel, and some folk do filler onto 2k epoxy primer. 2k epoxy ontop to keep out moisture & oil etc (or again if using cans, primer+colour, primer along being a bit porous)

On the no-access stuff, weld-through primer is usual but burns off at welds. Depending what/where etc, poss drill an access hole and use a good cavity wax like Dinitrol. Hole can be plugged with a grommet afterwards.

Underneath, back into the choice of primers first; epoxies or zinc being the usual ones. Lots of chat here about that, people have their own favourites. Then your stonechip and primer & colour or whatever you want to do there.

 

[pedrobedro]

Use schutz over the primer underneath the car for a factory look. For bare metal primer in spray cans get some Zinc182. You can fill the bare metal then prime and skim again to get the nicks out which you didn't see before you primed.

 

[sixtwoeight]

Thanks for the replies.
I've been going over old posts and I keep getting the impression that aerosol primers are really not very good. But on an ongoing project which will be worked on in the evenings what do i do to protect any bare metal, it would seem a lot of work to set up for 2k epoxy to protect a small patch every few days? I Like to do things as properly as possibly, so no point in going to the trouble of trying to do a good job if the products are not going to last?

 

[langy]

Thanks for the replies.
I've been going over old posts and I keep getting the impression that aerosol primers are really not very good. But on an ongoing project which will be worked on in the evenings what do i do to protect any bare metal, it would seem a lot of work to set up for 2k epoxy to protect a small patch every few days? I Like to do things as properly as possibly, so no point in going to the trouble of trying to do a good job if the products are not going to last?

Yep your right aerosols are crap, they mostly contain thinner, ordinary primer is porous so moisture will go stright through it and start rusting underneath where you won't see it.
The simple option for you is to either brush or roller 2K Epoxy primer on to the repaired bits, this will protect it and stop it rusting, when its time to paint just flat it down.

 

[steveo3002]

if you can afford the products...brush on some epoxy where you can then top coat or stonchip if underneath , if epoxy is too expensive then rattle can etch

dinitrol cavity wax for where you can get to

 

[sixtwoeight]

Thanks again for all the replies, at least it seems i have a couple of options..
First i will look at the prices of epoxy to brush on for the immediate protection.
Cheers

 

[GeorgiePorgie]

What would you protect the back of a patch with prior to welding in if there is no access to the back of it?

I find this irrelavent to painting or protecting with paint or any other protection simply because when you weld the patch in the weld will burn the protection and render it prone to rust.

High melting point grease will protect it better than any paint.

 

[Robotstar5]

I find this irrelavent to painting or protecting with paint or any other protection simply because when you weld the patch in the weld will burn the protection and render it prone to rust.

High melting point grease will protect it better than any paint.

Won't it burn when welding?

 

[vdubz]

Do as langy says and get yourself a tin of 2k epoxy and brush it over your repairs. I would epoxy over the welds followed by your filler and then some more epoxy over your filler to seal it, also i like to put a skim of fiberglass filler over welds as a bit of insurance incase there are any pin holes in your welds, although its probly not needed if you brush some epoxy on first.

 

[langy]

Thanks again for all the replies, at least it seems i have a couple of options..
First i will look at the prices of epoxy to brush on for the immediate protection.
Cheers

A litre of Epoxy is £15 plus hardener at another £15, not exactly dear for the best product around i would of thought

 

[sixtwoeight]

Fair point, thankyou