XPS and Epoxy

[fonsan]

https://www.homebuiltairplanes.com/foru ... ost-571806

"80gsm/10mm XPS backing is enough to require not-accidental force to push through a surface."

[GPW]

" I am starting to realize that what I am asking about is the rigidity of the structure and not the surface resistance to damage as it seems that the rigidity will dictate the thickness of the fiberglass cloth" .
If you're worried about the rigidity of the structure , just THICKER foam ... Using more f/glas for "structure" will only make it Heavier ...

[tony.latham]

and it seems to me that the more elegant solution is just to chose a heavier cloth instead of adding plywood to the mix.

There's a build thread here titled, The Poet Creek Express. I've wondered if KC ever regretted not sheathing it with thin plywood. He ended up with a ton of needed fairing. Keep in mind he's a bit of a perfectionist. Started in 2012 and it still sits in the shop.

https://www.tnttt.com/viewtopic.php?f=55&t=48630&hilit=poet

Here's a quote from one of his posts:

When I did the spline skim coat on the street side of the roof it seemed like the foam was high and the spars took more filler. That was in 90 deg weather. Now that I washed the amine and blocked it down again in 70 deg weather, the opposite is true; the spars are high and the foam is low, as evident by the darker and lighter strips visible in this pic.

You might take a gander at his build log--it's a biggee. If you have any questions about it, send him a PM. He's a good guy and quite the craftsman.

Tony

[fonsan]

" I am starting to realize that what I am asking about is the rigidity of the structure and not the surface resistance to damage as it seems that the rigidity will dictate the thickness of the fiberglass cloth" .
If you're worried about the rigidity of the structure , just THICKER foam ... Using more f/glas for "structure" will only make it Heavier ...

I tend to agree, https://explorecomposites.com/articles/ ... tructures/

Doubling thickness more than doubles the "Relative stiffness" and the stiffness gain seems to be even more advantageous past 1 inch (2.54cm)

I have 4,5 and 8 cm xps foam available to me in theory combinations could be glued (4+5 yielding 9cm)

In theory I could even glue lower density EPS to build thickness; XPS + EPS + XPS or simply EPS + XPS

However some tensile strength is needed in the skins otherwise the roof will sag and the walls will bulge out.

I am very much open for advice on which weight of cloth to provide the tensile strength needed and if I am correct in presuming that the tensile strength I am looking is the defining requirement for cloth weight

[OP827]

Having built my lifting roof camper with 1.5in fiberglass XPS sandwich panel roof and walls I would share some of my thoughts on the subject.

Apart from rigidity and structural strength theory of glass and foam sandwich there are other real world design cases/scenarios to consider.

What if it is raining and then the thin glass skin will amplify the rain sound into the cabin like a drum skin so the inhabitants will have to wear some ear plugs to be able to sleep? Thin fiberglass with XPS propagates the rain drop sound pretty good. Some people may like it and some may not.

What happens if some sizeable branch falls from a tree darting down towards the camper roof?

In short, I personally feel that a roof with some plywood skin and epoxied glass or multiple glass cloth layers would give more substantial sound proofing and falling subjects protection.

[jakejakejake]

I have been following yours on youtube and it is very inspiring.

Would it be feasible with a single layer of 6oz for large flat surfaces? (or even lighter)

If you would redo your camper would you consider using less epoxy and fiberglass?

Can't wait to see your camper fully finished

Thanks Fonsan! I absolutely overdid it with the glass in regards to weight. If light weight were the only parameter I was trying to meet I would be absolutely comfortable with a single ply of 6oz glass. Especially if you're okay with doing a little repair work here and there as needed.

The exterior of my build is three plies of 6oz glass with an additional 3 plies on all the radiused joints. I tend to be rough on things and live in an area with Gnarly thunderstorms, tornadoes, and hail on average of 1/2" diameter. Dale (the wonder dog) and I will find a nice ditch to lay in in the event of a tornado, but a hailstorm or three is not out of the question in its first season of use.

With all that said I am extremely light compared to commercial truck campers. Im estimating its around 200lbs currently and should be under 3-350 with the added weight of the 12v system, water system, 270 awning, etc. Most commercial options start at 750lbs and up. Heck even the fiberglass camper shell that I harvested the windows out of is significantly heavier than the total build as it sits.

Burt Rutan is the godfather of foam-core fiberglass. Incredible mind on that guy.

" I am starting to realize that what I am asking about is the rigidity of the structure and not the surface resistance to damage as it seems that the rigidity will dictate the thickness of the fiberglass cloth" .
If you're worried about the rigidity of the structure , just THICKER foam ... Using more f/glas for "structure" will only make it Heavier ...

I tend to agree, https://explorecomposites.com/articles/ ... tructures/

Doubling thickness more than doubles the "Relative stiffness" and the stiffness gain seems to be even more advantageous past 1 inch (2.54cm)

I have 4,5 and 8 cm xps foam available to me in theory combinations could be glued (4+5 yielding 9cm)

Absouletly correct! I would have never guessed that my roof would be walkable, but its extremely rigid with 2" or 5cm foam. As explore composites points out the foam is basically the "web" of the beam. Its takes much more force to deform a 12" beam vs an 8" with the same web thickness.

https://www.homebuiltairplanes.com/forums/threads/testing-xps-foam-for-epoxy-adhesion-bonding.34960/page-2#post-571806

"80gsm/10mm XPS backing is enough to require not-accidental force to push through a surface."

80gms is roughly 3osy I think? Freedom units is my forte...sorry. In my testing I could dent the foam with my thumb with a single layer of 4osy glass.

This brings up a good point. Make up a few test panels, maybe 20cmx20cm with varying layer counts and foam thickness, then do some destructive testing. Its great fun and will help you decide on what specs are most desirable to you.

[fonsan]

Having built my lifting roof camper with 1.5in fiberglass XPS sandwich panel roof and walls I would share some of my thoughts on the subject.

Apart from rigidity and structural strength theory of glass and foam sandwich there are other real world design cases/scenarios to consider.

What if it is raining and then the thin glass skin will amplify the rain sound into the cabin like a drum skin so the inhabitants will have to wear some ear plugs to be able to sleep? Thin fiberglass with XPS propagates the rain drop sound pretty good. Some people may like it and some may not.

What happens if some sizeable branch falls from a tree darting down towards the camper roof?

In short, I personally feel that a roof with some plywood skin and epoxied glass or multiple glass cloth layers would give more substantial sound proofing and falling subjects protection.

Good point about the noise, I will be using it mostly in southern Spain (where every drop of rain is celebrated these days) and mostly as a utility trailer with overnight capability so I think the tradeoff is stil worth it

In regards to the branch then I would repair it. I already have the trailer and I am targeting sub 1k dollar/euro build for a 3.1 * 2.4 * 1.8 box

[fonsan]

I have been following yours on youtube and it is very inspiring.

Would it be feasible with a single layer of 6oz for large flat surfaces? (or even lighter)

If you would redo your camper would you consider using less epoxy and fiberglass?

Can't wait to see your camper fully finished

Thanks Fonsan! I absolutely overdid it with the glass in regards to weight. If light weight were the only parameter I was trying to meet I would be absolutely comfortable with a single ply of 6oz glass. Especially if you're okay with doing a little repair work here and there as needed.

The exterior of my build is three plies of 6oz glass with an additional 3 plies on all the radiused joints. I tend to be rough on things and live in an area with Gnarly thunderstorms, tornadoes, and hail on average of 1/2" diameter. Dale (the wonder dog) and I will find a nice ditch to lay in in the event of a tornado, but a hailstorm or three is not out of the question in its first season of use.

With all that said I am extremely light compared to commercial truck campers. Im estimating its around 200lbs currently and should be under 3-350 with the added weight of the 12v system, water system, 270 awning, etc. Most commercial options start at 750lbs and up. Heck even the fiberglass camper shell that I harvested the windows out of is significantly heavier than the total build as it sits.

Burt Rutan is the godfather of foam-core fiberglass. Incredible mind on that guy.

" I am starting to realize that what I am asking about is the rigidity of the structure and not the surface resistance to damage as it seems that the rigidity will dictate the thickness of the fiberglass cloth" .
If you're worried about the rigidity of the structure , just THICKER foam ... Using more f/glas for "structure" will only make it Heavier ...

I tend to agree, https://explorecomposites.com/articles/ ... tructures/

Doubling thickness more than doubles the "Relative stiffness" and the stiffness gain seems to be even more advantageous past 1 inch (2.54cm)

I have 4,5 and 8 cm xps foam available to me in theory combinations could be glued (4+5 yielding 9cm)

Absouletly correct! I would have never guessed that my roof would be walkable, but its extremely rigid with 2" or 5cm foam. As explore composites points out the foam is basically the "web" of the beam. Its takes much more force to deform a 12" beam vs an 8" with the same web thickness.

https://www.homebuiltairplanes.com/forums/threads/testing-xps-foam-for-epoxy-adhesion-bonding.34960/page-2#post-571806

"80gsm/10mm XPS backing is enough to require not-accidental force to push through a surface."

80gms is roughly 3osy I think? Freedom units is my forte...sorry. In my testing I could dent the foam with my thumb with a single layer of 4osy glass.

This brings up a good point. Make up a few test panels, maybe 20cmx20cm with varying layer counts and foam thickness, then do some destructive testing. Its great fun and will help you decide on what specs are most desirable to you.

Thank you for the feedback , then I should go for either 6oz or 8oz (168gsm or 224 gsm) whatever I can get a hold of. Very interesting that 4oz will be dented by thumb pressure, that gives me an excellent idea of what I can expect. The savings of going to 4oz are minuscule and really low weight plain woven cloth is actually more expensive here than 6-8 oz.

You guys have some crazy weather to contend with over there. Mega hail is exceedingly rare here. Roof might become partially covered in huge residential style solar panels spanning the full width of the trailer, I think I just found another reason to mount them.

I already bought some XPS panels for experimentation: 300kpa 8cm and 300kpa 5cm (33kg/m3) and you would not believe how rigid they are just by themselves.

My plan is to make nichrome wire a foam cutter and basically build the full trailer out of foam dry fitting everything together (and sanding corners round) only gluing the individual wall, roof and floor panels. Then disassemble and in massive sweeps turning the panels into composite with the glass and epoxy leaving a few cm without glass on all sides of the wall panels. Glue all the box together and then bridge the glass between them over the rounded corners prepared earlier. I want to lay down as much epoxy as possible when the panels can lay on a flat surface avoiding having to battle epoxy that flowing of the surface.

Not going for pure box look but the front will be wedgeshaped and the rear needs to be stiffer as a major portion of the rear wall will be a garage door that opens up for loading and unloading the motorcycles.

The whole box will not be permanently fixed to the trailer. I aim to make the floor from plywood glued together with xps with a vinyl floor mat on top. I need to do some experimentation as it needs to support the weight of 500 pound motorcycles that have a contact patch of less than one square inch and the fixating points I will definitely steal the idea of hardpoints that you made.

[Pmullen503]

My trailer was built for the same purpose but not removable.

Your plan is good. I would recommend you cover the XPS floor with 1/4" (6 mm) plywood top and bottom, and glass that. It takes a lot of fg to handle point loads. That's how I did mine with a solid wood perimeter for bolting to the trailer. It's held fine for 10 years now.

The open end will definitely rack. If I had it to do over again, I'd add the largest corner gussets I could. Build the lightest door possible and/or hinge it at the bottom like a ramp.

I like the idea of doing most of the work flat. To keep the corners looking neat, lay down a strip of masking tape before you glass to define nice lines. Glass the corners out to where the tape is going over the tape. Then at the stage where epoxy is still soft but you can cut with a knife, slice through the glass at the tape edge. Peel off the tape and excess glass. I roll down that cut edge of fiberglass right after the cut to reduce the need to sand.

[jakejakejake]

I already bought some XPS panels for experimentation: 300kpa 8cm and 300kpa 5cm (33kg/m3) and you would not believe how rigid they are just by themselves.

This is an important detail I left out. The XPS foam I'm using is rated for 15psi/103kpa (If google conversion is correct) You may have better luck with lighter glass than I did, but as you said the really light stuff can actually be more expensive. I wouldn't worry about the extra few oz per meter and choose based on affordability.

My plan is to make nichrome wire a foam cutter and basically build the full trailer out of foam dry fitting everything together (and sanding corners round) only gluing the individual wall, roof and floor panels. Then disassemble and in massive sweeps turning the panels into composite with the glass and epoxy leaving a few cm without glass on all sides of the wall panels. Glue all the box together and then bridge the glass between them over the rounded corners prepared earlier. I want to lay down as much epoxy as possible when the panels can lay on a flat surface avoiding having to battle epoxy that flowing of the surface.

Sounds perfect, flat layups are the way to go! you may have seen me try and fail some over vertical work on YouTube. Never again!

Not going for pure box look but the front will be wedgeshaped and the rear needs to be stiffer as a major portion of the rear wall will be a garage door that opens up for loading and unloading the motorcycles.

This makes me think of a snowmobile trailer! Im not sure if you are familiar, but this picture may spark some new ideas. Door building takes significantly longer than I had anticipated.

[twisted lines]

This makes me think of a snowmobile trailer! Im not sure if you are familiar, but this picture may spark some new ideas. Door building takes significantly longer than I had anticipated.

And I spent days attempting the shape I am looking for; with a new program windows 7 won"t do
With Hours trying the next Radi And multiple times.

[jakejakejake]

And I spent days attempting the shape I am looking for; with a new program windows 7 won"t do
With Hours trying the next Radi And multiple times.

I couldn't live without traditional 2d autocad. I have partially learned ac3d and solid works many times and it will never be as intuitive as good ole 2d. Ive gotten really good at visualizing a 3d product from a 2d or isometric drawing.

[fonsan]

Sketching has begun

[jakejakejake]

Nice! The end wall looks plenty strong to resist racking as mentioned in a previous post.

[tony.latham]

Is the axle in the middle of the chassis frame? It looks like it needs to be moved a bit aft?

Tony