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Old 07-18-2017, 01:15 PM   #1
Bus Nut
Join Date: Oct 2015
Posts: 339
Year: 2003
Chassis: E-450
Engine: 7.3 Turbo
Opinions on Intumescent Paints and foam...

So we recently started this thread about spray foam and fire concerns:

We have our kit purchased and ready to go, but then got a little freaked out when we realized just how flammable the stuff is.

We've been weighing our options for a week. The two main things we considered were returning our kit and getting roxul comfortboard insulation or using the spray foam along with a fireproof coating.

We're currently leaning towards using the spray foam, covered with plywood, and coating it with intumescent paint.

We have a couple of questions...

1. Would you put the intumescent paint directly on the foam, just on the plywood, or on both the plywood and foam? (keep in mind this stuff is expensive)

2. Do any of you have experience with any of the many brands of intumescent paint out there? Is there any major difference or will they all perform similarly?

Our build thread
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Old 07-18-2017, 02:57 PM   #2
Join Date: Nov 2015
Location: Midwest
Posts: 2,573
Year: 2003
Coachwork: BlueBird
Chassis: TC2000
Engine: 5.9L Cummins
Rated Cap: '00
Stuff probably is carcinogenic anyway.

Many dangers with a RV- electrocution, propane explosion, black water drowning, crash, mold....

I have spray foam and the 1/4 plywood covering is adequate. Use plastic flex conduit and boxes and you will be fine.
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Old 07-18-2017, 03:22 PM   #3
Bus Crazy
Join Date: Feb 2012
Location: Salt Lake City Utah
Posts: 1,635
Year: 2000
Chassis: Blue Bird
Engine: ISC 8.3
Thanks for starting that thread. It has caused me some thought as well. Thought hasn't led to any resolutions yet. I haven't even convinced myself whether sprayed foam is significantly different to rigid foam boards as far as fire protection requirements.

The Green Building Advisor article linked in your other thread stressed that one must use the right intumescent paint with any particular foam. A specific brand of foam will have been tested with specific brand of paint, and only that specific combination technically qualifies for whatever rating it receives. If a person uses a different paint, even if it's "the same stuff" sold under a different brand name, it doesn't qualify for the rating. That's probably an issue for the litigious conventional building world where a contractor could be sued for not using a listed combination. Here in our DIY skoolie world there's no one but ourselves to sue for using a non-listed combination of products!

The GBA article also indicated that intumescent paint would be applied directly to the foam. Some codes allow plywood (3/4 minimum thickness I think, and tongue and groove is required) to serve as a thermal barrier, which apparently does one better than the mere ignition barrier that intumescent paint provides.

From that reading I came away with the idea that an intumescent paint is an ignition barrier for use in unoccupied spaces like attics or crawl spaces. I suppose its purpose might be to prevent accidental ignition from sources that might ordinarily be present in those spaces, such as flame from a torch sweating copper pipes together or sparks from cutting metal framing. If not for the paint coating foam in those places would have been left completely exposed.

Will the insulation in your bus be exposed, or will other materials go onto your walls and ceiling to cover the foam? Would it be reasonable to expect one of those to provide an ignition barrier instead?
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Old 07-18-2017, 06:17 PM   #4
Bus Nut
Join Date: Oct 2015
Posts: 339
Year: 2003
Chassis: E-450
Engine: 7.3 Turbo
Yes, there certainly are a lot of dangers. We're learning that quickly as we try our best to limit them.

I've done my own testing, and it has led me to believe that foam board is just as flammable as the spray stuff. I haven't actually tested the spray, but I had foam board on hand and it went up extremely quickly with a ton of black smoke.

And yes, you are correct. To satisfy code requirements in traditional buildings that will actually be inspected, the foam and paint brand matter. I think the reason comes down to the fact that the intumescent paint isn't technically a barrier, but it can qualify as an "alternate assembly". Since getting qualified as an alternate assembly requires specific testing, foam companies are pretty much only going to test their product with more of their own product. This way you have to buy both from them instead of shopping around. Again, this is just my take on the matter after reading a ton.

And yes, the code for spray foam thermal barriers has been updated to include 23/32" plywood as an acceptable thermal barrier. I have found reason to believe that thinner plywood may soon be accepted as well, though I'm not positive.

Like you said though, we're not exactly worried about code here in skoolie land. Our goal is to make it as safe as possible and limit the odds of us waking up in an oven one night.

So the walls will definitely be covered, and to make it extra safe, we're probably going to use the paint even if it would technically pass traditional building codes without it.

We're also leaning towards keeping all electrical wires inside the first layer of plywood and separated from the foam. We have a short bus, so the entire length of the walls will be covered with built in furniture and cabinets anyway. We'll see...
Our build thread
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Old 07-18-2017, 06:20 PM   #5
Bus Crazy
Join Date: Mar 2011
Location: Oregon/Philippines
Posts: 1,660
always put wires, etc., in their own conduit, after all, one might want to change or pull one of them
Jesus Christ... Conversion in progress.
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fire, fireproof, foam, intumescent paint, spray foam

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