Pre flight foamie build sanity check...

Canvas covered foamies (Thrifty Alternatives...)

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Pre flight foamie build sanity check...

Postby dbhosttexas » Wed Sep 18, 2019 10:25 am

Okay probably some dumb questions here, but I am getting confusing info online about this and want to narrow it down for my foamie build...

#1. Recommended foam appears to be XPS (the pink stuff).
#2. Recommended adhesive for foam to foam bonding is Gorilla Glue. But which one? Gorilla makes a TON of different glues. I have seen some folks use expanding foam as an adhesive between panels as well. What works well?
#3. The skin / fabric for the PMF. I have seen TONS of folks here talk about canvas, but I have also seen discussion about using old bed sheets. Which is it? King size sheets are $1.00 a piece at thrift stores near me. Goodwill charges more, but VFW thrift shop has them more often and again, for dirt cheap.
#4. Is it Titebond II in a dillution and if so at what ratio, or is it Glidden / PPG Gripper primer, and is it straight up or dilluted and at what ratio? I already have 2 gallons of TBII I got for another application that needs to be used for something now...
#5. What is an appropriate top coat / paint for the finished product?
#6. Does a foamie need wood reinforcements to support things like door hinges, windows, etc...? I am thinking it does but I haven't tried yet and figured why waste the time, effort and money making mistakes?
#7. If using fiberglass instead of PMF, am I correct in that you need to use Epoxy resin if you are using XPS foam, but Polyester Resin is fine with Polyiso foam?
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Re: Pre flight foamie build sanity check...

Postby stcyrwm » Wed Sep 18, 2019 11:33 am

Not dumb at all. I can't answer as I am a newb but would love to see all the answers in one place. You'll probably get some contradictory responses but either way I think it'll be helpful...

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Re: Pre flight foamie build sanity check...

Postby tony.latham » Wed Sep 18, 2019 1:39 pm

#7. If using fiberglass instead of PMF, am I correct in that you need to use Epoxy resin if you are using XPS foam, but Polyester Resin is fine with Polyiso foam?


I can answer that one. Polyester resin dissolves XPS foam. Somebody on here was having luck with polyester resin on poly foam but I have not tried it.

Me? I quit using polyester resin two decades ago. Epoxy is a much better product.

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:thinking:

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Re: Pre flight foamie build sanity check...

Postby RJ Howell » Wed Sep 18, 2019 3:38 pm

dbhosttexas wrote:Okay probably some dumb questions here, but I am getting confusing info online about this and want to narrow it down for my foamie build...

#1. Recommended foam appears to be XPS (the pink stuff).

Yes! Works real well! I went 1 1/2" yet most go 2".

#2. Recommended adhesive for foam to foam bonding is Gorilla Glue. But which one? Gorilla makes a TON of different glues. I have seen some folks use expanding foam as an adhesive between panels as well. What works well?

I used the standard spray with water . There is a discussion of the tube adhesive that seems to be much easier to use and very strong.

#3. The skin / fabric for the PMF. I have seen TONS of folks here talk about canvas, but I have also seen discussion about using old bed sheets. Which is it? King size sheets are $1.00 a piece at thrift stores near me. Goodwill charges more, but VFW thrift shop has them more often and again, for dirt cheap.

I did bedsheet on the interior. Now that I've skinned my exterior, I see why canvas is used. So much stronger! There is also a thread on another supplier of better canvas than the HF stuff. I would check that out.

#4. Is it Titebond II in a dillution and if so at what ratio, or is it Glidden / PPG Gripper primer, and is it straight up or dilluted and at what ratio? I already have 2 gallons of TBII I got for another application that needs to be used for something now...

The Glidden Gripper is gone now. PPG version is garbage. I used SW Pro-Cryl yet there bonding primer seems nice, just haven't tried yet. TB2 is real good over plywood or bare foam (as I have read). I faired my foam and the TB2 tests didn't work for me. I went primer.

#5. What is an appropriate top coat / paint for the finished product?

Start with water based, end with water based. I'm a SW fan, yet other products would work as well.

#6. Does a foamie need wood reinforcements to support things like door hinges, windows, etc...? I am thinking it does but I haven't tried yet and figured why waste the time, effort and money making mistakes?

I say yes. What and how much is determined by what you want to do. I routed in a few sections of plywood where I thought I would need strength or attachment. Who I saw what it increased, I realized I could have gone much further with my build.

#7. If using fiberglass instead of PMF, am I correct in that you need to use Epoxy resin if you are using XPS foam, but Polyester Resin is fine with Polyiso foam?


For me, the juries out whether going PMF (correctly) is overall cheaper than PMF.. My quality primer costs retail $82 a gallon and I used close to two. My quality top coat costs retail $42 a gallon. I have a commercial account so it cost me much less, yet it's not really cheap to do it right. And you do want it to last!

Hope some of this helps and I'm certain others will chime in.
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Re: Pre flight foamie build sanity check...

Postby tony.latham » Wed Sep 18, 2019 4:59 pm

For me, the juries out whether going PMF (correctly) is overall cheaper than PMF..


I fiberglassed (with epoxy) my nearly-done 5' x 10" teardrop for $200. I don't understand why PMF is called poor man's fiberglass. Is it really any cheaper than glassing?

I also don't get why some builders seem to shy away from fiberglassing. It's not alchemy.

:thinking:

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Re: Pre flight foamie build sanity check...

Postby Pmullen503 » Wed Sep 18, 2019 5:13 pm

I used PMF over foam and recommend it. I used TB2, thinned 10% with water. I bought canvas yardage to get long pieces. It has a finer weave than drop cloths and it looks better when done. You need to sand or put lots of little holes in the foam. The factory finish of the foam is too slick.

I've built several wooden boats with epoxy over wood and the resin waterproofs the wood. Not really needed with foam but nothing wrong with that and you can sand and fill as smooth as you want.

Canvas drinks up a lot of paint. I got mismixed paint cheap and used that for the first couple coats.
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Re: Pre flight foamie build sanity check...

Postby GPW » Thu Sep 19, 2019 6:21 am

JMHO :
PMF works and is Cheaper if you do it the right way;) Although we LOVE Fiberglass , It's always the temptation to go for a full on shiny finish which is just a lot of work … With PMF it's basically “weave" or nothing …. best thing is you have a CHOICE !!! :thumbsup:

As it turns out, although collectively we ( all of us ) in the beginning to encourage participation and creativity , didn’t want to make any RULES , it has evolved over the years , methods that work Better than others … Easier and cheaper too … ;)
The whole point of a Foamie is Cheap and Easy !!! A “hard tent” :D But with “No Rules” you can make it into ANYTHING YOU want !!! :thumbsup:

And just to mention , working for years with Epoxy , we developed a “sensitivity” ( allergy ) to the material that makes us break out in itchy red spots … Not Fun !!
TB2 , GG , water based Paints and primers , all have worked Great for me ( No spots either :R ) 6 years living outside and counting …
There’s no place like Foam !
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Re: Pre flight foamie build sanity check...

Postby GPW » Thu Sep 19, 2019 6:31 am

Many very talented People here have successfully built some GREAT Foamie trailers :thumbsup: … Just find one you like and check out their build thread …
There’s no place like Foam !
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Re: Pre flight foamie build sanity check...

Postby tony.latham » Thu Sep 19, 2019 9:47 am

and is Cheaper if you do it the right way …


So... what does it cost to PMF a teardrop?

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Re: Pre flight foamie build sanity check...

Postby RJ Howell » Thu Sep 19, 2019 10:24 am

tony.latham wrote:
and is Cheaper if you do it the right way …


So... what does it cost to PMF a teardrop?

Tony


So the question becomes are you for $200 only doing the exterior? Also your cost of finishing over should be added.
What is your cost with both these added in?

My notes only on this, others may have different costs.
Using cheaper (or great deal on paints) probably around $100 (add for material inside, paint covered in this)
My process $185, canvas outside, bedsheet interior (I had the bedsheets, old drop cloths)

I've done fiberglassing in the past and debated doing it on my topper. I think over-all fiberglassing would be easier, quicker and gives you a real clean surface to finish. Fairing is also much easier to do. Say you want to add a custom rain cap (or anything..), you can with fiberglass. Fiberglass brings forward so many possibilities.

I see PMF can be done reasonably inexpensive, yet in my mind, The Jury is still out on if better or truly that much less expensive... :thinking:

I like how the canvas (PMF) looks, yet I do believe on my ultimate build, I will go fiberglass.

MHO only.
Last edited by RJ Howell on Thu Sep 19, 2019 10:26 am, edited 1 time in total.
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Re: Pre flight foamie build sanity check...

Postby dbhosttexas » Thu Sep 19, 2019 10:26 am

GPW wrote:JMHO :
PMF works and is Cheaper if you do it the right way;) Although we LOVE Fiberglass , It's always the temptation to go for a full on shiny finish which is just a lot of work … With PMF it's basically “weave" or nothing …. best thing is you have a CHOICE !!! :thumbsup:

As it turns out, although collectively we ( all of us ) in the beginning to encourage participation and creativity , didn’t want to make any RULES , it has evolved over the years , methods that work Better than others … Easier and cheaper too … ;)
The whole point of a Foamie is Cheap and Easy !!! A “hard tent” :D But with “No Rules” you can make it into ANYTHING YOU want !!! :thumbsup:

And just to mention , working for years with Epoxy , we developed a “sensitivity” ( allergy ) to the material that makes us break out in itchy red spots … Not Fun !!
TB2 , GG , water based Paints and primers , all have worked Great for me ( No spots either :R ) 6 years living outside and counting …


You kind of hit at something I am concerned about. I know there is nothing, or at least next to nothing in TBII to become allergic to. No formaldehyde or anything like that, no nasty offgassing etc...

However I have no idea how strong PMF is, assuming say it is made using XPS, TBII, used sheets, and a couple of coats of "oops" exterior paint before the final color coat goes on. How strong can that be? Or assuming canvas instead of sheets, how strong can that be, how much less than fiberglass could it possibly be?

I know from being around boats, fiberglass resin continues to offgas for a very long time, years, and considering the limited size of the truck camper, or a teardrop or whatever tiny camper, I am not sure it's ideal unless that offgassing can be encouraged to complete more rapidly...

I just have visions of structural nightmares with PMF, I have experience working with fiberglass, although it is quite old now (last time I worked it was over 20 years ago).

Sorry about hitting with so many questions, I am just trying to get my head around this before I dedicate what budget I do have to making this happen...
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Re: Pre flight foamie build sanity check...

Postby Pmullen503 » Thu Sep 19, 2019 11:18 am

You should make yourself a sample of PMF and Epoxy/glass over foam. Get some 2" foam and make samples at least a foot wide and a couple feet long. Let them cure long enough to be representative of a real project then go at them with likely hazards and eventually see how much force it takes to break them. And see how much they weigh.

IMO, having built boats with wood and epoxy/glass and a trailer with foam with PMF, I prefer PMF over foam. The canvas stays flexible over the soft substrate and really is self healing from dents and dings. Epoxy glass is relatively less flexible and if stressed too much will break or delaminate.

When you consider the cost of the rest of the trailer and the time involved, what extra cost there is to epoxy/glass is small (same thing with bed sheets vs canvas.) The idea with foamies is cheap, light and fast. If your goals are compatible with that, you're good. If a really smooth finish is what you want, I would go epoxy/glass but over wood, not foam. It's really hard to sand fiberglass flat over a soft substrate unless it's quite thick (which defeats the weight saving benefit of foam.)
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Re: Pre flight foamie build sanity check...

Postby RJ Howell » Thu Sep 19, 2019 1:17 pm

Pmullen503 wrote: The canvas stays flexible over the soft substrate and really is self healing from dents and dings. Epoxy glass is relatively less flexible and if stressed too much will break or delaminate.

That is a great point! I'm finding the PMF (canvas) to be very strong, as others have said I would see as I built and covered. Mine has yet to cure, but very strong in it's current stage of drying. I have a couple SIP samples from another, from another group that is very strong with fiberglass on both sides. The one that has my attention is the gel-coated one. I guess one could gel-coat over PMF, but I don't know for certain..

It's really hard to sand fiberglass flat over a soft substrate unless it's quite thick (which defeats the weight saving benefit of foam.)


Another great point! I find the foam to be very stiff once all is connected. Yet I bend/stressed the foam to get the most out of it. I primed, faired and sanded much like doing fiberglass and didn't find the foam all that soft.. Yet that was only on the seams and the enforcement there of.

Again, only MHO of what I've done.
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Re: Pre flight foamie build sanity check...

Postby tony.latham » Thu Sep 19, 2019 1:32 pm

So the question becomes are you for $200 only doing the exterior? Also your cost of finishing over should be added.
What is your cost with both these added in?


The cost of adding paint for either PMF or fiberglass should be similar. I used Monstaliner, but it's expensive. I could have used two quarts of enamel or about $50.

And yes, that's only the exterior. I build with wood... so it's already finished inside.

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Re: Pre flight foamie build sanity check...

Postby tony.latham » Thu Sep 19, 2019 1:37 pm

Epoxy glass is relatively less flexible and if stressed too much will break or delaminate.


Glass over foam is a common method of aircraft construction... If properly constructed, it won't break.

Somebody mentioned resin outgassing. I gave up on polyester resin many years ago. Epoxy doesn't outgas.

Again, I'm asking what it costs to PMF a teardrop. I'm curious.

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