welding aluminum after siliconed

[muddstopper]

Got a little boat welding project. Aluminum boat that is separating at the seam. Long crack, 18in to 2 ft long. Owner has been covering crack with silicon to stop the leak. Of course the crack keeps growing and only real fix is to weld. Anyways, I dont see anyway to get behind the crack to remove any silicon that has been pushed thru the crack during application. I will have to tig the weld since I dont own a spool gun and just wondering if cleaning the outside only will be good enough to get a decent weld.

 

[Sysop]

It will probably cause issues with the weld. I would drill a hole at each end of the crack and grind away the contaminated edges then fill with weld.

Not sure about the type of aluminum used in a boat versus what Ford is using on their trucks, but Ford says standard silicone sealant (the stuff that has the vinegar type smell) shouldn't be used on the aluminum panels as it will cause corrosion.

 

[muddstopper]

I think most aluminum boats are 5052 or 5086 aluminum but this is a 1980's something boat. Not sure of the thickness, less than .125 I am sure. I have only seen pictures of the crack and it looks like it is starting to get separated pretty wide. I am hoping the heating and cleaning action of the torch will take care of the silicon that has been pushed thru the crack. The weld side I can get to easy peezy. The crack is in the corner where the front of the boat sweeps up from bottom to top, under the front deck. He says he hasnt hit anything with the boat and I suspect that hitting waves at speed has just beat the boat until its falling apart. Only reason I am even considering trying to fix is because I am thinking about buying and it is super cheap.

 

[RedNeckGeek]

Were it mine, I'd clean it as best I could then just give it a try. If it bubbles and spits, grind out the bad area and reweld.

Or cut a patch to go over the crack and just fillet weld the edges.

 

[Oldoak]

The area of aluminum to be welded must be absolutely clean with no ruminants of silicone, paint or any other contaminates. Also, unless you have a high frequency unit to go along with you tig welding equipment, you are not going to weld aluminum.

 

[TMGT]

Clean and try to burn it out with a propane torch then clean it again with standard procedure of dedicated stainless brush and acetone.
It'll be hard going most likely.

Don't use an acetylene torch.

 

[muddstopper]

guess I wont be welding the boat, guy called a little while ago and said he had sold it. Some of the suggestions where pretty much what I had planned. Clean as best I could and wipe with acetone and take care of any bubbles as they popped up. I think it would have been a fairly easy job, but did get to thinking if one side was cracked, just what kind of shape was the other side in. Might have been welding on it for days instead of just a few hours.

 

[Stimw]

Worst aluminum that I have ever welded was alum floor in refer semi trailer!
It was contaminated with animal fat and once you got it clean enough to weld then the foam insulation would out-gas , bubble and contaminated to weld again.
Ended up with the bird poop guy didn't know how to weld look.
I think you dodged the bullet on this one!
The heat would keep contaminating the weld.

 

[Arc weld]

Was the boat originally welded? If it was riveted, it couldn't be successfully welded.

 

[TMGT]

Worst for me is working on trash trucks and walking floor trailers used to haul trash, talk about nasty smells and and contamination. Doesn't matter how much you clean it, it's always somthing hiding in the cracks.