Welding Joints, butt weld lap joint....what do you do?

[daveq]

Just wondering what is the better option for welding, not talking about replacement panels, but for sheet metal do you use a butt weld or recess the remaining existing edge and overlap by a few mm?

[mgb1978]

I always do an overlap joint and weld both sides if possible. This is mainly because I use a cheap gasless mig with flux cored wire and it just has to look at a butt joint to burn a hole.
Also for patching floors etc. i think the overlap gives a bit more strength to the repair.

[kona]

It would make a great sticky to just highlight the different welds needed at each part of the usual mini spots.....

[just_st3v3n]

got this ages ago....










just a pity i dont have a spot welder...

steven

[GTM Coupe]

A straight butt weld is sufficent if you get full penetration, remember excessive heat will distort the panel, so lots of little spots is best practise. If you are patching rust and the patch won't be seen then an overlap can be and is often prefered so as to find good metal.

[kona]

would overlapping the joint not promote more rust? sorry Ive no idea! ha ha but Im interested because Im gunna be getting stuck in during the summer!


Steven thats deadly!! makes it look easy ha ha.

[mgb1978]

An overlap joint shouldn't be a rust trap if you use a decent amount of seam sealer. The reason that certain parts of a mini rust more than others is usually because of water traps or just poor design.
Also if you use a weld-thru zinc primer before welding some of it "should" stay around the joint and help to prolong the life of the repair.

[GTM Coupe]

Even before welding you should have cleaned back the surface to bear steel this in theory reduces the risk of rust under the patch, mgb1978 is correct by saying to use a weld through primer and a good seam sealer after. The whole idea of the patch weld was to get the strength back into the metal surface, usually where the rust has formed will be the thinnest part of the metal and this makes welding very difficult and the end strength reduced. You need to get back to typical gauge material and this is why the patch is usually bigger.