Anyone create FRP Board and Polystyrene sandwich for decking.

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Don't fool yourself into thinking you'll need less support/framing ...

You will save weight and have better water resistance, if properly built, but at more expense, as most recommed epoxies for foam core builds. Check out if you go that route.
Thanks for the response. Saving weight is a top concern.
I have searched, but have not found an example of dual sided FRP/Polystyrene laminate used on our boats. Am I understanding you correctly that you recommend using epoxy to join the layers? I can see where it would probably have better shear characteristics than warm contact adhesives.

My 1436 Alumacraft has height difference between the first and middle seat that leads me to believe I can lay the laminate material on the top of the middle seat, and add a lip to back part of the front seat. I suppose the only way to tell how much framing is needed is to build the laminate and then test the load bearing characteristics.
Something else you'll want to consider is the compresive strength of the foam. If you're going to be standing on it, it's something to consider.
I spoke with the folks at Raka and ordered some epoxy. It will be a fairly pricey experiment, but I think it is worth a shot. I'll post my progress here.
Definitely watching this one. I am curious how you plan on testing your composite. I’ve definitely gone the make it and see how it goes route, but with this kind of project I could see there being a lot on excess that could be used as test material.

What might be worth trying is adding some internal structure to your build. If you can cut some strips of the FRP and apply it to the cut edges of the insulation before sandwiching. You could also introduce some of these strips where heavier loads are expected.
When you post your results can weigh it also so I can figure the weight of a square foot? I'd appreciate it.
Pulled some Q&A from HD on their product. Says that it is polyester based.

Q:Can these panels be glued directly to rigid foam insulation That has been glued to masonry walls?
bylando|May 26, 2021

A: Yes. But most rigid foam Insulation has a plastic finish on it and over time the plastic will start to pull away from the foam.
byThomas|May 27, 2021

A: Yes the panels can be glued as mentioned. Make sure that the foam insulation is listed as compatible with the adhesive used and that the adhesive is listed for use with the FRP Board.
byPV|May 28, 2021

A: Hi Lando, Make sure substrate surfaces are non‐painted, clean and dry. Wall surfaces should be smooth & flush. Please keep in mind that FRP will follow the contours of the substrate, so any major imperfections in the substrate may show through the product. Thanks, -Stabilit America
byStabilit|May 27, 2021
byTERRY|Dec 26, 2016

A: Unishear. Not every body has one & they’re not cheap. Very little dust, clean cuts & scrollable ( s-turns ) If you know a good tinknocker (sheetmetal mechanic) see if you can borrow it! They are the ultimate tool for FRP. Outlet openings... rotozip it w/ wood saber bit...holes... use appropriate sized holesaw. 100s of sq.ft installed,little dust, clean cuts,no itching or scratchy eyes!
byKris|Jun 25,

A: Use a plexiglass or glass cutter tool. They won't have the same problems that a utility knife has, and they're less than $10. I'd buy both the one with a wheel and the one that looks kind of like a chisel.
byDavid|Jan 11,

A: Use good quality offset tin snips. Easy to set up and cut. Very precise control of cut. NO DUST! Make sure frp is not too cold. To cut out holes for outlets etc. start with hole saw or drill small starter hole with a conventional bit or paddle bit. Make sure that you have a scrap of wood below panel so that when you drill the hole, the frp does not break unevenly when the bit comes through the back. The drilling may generate small amount of dust. Once starter hole is made then use the left or right shears to cut the opening that you have marked out with a pencil or marker. This method uses less time when you figure in the safety prep, clean up and set up required for any sawing method.
byPV|Apr 8, 2021

A: I just re-did a huge commercial kitchen and here is what we tried. I started off by using a razor blade as other comments have mentioned and that was taking way too long. The blades were quick to dull and the tips kept snapping. We next tried a skil saw and yes its doable but you need hand protection and eye/face protection as this stuff once cut produces sharp small shards that give you insulation type itching and the projectiles are laser guided to go straight into your eyeballs. We next tried a jig saw which was a little better but the cuts were slow, a little jagged and very rough even with different teeth quantities. The ultimate best experience we had was using an oscillating tool. Wow. Very smooth and quick cuts on long strips, easy to free hand and cutting out outlet and switch holes was a breeze. Every power tool company makes one so just look it up on Home Depots website. The one we happened to have was a Porter Cable. I could care less on the brand you get but I cannot recommend an oscillating tool for this job enough. Happy Installs Folks!
byStevo|Jun 30, 2021

A: Skill saw and a shop vac. This stuff is very splintery so wear glasses, gloves and a (snug fitting) long sleeve shirt.
byDag|Jun 28, 2017

A: Use your plywood blade, turned backwards. Wear goggles and gloves. Same as you would do with thin aluminum.
byHopeithelps|Jul 27, 2021

A: I have been a building mechanic for years. Used this stuff everywhere you can think of because of its durability and longevity and I have to say that the only way to cut this stuff is with a 4"grinder and a cutting disk. Like a hot knife through butter. Also with a little know how and a torch or wheat burner you can wrap cylinders and corners, although I would not recommend this without a bit of practice in a non flammable environment.
byKnighttof7|Jul 1, 2021
Thanks for posting that info. I expect that the weight will be around 1.35 pounds per square foot. The encouraging thing is that my 1436 will only require roughly 42" square area to cover the front part of the boat.
The info on the plastic coating is good info...I'll be stripping the plastic off mine before I do the laminating.
I'd like to find some 1" in foamular 250, but there is only 150 available in my area. The FRP should spread my weight sufficiently. I guess only testing will tell.
Just an update. I'm starting on this project tomorrow. If the HD styrene sheet has a plastic backing, it will be removed. I also plan on poking small holes in the surface of the foam to allow some 'teeth' for the epoxy. We did this for balsa sheeted foam wings on RC airplanes back in the day. I'm picking up a new diamond tooth oscillating blade to cut the FRP board as well. I'm looking at the possibility of laying in a 1" square aluminum tube that will span the greatest run of the composite board. We'll see on that one, as a few things have to align size wise to make that possible.

I'll show some testing soon.
At the risk of over complicating your project (like I do with mine), do you know how fiberglass would work with you adhesive? I remember in a Nidacore sample pack there was a composite that had holes through the core, laced with unidirectional glass. Might be overkill.

Looking forward to seeing your progress.
I picked up the materials from HD today. I was actually surprised at how pliable the FRP board is. That being said, when I put a piece of 1" formular board in a sandwich, it was very rigid. I have a 1' X 2' test that I'll be assembling tomorrow. I ended up using heavy duty siding shears to trim it, and have a blister on my finger for my efforts.

I did complete putting the formular inserts between the ribs, and laying in the FRP board on my 1436's mid-section. I just have to install a few 'L' brackets to keep it down.
Lammichael6499, I was unaware of Coosa Board till your post. I did some quick research. It is more appears to be much more structurally rigid. Weight is about 1 pound per square foot at 1/2" thickness. A 4x8 sheet of 1/2" is ~350-370 dollars. I think that you would end up with less weight per square foot using Coosa Board, but couldn't find any load bearing examples in my quick search. I'm sure they are out there. My front deck could use a 4' X 4' sheet, so there is a large savings there if you can get by with less than a sheet.

The FRP is flimsy, but dense and tough. It is very water resistant as well. I'll be straightforward to say that I'm a beginner at this, no expert at all. I just thought this might solve some issues I was having engineering a front deck for my jon boat. Since I didn't find any evidence of people trying the FRP/EPX/FRP sandwich, I figured, what the heck. I was going to do my mid-section with FRP board anyway, so I had everything except the epoxy to test it out.

The 1' X 2' test panel is curing now. I'll let it sit overnight and do some preliminary checks tomorrow evening.

I will add that I have 30+ years experience building giant scale RC airplanes. I have done a lot of work with foam, fiberglass cloth, fiberglass and epoxy resins over the years and am comfortable working with them.
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1/2” Coosa is stronger and lighter than 1/2” plywood. It’s used in boats for subfloors, transoms, etc. I’ll never use plywood in a boat again.
And Coosa board is really expensive in the scheme of things. I can see why someone would search for a alternative.
I thought that you were sandwiching insulation foam (pink and blue stuff) between sheets of FRP. That would be a huge weight savings over Coosa and cost savings over decent plywood. Areas where you need to use fasteners or are concerned about impact resistance could be reinforced with plywood.

If Coosa was new to you, check out Divinycell and CarbonCore.
I am sandwiching pink formular 150 insulation board between two sheets of FRP.

Tonight I weighed my 1' x 2' test board. The weight is 1.3 pounds per square foot. The weight is pretty good. Coosa board is 1 pound per square foot. 1/2" marine plywood is 1.6 pounds per square foot. The hoped for, but unknown attribute was the strength of the laminated board. I used Raka 900 medium resin combined with Raka 608 medium hardner. It was cured 36 hours.

I was able to support the last two inches of the test board on each end and stand on one foot in the center,(I weigh 175 lbs). There appeared to be only a very slight deflection. This was very encouraging, as a sheet that is 40" X 46" with a center support should be plenty strong enough for daily use. I am pretty certain that 1/2" plywood in these dimensions would have deflected much further and possible have broken.


At this point, the only real complication I can envision will be the actual mechanical process of performing the lamination of the main components. From my RC airplane experience I know that unless you can support the entire structure evenly, it is difficult to keep the components in 100% contact and aligned. This means that it will be a challenge to find a flat surface, a flat top plate and enough weights to ensure the even binding that is critical to the strength of the final product. I think that vacuum bagging is the right solution, but I'll have to research how to set this up and execute it for this crazy shape.

I'll do a little head scratching on the next step, but so far it looks like this home crafted composite board has promise.

FRP board at Home Depot was $41 per sheet 4X8 sheet.
Pink formular 150 insulation board was $20 per 4X8 sheet.
Raka Epoxy (1.5 Gallon kit) was $140 shipped. I used 6 ounces on the 1' X 2' test panel with some left over.
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Very interesting experiment. Sounds successful.
In my experience, the failure in the foam core is from delamination over time. Pink board is pretty durable, so very interested to see how well this holds up.

I'm about to re-deck two boats, and was planning to use 1/2" ply on the floor, ($31/sheet) as originally used with original supports. For the front and rear decks, I typically use 5/8" plywood ($46/sheet) with good success. I have never weighed the wood, but I will be watching your experiment with great interest.

I bought 3/4" Coosa decking for $179/sheet a couple of years ago. Looks like it's doubled in price. I've held off on the work for awhile, hoping prices will come back to earth.

Thanks for sharing.

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