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Old 04-01-2022, 09:58 PM   #1
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Not removing inner shell?

I have a shuttle bus. Fiberglass shell.

I am insulating it and my plan is to not remove the inside fiber glass shell. I want to just attach foam board insulation directly against the factory walls and ceiling.

But every conversion online I've seen first removes the inside shell. Why is this? Is it just to gain an extra half inch? Will I regret not removing it?

Second question, what is the best glue for foam board? Liquid Nails? Great Stuff? Something else?

Thanks!

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Old 04-02-2022, 11:43 AM   #2
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Liquid Nails is a total fail for foam board. Gorilla Glue construction adhesive (the stuff in a tube that you put in a dispenser gun, not the little glue bottle stuff) works very well.
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Old 04-02-2022, 12:45 PM   #3
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Lepages/loctite PL400 exterior grade construction adhesive works on foam board. It doesn’t dry completely hard and tacks up fairly quickly.
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Old 04-02-2022, 01:02 PM   #4
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Foam, glue and long term

So, what I see happen with foam and glues, 20 years later. The glue stays stuck to the foam, but the foam tears away from the foam. What you see is the glue, whatever kind you use, and a thin layer foam stuck to the glue and the foam laying on the ground.

This come from being around boats and motor homes where glue and foam is used.

I advocate the use of a screw with a large plastic washer 2 to 4 diameter. Make sure the screw only goes through the inner fiberglass panel. All of the shuttle bodies I have worked are built the same. Outer layer of fiberglass, layer of cardboard honeycomb, then inner shell of fiberglass. Places where things needed a good grip, wood was used instead of cardboard honeycomb. If you take off those smooth inner panels, you can see the wood. I think of the inner panels as redundant and just extra weight. I could also see where water had gotten to the wood or honeycomb areas and needed repairs. On these shuttles when I took up the wood floor, you looked at the ground under the shuttle body, the should be sprayed with some type of agent, I kind of fancy the idea of ziebart under body coating. It is a thick waxy like coating. I think bed liner might work well too.

William
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Old 04-02-2022, 01:48 PM   #5
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Such a great question. All the info out there seems to be on how to do everything the hardest possible way! I have a sheet metal ceiling that I a definitely NOT taking down, but I might like to cover it with something better looking.
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Old 04-02-2022, 02:02 PM   #6
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Quote:
Originally Posted by magnakansas View Post
So, what I see happen with foam and glues, 20 years later. The glue stays stuck to the foam, but the foam tears away from the foam. What you see is the glue, whatever kind you use, and a thin layer foam stuck to the glue and the foam laying on the ground.

This come from being around boats and motor homes where glue and foam is used.

I advocate the use of a screw with a large plastic washer 2” to 4” diameter. Make sure the screw only goes through the inner fiberglass panel. All of the shuttle bodies I have worked are built the same. Outer layer of fiberglass, layer of cardboard honeycomb, then inner shell of fiberglass. Places where things needed a good grip, wood was used instead of cardboard honeycomb. If you take off those smooth inner panels, you can see the wood. I think of the inner panels as redundant and just extra weight. I could also see where water had gotten to the wood or honeycomb areas and needed repairs. On these shuttles when I took up the wood floor, you looked at the ground under the shuttle body, the should be sprayed with some type of agent, I kind of fancy the idea of ziebart under body coating. It is a thick waxy like coating. I think bed liner might work well too.

William
Great advise, William. I often use adheasives in conjunction with mechanical fasteners, when bonding materials.


I suggest Insulation Plates & Screws with an urethane based adheasive, Loctite PL400
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Old 04-02-2022, 04:26 PM   #7
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Thank you! Along with the adhesive I was planning on using washers and sandwich it with lauan or something similar.

My biggest question though is why does everyone remove the inner fiberglass shell? I have looked through hundreds of youtube videos for someone that insulated their bus without removing the inner walls and found zero examples. Is removing them important for some reason other than gaining a half inch of space? I'm thinking leaving them could make it more structural, be easier and there would be less that could go wrong. This is my first conversion and I don't want to do something I later regret but I also want to take the simplest route.


Any tips on how to keep a bus cool in the summer? I have to park in full sun for solar. One idea I had was to add a radiator fan to the floor so I could pull in air cooled by the shade under the bus. I haven't seen anyone do this and it seems to me like it will work much better than a roof fan.
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Old 04-09-2022, 03:38 PM   #8
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I have a fiberglass shell too... for me it was no option it had to be removed... the outer shell is 95% detached, whatever they caulked it on with (looks like bathroom drain caulk ) didn't work. I have to pull the outer shell as well.
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Old 04-09-2022, 03:47 PM   #9
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The inner fiberglass liner provides no structural strength. Removing it allows lights and wiring to be more easily run and hidden, in addition to adding insulation/soundproofing.
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Old 04-09-2022, 06:42 PM   #10
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The inner shell as built is important for the total strength. With an inner and an outer with a core it is strong. As long as the core is in good shape , dry and still bonded then all is well and the inner should stay. However window leaks, roof hatch leaks etc often get the core wet, and everything starts to come apart. In boat building we then remove the inner , and all core material, replace the core and fiberglass and new inner , properly bonded to the new core. Sometimes a new core is skipped in favor of adding and few more layers of fiberglass if not in a high stress area, or where fittings need to be attached.
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Old 04-10-2022, 01:47 AM   #11
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Quote:
Originally Posted by duck View Post
I have a shuttle bus. Fiberglass shell.

I am insulating it and my plan is to not remove the inside fiber glass shell. I want to just attach foam board insulation directly against the factory walls and ceiling.

But every conversion online I've seen first removes the inside shell. Why is this? Is it just to gain an extra half inch? Will I regret not removing it?

Second question, what is the best glue for foam board? Liquid Nails? Great Stuff? Something else?

Thanks!
People remove the walls and ceiling mostly because they
1) have a fear of moldy insulation hidden behind the panels
2) want to have a fully custom interior different than a stock look

I have metal walls and a metal roof in a bus from the desert and lucked out. Zero rust anywhere. I left the walls and roof alone and am building as much as possible 32" or lower to stay under the side windows. Living in a desert for as long as I have has acclimated me to heat so a home made swamp cooler for "AC" on really bad nights, some screens for over the open windows for the bad days and a couple of 12v fans to move the air and everything will be Awesomesauce.
Winter here is mild so a couple of extra blankets on the bed and a buddy heater near by will be more than enough.

And if a freak winter freeze heads my way...there's always Florida for a few months.
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Old 05-11-2022, 04:14 PM   #12
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Did you end up keeping your fiber glass shell, or remove it? I also have a fiberglass shell that I am debating removing.
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