Re: "great stuff" foam filler. thoughts?
i may be looking at the wrong place for it, but i see the 2 part pourable foam costing 62$ for 8 cubic feet. at 5$ a can, i can get 13 or so of these cans at the same price, which i would assume would be more than 8 cubic feet but it's hard telling they don't really say how far the can goes. i wouldn't have to mix anyhing, and i can get it as i need it and not have to order it. maybe it's too good to be true....
Well, I actually looked at this too. The 2 lb density pourable polyurethane foam at USComposites costs as you say $62 for 8 cubic feet.
The Great Stuff in cans is a slightly lower density, which means it'll give more floatation value and less structural value, but let's ignore that for now.
From Dow chemical's FAQ on Great Stuff:
"
How much foam is in a can of GREAT STUFF?? The theoretical yield of a can of GREAT STUFF? is measured in lineal feet of a 3/8?? 1/2? diameter bead. One 12 oz. can of GREAT STUFF? has about 250 lineal feet. One 16 oz. can has about 335 feet. One 20 oz. can has about 420 feet. One 6 oz. can yields approximately 120 feet."
So, we can calculate the volume of the foam in a can of great stuff using this. We'll assume you're getting the largest can possible at the price you list, since you didn't mention size. We'll also assume you get the full theoretical yield because you're using the can at the perfect temperature and not getting any clogs or wasted foam.
We can treat the 420 foot linear bead mentioned as a 420 foot tall half inch diameter column. According to the formula for volume of a column, it would be pi * radius squared * height, or 3.1415 * 0.25 * 5040 (in inches). That's 3958 cubic inches. One cubic foot is 1728 cubic inches, or 2.3 cubic feet.
**Edit** I muffed a calculation here. Correct numbers are in the following posts, but should be 3.1415*0.0625*5040=989.58 cubic inches. So to get 8 cf of foam you'll need 14 cans of great stuff. Which makes my point better than my original calculations.
**Edit**
The cheapest I've seen the 20 oz cans for is $8.50 in a pack of 12. At that price you're paying $120 for your fourteen cans, which is much more than the price of the pourable.
Also, it's not the cheapest way to put foam in place
The prize for that is taken by using pourable foam filled with cheaper polystyrene or polyisocyanate (pink or blue) foam or other filler. What you do is cut enough pieces of the cheap foam to fill the space in question loosely. Then you mix enough pourable foam to fill the cracks, pour it on the bottom, then put the cheap foam in on top of it and weight the mix down with something that lets air escape.
If you calculate the pourable amount right it'll rise up through/around the cheap foam and glue it all together, glue the mess into the compartment, fill up any bubbles, and rise to the top, where you can shave it off level.
To go even cheaper, collect any foam, plastic bottles, anything foam or sealed that will hold air and not crush easily once sealed. Fill the compartment and fill around it with pourable. The pourable polyurethane foam will stick to just about anything and it's compatible with just about any material.
Bear in mind that using "fillers" like this is cheap, but you'll pay a price for it if you ever need to remove the foam, plus it does take a lot of soda bottles to fill up a boat hull
Erik
