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Old 05-18-2017, 07:13 PM   #1
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Insulation, *again*

So I have an idea I'm playing around with. Say I get a small amount of spray foam DIY, and spray one layer, just enough to cover the surface, and immediately jam a precut board of rigid foam insulation in it, squish and seal. Would this work? Would it not cure properly that way?

Assuming it WOULD work, I'd do a layer of reflectix on top of that and call it done.

Trying to combine layers of insulation and get the best benefits of each in the mix. Spray foam granting some structural stability and soundproofing qualities, rigid foam taking up the bulk of space and cost, but also being foam, which is pretty good, and reflectix giving a good radiant barrier for a heat envelope.

Whatcha think? Bad planning? or good idea: try it?
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Old 05-18-2017, 07:28 PM   #2
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It's interesting to see that idea come up now and then. I had the same plan at one time. Apparently the spray foam won't cure properly if it's not exposed to air. I thought that would be a good way to glue in panels of rigid insulation, using spray foam. Apparently it's been tried. Some very interesting methods have been tried at times.

So, this is showing a good thought process. I never experimented with trying this type of application, rather choosing to take the word of experience in this case. It's kind of a big deal for one of us to mess up the insulation bad enough that we have to tear it out again.
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Old 05-18-2017, 08:00 PM   #3
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I have a little different speculation on the idea.. I think a 2-part foam will cure fine, but that it'll cure so fast that the stuff at the beginning of the panel will be somewhere between firm and hard before you've finished spraying and it wouldn't be possible to press the foam board into it.
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Old 05-18-2017, 08:06 PM   #4
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I have seen this done with recycled refrigerator foam and it did sorta "glue" it onto the spray foam, however it was a terrible botch job, there were several gaps because the foam didn't expand well that needed to be filled. So I would say success is about 50/50.
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Old 05-18-2017, 08:45 PM   #5
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Well I know people are using spray foam to seal the EDGES of rigid foam against it's sides, but I thought spray foaming the wall thinly in the first place would provide a better seal and prevent condensation better, otherwise won't you just get condensation right there in the middle of the foam panel where there was no foam? Or do you think it really works the same? Concerned about details here... lol

Also, how fast does foam really start to harden? I watched a video where within several minutes of spraying the stuff on a test board, he touched it and it tore, so he reapplied. It didn't seem to cure very fast, it wouldn't take me several minutes to add a board of rigid foam, I'd go bit by bit and be careful.

I'm really loving this discussion, moar plz!
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Old 05-18-2017, 09:13 PM   #6
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Originally Posted by DreamWeaverBus View Post
So I have an idea I'm playing around with. Say I get a small amount of spray foam DIY, and spray one layer, just enough to cover the surface, and immediately jam a precut board of rigid foam insulation in it, squish and seal. Would this work? Would it not cure properly that way?

Assuming it WOULD work, I'd do a layer of reflectix on top of that and call it done.

Trying to combine layers of insulation and get the best benefits of each in the mix. Spray foam granting some structural stability and soundproofing qualities, rigid foam taking up the bulk of space and cost, but also being foam, which is pretty good, and reflectix giving a good radiant barrier for a heat envelope.

Whatcha think? Bad planning? or good idea: try it?
You're thinking similar to me about it.
I'm buying one, MAYBE two of the spray foam diy kits and will be using foam board for the "bulk", and the spray for the odd areas and stuff. you dig?
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Old 05-18-2017, 09:17 PM   #7
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I was told the foam around the edges sets up fine after you press the rigid insulation panel into it, but that the area in the middle of the panel tends to turn to goo. I never tried it, but I'd imagine if it were possible it would work a lot better with two sets of hands. It still sounds interesting, but I'm not willing to spend the money to try it when it's already reported as not working.
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Old 05-18-2017, 09:19 PM   #8
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I was told the foam around the edges sets up fine after you press the rigid insulation panel into it, but that the area in the middle of the panel tends to turn to goo. I never tried it, but I'd imagine if it were possible it would work a lot better with two sets of hands. It still sounds interesting, but I'm not willing to spend the money to try it when it's already reported as not working.
I'll be putting in the foam board, then the spray foam. I don't see how there'd be any problem doing that at all. WHo's reported that as not working??
We aren't talking about using "Great Stuff"... That stuff is corrosive in a bus-type environment.
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Old 05-18-2017, 09:45 PM   #9
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You're thinking similar to me about it.
I'm buying one, MAYBE two of the spray foam diy kits and will be using foam board for the "bulk", and the spray for the odd areas and stuff. you dig?
I dig, but I'm thinking backwards to you, I was thinking spray foam first, then squish rigid foam on top. Everything I've been reading has people doing like you though, spray foam in between and on top of the rigid foam.

I guess I could do it either way, I just thought as long as it cures right under the middle of the board, it would work better underneath rather than around and on top.

But Robin says apparently it gets gooey in the middle, so mb spray foam on top is better if I wanna do it that way.

I was thinking one, MB two kits tops as well, but I'll need to run the numbers again on a hypothetical bus I haven't bought yet, for an insulation budget. I'd hate to spend more than 2K on insulation, my budget is small, and I'm basically using 2k for the bus, 2k for plumbing, 3k for electrical system, and the other 3-4k is for everything else, like insulation and extra odds and ends, out of a 10-12k budget. (I already factored in extra cash on the plumbing and electrical budgets.)

I plan on moving north so insulation will need to be good, if not great, but cost is a factor and you get what you pay for, so I'm not sure how to do the best insulation for the cheapest price. Here in Southern Illinois I doubt I'm gonna get an $800 spray foam estimate. 1K minimum for DIY job.

Again, I need to rerun the numbers but if I gave 1k for DIY spray foam kits, which would give me roughly two kits, then add in reflectix, and add in some rigid foam, my lowball GUESS is 2-2.5K, based on my budgeting recently, for 750 square feet of floor, wall, and ceiling.

I'd ideally like to get a ten window bus.
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Old 05-18-2017, 09:49 PM   #10
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I'd forget the reflectix. A bunch of foam would be immensely superior to bubble wrap with mylar.
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Old 05-19-2017, 12:40 AM   #11
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From what I understand, reflextix doesn't do anything without an air gap around it. Even then, the r values you may see being attached to it are for the "system" which includes the insulation its on top of. It may make sense to use it when you have a ton of space and you're already using real insulation to the fullest reasonable extent...

But this is a bus. You have limited room for insulation, so it shouldn't be wasted on something that isn't actually insulation.

That's what I gleamed from reading about a million articles on insulation from all over the internet.
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Old 05-19-2017, 12:49 AM   #12
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Do you really think I should? If I don't do foam, I'm definitely doing reflectix and rigid foam, probably with spray foam at least between the sides, I looked earlier for the link but couldn't find it, but I had a site that had pictures of using fiberglass batting vs. reflectix to insulate a box being heated by a lamp, and reflectix worked way better at reflecting radiant heat. Thought it'd help keep a toasty heat envelope in my skoolie.

Ugh, still chasing my insulation tail. I don't wanna end up freezing my ass off and dealing with condensation after moving north. But I'm not sure I can afford a full spray foam job. Surely one can do decent insulation without spray foam? or with small amounts?
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Old 05-19-2017, 12:53 AM   #13
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Right, but as soon as it is closed in, it won't do anything. Like literally nothing at all. It has to have open air around it.

Here is one of many threads I found about it:

I *finally* get it: Reflectix or foil need an air gap
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Old 05-19-2017, 12:56 AM   #14
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ECCB, I may have asked you this before, but why is spray can foam corrosive in a bus? Is it because it is moisture cured as opposed to chemically? Or is it something in the actual foam. I know they are both polyurethane based, but can't find much about what else.
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Old 05-19-2017, 01:04 AM   #15
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Thanks PigPen, I'll try to do yet even more reading... lol
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Old 05-19-2017, 05:48 AM   #16
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Reflectix is a radiant barrier, designed to trap in heat. If you decide to use it, put foam against the bus, and reflectix on the inside, then put a thin panel over it (can be tin, aluminum, wood, whatever u want) and you'll be good. Do not put reflectix against the bus, you will create a barrier of heat and moisture between the metal and the reflectix, you need the foam to be the barrier from the outside and the reflectix on the inside to trap in heat (or cold, as long as you have a continuous source like AC)
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Old 05-19-2017, 06:48 AM   #17
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Do you really think I should? If I don't do foam, I'm definitely doing reflectix and rigid foam, probably with spray foam at least between the sides, I looked earlier for the link but couldn't find it, but I had a site that had pictures of using fiberglass batting vs. reflectix to insulate a box being heated by a lamp, and reflectix worked way better at reflecting radiant heat. Thought it'd help keep a toasty heat envelope in my skoolie.

Ugh, still chasing my insulation tail. I don't wanna end up freezing my ass off and dealing with condensation after moving north. But I'm not sure I can afford a full spray foam job. Surely one can do decent insulation without spray foam? or with small amounts?
wait till you can afford the spray foam. even a cheap conversion is going to cost 10 grand. converting a bus is not cheap.
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Old 05-19-2017, 09:05 AM   #18
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Do you really think I should? If I don't do foam, I'm definitely doing reflectix and rigid foam, probably with spray foam at least between the sides
Go with one or the other, either rigid or spray, I wouldn't recommend both. The spray foam will do everything the rigid foam will do and more, rigid foam is just fine too, but u shouldn't need both.

Just be sure the reflectix is on the INSIDE of the cab, not on the outside touching the bus shell.
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Old 05-19-2017, 09:15 AM   #19
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I've had a thought for a while but I haven't had time to completely think it through... but what about using severely undersized rigid panels and spray foaming around it? The panels would leave a sizable gap (2-3 inches maybe?) around the edges... enough to get a good amount of spray. The rigid foam basically turns into cheap filler in the flat/easy to access parts.

What's the benefit of spray foam over rigid in the large space between ribs? I hear it adds rigidity but would spraying around rigid foam also add rigidity?

Could you still spray a layer over the spray surrounded rigid foam? Say... 2" rigid foam and another 1" of spray on top?

I'm not really asking these questions directly... they are more rhetorical/hypothetical. This is just the line of thinking I've been having lately.
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Old 05-19-2017, 09:19 AM   #20
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You really don't want to mix both, you can...but you shouldn't. If you're going to spray foam, spray everything. Gaps = moisture pits, even if you think you have that rigid foam tight, eventually movement will widen the gap and over time moisture and then mold.

Either spray foam completely, or rigid foam/reflectix imho
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