I need suggestions for above waterline body filler

ive used lightweight "fairing " compound on f/g boats in the past for very thin fills over a small area ( say a foot square) that were shallow ( say 1/4" max)...are these fillers acceptable for use on aluminum ...I liked that these fillers were ultra lightweight & im almost sure there wont be a problem using them on aluminum but I wouldn't mind getting some input from somebody with experience using this kind of filler on aluminum...it will be used in very small amounts to radius square corners. example: weld 2 2"-4 " aluminum tubes together along their entire length say 6 or 8 inches (for tachometers) ...dress your weld slightly & fill with lightweight fairing compound to improve aesthetics before painting . or would plastic or glass with f/g strand ( tiger hair) be better ?

 

I am not an expert in filling materials but put together two materials with different coefficients of expansion can be a problem.

 

I wonder if it works with fiberglass well because its a polyester product ?..this begs the question of why does plastic body filler work on metal.. like on cars... I know its common practice to fill small areas on aluminum boats as I watched a video where a sailboat builder that worked in aluminum stated that he would use 22 pounds of filler on average per build but had knocked it down to 1 pound after he engineered a way to build his hulls out of one huge sheet...he cut a shape out of the sheet that allowed one piece to drape over the hull & seam up where he cut it out ....impressive...so I know fillers used & I agree with what you said .. but theres got to be a filler for aluminum boats ...and at that there has to be one that's better than another ,.. I guess that would be one that expanded at a similar rate as aluminum

 

The problem usually associated with polyester fillers are: grip to some substrates and porosity to moisture. These types of fillers also don't like much vibration and tend to "circle out" if exposed to much.

If applied thin and to a well toothed surface, it can work. 1/16" or less is preferred and up to an 1/8" if the materials are physically similar. These types of fillers work with 'glass boats, because they're basically the same material, which eliminates one of the big concerns.

If using over aluminum apply directly after scratching up the surface with an aggressive grit paper and keep it thin.

 

If you stay within one manufacturers "system" from primers to fillers to top coats then you should have no compatibility problems and recourse should there be a problem, otherwise they will all just point at each other.

 

thanks guys..i went to the Newport (RI) boat show & found a product to suit me ,its called ez fair & its a 2 part epoxy type fairing compound that sands nicely in about 3 hours after application & turns to about a bulletproof steel like product after a day or so...it looks like a pretty good soloution ...PAR: I didn't know that ,about vibration ,now that you said it I guess that one shoulda been a no brainer & KEYDISEASE: I absoloutely agree to pick one system & stay wholly within that system, ..good advice,..i found a handful of paints mostly polyeurathanes..when its time to paint do you guys have any suggestions other than awlgrip?..( that's all I`ve ever used)..I have no problem with awlgrip but im always looking for a better way