spray foam for floatation?!?!

[Ready2Fish]

i have already decked my boat exactly the way i need and want for it to look and weeded out all of my little problems etc. but im wondering what does everyone think of spray foaming underneath the deck directly on a cleaned floor about 6 inches under front deck (roughly 60 inches of floor) and about 8" thick in the back deck with a battery compartment built in

[Way2slow]

You should use a closed cell flotation foam. It comes as a two part chemical you mix and pour into the cavity. You can get different bouyance level based on density. Just be very care, the stuff expands as much as 10:1 and it don't mind busting out the floor if you put too much in a confined space. You also only have about 10 seconds from the time you finish mixing to get it poured into you access holes. Do your homework on it before using it.

I use an electric drill and a small paint mixer. The better it's mixed and the hotter it is, the better it expands. I also make me a bunch of paper funnels because you're only going to get one pour through each. It's better to mix two or three times to fill an area than to try and mix once and put too much.   I also bore 1" holes about a foot apart in each area to pour into.  I cover the whole area with fiber glass matt when done but you could probably just pour some resin over them.

[fishfordollars]

Definately use the closed cell foam. Otherwise it will absorbe everything it contacts. Will end up weighing ten times what it started at.

[Ready2Fish]

thanks, i will try to locate that stuff. first i have heard of it! i am going to be using "great stuff" gaps and cracks and im not sure if you have had any experince with it but i use it quite often and it acts about like the stuff you speak of, it fluffs up ten fold  but it comes with a nozzle and will run til you let it dry.. i will have to give both a try

[Ready2Fish]

whats everyones thoughts on thompsons water seal VS fiberglass resin on my plywood??

[Way2slow]

Something like this is what you're looking for but you migth want to shop around for pricing  http://www.marinefoam.com/polyurethanefoam.html?gclid=CJ3Oo5Gk5p8CFQqF7QodN0XEHA&lcode=AB203

As for the cans of stuff from Home Depot, I'm not sure they are closed cell or not.  As mentioned, if not closed cell it will assorb water and hold it like a sponge, for a long time.  It's very hard, if not almost impossible to get dried out after it assorbs it.

As for Thomson's Water Seal.  I've never and would never use something like that.  If it's a boat I care enough about to put the time and money in to restore/fix it up, I'm going to do it right.  Doing it right means glassing the floor.  Now if it's a jon that I'm just putting a floor in to cut down noise, Thomson's might be OK but that's something that can easily be replaced when it starts to rot or get soft.