Spray foam will also wrap the sides of the trailer, and the front and back panel. It does not seem to harm the curved sides, as there is no place for the metal to warp too. I did alot of reasearch on the subject, but the one thing that was missed is that the really good foam insulation generates heat, and a alot of it. Over 200* You wont notice the panels warping at first, but as they cool it will look like a wave, the metal is just too thin. Spray foam works great on automotive sheet metal, and fiberglass. Plus the stuff is a real mess to clean up, and you will spend countless hours triming it down so you can get the walls back in. There is some foams that dont use as much heat, but they are worth paying the money for. Do yourself a favor, stick with foil and pink insulation, it easy to work with and it works great for keeping heat in when you want it and keeping heat out when you need it. I'm sure nobody want's to have to reskin there intire tralier twice like I did !
Spray foam will also wrap the sides of the trailer, and the front and back panel. It does not seem to harm the curved sides, as there is no place for the metal to warp too. I did alot of reasearch on the subject, but the one thing that was missed is that the really good foam insulation generates heat, and a alot of it. Over 200* You wont notice the panels warping at first, but as they cool it will look like a wave, the metal is just too thin. Spray foam works great on automotive sheet metal, and fiberglass. Plus the stuff is a real mess to clean up, and you will spend countless hours triming it down so you can get the walls back in. There is some foams that dont use as much heat, but they are worth paying the money for. Do yourself a favor, stick with foil and pink insulation, it easy to work with and it works great for keeping heat in when you want it and keeping heat out when you need it. I'm sure nobody want's to have to reskin there intire tralier twice like I did !
Thank you Dan Clayton;
I have tried to convince everyone in a gentle way that spray foams will absorb moisture in uncontrolled environment. Pour foams have numerous pitfalls such as, Difficulties In Application, Heat Distortion, Expansion Distortion, Fragmentation Due to Vibrations and flex, and a host of other related problems. As you have said Dan, pour foam generates high heat which will deform inner and outer skins by bulging them out, as it is generating a lot of pressure during the chemical reaction. Heat alone will bulge out outer panels. For those who do not believe it, set your hair dryer on high and heat one panel for 10 minutes. If that does not convince you to abandon the idea, nothing will, and you will ruin your AS. For the individuals who would like to tell me that their AS sits in a 160 degree desert heat and the panels do not distort, I will say this. Gradual heating of AS by the hot sun expands entire trailer evenly. This is why panels do not bulge. The aluminum ribs are of the same temperature then, and expand at the same rate with the skins. Aluminum has a very high expansion rate once it is heated. When you pour foam into one section, only that section is heated by the reaction in the setting foam to about 200 degrees. Surrounding areas are of ambient temperature and cannot expand at the same rate. The expanded material has to go somewhere. The ribs will contain that expansion and the only place the skin can go, is out.
I have worked with many different pour foams for forty years. If you think that you know more, go ahead and see for yourself. Just to encapsulate and insulate my plastic tub into a 3MM plywood walled enclosure, I had to do eight consecutive small layer pours to keep the heat from melting the tub. Have I had poured it in one shot, my tub would have been molted mess. One thing is for certain, there is much more to foams than you think. Low temperature setting foams are too expensive and still have many future negatives connected with application in flexing AS shell. Why are some people insisting on getting in trouble? Sorry for being blunt in getting my point across, but I hate to see another person going through what Mr, Clayton has gone through. I do not wish to waste my time to comment anymore on this issue. I am certain that at least some will appreciate your story Mr, Clayton. Thank you "Boatdoc"
The data will be in the next three posts, with a summary at the end.
First, the box insulationn was enhanced. Overall the insulation was increased an average of 55% from previous tests.
Second, it was plain that wind velocity had a significant impact on the data, so some of the panels showed wide variations in insulating capability, just from the differing winds on a particular test night.
Third, two test parameters were used--how fast did the water bottle cool down and how warm was the inside panel compared to the inside air. I assumed these would provide the same answer, but they did not. Correlation was fair, so you'll have to decide for yourself which was the better data.
Here's the raw data charts:
Air only. This panel had nothing inside.
Bubble foil from Home Depot. The foil was suspended mid-way between the panels and glued in place so there was no air leakage path. Due to unexpected data, both this panel and the Prodex panel were dissassembled to check that the seals were good inside--they were.
Canned Foam. This was the "doesn't bow window frames" version of Great Stuff. It remained flexible (maybe it won't turn to dust as the Airstream flexes) and did not keep expanding when it came to a panel or foil. I think this has some useful applications in our Airstreams, but in small areas.
Cannned foam with Rib. A 10" by 1" channel was cut into the foam along one edge of the panel and a rib installed with 5 pop rivets on each face. The voids were re-filled with foam. This was the only test with a rib, but shows the significant effect that the conductive metal path has on total insulation capability. I did some back of the envelope calculations and it turns out that this construction had approximately the same rib length per unit area of panel as the Airstream shell has, within a factor of 2.
Glass Mat. I have two panels, one moderately shiny and the other moderately dull. I only used the dull one in this test.
Prodex. Thanks to Craig (2333), I had a few square feet of Prodex. This panel was perhaps the best made of all of them.
Prodex w/ 1/2" of Glass Mat. The previous panel was opened and 1/2" of glass mat was placed on the inside side of the prodex, eg, the side toward the inside of the box (shell). Due to the way the prodex had been put in the panel in the first place, this resulted in a panel with 3/4" airspace on the outer side, the Prodex, then the remaining 1/2" full of glass mat.
Prodex w/ full Glass Mat. This was the styrene panel (see data in the next post). All the styrene in the center 10" x 10" space was removed and a sheet of 12x12" prodex, with edges folded up along the insides and glued, was placed against the outer panel. The remaining space was filled with glass mat.
Styrene 1-1/2". This was a frivolity. It was just solid pink polystyrene foam with an aluminum panel glued (at the edges) on both sides. It performed wonderfully, but you'd never achieve this kind of quality, leak-free, conformal insallation in real life. But it does give one an idea of what good insulation can do.
Styrene 1/2". The above panel was opened and the interior 10x10" area was hogged out, leaving 1/2" of styrene against the inner panel. This was a more representative test, since the styrene had been installed in 3" wide strips, so now the slight gaps were able to contribute some leakage.
Here's all the data in one chart. The 080322DA number is the year/month/day and file ID, so I can find the original data if you want to see it. You can have as much fun as I've had, well, NOT....
If you average the data, then sort it (left colum is based on heat loss, right colum is based on inside panel temperature), you can rank order the quality of the panels as shown here.
It should be no surprise that the rib just killed the insulating quality of the panel it was installed in. The real surprise is the variability of the Prodex panels with glass mat. Either the wind really affected these tests or it's true that the Prodex doesn't like to touch the wall--it may perform poorly when conduction is a big factor. Either way, the Prodex did OK. But for all of you who are not tearing out your inner shell walls and are keeping your glass mats, you should be happy with its consistent good performance.
That's all for now. Next tests will be to see how these panels do in the hot sun. Sunlight provides about 100 watts/sq foot of radiation, so maybe I can do some hot tests with a heat lamp and not wait for summer...
Let us not forget that Kip (AEROWOOD) made this possible with his generous donation of the 12x12 aluminum panels, way back before I knew him. Thanks, Kip.
Using a wet-bulb type thermosensor along with OAT unit could help correlate the wind factor, if desired, though you may have to wait until next winter
Thank you for taking the time to maintain precision across the samplings - I've been waiting for your results!!
It looks like I will be trying to incorporate your 1-1/2" foam at least in the center run of the ceiling, I have a band saw and know how to use it to achieve the barrel-stave effect so it may get continued out to the ceiling edges too. I've installed tractor-trailer loads of ceiling tile and drywall back working summers in High School to it should be an easy puzzle.
I also have purchased silicone sheet to cut strips out of to be thermal barriers for the ribs - material identical to Aircraft Spruces' silicone cowl seal ribbon. I am planning on doubling or tripling up on the rivets at a minimum in case I am unable to get a solid clamp from them....
Next tests will be to see how these panels do in the hot sun. Sunlight provides about 100 watts/sq foot of radiation, so maybe I can do some hot tests with a heat lamp and not wait for summer...
Since I live and play in the deep south I will be very interested in those results! We do not have to worry too much about heat loss around here.
Thanks Zep for all your work and for sharing this with us.
My premise right along for saying that I thought reflective foil was a better insluation product than most was that it seems to be better at blocking radiant heat loss than the other types of products are. The other part of my premise is that the major component of heat loss through walls and especially ceilings is radiant. My thought then is to block the radiant heat loss and most of the job is done.
One thing that I am still a bit puzzeled about with your measurement technique is how you determine what type of heat loss you are measuring? It seems to me that if you have a box that has warm air on the inside that you are really measuring heat loss by convection and conduction. Do you think that your tests accurately reflect (pardon the pun) the heat loss do to radiant effects? That is the particular type of heat loss that I was trying to measure with my setup where I had ambient air on each side of the panel and used the sun as a radiant heat source on one side.
I hate using 20/20 hind sight (for those finished with reinsulating) but when conduction and radiation heat flow are addressed then convection ramps up in importance - there should be baffles placed regularly to keep airflow down inbetween ribs, like fire stops placed in wall cavities...
...... there should be baffles placed regularly to keep airflow down inbetween ribs, like fire stops placed in wall cavities...
I guess there's still a lot of stuff I don't understand about the whole insulation issue. Are you saying that movement of air inside the walls should be kept to a minimum? As in, don't allow air from one portion of the wall to move to another portion thru normal heating and cooling?
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