[HitMissTom]

Practicing TIG welding a T-Joint weld on 1/8” steel plate/strap about 2" by 5", argon 15cfh, er70S-2, #5cup gas lens, 3/32 thoriated tungsten, about 85A, which has been cleaned down to bare metal (including the bottom edge of the vertical T) and acetone wiped, I experience the following problem. I tack both sides to keep the vertical piece straight up. Then weld one side and it comes out fairly good. For safety I reclean the unwelded side by wire brushing. When welding this second side of the T-Joint I get a lot of porosity and a horrible weld. Contamination! I did have it down to clean bare metal, so any suggestions would be appreciated.
I cut it and tried Jody's (Weldmonger video) penetration test and the first side looked good, not so much on the second side.

[Poland308]

Did you grind the 1/8 in edge of the plate too?

[LtBadd]

Practicing TIG welding a T-Joint weld on 1/8” steel plate/strap about 2" by 5", argon 15cfh, er70S-2, #5cup gas lens, 3/32 thoriated tungsten, about 85A, which has been cleaned down to bare metal (including the bottom edge of the vertical T) and acetone wiped, I experience the following problem. I tack both sides to keep the vertical piece straight up. Then weld one side and it comes out fairly good. For safety I reclean the unwelded side by wire brushing. When welding this second side of the T-Joint I get a lot of porosity and a horrible weld. Contamination! I did have it down to clean bare metal, so any suggestions would be appreciated.
I cut it and tried Jody's (Weldmonger video) penetration test and the first side looked good, not so much on the second side.

Hi Tom
I'm going to guess that even though you cleaned to the bare metal first, the second side was contaminated (got too hot) from welding the first side, especially the bottom edge of the vertical T.

[HitMissTom]

Did you grind the 1/8 in edge of the plate too?

Yes, all areas touching were cleaned to bare metal. Another post suggested heat may be the problem. Seems logical to me at least.

[big gear head]

When you weld the first side the metal will oxidize where the 2 pieces meet. You can't get between them to clean this before welding the second side. While welding the second side you will pull this oxidization out of the gap between the 2 pieces of metal, which will cause the porosity that you are getting. It can be hard to weld both sides of a thin T joint. Try running a smaller bead on both sides so that you don't heat the metal as much. Your tacks need to be small too.

[Poland308]

Or as long as no one freaks out you might be able to grind a little with a thin wheel into the joint on the second side.

[HitMissTom]

Want to thank all for the great information and help with this topic. It really helps when something is going wrong to get help on how to fix it when learning. Thanks again Hit-n-Miss Tom