Do Weld-Thru Primers Work?

[twodoorhardtop]

I am restoring a classic car and will be Mig welding new steel sheet metal after cutting away the old rusted metal. Some will be lap joint plug welds and would like to protect between the lap seams from long term corrosion as best as possible. I've found a few companies that make a weld-thru primer. Most are Zinc rich but one contains aluminum. They say they are good for Mig welding. I don't see how it can work very well, since Zinc oxidizes and vaporizes at a lower temp than the melting temp. of steel causing cracking/spattering and is why its more difficult to weld galvanized. Aluminum seems like it would have a similar problem. Do they add another chemical to alleviate the problem? Anyone have any experience MIGing with a weld-thru primer?

TIA
Mark

 

[sayee1]

MIG welding thru' weldable primers can be done effectively using Deoxyaluminite or Bloxide
See

http://www.aaccobraze.com/page7.html

or

http://www.bjwe.com/tempil/pyrometalpaint.htm

/

http://www.bjwe.com/zzpdf/tempil/t13.pdf

We use these primers for MIG, FCAW- gas shielded as well as self shielded welding effectively for structurals without problems and have qualified PQRs as per AWS D1.1 and ASME Section IX undergoing full mechanical tests after welding on these primers without any problems.

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
The whole of science is nothing more than a refinement of everyday thinking!!!

 

[stanweld]

Deoxyalminite coatings have been used effectively for over 20 years. I have impact test qualified welding procedures with coupons coated with Deoxyaluminite at -50 F nearly 25 years ago using "short-arc" GMAW.

 

[twodoorhardtop]

Thanks sayeeprasadr and Stanweld,

Very interesting. Okay so the aluminum based ones work as far as being weldable. Now, how good are they for corrosion resistance? Months, years? The Bloxide says extended periods and that is before heating.
I found on another message board that U-Pol Weld#2 which is zinc rich is more weldable than say the 3m brand. I'm thinking the Zinc rich primer may not give as good of a weld but better corrosion resistance. Weld strength isn't as important in my application. Any more comments apprecated.

 

[stanweld]

These thin primers are used to protect the steel from rusting for a limited time prior to welding and are used to limit joint preparation. They do not provide protection of 2-mil thick applied zinc rich coating like Carbozinc 11. The thin weldable zinc primers are also easy to weld over with GMAW. After welding you can prepare the weld and adjacent sheet steel with a suitable automotive primer.