Comparing weights of building methods.

[Newb1]

I did look in archives 1st and couldn't find my answer.
I know this is not a simple question but I'm wondering about the weight of going fiberglass over foam (foamie) vs a regular sticks and aluminum siding trailer. If 2 trailers were built as close to the exact same size, thicknesses, etc, which would weigh more?
I know fiberglass depends on matting, layers etc., but I'm trying to figure out which would (IN THEORY) weigh less and maybe, by how much, before I choose what path to go down.
If you have an idea of a way to build a very strong but light weight camper, Id like to hear that as well.
thanks

[John61CT]

Nitpicky I know, but using fiberglass over foam is not "foamie", that term is specifically for canvas / glue / primer.

And any technique can be heavy or light,

the key to light weight is engineering with that as the priority, willingness to sacrifice strength

accepting the absolute lowest strength that is "just strong enough" and no more.

But in general using foam for structure rather than plywood, and leaving out the metal tends to be a lot lighter of course.

Getting **lots** of strength, at **minimum** weight, is where you start getting real advantages consulting professionals.

[saltydawg]

Okay the lightest trailer you could make with any real strength would be a foam body with hand laid glass on it. a 5 by 8 tear drop body could weigh less than 200 lbs. But its a lot of work, and wont be the greatest when it come to puncture resistance. If you put more glass on it to make it more resistant to puncture the weight adds up quick. This is where you get into using premade skins and making your own panels.

I have done this, the skins I used they say are .3 lbs a square foot, my floor panel which is 10 by 5.5 weights about 60 lbs. My walls with 10 lbs of steel built into to them to brace a pop top weigh around 65 to 75 lbs. I moved them around by myself quite a lot including putting them on and taking them off a shelf 6 feet off the ground. I can take a 2.5 foot by 8 inch panel and put it on a step and stand on it ( i weigh just over 200 lbs ) my total body weight maybe around 400 lbs for a 12 by 5.5 by 5.5 trailer

I have my threads in the skinning section and here in GD. But if you want a complete over view go over to https://expeditionportal.com/forum/threads/sawtooth-unlimited-off-road-pop-top-camper-trailer.183743/ and look at that thread, its a complete build thread with lots of pics and videos. I am basically coping the contruction method.

I am high and dry over there, I have a build thread there.
https://expeditionportal.com/forum/thre ... ed.217954/

plus some other threads here about what I did along the way
http://tnttt.com/viewtopic.php?f=2&t=73133
http://tnttt.com/viewtopic.php?f=65&t=73093

[John61CT]

Is using fiberglass really lighter than bedsheets and paint?

Don't you need UV protection over the glass anyway?

I do not care much about surface aesthetics much, thus puncture resistance neither, need 3-4" thick insulation anyway, and PMF is so easy to fix as needed, even in the field.

[RJ Howell]

Sheet of xps foam (4x8) weighs in at 8-9lbs (1-2" foam) compared to 1/4" plywood at 22lbs. .040 aluminum skin runs 27lbs a sheet vs fiberglass at 16lbs (4oz cloth and resin apron.).

I lean towards foamies being lighter.. even doing PMF I see them as lighter.

[saltydawg]

John for a trailer that is not a house anything over 1.5 inches of foam is a waste. Sure using a bedsheet and 15 lbs a gallon of house paint might be lighter but it would be very easily damaged as well as not strong enough for more than a 4x8 teardrop that never sees anything rougher than a pot hole.

At a min I would save use canvas and i think most people use 6 to 10 oz canvas which is in the same range as fiberglass. plus they use gallons of glue and paint at 10-15 lbs a gallon. Yes epoxy weighs the same but you dont need as much.

Go look at stryomax trailer from Australia, they build 30 foot long trailers that are for offroad with nothing but 1 inch of foam and fiberglass skins. Do you really thing PMF could do that?

[Newb1]

replies;
--> John61CT - ""Nitpicky I know, but using fiberglass over foam is not "foamie", that term is specifically for canvas / glue / primer."" -- I didnt know. I thought using foam was a foamie and canvas/glue/primer was called PMF, 1 of many ways to cover your foamie as in pmf, glass, aluminum skin etc...
""Getting **lots** of strength, at **minimum** weight, is where you start getting real advantages consulting professionals"" -- I know, but thats not in my budget and I dont know of any anyway.
thanks

--> saltydawg - Great info, Ill go do some research, Exactly what I was looking for. I love details and exact specs to compare things.
thanks

--> John61CT ""Is using fiberglass really lighter than bedsheets and paint?"" - I tend to go WAY off any trail so yes, I want/need strong exterior for branches, etc..
""Don't you need UV protection over the glass anyway?"" - since its always outside, Im guessing I do.
""PMF is so easy to fix as needed, even in the field."" - OK but fiberglass can be done anywhere too I think.
thanks

--> RJ Howell - Thanks, I like the details in comparing options.
thanks


Thanks to all, it helps

[saltydawg]

opps forgot the uv protection. over epoxy yes, unless you use uv stabilized epoxy. If the skin is polyester no you dont.

[greygoos]

Nitpicky I know, but using fiberglass over foam is not "foamie", that term is specifically for canvas / glue / primer.

And any technique can be heavy or light,

the key to light weight is engineering with that as the priority, willingness to sacrifice strength

accepting the absolute lowest strength that is "just strong enough" and no more.

But in general using foam for structure rather than plywood, and leaving out the metal tends to be a lot lighter of course.

Getting **lots** of strength, at **minimum** weight, is where you start getting real advantages consulting professionals.

I must have missed that, can you show me how you came to that conclusion? I am very curious.I believe the first foam trailer on here was foam covered in fiberglass. I am not trying to be controversial just trying to get my facts straight. Thank

[saywhatthat]

Why would anyone WASTE cash on epoxy over foam. Anyone tells you that Poly resin will eat the right foam HAS no clue. There pis off that they wasted there cash. Are 100 year pods are about 145 lbs with glass out side 1'' of THE RIGHT FOAM glass on the inside .With willy windows 4.5 wide 4.5 height b 8 foot long Using a fiberglass trailtop component frame kit. poly resin is about 9 lbs a gal

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[Squigie]

Strongest and lightest (while relatively affordable and usable) is going to be a tubular carbon fiber monocoque with hemispherical ends, sealed with a top coat for UV protection. - A torpedo, essentially.
As expensive as carbon fiber is, I still think it could be used to produce a stronger teardrop shaped monocoque, that doesn't need as much of a frame and doesn't cost as much as many of the over-built stick or skeleton builds here.

But foam and glass vs sticks and aluminum get very tricky to compare. Fiberglass is heavy. But most people over-build with lumber. Aluminum skins are a light way to finish. But foam is lighter.
It's more about an individual's own build techniques than the materials, alone.

I must have missed that, can you show me how you came to that conclusion? I am very curious.I believe the first foam trailer on here was foam covered in fiberglass. I am not trying to be controversial just trying to get my facts straight. Thank

Indeed.
To me, that's more personal opinion than hard and fast definition.
To John, a "foamie" may only qualify with his parameters.
But to many here - as I've seen in discussions and many builds - "foamie" is pretty much anything where the structure is built with foam and covered to strengthen it.

To me, that "foamie" definition is a bit like arguing that "sandwich" walls are only sandwich walls when you use XPS for the insulation.

But, I've seen similar arguments about shapes. People have their own opinions.
"It ain't a teardrop if it looks like a toaster."
"It can't be a standy if you have to hunch."
"That' isn't a trolley top, because it doesn't have windows."
"It's not a square-drop if it has angles."
"A v-nose is not a teardrop."
And even an argument against being a foamie, again: "It isn't a real foamie if you use a PVC frame."

I don't think there's any point in nitpicking basic concepts, especially while discussing build techniques in general.

[saltydawg]

Why would anyone WASTE cash on epoxy over foam. Anyone tells you that Poly resin will eat the right foam HAS no clue. There pis off that they wasted there cash. ... with glass out side 1'' of THE RIGHT FOAM glass on the inside .

Your right polyester resin works with polyurethane foam, it will eat polystyrene foam. There are paints you can paint it with then use polyester resin, but make sure you use it right and enough of it.

Now polyurethane foam costs many times what eps costs. from fiberglast.com 1/2 inch 32x48 foam is 62 bucks a piece. 57 if you buy 10 of them. I paid 20 bucks a 4x8 sheet of 1 inch 25 psi dow foam, which would work out to 171 bucks for 4x8 for polyurethane foam but its only a half inch thick. So lets say its 50 % more for 1 inch polyurethane foam thats still $256 for a 4x8 x 1 inch piece I think the $226 bucks savings on the foam more than paid for the 30 bucks in epoxy I used per sheet.

Now I will say I do know what I am talking about. Lets see my experience with resins, I used to repair sailboats that had hull damage as a side job when I had a boat. If I did not know what I was doing the word of mouth would have killed me. Also I did the mold making and fiber glass layup of a commercial RC submarine hull that was 9 feet long.

Now what are you doing, you making a bunch of fiberglass pieces and using spray foam to seal and insulate them after you glue them together. You throw words out like " Anyone tells you that Poly resin will eat the right foam HAS no clue" yet you dont explain what the "right" foam is ( polyurethane foam ) . You do have a good idea on selling premade parts that can be cut and glued together to make a teardrop body to what the end user wants, but you weaken your system by using home depot spray foam to insulate it.

Epoxy is not a waste, go read sailboat sites on what happens when people use polyester resin to repair polyester resin boats. the patches fail. There is a reason why almost every company that works on sailboat hulls uses epoxy for repairs, and its not because they want to WASTE money. There is a reason why people use titebond to hold canvas on a foamy and not polyester resin which is cheaper than titebond.

[saywhatthat]

Fiberglass is heavy? Yes a full fiberglass trailer maybe heavy . with the RIGHT FOAM . the foam is the structural . the glass keeps you from putting your finger through the foam. again a wast of time and cash paints you can paint it with then use polyester resin, but make sure you use it right and enough of it. if you time gose for $.10 a hour you save some cash and have a weak piece of crap how Hard can it be use the right structural foam about $20.00 a sheet

[saywhatthat]

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Boats set in water trailers not so much .Iso insulation $20 a sheet at home depot. the design we use is not flat . we glue are wet lay up glass on sheet foam . Use can foam to back fill raise parts Don't let the name of the foam fool you it safe

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[saltydawg]

Yes Polyisocyanurate foam works with poly resin, but its weaker than eps. It is also very bad to breath its dust, and its fumes from burning will kill you. In your case your building a frame from fiber glass pieces then insulating with the foam, that works. It would not work as well in a foamy due to strength. Thats why when you buy it, its has the foil backing, it makes it a lot stronger than with out the foil