sporadic blisters ( aluminium structure )

[golf]

boat is of 6mm Sheet Aluminium build ..skimmed with filler similar to car body filler then spray finished . When new undistinguishable to GRP . boat now 20 yrs old and some areas are blistering with water trapped behind blister .. ??? does not occur below water line for some unknown reason??
problem all on starboard side and covers three areas of aprox 1/2 sq. mtr total .
whats best method of repair and any means of preventing recurance .One area is new paint are which has only blistered between old and new paint skin?
all replies welcome .

 

[Ships_Cat]

Really needs someone to look at it to tell, but I would suspect that it is related to areas less well prepared before the original painting (or the recoat in the case of the new bit you mention). The aluminium should be machine sanded so surface is well scratched before the first coat sprayed to the paint manufacturer's instructions.

The above assuming that there is not a corrosion problem as you have not mentioned there being one.

John

 

[tcm]

i wd guess diferential exspanison causes cracks in paint above waterline, not below with watercooled everything. There is of course rainwater under the blistering but essentially it is the corrosion of the aluminium imho.

Fairly normal to have to sand down ally and repaint every so often, and 20 yrs is damn good imho.

I wd sand and sand and then get ready with primer and do a final sand and spray immediately behind, two people one then other.