How to glue XPS together – turn 1″ into 3″
Hi, I am in zone 4a and I just picked up a bunch of recycled 1″ XPS (25psi).
I would appreciate a sanity check on my strategy.
I am going to stack 3 layers of it under my slab to create a 3″ insulation total.
Since it is fairly thin layers, my strategy is to make a very flat small gravel layer of rock under the foam. Then to stagger the joints as I install it and glue the layers together, so it withstands walking on it for installing plastic, rebar, pex, and concrete pour.
My fear is that 1″ thick will be more prone to break, whereas a 3″ layer will be much stronger.
I was thinking to use my spray foam gun and run a zig zag pattern of the spray foam to act as a glue while staggering the seams.
CONCERN: While spray foam glues very well, my concenr is that of expansion and creating air gaps. I am thinking??? that I can just ensure I put a thin layer while zig zagging the foam???
Alternatively, I thought I could make 3″ thick boards the same way and not have staggered seams.
FYI, these boards came off an old chicken house and are 4ft x 27ft x 1in and are essentially fomular 250 (25psi foam).
I figured the density by cutting a 1″ x 12″ x 12″ piece, weighed it and multiplied the weight by 12 to get a 1.6lb weight which is the density of fomular 250. fomular 150 is 1.3lb per cubic foot of foam and it has a 15psi load limit.
Thank you for your advice.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part