Weld through primer

[66FBCharger]

When welding panels or patches into your car, do you use weld through primer? What are the pros and the cons of using it? Does it affect how easy or difficult it is to start a bead?

[Domino]

I used it a lot on my '70.  Several brands from $18 SEM to $4 a can.
For me they all caused splatter and poor flow.  It also gives off gas as it burns and caused molten plug welds to blow out just as they were filled up with weld pool, burning me pretty good on countless occasions.

For plug welds, I started running the tip of a file in the drilled hole to scrape the primer off the backing metal before welding.  That helped the flow and splatter, and still gave me the corrosion protection between layers.  

Although, in retrospect I'm not sure the primer is worth the aggravation for a garage kept car.

[NHCharger]

I agree with Domino. I use the SEM weld through primer, same issues as he describes. I initially tried to turn up the heat but that caused me to burn through the metal.

[Domino]

I agree with Domino. I use the SEM weld through primer, same issues as he describes. I initially tried to turn up the heat but that caused me to burn through the metal.

I played with the wire size (and heat) too... 0.030" vs 0.023"  no quick fix there either
even tried copper and zinc primers

[66FBCharger]

So I guess weld through primer is not worth using.

[Troy]

I used the Copper type (Eastwood brand I believe) and it seemed to work well compared to other areas that I had welded. Welder seemed happier at least.

Troy

[Domino]

So I guess weld through primer is not worth using.

Really should wear a respirator burning that stuff off, guess that's another consideration.

[elitecustombody]

I've tried many ,SEM copper seems to work much better than others

[richRTSE]

I tried the copper primer from UPOL when doing my floor pans and I was pretty happy with it...I'd use it again.

[Silver R/T]

I've tried many ,SEM copper seems to work much better than others

Personally I like all SEM products, haven't had problems with any of them so far

[elitecustombody]

I've tried many ,SEM copper seems to work much better than others

Personally I like all SEM products, haven't had problems with any of them so far

I can't argue with you there. SEM has great products.I use their stuff all the time