Aluminium boat trailer flaking / disintegrating

A. Hi Paul. The bad news is that this sounds like an old aluminum outboard motor I had which just crumbled away. There were areas that looked halfway between aluminum and what an aluminum colored sugar cube would look like. And it had zero structural integrity; you could just break pieces off with your fingers.

A trailer with no structural integrity sounds dangerous, so I'd suggest that you have it lightly sandblasted to see how much sound metal you actually have left. Alternately you could just blast it with a pressure washer and see what happens. But there's really no sense trying to fool yourself about how much worthwhile aluminum is still there, or trying to encapsulate porous powdery aluminum into a clear coat to pretend it's still aluminum.

After you've blasted or pressure washed it, you could try treating with a "salt remover", then clear coating it.

I don't know whether this happens because of the aluminum sitting for prolonged periods in salt water, or from galvanic corrosion of the aluminum caused by contact with the steel because I also bought my motor many years old, but my guess is that the aluminum on your trailer was in terrible shape long before you bought it.

Regards,