What paint to use after welding?

Post by **pmdavies** » Thu Sep 25, 2008 1:23 pm

Hi

Am doing quite a lot of welding underneath and wondered what is the best way to protect it afterwards? I've got some Zinc 182 primer in the garage but don't know what to use on top. Or is there something that doesn't need primer which would be easier? Don't really want to use underseal.

Also, what about protection inside the new box sections, the bits you can't get to with a brush. I seem to have inherited an unopened can of Waxoil but how do you get it in?

Thanks

Pete

Post by **bmcecosse** » Thu Sep 25, 2008 6:39 pm

Coat with Jenolite or similar to 'kill' any remaining rust, then your zinc primer followed by chassis black. The thick black 'garden gate' paint in some of the £ shops is absolutely excellent!
The waxoyl needs to be sprayed in - capture all the old spray bottles from under the sink, then thin the waxoyl with a little white spirit and warm it up in a bucket of hot water - shake the bottle, and spray away!

Post by **MoggyTech** » Thu Sep 25, 2008 6:40 pm

Seam seal the welds both sides if possible, then zinc prime, then chassis black.

Waxoyl sprayers are uselss, and it's best applied with a paraffin gun and compressor to atomize the spray. Do not over apply the waxoyl in box sections, it can trap moisture, aim for a fine mist to cover everything.

Post by **rayofleamington** » Thu Sep 25, 2008 7:16 pm

If possible, use weld-thru zinc rich primer on the bare metal before welding toghether - that way you get some protection on the parts you can't reach afterwards. I seam sealer after zinc priming, then paint - however if you don't waxoil inside all the box sections they will rust out from the inside, so the shiny paint won't help. Make sure sills and box sections have plenty of drain holes and they are not blocked! Modern panels come without these - maybe to increase the rate at which they need re-replacing?

Paint is usually ineffective on a rusty surface as it will lift straight off when the metal continues to rust and make things worse by holding water to the surface. Therefore thick paint and/or cacky underseal black globby stuff is best avoided unless the surface is right for it.

Post by **pmdavies** » Fri Sep 26, 2008 1:52 pm

Thanks guys, forgot about the seam sealer, think I've got some in the garage, it's in the 'that'll come in handy one day' section!

Post by **pmdavies** » Fri Sep 26, 2008 1:52 pm

Thanks guys, forgot about the seam sealer, think I've got some in the garage, it's in the 'that'll come in handy one day' section!

Post by **bmcecosse** » Fri Sep 26, 2008 6:39 pm

Well - I have used seam sealer in the past, but that was on a brand new (Mini) bodyshell. Where it's a welded up seam - you may just trap rust/unfinished steel in the seam with that sealer. I URGE you to be generous with the Jenolite - especially at the seams - it etches the steel anyway for good adhesion - and then seal or paint as you wish!

linearaudio · Post by **linearaudio** » Fri Sep 26, 2008 7:20 pm

For rusty-but-sound metal I have found POR-15 excellent-it grips with a vengeance. However it's useless on good metal (just peels off) unless you use the also expensive preparation/etch system, so ultimately becomes VERY costly!

Post by **chickenjohn** » Sat Sep 27, 2008 1:02 pm

I pretty much agree with all the above advice- remove all rust, then zinc prime, then seam seal the joints, then paint with chassis black. When this is dry use underbody wax underneath and cavity wax in all cavities.

Its best to butt weld all repairs, where possible to avoid making new rust trap steel sandwiches, with butt welded repairs you can clean and paint both sides. If you have to have an overlap, for example where the car was overlapped and spot welded originally, then use weld thru primer, as stated, drill/ punch holes every inch/ 1/2 inch and plug weld these areas, then seams seal etc.

I also drill drain holes where they should be.

Post by **bigginger** » Sat Sep 27, 2008 5:11 pm

chickenjohn wrote:Its best to butt weld all repairs,.

I hate to contradict ypu here, but that's simply not true. In SOME cases, a butt weld is best, but being the weakest form of weld it isn't in lots of others.

Post by **chickenjohn** » Sat Sep 27, 2008 7:12 pm

bigginger wrote:
chickenjohn wrote:Its best to butt weld all repairs,.
I hate to contradict ypu here, but that's simply not true. In SOME cases, a butt weld is best, but being the weakest form of weld it isn't in lots of others.

I have to disagree here. Butt welds are stronger and better. No overlap and its closer to the original structure. On the Mig welding.co.uk site the consensus if butt welds are stronger than lap welds. Complete penetration between the two pieces. Lap welds are fine for "get through the MOT jobs" but restorations should be butt welds, where possible. If there is an overlap- as the original structure- should be plug welded or spot welded.

Post by **bigginger** » Sat Sep 27, 2008 7:26 pm

Then we have to agree to disagree

linearaudio · Post by **linearaudio** » Sat Sep 27, 2008 9:56 pm

I'm with you bigginger, but mainly because butt welding bodywork with a stick welder is a bit much even for me!

Post by **bmcecosse** » Sat Sep 27, 2008 10:09 pm

I would say - if patching in sheet metal to replace a rusted out hole - then butt welding an exact fitting patch and grinding away excessive weld etc so the patch 'disappears' is the ideal way to go. But for large sections of new panel - an overlap is very much easier to do - and if welded on both sides of the lap will be very strong.

Post by **chickenjohn** » Sun Sep 28, 2008 12:04 am

When I was learning to weld (on my Traveller!) I started with lap weld repairs- as that was all i was confident with. By the end of the resto, all my repairs were butt welds. But I did use zinc weld thru spray and seam seal the laps, then waxoyl on the outside. Since then, all the advice from various good sources had been to butt weld rather than lap for car panel repairs, i.e repair as a sngle skin where there was a single skin originally.

But, I guess as always- each to their own! Yes, lap welding repairs are easier to do, but on a restoration course, they will teach you to make the patch accurately to fit the hole with at most a 1mm gap and to butt weld it in. Then as BMC says, grind the excess to make as close a perfect repair as you can. Depends on your skill and patience!