Spray Foam for insulation?

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Spray Foam for insulation?

Postby clamlamp » Thu Feb 08, 2018 10:29 am

Hi just wondering if anyone used spray foam for insulation instead of foam boards? If so, what is your experience? Or why would you not want to use spray foam over foam boards?
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Re: Spray Foam for insulation?

Postby les45 » Thu Feb 08, 2018 11:14 am

Spray foam will bulge or bend when it is constrained. It usually expands beyond the limits and is very difficult to trim down after it hardens. I tried to use it on replacement house windows (the non bulging type) and it still created so much of a mess that I ended up using latex caulk instead. It can be done but I would think that it would be a lot of work to make it fit right.
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Re: Spray Foam for insulation?

Postby John61CT » Thu Feb 08, 2018 12:52 pm

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Re: Spray Foam for insulation?

Postby KTM_Guy » Thu Feb 08, 2018 11:51 pm

I asume you are talking one of the spray foam systems that come in a two parts with a gun and mixing tips? And not something like Great Stuff. I wouldn't use Great Stuff because it is hard to get and even thickness over a large area. The two part foam systems would work great in walls where you can use studs or the skeleton boards to cut off the over fill with a hand saw or hot wire knife. The problem I see is with the curved roof. I've never had luck with hot wire cutters over a foot or two. If you cut from spar to spar you could be cutting a lot of needed foam off in the curved sections. Back years ago when I was using the stuff I never sanded it so I don't know if that is and option using a disk sander. I am a few weeks away from insulating my roof and maybe I should look into it a bit more. I planned for 1.5" rigid foam and I can only find 1" in my area so need to come up with a plan B.

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Re: Spray Foam for insulation?

Postby John61CT » Fri Feb 09, 2018 12:22 am

Glue rigid panels up, then fill the gaps, finish with light fast passes to build up a bit more depth.

If you're really OCD, include small battens and glue a final 1/2" inner panel with holes every 4", and poke the spray in with a little spritz in each.

Have flat ply, sprayed with release or covered in plastic and poles ready to hold up with a little pressure as you go, but only put them up just after any (ideally very little) excess comes out the holes.

Otherwise a little irregular air gap does no harm.

I agree sawing large areas parallel to the surface is a major PITA and waste of material.
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Re: Spray Foam for insulation?

Postby mallymal » Sun Feb 11, 2018 4:31 pm

Someone posted a link on here a while ago to some kind of applicator that went on a regular can of foam, but spread it in a wider & thinner layer onto the board. Sorry can’t find the actual post, but someone may remember it :roll:
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Re: Spray Foam for insulation?

Postby szern » Thu Feb 15, 2018 7:06 pm

I am almost finished insulating my roof with extruded polystyrene - I used 2 layers of 3/4 inch to give me a total of 1.5 inches of insulation. I did my best to cut the insulation to fit tightly but there are wires and such to go around so I do have some small gaps. Does anyone suggest Great Stuff to fill in those small gaps or is that a pain as well? This is my first build so I'll take any advice I can get. Thanks!
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Re: Spray Foam for insulation?

Postby John61CT » Fri Feb 16, 2018 10:23 am

It's fine if the small qty required is too small for 2-part.

Loctite makes one too, haven't seen a comparison, may be higher % closed cell.
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Re: Spray Foam for insulation?

Postby clamlamp » Fri Feb 16, 2018 3:16 pm

Ya i plan to use it around my wiring. Good question.

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