Mounting an aluminum swim deck on my boat. Will through bolt it of course but what should I use 3M 4200 or 5200 adheasive / sealer?????

I don't recommend 5200. You may need to replace or repair that platform sometime!

I agree. 5200 is for PERMANENT installations ( like through-hulls and trim tabs) and bonding floors and such.

If you use 5200 you don't need bolts

Racer

Thats funny

I put made the mistake of my life when I put my transom assemblies on with 5200 It is going to SUCK to get them off.

on the 5200 or 4200 .. can you use acetone or ? to clean the joints when you first install something ?

Acetone is fine for cleanig surface prior to using 5200
One time we had a boat come in the shop for a steering cable that required removing the motor.This was a 200 Merc, I removed all the bolts and the motor was still hanging on with the 5200. After working for an hour or so it came off with a big chunk of gel-coat not good!