Any welders on here?

Are there any aluminum welders on here? I am pretty good at tigging nice clean new aluminum but I have one heck of a time doing repairs on a 20+ year old aluminum boat. Could anyone share some tips on how to clean an old boat up so you can make effective welds? The newest boat I need to repair has a crack right down the center of a rib on the bottom of the boat, kicker is that it is directly under the rear bench which I know is filled with foam. I can clean the outside pretty well but I am still going to suck trash from the inside that I can't clean.

Humm #-o I no what your saying but don't usually have that problem.Matter of fact I just did 3 welds on an aluminum that was painted on the inside.Ya, you burnt the paint, but no problem welding.Maybe your using too much heat to start.Heat it up slower so any impurities on the other side can mostly burn off instead of flowing to the top of your weld.Flow a little more argon.

I'll give it a try makes sense as the old guy who taught me to tig aluminum always told me I had to learn to be more patient.

Dont go for full penetration. Using pulse method and use smaller filler rod and direct heat to rod end as opposed to puddle then feed rod in. Otherwise you will pull shtuff from below.
That's what I do in that situation.

All in all it didn't turn out too bad I ended up fixing one crack and four holes plus I helped the guy rebuck a few leaky rivets and now he is leak free. Kinda got off to a rough start but towards the end I got the hang of it, the hull was paper thin from being drug along the ground all it life which always makes it alittle more interesting...