Bare metal rust prevention

[Disgusted]

I have cut some rusty bits out of my Renault 4 and I am making some new bits to go in.

I suspect I may be opening a can of worms, but what is the best way to protect against future corrosion? On previous cars I have just primed and painted but the rust has returned after a couple of years.

I was thinking of possibly using a weld-through primer before welding the bits in, followed by a zinc primer, then several coats of paint.

The part I am doing is on the sill, so obviously will get mud/water/stones but is less visible than other areas.

 

[Azazello]

I am interested too, have seen some resotirng spraying something before welding but never understood what kind of products were them...

 

[malcolm]

Epoxy primer seems to be the favourite these days. If the area is prone to stone chip then an anti-stone chip primer on top of that, then body colour or whatever other top coat finish you fancy.

I wouldn't bother with weld through primer - it burns off where you weld so doesn't give much advantage.

 

[Azazello]

It is important even to say that you can't use primer over rust; you have to completely remove it sanding, but is difficult: I think that the best results are sandblasting and phosphatants...

 

[JonathanT]

Hmmm stood wondering what to buy in Halfords yesterday at exactly the same junction as you Dusgusted. Eventually came away with weld through primer as I thought I could use it on the hither to hidden meeting faces of the new bits. Then considered (but didn't buy) etch primer for all the bare metal. Have been putting on a rust convertor like jenolite on. on any vaguely rusty bits after a really thorough clean up with everything I could think of. It's turned the previous rusty patches purple and then black.... My fingers look similar

 

[Tomcat]

Hmmm stood wondering what to buy in Halfords yesterday at exactly the same junction as you Dusgusted. Eventually came away with weld through primer as I thought I could use it on the hither to hidden meeting faces of the new bits. Then considered (but didn't buy) etch primer for all the bare metal. Have been putting on a rust convertor like jenolite on. on any vaguely rusty bits after a really thorough clean up with everything I could think of. It's turned the previous rusty patches purple and then black.... My fingers look similar

I have had 'success' with 2 coats of Kurust, then etch primer, one coat primer then colour. Has worked well in the past.

 

[Cornish4]

I'm just in the middle of replacing the bonnet on my 4. The original is very rusty along the bottom edge under the sidelights. I've managed to get another bonnet from Andrew, aka renault4mad, down at Penzance, but it's spotted all over with rust, far too many to tackle with Kurust so I've taken the risk after sanding it down of spraying high-build primer on. Well hey, the car isn't immaculate, but it's solid, that's all that matters, isn't it? If later on rust starts to rear its ugly head so be it. I'll worry about that if and when it happens, in the mean time.......

 

[JonathanT]

Forge on...,

 

[Cornish4]

Oh yes Jonathan, and enjoy. :-)