Fiberglass vs PMF

[Jimmytg]

Hello,

For the exterior finish of my foamy plan, I am going back and forth between using fiberglass or PMF. Besides the fact that fiberglass is significantly more expensive, what are the benefits or downsides to fiberglass vs PMF?

Is fibergalss stronger than PMF? Is it easier or harder to finish / sand? Does it weigh more as a finished product than if you would use PMF?

Just looking for some guidance and your personal experiences with the applications, durability, etc., of using both fiberglass or PMF.

Thanks!

 

[Pmullen503]

It depends a lot on how skillful you are at fiberglassing. I just finished a trailer using epoxy and glass cloth. But that was over wood and I'd recommend glass over wood because wood can rot and epoxy/fiberglass is better than PMF in that regard. PMF is easier for most people.

Over foam it really depends on getting a good application from the start. The issue is that the foam is much softer than the glass so you really can't put the pressure on it while sanding. You can't grind on it the way you can over wood. You also have to be a little concerned with heat build up. It would take a lot of friction to generate enough heat to damage the foam but it's something to keep it mind.

I've done a fair amount of glassing over foam with excellent results so it can be done. Do yourself a favor and spend the extra money to get a low viscosity, non-blushing resin. Practice on something smaller first. Use a scraper to get the cloth down onto the foam without excess resin. Then come back when it's starting to gel but still green and roll on 2 more coats of resin to fill the weave (that's why you want non-blushing resin).

Plan for an entire (long) day to complete the job. If you let the epoxy fully cure, you should sand between coats.

A good application requires just a light sanding to prep it for paint after it's cured for several days.

 

[Jimmytg]

This is fantastic information, and I appreciate you sharing your knowledge and experience with me! It's definitely given me some things to dig into and do some research on.



As a follow-up question, if I were to fiberglass the outside, how would you finish the inside of the foam in the camper? Would you fiberglass it, pmf, or not do anything and just put the 1/8 inch plywood panels up?



Thanks a bunch, Pmullen!

 

[Pmullen503]

The inside finish is up to you. You don't have to FG or PMF under 1/8 Luan, it's stronger than either.

On mine, I covered the insides first while I could lay them flat rather than trying to do it after it was assembled. With ply you would pretty much have to to use large sheets. You could put you finish on as well, rout channels for shelves and bulkheads, run wires. Lots of things are easier when it's laying flat.

If you use PMF on the inside, preshrink the canvas or the whole sheet will bow (you can guess how I figured that out.) After assembly, I taped the inside corners with 6" strips of canvas.

 

[Tony Latham]

Do yourself a favor and spend the extra money to get a low viscosity, non-blushing resin.

Keep in mind that Mullan is referring to epoxy resin, not polyester. Polyester resin will dissolve most foam.

With wooden teardrops that will be painted, I advocate for using fiberglass/epoxy to seal the wood. It's not difficult, and the learning curve should be the same or not much steeper than PMF. But, I've never done PMF.

In that video, I keep going over to a set of pumps–purchased from Raka when I ordered the resin. Makes for easy-peasy batches.

The not-so-secret secret of using epoxy is to mix small batches. Less than a cup or so, otherwise it will "go off" in the container. But once you've poured it out on the glass, you've plenty of time.

Tony

 

[Jimmytg]

I appreciate the information, and thanks a bunch for the video link!

Thanks Tony!

 

[Paintsalot]

Hey Jimmy- I’m not an expert on this, but I’m about to use PMF on my folding wooden camper roof. It’s a Roma inspired Vardo sort of design. You can see more over in build forum on this site.

I found a thread from back in 2015 with some analysis on your 2 options, here
Thread 'PMF vs Epoxy/Glass - TPCE Wants Your Vote'
PMF vs Epoxy/Glass - TPCE Wants Your Vote

I would go with 1/8” plywood interior. Or what about unpainted fabric- heavy duck fabric interior. There are thin cedar paneling boards at Lowe’s/Home Depot too. Something nice to touch. I’m using cork inside my build- probably not for everybody. Cork is a really good sound insulator, and it’s mildew resistant, and fire resistant I believe.

 

[Jimmytg]

I just checked out your build progress and that is incredibly cool!

I appreciate the link to the pmf/epoxy question, and thanks also for your guidance, direction and suggestions!

 

[Jwh92020]

I just finished covering my 5x8 square drop with PMF (fiberglass & I are incompatible - I developed an "intolerance to it years ago helping a neighbor build custom surfboards), and I have to say it was a muche easier process than I thought it would be. Her's a link to my build if you want to check it out.

First 5x8 square Drop Build

After 20+ cargo trailer conversions a 3 frame up "standy" builds, I thought I'd try ma hand at a 5x8 square drop.I managed to find a 5x8 Ironton (Northern Tool) trailer brand new in the boxes on Marketplace for $ 450, so I grabbed it. I got he trailer assembled, deck built and insulated and now...

www.tnttt.com

 

[Jimmytg]

Love it! Just watched your videos. Great info.

Thanks Jwh!

 

[Jwh92020]

Love it! Just watched your videos. Great info.

Thanks Jwh!

Good luck whichever way you go.

 

[Kaida]

Keep in mind that Mullan is referring to epoxy resin, not polyester. Polyester resin will dissolve most foam.

With wooden teardrops that will be painted, I advocate for using fiberglass/epoxy to seal the wood. It's not difficult, and the learning curve should be the same or not much steeper than PMF. But, I've never done PMF.

In that video, I keep going over to a set of pumps–purchased from Raka when I ordered the resin. Makes for easy-peasy batches.

The not-so-secret secret of using epoxy is to mix small batches. Less than a cup or so, otherwise it will "go off" in the container. But once you've poured it out on the glass, you've plenty of time.

Tony

Could the two in your picture work for a foamie?

 

[Tony Latham]

Could the two in your picture work for a foamie?

Epoxy/fiberglass works fine over any of the foam boards. Burt Rutan designed and built many different airplanes using the system.

Burt Rutan - Wikipedia

T

 

[ghcoe]

A easy interior cover is indoor/outdoor carpet.

 

[6912]

I think for most PMF is fine. how will you use
We have to have trailers that have to take a beating rentals | SO we do real fiberglass . we use glue and go style easiest way to build a 100 year are more trailer .Don't even need to cut a straight line
There is 8 year-old girls building go together like a Erector Set

 

[6912]

Polyester resin will dissolve most foam.
not home depo ico foam .must remove foil weak glue bond
if using ploy resin on can are pore. no more than 2 layers at first. Heat will melt foam In the picture ploy resin over HD ice foam