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 Welding Painting and Sealing
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stevebod
V4 Fanatic

United Kingdom
316 Posts

Posted - 22 Apr 2013 :  09:05:32 Show Profile Visit stevebod's Homepage Reply with Quote
Hi There,
I plan to sort out some rust on the front of the floor pan on my 96 this summer (if we get one).
I am competent at welding but I've not done much work on cars.
What is the recommended way to paint and seal the joint afterwards?
Looking at the rust area yesterday I think there will be some butt welding required but also the removal and replacement of some spot welded joints.
Specifically then:
1) What paint is best to use to prevent rust reoccurring? Do people use POR 15 or anything special like that?
2) Because it is the front edge of the floor that I'm repairing, what sort of stone guard or underseal should I use?
3) How should I seal panel joins? I saw some zinc based primer in the Frost catalogue that claimed you could weld through it. Has anyone tried this?
Any help would be appreciated.
Cheers,
Steve

hillbilly
V4 Fanatic

United Kingdom
225 Posts

Posted - 22 Apr 2013 :  17:51:54 Show Profile Reply with Quote
Hi Steve, I used POR 15 on all of the bare metal on mine having first cleaned and primed with the phosphate spray, It seems very good and it is definately hard and will take an impact, do follow the instructions regarding putting cling film over the can before replacing the lid or you will be cutting the lid off the can.... I decanted into jam jars so I could use small amounts at a time.
Tiger seal is a good panel to panel joint sealer.
Hope this helps....
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ade
V4 Fan

United Kingdom
171 Posts

Posted - 23 Apr 2013 :  18:26:48 Show Profile Reply with Quote
with any paint, preparation is vital....POR15 is quite choosy about prep...i'm not convinced when i've used weld-thro zinc primers that the weld is as penetrative as without a primer....rust will start right in the joint, where preparation is difficult....sometimes, i'll not paint at all, but flood all joints first with very thin rust-preventative fluid, then heavier-bodied stuff to seal the open joint...sometimes, i flood the welded joint with zinc-rich paint, or an epoxy paint system....
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Dirtbiker
V4 Mad

United Kingdom
637 Posts

Posted - 29 Apr 2013 :  21:49:52 Show Profile Visit Dirtbiker's Homepage Reply with Quote
Hi,
I would be interested to hear peoples thoughts on painting the underside. I had some info from Woody and Ratty on my thread ages ago but more tales of peoples experiences would be good as I've never done anything like this before.
My main questions revolve around when to seam seal (bare metal or after primer or different for different products) and what kind of stonechip to use.
I like the idea of just using chassis paint as I don't like the way underseal traps moisture - is stonechip the same? Also would just using chassis paint be less durable and very noisy?
Any thoughts appreciated.
Cheers
Gareth
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hillbilly
V4 Fanatic

United Kingdom
225 Posts

Posted - 29 Apr 2013 :  22:30:57 Show Profile Reply with Quote
Hi Gareth,
First my experience with seam sealer, I have removed seam sealer (with difficulty) from various cars I have rebuilt in the past and it is usually applied to bare metal however some sealers will soften when they come into contact with oil so if you intend to wax oil and it can leach into the faying edges where the sealer is applied make sure it is compatable, the brush on sealer supplied by Frost will soften in contact with oil.
Underseal will also soften when in contact with oil in fact I use oil to remove underseal this is not the case with anti chipping. There are water and solvent based products and I have used both, the solvent based is easier to use and with both bases you will need to prime first. The main attribute with antichipping is it is a very hard durable base to paint over and if you thin to approx 10% it will leave a smooth finish so you can spray door bottoms, sill sections and areas on the outside of the wings around the arches and it will not show.Hope this helps
Bill
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Dirtbiker
V4 Mad

United Kingdom
637 Posts

Posted - 30 Apr 2013 :  21:19:04 Show Profile Visit Dirtbiker's Homepage Reply with Quote
Cheers Bill, your car looks great by the way.
Interesting about the oil - I used to drive my SAAB with oil leaking out like an environmental disaster leading to an oil soaked underneath. And now the underseal peels off in lovely giant sheets leaving grey primer looking like new.
So my next question is what would you do if the original primer is good - stonechip over the top then paint?
I will definitely be spraying - do you need a special gun for stonechip?

Cheers

Gareth
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hillbilly
V4 Fanatic

United Kingdom
225 Posts

Posted - 30 Apr 2013 :  23:20:26 Show Profile Reply with Quote
Thanks for the comments, I am really pleased with it and use it as my everyday car.
The underside of my car had all of the underseal removed I then keyed the original finish with production paper (nice and coarse 120, Degreased the car with water soluble degreaser, then washed it with soap and water,then water before a couple of coats of primer then spraying with Gravitex antichiping. You really need a shutz gun for the antichiping and run about 80 psi but the guns are cheap and you can use them for waxoil afterwards. I applied a water based antichiping to my pick up 14 years ago and it still looks good, you can get gravitex in Black, White and Grey. Be carefull as petrol will react with it.
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R4V4
Starting Member

United Kingdom
21 Posts

Posted - 03 May 2013 :  00:05:04 Show Profile Reply with Quote
Very interesting topic, I am just at the stage where I have finished welding repairs to both rear inner wings ie removed and repaired suspension strengtheners , mud flap assemblies and mountings etc. Do I seam seal round everything I have welded to the inner wings, Do I etch prime then stonechip and paint body colour then wax oil? All I do know is that most of the areas that I have had to repair are those where something is attached to the inner wing (brackets, reinforcement etc ) and water has crept in and corroded the area
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hillbilly
V4 Fanatic

United Kingdom
225 Posts

Posted - 03 May 2013 :  19:14:18 Show Profile Reply with Quote
I seam sealed all welded joints with tiger seal applied with a skeleton gun then fingered into the joints, Primer applied to everything after keying and degreasing then antichipping and finally as I applied colour coat I oversprayed onto anti chip. Then when all painting finished apply hot wax oil or dewatering oil if you can get it.
For bare metal area's you can use micasous metal oxide as an alternative to etch prime.
I thin wax oil with dewatering oil as it penetrates better.
A problem with continuous welding as oposed to spot welding is obviously the amount of heat introduced to the steel unfortunately this prepares the steel for oxidisation (rust)so cleaning welds when cold with a wire brush and flap wheel will help then treat asap.
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rsimps
V4 Guru

United Kingdom
1616 Posts

Posted - 15 May 2013 :  08:09:16 Show Profile Reply with Quote
If you want to paint or spray stonechip on the underside you need to remove all traces for the under seal. I just went down the blow torch route, then used parafin, then general thinners. Stone chip seems very fussy about the paint/metal being clean. I clean off the weld and use some of Frosts/por antirust stuff (clear blue stuff) on the joint, give it a few minuites then wipe it dryish with a cloth and let it dry (it works better this way). I then use a heavy brush on zinc primer over the whole underside of the car. At this point I will either use hammerite underseal if its a road car or stone chip, 2 pac primer then paint with 2 pac if its a competition car. I find normal go tacky underseal easier to maintain on a road car, rust still develops below stone chip.
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