| Author |
Message |
Bob Wood (67.37.79.61)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 11, 2002 - 11:12 am: | |
Insulated the bus with foam board, and wonder if I should install a plastic moisture barrier before I put the plywood on the walls and ceiling. Is this worthwhile or a waste of time and money? Any ideas? |
Ronnie (24.162.237.118)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 11, 2002 - 8:22 pm: | |
Waste of time. Reason of my thoughts are....In homes you apply plastic on walls before sheetrock in time mold will form inside the walls .
Simple put if you take a stick and put it under a piece of plastic in the desert on the hottest day and come back the next water will be at the top under the plastic . Water around steal creates rust . At any rate it does form a barrier for more insolation .
In a bus if there is no way for water to enter or rise from beneith it may work . I am just creating a negetive post to ponder on for others that will differ . If water cannot get in then surely some will say no mold . Steal has no water but wood you apply inside does . |
R.C.Bishop (128.123.88.5)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 22, 2002 - 11:26 pm: | |
Interesting question AND response. I have wondered the same. Houses "breathe" differently than a steel and aluminum structure and no doubt busses have many points of entry for air......BUT
The big question for me is, will that barrier, between insulation board and the "inside skin" provide enough moisture to rust the steel structure? It makes sense that a barrier would cut down on entry of many things including dirt, dust, diesel fumes, noise, etc, but if it allows a moisture content to be retained, as with fiberglass insulation, which causes much of the rust we encounter in these coaches, the trade off might not be worth it.
My guess is that the outside skin "openings
and numerous ways air can get in would prevent that from happening. Having said that, many coaches have rust in the structure, so that might not be a valid conclusion.
I am at that point, just now, and look forward to input from some of the experts out there.
Thanx,
RCB |
Buswarrior (Buswarrior) (64.229.214.213)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 23, 2002 - 2:23 am: | |
Hello all.
Inside of the coach sees a big swing in humidity both when we live in it and when it is left sitting.
We all wake up to wet windows on occasion.
If you leave your maintenance binder open on the table to the same page and close up the bus for a few weeks, the exposed top pages get all wrinkled as if you had sprayed water on it.
I'm sure that there are others here better equipped to explain the propensity of the big metal cans that are our buses to retain heat from the day, and what that may mean as it cools as the night wears on in the way of condensation in every nook and cranny, and then the slow warming through the day again, which doesn't dry things particularly well.
Never mind that some wet may be finding its way into the walls from the outside, which bypasses the vapour barrier.(how often does your house experience 100+ mph wind driven rain going down the highway into a modest headwind?)
These are extremes that our houses do not normally experience, so our assumptions about moisture barriers and their value may not be valid.
If lots of wet can get in, will we be able to effectively block it from entering the insulation from either direction, or maybe best that we leave the wet a way out?
Sorry, decision is still hard to make.
happy coaching,
buswarrior |
FAST FRED (209.26.87.37)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 23, 2002 - 4:13 pm: | |
Of course GM solved the problem by putting the insulation in a vapor tight bag.
Neat , cheap , effective, so why mess with sucess?
FAST FRED |
R.C.Bishop (128.123.88.12)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 23, 2002 - 7:16 pm: | |
Fred, how does that solve the problem of moisture buildup on the surfaces? I have removed all the fiberglass and have put in insulation board..1.5 inches for the most part,which, of course itself sheds water. I have left plenty of places for "a way out", not sealing joints etc. But more than a little curious if putting a barrier on would exacerbate a problem...somewhere. Most moisture barriers that I have experience with have been placed on the outside of the sheathing of a structure and therefore no problem with mildew on the inside of the house. Metal, as we all know is considerably different.
I am tempted to try coating each frame memeber, on the inside, with something like a bedliner, but am not sure that will solve ANYTHING. I did note this past fall and winter that when the windows were off, when putting on new metal, the entire bus seemed to have A LOT of condensation inside. After the sides were closed up, there was almost none. Which brings me to the reason I wrote in the first place. I wonder if, now, putting an inside skin on will draw that moisture and should I put on a vapor wrap first, etc, etc, etc...
Thanx for the input from both of you. There may not be a practical answer. Could be a convertible top would dry it out...LOL
RCB |
George Myers (12.85.0.134)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 24, 2002 - 10:09 am: | |
My solution was to put 1/2 inch foam board insulation over the wall. This covered the blocks between the ribs and the steel ribs. The steel structure of the coach conducts the heat through as if there was no insulation at those points (because there isn't). I call this a thermal sieve. The metal on the roof acts as a solar collector, the structure (ribs) passes it through, and the material covering the inside radiates it into the coach. Placing insulation over the structure makes a significant difference in the temperature of your ceiling and walls. It also acts as a vapor barrier.
George Myers |
dick hall (Dick) (205.188.193.26)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 24, 2002 - 3:33 pm: | |
bob
for what it's worth i have always sealed the metal walls from inside before insulating to protect the metal from rusting. there is a product called por-15 that when sprayed on metal virtually seals it from moisture so it can't rust. you can even spray it over rusted areas and it stops further rusting. i also use it when restoring old cars. check with your local automotive paint store.
dick |
R.C.Bishop (128.123.88.22)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 24, 2002 - 10:53 pm: | |
Thanx Dick. I'll check out that Por-15. Is that sort of an undercoating material like they sprayed on autos in the distant past? I think my bus has it all over the top and most framing members. Tough as ole' Harry and seems to have done exactly as you described. Does the stuff spray with a conventional air gun, or does it require special equipment?
George, If I am reading you right, you used insulation board BETWEEN the framing members, then AGAIN after you installed the Plywood( or whatever) walls over the framing members? If that is the case, what happens to the moisture buildup on the metal (that naturally occurs)?
I think Dick has a solution that will solve the problem I imagine in my mind's eye.
Thanx, guys!
RCB |
George Myers (12.85.15.214)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 25, 2002 - 10:22 am: | |
The blocks are sealed to the framework with construction adhesive on two sides and expanding foam on the other two. The insulation over the entire wall is sealed (contact cement) over that. Aluminum insulation tape is used to cover all seams. Then the plywood and Formica were added (contact cement).
My experience has been that if the moisture can get out, it will get in much easier and accumulate. My approach was to seal everything as best I could. Great care was taken around the windows to seal the blocks, then seal the covering insulation, then the plywood/Formica. Each layer was sealed with aluminum tape. I also used the tape to sealed where the outside metal bonds to the structure. The only opening is at the bottom where water could run out, but even this is tightly closed even though it is not sealed. This is all spelled out in my video.
George Myers |
R.C.Bishop (128.123.88.24)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 25, 2002 - 10:50 pm: | |
Thanx, George, for the detail. I'll check it out
RCB |
Tom Caffrey (Pvcces) (12.146.33.82)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 31, 2002 - 11:16 pm: | |
Bob, If you think about where and when you see moisture condensing on a surface, you will see what is necessary.
The moisture always forms on the warm side of a moisture barrier, be it a sheet of plastic, glass or metal.
This is because the cool side of the surface causes the moisture in the warmer(and wetter) air to condense. Cooler air cannot hold the moisture that warmer air can.
If your coach was always in cold country so that you heat the inside, the vapor barrier would need to go inside the insulation.
If your coach was always in hot country so that you cool the inside, the vapor barrier would need to go outside the insulation.
For a changing environment, you should vapor barrier both sides of the insulation, just as the bus manufacturers did.
The use of better insulation does not change where the vapor barrier needs to be unless the insulation will not permit any moisture to enter it. Then, you don't need the vapor barrier.
Good luck on your insulation. I hope what I've said helps!
Tom Caffrey PD4106-2576 |
RJ Long (Rjlong) (24.127.8.58)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 01, 2002 - 12:01 am: | |
Tom -
So that brings up this question:
Do you use moisture barriers w/ spray foam insulation??
RJ
PD4106-2784
Fresno CA |
john wood (206.252.234.4)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 01, 2002 - 4:19 pm: | |
Spray foam is a vapor barrier!
Next problem is thermal bridges where steel framework bridges through from the outside to the interior finish. This is where you will see condensation form in cold weather as the dew point is usually at the surface where the bridge is. In the cavity where the foam is, the dew point is actually somewhere inside the wall. If you use a foam, which is less permeable to vapor, then condensate cannot form and ruin the insulation value, or the framework.
Moral is: use a thermal break of some sort over the structure. Wood furring strips perpendicular to framing and foamed out to interior finish. Good for both temperature extremes. |
Tom Caffrey (Pvcces) (12.146.33.16)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 02, 2002 - 12:43 am: | |
I would want to check on the permeabilty of the foam to be used. If I didn't know what the foam would do, I would probably use a vapor barrier.
Some foams soak up so much water, they have very little insulating value left. The sprayed yellow foam in our boat's hold has enough water to drip on you if you scratch it.
Some foams are much better, so finding out what was available would be best, I would think.
FWIW
Tom Caffrey PD4106-2576 |
|