Did a small plug weld in acid test

[Vinnie]

I'm planning on having my car dipped at some pont. One of the dips is in in phosphoric acid to de-rust the car. One point of great concern to me are all the plug welds I'm doing and have done. Since I'm taking so long rust may creep in where the metal is unprotected between the 2 sheets around the plug weld. So I thought I'd test this myself. I used 75% acid and made a 50/50 mixture with water and the temp was about 50 degrees Celcius. I put the test welds in and let it sit for only 15 minutes. When I took it out there was no rust next to the welds. There were a few spots where 15 minutes was a bit too short but had started to get smaller. See for yourself:

 

[Don C]

I would consider using a weld through primer on overlapping surfaces

Weld Through Primer: Complete Guide And Best Products - Metalworkmasters.com

Eastwood, SEM, DupliColor and others make it.

 

[Bentworker]

You need to do a control piece or three that is not dipped and repeat the test a few times.

Performing a test the way you did may lead to a false conclusion.

 

[Vinnie]

I would consider using a weld through primer on overlapping surfaces

Weld Through Primer: Complete Guide And Best Products - Metalworkmasters.com

Eastwood, SEM, DupliColor and others make it.

I'm using 3M weld thru on the car. But the first of the 3 dips my car will get is one that strips paint etc so maybe also the weld thru primer... Nevertheless, I am currently using that. It gets burned away close to the weld though.

 

[Vinnie]

You need to do a control piece or three that is not dipped and repeat the test a few times.

Performing a test the way you did may lead to a false conclusion.

A control piece that is not dipped? It will remain rusty. What would it show? There is no other way the rust could've gone away apart from the acid...

 

[Bentworker]

A control piece that is not dipped? It will remain rusty. What would it show? There is no other way the rust could've gone away apart from the acid...

Copy - I missed what you were testing...

I thought you were testing to see if the Phosphoric acid weakened the welds, I missed the fact you were testing how effective it was at rust removal inside the lap joint. 

Now I get it - facepalming now.

 

[Vinnie]

Copy - I missed what you were testing...

I thought you were testing to see if the Phosphoric acid weakened the welds, I missed the fact you were testing how effective it was at rust removal inside the lap joint. 

Now I get it - facepalming now.

Oh, you just taught me a new word: lap joint! Thank you