Spray Foam Between Belly skin and floor

[rickysaetta]

I'm renovating a 1970 24' Tradewind. Im planning on using closed cell spray foam for the walls and ceiling but was thinking about using it for the floor as well.

Does anyone have any success or opinion on this?

I figured i would box out the areas i would need for plumbing repair and not foam those.

[DFlores]

When I took apart my 68 there was spray foam insulation in / on and around the frame. I am guessing it was built that way not really sure. Played he’ll getting it off. So I guess it works

[Wabbiteer]

To say I’ve become allergic to being cold would be accurate – sometimes I’d rather be digging up wasp nests in shorts and sandals than shoveling snow at 10°F w/ 20mph winds. So yeah, I’ve thought a great bunch about making my project trailer(s) into body armor against subzero and other lethal weather...

Want to say some other brand trailer comes with spray foam, okay - that was incorporated with brand new materials supplied with carefully spec'd proprietary surface treatments, processes & primers sold by some vendor as a package, not into a fifty-year-old piece of lawn furniture having its age outed.

Spray foam on an ancient Airstream is* gambling, not so bad if it’s your forever-trailer & monies but don’t sell your problems off to some unsuspecting family that have it bloom into a little shop of horrors a few years down the line. New York & New England gets a lot of rain & snow, if this was a Southwest trailer your long term odds would be better...

So we want to spray foam the shell… Read up on passivating aluminum - to get anything to bond to & not be undercut by existing & new corrosion overnight then ALL aluminum surfaces have to be properly prepared – mechanically cleaned, degreased, acid washed, then a chromate passivation process successfully accomplished… General Aviation hobbyists wade through this all the time, if you’re going down that path the degreaser to use is ‘simple green extreme’ to avoid corrosive chemicals, where just the detergent used corrodes cleaned aluminum and blocks later chromate processes that then invites oxidation to cleave away any bonded material, paint or adhesive.

Anyhow, I've seen a '68 that the back eight foot subfloor sprayfoam insulated area was stained tan/brown foam with near-zero steel in metal form remaining from moisture intrusion feeding rust that burned the iron into something like water soluble clay - and I'm not exaggerating. Owner was near tears reaching for any solution not involving a store-bought frame & extra year(s) project time. Yes, in this case there may have been salts/uric acid from plumbing seeps involved, and the foam was likely not what is sold these days as it had turned brittle/crunchy yet was welded to everything as good as a heavy Minnesota morning frost.

Sprayfoam under the floor? Things one should be doing anyway: Three coats of POR-15 on properly prepared iron metal, flooring plywood with 3 coats primer & 3 coats porch paint applied. Have shell 110% weather-tight, missed/loose rivets and seams addressed, all gaskets perfect. Get the belly wraps under the shell. Have a redesigned ladder-frame-through-shell plan front & back. The list is nearly endless.

I’m sure I missed things, fatigued already from 60-minutes to write that and chores & errands are pelting me about the head and shoulders…

Pssst, hey youse... https://www.amazon.com//dp/B01DLQU2PW <--canned sprayfoam applicator gun w/ low-exspansion door/window safe foam and poly-iso foil backed insulation board using foam and 3M90 as adhesive IS the equal or superior to froth-pac sprayfoam.. .

[SilverHouseDreams]

I don't have anything of value to add, other than to see if anyone has come across or used products from this place: https://sprayfoamkit.com/product-features-uses/

[Streamracer]

Not sure how it would all work out, but in my own dealing with spray foam, instead of spraying directly into the cavity, we sprayed into large plastic bags which would still form around the item. One on each side then if you ever needed to remove the foam was not stuck to everything and you could reinstall it later.

[perryg114]

Spray foam probably has the best R value per its thickness but trapping moisture between skin and foam concerns me and even more so in the frame and floor area. It is hard to keep these things water tight and the spray foam like the pink fiberglass will trap and hold the moisture even more than the fiberglass. I would use layers if rigid foam combined with a radiation barrier.

Perry

[tbashin]

Use styrofoam in the thickness you need. Less gamble with water or moisture issues going that route. Home improvement stores have several thicknesses available in store.

[sallye]

Originally Posted by Streamracer

Not sure how it would all work out, but in my own dealing with spray foam, instead of spraying directly into the cavity, we sprayed into large plastic bags which would still form around the item. One on each side then if you ever needed to remove the foam was not stuck to everything and you could reinstall it later.

Wow, what a great idea! I'm going to remember that for when I use this stuff around the house.

[Ralph12]

My 1978 Avion 28J uses it all around keeps very warm at 30 deg. F, it's sandwiched in the floor

[Dingo Girl]

Road vibrations could turn the spray foam to dust.

[bradt]

I plan to write more about this later to report what I found as I disassembled my Airstream this summer. Briefly, my comment is to use care to not create any moisture trap situations. The plywood needs to be able to dry if it gets moisture in it. There are many perforations and situations that can introduce small amounts of moisture that travels horizontally thru the plywood. If the plywood is sealed on the bottom and covered with vinyl flooring on the top, the water can't get out. I chose to remove the bubble foil from the bottom of my floor after finding puddles of trapped water which caused floor failure.
The floor is sealed on the top by the vinyl. Leave a ventilated air gap underneath the raw plywood so it can dry as necessary. Avoid sealing the plywood with water proof coatings.
For example, you could apply blocks of 2" rigid foam to the back of the belly pan, not touching the plywood, to provide insulation without creating a moisture trap in the plywood.
Additional comment is that once spray foam is applied, it is harder to work on unplanned problems later.
Good luck with your project!
Brad

[rugjenkins]

I spray foamed my argosy! No regrets. I used 2 inch foam board for the floor in belly pan area.

[Gale]

When you start to lay flooring down if you do a vapor barrier for laminate there is now a barrier that has foil on down side to reflect some of the cold under foot.

[Burnside Bob]

Originally Posted by bradt

I plan to write more about this later to report what I found as I disassembled my Airstream this summer. Briefly, my comment is to use care to not create any moisture trap situations. The plywood needs to be able to dry if it gets moisture in it. There are many perforations and situations that can introduce small amounts of moisture that travels horizontally thru the plywood. If the plywood is sealed on the bottom and covered with vinyl flooring on the top, the water can't get out. I chose to remove the bubble foil from the bottom of my floor after finding puddles of trapped water which caused floor failure.
The floor is sealed on the top by the vinyl. Leave a ventilated air gap underneath the raw plywood so it can dry as necessary. Avoid sealing the plywood with water proof coatings.
For example, you could apply blocks of 2" rigid foam to the back of the belly pan, not touching the plywood, to provide insulation without creating a moisture trap in the plywood.
Additional comment is that once spray foam is applied, it is harder to work on unplanned problems later.
Good luck with your project!
Brad

Ditto Brad's observations.

Playing devil's advocate here. I hate being cold, too, BUT:

Unless you can seal both the inside and outside shells against air intrusion, you will have condensation in your walls, causing mischief. Maybe not now, or next year, but sometime down the road. So while the foam might seem a tremendous idea it brings unintended consequences and makes any future repairs much more difficult.

And lets suppose, for a moment, you could seal your Airstream airtight. Its a nice cold night, and you shut the door, vents, and windows for that long winter's nap. How long will you last with the available oxygen?

So just maybe there's a reason why a stock Airstream comes with fiberglass batting and an unsealed plywood floor. There has to be a way for you and your Airstream to breath.

[J. Morgan]

Bob, do you suppose your trailer would have survived the fire had it been spray foamed?

The cool thing about fiberglass is that it will not burn.

About two weeks ago while I was polishing I had my son install a cool America shaped patch in place of an old square patch. In the course of doing this he unknowingly drilled into a 120V wire near an outlet.

A few days later Elizabeth was sitting on the bed and heard a “pop”, and then another.....

So I pulled the outlet and the outlet box to find both the black and white wires burned in half, obviously they had been arcing.

The fiberglass was stained a little, but nothing close to fire... Would spray foam, even the fire retardant varieties have performed in a like manner?

Say the foam wouldn’t have burned, how much more work would it have been for me to fix the wire had it been encapsulated in foam? As it was, I was able to do a quick fix by pulling some slack into the box and hooking everything back up.

I almost used spray foam in my trailer reconstruction, but since then I have been happy that I didn’t. Just my take...

[PaulnGina]

I don't know the exact process they followed, but our 1987 Avion has a plywood/foam sandwich on the floor and spray-on-now-rigid foam in the walls and ceiling...... very comfy, and it has lasted all these years and lots of miles.

If you can figure out how to do it as a refurb, it will insulate very well compared to the fiberglass.

[Burnside Bob]

Originally Posted by J. Morgan

Bob, do you suppose your trailer would have survived the fire had it been spray foamed?

The cool thing about fiberglass is that it will not burn.

Hey, J. Morgan remembers our trailer, The Phoenix, was stored in an RV storage facility that caught fire.

Yes, Phoenix would have survived. Nothing inside the outer skin got hot enough to burn, so unless gasses from heated foam had a lower flash point, foam insulation wouldn't have been an issue.

As it was, the exterior aluminum shell and frame members got hot enough the insulation on the 12V wires melted where they crossed frame members in the ceiling. The insulation on Romex has a higher heat rating and the Romex wiring to the AC survived OK.

Needless to say, had to rewire all of the 12V in the ceiling. Removing cooked foam insulation would have made that job much more time consuming.

Since I had the center panel and insulation out, I was able to install HDMI cables and other upgrade wiring easily. These tasks would be more difficult with foam.

* * * * * * *

Anyhow, the point of my earlier post is to be mindful of all factors when considering something like foam. I'm not saying don't ever use foam insulation in your trailer, but don't expect foam insulation to be trouble free and be aware foam may aggravate/cause other problems over the long term. It's hard to know when to leave well enough alone, but I'm happy I didn't go with foam on the Phoenix.

[AlinCal]

My first thought was "how would you do it?" As said elsewhere you need to completely fill the space to avoid condensation. I work around it often in the trades and I have only seen it used in ceiling or roof bays and walls, so if doing a wall the exterior siding or sheer is in place and they then spray the wall cavity overfilling a bit then later screed it off flat so that the wall board is right against it. From the exterior in you first need your vapor barrier, then the spray foam, then your interior wall and finish.
If doing a ceiling you then need a ventilated attic structure above, unless you spray against the roof sheeting making a solid mass of insulation with no voids. With an Airstream Im not sure how you could provide any vapor barrier? Not sure how much it would be needed in an aluminum trailer with no wood structure? I think we would mostly agree that there is still condensation taking place in the batt insulated walls.
Many different types but the Isynene product I see is somewhat flame retardant , I use a torch around it to do my soldering for the copper plumbing and it will take a direct flame for a second then smokes without igniting, the smoke is extreemly unpleasant and to be avoided. It is very easy to remove when needed, grab it with your hand and pull out chunks.
The last thing is the thought of it turning to dust from vibration is hard for me to picture and I am not in that camp at all.
All this is from working with the Icynene products that are mixed on site in a mobil plant and have no idea if its pertinent to any other spray foam out there.