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Old 03-13-2010, 04:05 PM
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Epoxy resin instead of epoxy primer

Oh what the heck! Let's see if this question gets any opinions. I have been doing a lot of boat resto and fiberglass work over the past 5 years. Now I am trying my hand at a street rod project. I have been following all the debates on the various rust threads and have decided that for what I am doing and what I want out of life...

I want to prime "hidden" surfaces with a 2-part epoxy "something" instead of any of the other bazillion ideas everyone has. So here's my thought/question. If 2-part epoxy primer is the shizzle for coating bare clean metal, and if I am going to prep a lap joint before spot welding, then instead of opening up a couple of cans of 2 part epoxy primer ...

Why couldn't I use something like the West System epoxy resin and just coat those small areas of my lap joints with this instead of primer? The advantage I see is I can use their dispensers (which I am very familiar with) and just squirt small amounts of the epoxy system into a little paper cup (like I have been doing for 5 years with fiberglass repairs) , the mix and then brush some onto the freshly cleaned surfaces of my soon to be lap joints.

That way I am only using a little bit of resin and everything stays nice and neat and inexpensive. And I would assume the 2-part epoxy fiberglass resin will seal off the surface of the metal as well or better than the spray on primer. And I don't have the mess, waste or expense of the automotive epoxy primer systems.

Attached photo is an example - that whole joint between the two cab sections is a lap joint that I will spot weld or stitch weld and then apply seam sealer to. But before I start welding I want to sand, clean and prime the mating surfaces.

BTW... I don't care if my project rusts in 45 years. I will be dead then. I just want to do some common sense insurance and call it good. For what I am trying to do, I would rather drive my truck project earlier rather than spend extras weeks/months of my life trying to defy the laws of physics by stopping all rust possibilities.
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Last edited by sparkydog; 03-13-2010 at 04:13 PM.
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Old 03-13-2010, 06:20 PM
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The welding heat will burn your epoxy, the smoke will not be happy for you or the weld. The heat will remelt the epoxy and it WILL run into the weld making a mess of the weld.

You could weld the joint, clean it up and apply the epoxy then heat it with a heat gun, it will thin out and run into & thru the joint sealing everything.
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Old 03-13-2010, 07:29 PM
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I have also read many of the rust encapsulator and rust converter threads. It seems like it all depends on whether the person is a professional body man or a DIY as to whether you like them or not. Most of the pros seem to dislike them and recommend epoxy primer. I am going to try something I think could be considered a hybrid of both products, epoxy mastic. It's a two part system made to be applied directly to rusty metal. I called PPG, the company that I bought the product from and they told me the consistency of their product is like a heavy paint but can be thinned with Xylene. If you thinned it enough, but not too much, it should flow into seams like what you're talking about.
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Old 03-13-2010, 08:32 PM
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Main thing is to seal the metal from air/water to stop or slow down rust..on those laps it is a good place to use a weld through primer and then seal the joint with a seam sealer after the epoxy primer..for the OP if you have the west system on hand it would make a great seam sealer for the rest of us the urethane stuff in a tube works just fine..

I have tried most all of it and now do what is known to work..
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Old 03-13-2010, 10:32 PM
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Funny that this came up today. I try not to do too many lap welds, but sometimes it can't be avoided. I share your feeling too about slowing the rust, but wanting to get the car done as well.
Today, I needed to do a lap weld and didn't have any weld through primer, but I did have some rustoleum brand barbecue grill paint, so I painted both pieces, and then put them together, wiped along the edge with mineral spirits to remove the paint, and welded them. I think it'll outlive me.
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Old 03-14-2010, 07:46 AM
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rust o lium also makes a cold galvinizing comouund that makes a pretty darn good weld thru primer.93% zinc 6.00 a 20oz can, available at lowes I like it...BTW epoxy primer does nothing to stop rust ,if you put it over rust, it'll come right back ,rust has to be given attention before epoxy...

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