KW-rscos

Just about to send the Cossie in for welding and will be grinding the underside back to bare metal, my question is, should I use mastic 121 straight onto the bare metal once all the welding is done or is there anything else I should be using for future proofing my hard work?

Regards
Kieren

3i Jim

You'll need to prep the areas in question by using a red scotch just to give it a key. Etch prime the bare metal first. There are many sealant products out there, I personally like teroson adhesive sealer for older cars and teroson 6in1 for modern ones. Once you've sealed up all the seams you'll then need to spray underseal or stonechip on the areas in questions or the whole underside. Underseal stays tacky and can't be painted over, stonechip dries and can be painted over. Once that stage is done and dry you'll then need to spray cavity wax inside all the chassis rails, sills etc, buy the proper wax spray gun with the long nozzle. If you end up buying waxoyl make sure you warm it up first before applying, get it nice and runny and it'll flow into all the crevasses and set, protecting the metalwork. Don't bother with aerosol cavity wax. You can also spray the cavity wax over the stonechip or underseal if you wanted to. I restore classic cars for a living, I Hope this will put you in the right direction.

stevieturbo

I think it is correct to use seam sealer before painting. It adheres better to bare metal.

Might also be worth heating the metal first, to try and ensure no moisture or damp whatsoever is in there before it's sealed.

3i Jim

The sealer will adhere to etch just as good as on bare metal. Plus it's offers extra protection. If you get an air bubble/pin hole in the sealer without the etch you'll end up with trapped water attacking bare metal.

Mark V8

iTrader: (2)

Don't use etch if you're going to use 121 Mastic.

121 epoxy mastic sticks straight to bare steel better than etch primer

I would seam seal after using the epoxy as the epoxy will work is way into the seams a bit first anyway.

KW-rscos

So consensus is to 121 epoxy mastic the bare metal, then seam seal it?

Can I then paint over all of this body colour or should I primer it first? And will this stop the rust coming back, bearing in mind I am using new metal where there currently is rust? I do not want to be doing this again in 5-10 years.

Mark V8

iTrader: (2)

You can go over it with regular paint, but it will need sanding first.

Epoxy Mastic is very tough and not much fun to sand though!

I went over the 121 on my Sierra with custom epoxy and then 2 pack colour.



http://www.rust.co.uk/filestore/3%20...MARY%20PDF.pdf

KW-rscos

Bloody hell, that looks very nice!! And in the article it seems to come out head and shoulders above the others!

The only other thing is, once the welding is all done and the car is back to bare metal, should I clean it or treat it with anything before using the 121 epoxy mastic?

Thank you for the advice, mucho appreciated!

3i Jim

Sorry, I thought mastic 121 was a seam sealant. In which case don't etch it.

Mark V8

iTrader: (2)

I just wiped it over with thinners before painting.

Getting it back to bare metal is good enough to give the paint a key in my opinion.

KW-rscos

Well I would be using a wire brush on an angle grinder, so I would have though there would be enough of a key. Did you brush your Mark?

Him what other cavity waxes would you recommend, I only know of waxoyl...

3i Jim

3m, bodyline, tetrosil, they're all very similar, you can get them I 5litre cans. Like I say get the proper spray gun with the lance so you can get in all the hard to reach areas.

Mark V8

iTrader: (2)

I used wire wheels in an electric drill along with a DA sander on the easier bits to get to.

I got through 3 drills doing the underside of my car though



Tried a side grinder but found it spun the wire wheels so fast that it tended to 'burnish' the steel and give it more of a shine.

3i Jim

Very nice

KW-rscos

Fair play, how long did that take?

Mark V8

iTrader: (2)

Forever

KW-rscos

Great

Did you use any chemicals or literally just the drill and wire brush?

Mark V8

iTrader: (2)

Just drill and wire brush, I was worried about any stripping chemicals getting between the seams - plenty of horror stories about acid dipping out there

With an electric drill you can keep changing the direction of rotation of the brush giving it more 'bite'

When the brushes get blunt, spin them up in the drill and tickle them with a side grinder - this sharpens all the wire points and makes them cut like new