Bartman Posted June 18, 2007 Share Posted June 18, 2007 I have a set of Bad Dog framerails that I wil be installing and I need to figure out the best way to prepare the surface. I've searched here and on other sites and there doesn't seem to be a good consensus on the use of weld-thru primer. Some people swear by it, and others think it's a waste and can actually make the weld weaker. Here's some info I found: http://www.autobodystore.com/forum/archive/index.php/t-1351.html http://www.autobodyonline.com/whatsnew/feature/archive_story.cfm?date=05/05/2003 This last link states that "Research over the past year or so has found welding through weld-thru primer makes a weak weld because weld-thru primer doesn’t strike the arc well, creating poor penetration. And the zinc in the weld-thru primer combines with the weld, making the weld weaker." It also states that "Damlier-Chrysler recently stated that shops should not use weld-thru primer on anything on any of their cars, period.†The first link is more towards which of the weld-thru primers work best. So I'm going to clean up my floorpans and stock framerails before stitch welding on my Bad Dog framerails. Should I prep the inside of the new framerails and the area that wil be covered by them or not? I am planning on using seam sealer as well and attempting to completely seal the new framerails to my car so maybe rust shouldn't be an issue anyway. Quote Link to comment Share on other sites More sharing options...
Guest TeamNissan Posted June 18, 2007 Share Posted June 18, 2007 I personally HATE weld through primer. I would por the inside, then weld, then seal. Some spots of the por may bubble or flake from the welding but you at least wont have bare metal in there. You know even sealed, rust always finds a way, a pin hole, anything. Thats my .02, hope it helps. Quote Link to comment Share on other sites More sharing options...
240zV8 Posted June 18, 2007 Share Posted June 18, 2007 you should be fine doing like he said ^. plus ur in CA, u don't get rust, lol. Quote Link to comment Share on other sites More sharing options...
zcarnut Posted June 18, 2007 Share Posted June 18, 2007 A few years ago one of the automotive paint and body trade magazines BodyShop Business did an in depth evaluation of weld through primers including long term rust protection. I’ll look for the exact article but, in a nutshell their results were that none of the available weld through primers were as effective as [good old] epoxy primer. So, I’m not surprised by the Damlier-Chrysler statement... Quote Link to comment Share on other sites More sharing options...
johnc Posted June 18, 2007 Share Posted June 18, 2007 I use weld through primer (3M's brand) to coat the inside of sheet metal parts I'm welding on to the car. I do not use it on the external parts where I'm welding. Its much better (from a weld strength/contamination perspective) to have a weld through primer behind your weld then POR. I tried to weld a steel patch panel on a car where the customer had applied POR to the back, forget it! Quote Link to comment Share on other sites More sharing options...
Guest TeamNissan Posted June 18, 2007 Share Posted June 18, 2007 What did you have trouble with john? I have been doing it to mine for a while now and didn't really have any trouble. Quote Link to comment Share on other sites More sharing options...
johnc Posted June 19, 2007 Share Posted June 19, 2007 My mistake, the customer had used Easwood's rust encapsulator to coat his parts, not POR. Quote Link to comment Share on other sites More sharing options...
Guest TeamNissan Posted June 19, 2007 Share Posted June 19, 2007 Ya, I only ask because when I replaced my dog legs I painted the back with por and it didn't really give me any trouble. I mean its not perfect for the application but its still better then bare metal in my opinion. Quote Link to comment Share on other sites More sharing options...
Bartman Posted June 19, 2007 Author Share Posted June 19, 2007 So, I'm thinking that I can POR the inside of the new framerails (not the bottom of the flanges that are welded to the floorpan) and the outside of the old ones, but leave it bare on both the old and new where I'm going to be welding. Then seam seal as necessary and POR everything that's exposed after the welding is completed. Does this sounds like a good plan? Quote Link to comment Share on other sites More sharing options...
Guest TeamNissan Posted June 19, 2007 Share Posted June 19, 2007 Sounds good to me. Quote Link to comment Share on other sites More sharing options...
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