Mastic after welding?

[White230CE]

Hi all,

The edge of the outer rear wheel arch of my coupe had rusted at the bottom where it meets the sill. The edge of the inner arch was not too bad.

I took it to the welder, who put in two new patches on the outer arch. He did not weld the patch to the inner arch, and instead wanted to mastic the edge of the outer wheel arch where it joins the edge of the inner wheel arch. He said that at the factory, the inner was spot-welded to the outer, the gaps would have been masticked, then the whole lot sealed with rubber underseal.

I wasn't sure if mastic was the correct course, so I said I would do it myself, and left.

Should I mastic the join? Alternatively, should I etch prime and paint the bare metal and the area between the arches (the inner arch hasn't been touched, so will need to clean it up), followed by clear waxoyl, then black waxoyl?

Thanks for any advice.

 

[teddycatkin]

Yes he was correct the factory welds are all spot--but when repairing its normal to do a running weld-- if done well by a competant welder you should not need mastic to fill the gaps ?
Then clean it all up -etch prime -paint -waxoyl either (but black is a bit messy ?)

 

[White230CE]

Thanks Teddy.

He implied that there would be a problem if he did a running weld. Would there be?

As it is, there is a gap - not even a spot weld as far as I can see. If I don't insist on a running weld, should I mastic the gap or not?

Thanks.

 

[television]

This is a hard one to answer,, number one you do not want any water building up in any seam. If I used a mastic, then I would use waxoil on top, this keeps it soft, ensuring that it is in good contact with the metal. the only problem with mastic's was when contact with the metal was lost allowing damp in. Modern versions are much better.

Running welds can do damage to panels, a very hard choice, I think that I would go with the mastic route

 

[White230CE]

Thanks Malcolm. Should I spray waxoyl into the gap before I mastic or will that affect adhesion?

 

[Xtractorfan]

Well mastic I think is the building sealer, what you need is ADHESIVE SEAM SEALER, this stricks as well as seals the joint, and provides a good quality waterproof joint, clean well with a wire brush, spray some acid /etch primer on to the weld and the bare metal, allow to dry and then seal with the Seam sealer.. allow this to dry overnight and then spray over with a quality stone chip or body schutz, allow to dry again then apply the black waxoyl...no need to use the clear waxoyl..unless to the inside

 

[television]

Thanks Malcolm. Should I spray waxoyl into the gap before I mastic or will that affect adhesion?

No you cannot do that Xtractorfan has given you the best way to do it,,that would be perfect

 

[White230CE]

Well mastic I think is the building sealer, what you need is ADHESIVE SEAM SEALER, this stricks as well as seals the joint, and provides a good quality waterproof joint, clean well with a wire brush, spray some acid /etch primer on to the weld and the bare metal, allow to dry and then seal with the Seam sealer.. allow this to dry overnight and then spray over with a quality stone chip or body schutz, allow to dry again then apply the black waxoyl...no need to use the clear waxoyl..unless to the inside

Many thanks XtractorFan.

I saw something in Hellfrauds called 'Upol Grey Stripe'. Is that a suitable seam sealer, or should I go to a specialist shop, and if so, is there a name I should ask for please?

I've got Hammerite Spray-on Stonechip. Is that 'quality'?

As for using the clear waxoyl 'to the inside', do you mean I spray it into the gap? If so, when?

Thanks again.

 

[television]

Many thanks XtractorFan.

I saw something in Hellfrauds called 'Upol Grey Stripe'. Is that a suitable seam sealer, or should I go to a specialist shop, and if so, is there a name I should ask for please?

I've got Hammerite Spray-on Stonechip. Is that 'quality'?

As for using the clear waxoyl 'to the inside', do you mean I spray it into the gap? If so, when?

Thanks again.

Fill the gap with the mastic strip, spray it then waxoil as the very last thing

 

[Xtractorfan]

there are a few good ones available ..look for the word ADHESIVE on the tube ..if so it can be used to bond panels together without welding, but who would dare not weld.....as for the clear waxoyl spray it on the inside of the panel ..ie on the back ..hidden bit of the weld and only after you have seam sealed and stonechipped the outside of the weld..
The welded area must be clean and grease free for the etch/acid primer to work
if you still arent clear about the procedure i will go thru it again if u need me too

 

[White230CE]

Thank you both, Malcolm and XtractorFan. I understand now.