Cleaning an aluminum pontoon boat CRUD on toons

[Fasman]

I cut about 2/3 of an inch of crud off with water and heat. Now I am left with the "concrete" bottom coat. I just used acid ( aluminum brightener) and it worked JUST A LITTLE bit....

Aluminum looks good but barely touched the "concrete" I think my only choice is to wet sandblast but thought I would ask if anyone knows of a product that I might use to cut the SCUM.... the edges came off great but the "heart" will not budge I even went straight acid on a small section and it bubbled but didnt change much at all. Thats as hot as I can get it.

Any suggestions. It is the area below the waterline that is giving me troubles if I blast it I thought I could wet sand it to remove the pits

[814jeffw]

Not sure what your aluminum brighteners' active acid is, but try oxalic acid. I use it all the time in the Fall for bottom cleaning of boats. BUT you may be dealing with some type of scum that is different from what we have here and the oxalic may not work. Pontoons can be tough, especially if neglected, as it sounds like the ones you're dealing with were.

Jeff