[Non Corsa] Grinding off welds?

[Danny]

Quick question:
My sills have been patched up as they're getting pretty crusty.
If I grind off the surface of the welds to get a reasonably smooth surface to stick some hammerite over, will it be okay, or will the plate fall off?
I know it's a bodge, but I can't afford to get the whole sills replaced, and it looks a right state as it is.

[CorsaEdi]

Not quite sure what you mean but anyway

If the weld on the plate is strong enough then you should grind the weld down smooth to tidy it up, if it falls off then you need to weld it better if it stays on then your sorted, u just welded two plates on to my impreza and I ground down the welds and went put a bit of filler all way round the plate to tidy it up then painted it with waxoyl. Hth

[Danny]

What you've described you've done, is what I'm planning.
I'm not clued up on welding though, so didn't know if grinding off the visible welding would be the only thing holding it on, or if it's just overspill.

[Dave]

If it's the only thing holding the plate on, then it hasn't been welded properly, and the weld is cold. It should be a nice hot weld, with a fair amount of penetration, its the heat penetration that welds the gap between panels and stops the weld from just sitting on top of the panel.

[Danny]

Excellent. The grinder and hammerite comes out at the weekend then

[CorsaEdi]

Any pics if the welding and what welder are you using? Mig? Arc?

[Danny]

Grinding off welds?

I didn't do it. Was done by my local garage.
They're good though, will be a proper job.

[CorsaEdi]

I would of thought the garage would grind them down :/

[Taurus]

Depends on what you want to pay. Most of the cost is making it look nice afterwards, the actual welding is dirt cheap.

Best bit of kit for making welds look good is a powerfile with a ceramic belt, does a cracking job of smoothing it out. And don't use Hammerite, it's useless on car bodywork. Too brittle, it'll crack and then moisture will get behind it. Either use Ronseal No Rust which remains slightly flexible, or better still, give it a coat of acid etch, then use something like Comma underbody seal (if you want a black finish).

[Danny]

Grinding off welds?

Here's the offending areas:

[Danny]

So, grind it smooth, bit of this:
Car Body Filler & Car Paint Preparation | Halfords UK
Then a bit of this:
Comma USA500M 500ml Underbody Seal : Amazon.co.uk: Automotive

If I can't get it looking decent with a grinder can I skim a bit of filler over it before the etch primer or will it just fall straight off?

[Vegas]

Grinder should make surface rough enough for filler to stick to

[Williamcorsa]

I would grind down the weld using the flap disk and give the surface a good key before using acid etch primer then seam seal the welds and then spray another coat of normal primer on top before painting.

[Taurus]

Just a thought - don't buy that underbody spray from Amazon, it's about twice the price of buying it from a local factors.

[Danny]

I don't plan to, was just the first I found on Google.