I am working on making outdoor dog playground equipment. (basic equipment for training puppies)
The first prototypes were made out of some inexpensive sanded plywood from Home Depot. ($32 a sheet) Which carved beautiful, looked great and disintegrated in the recent rains. 
The glue melted and the wood grew some kind of white mold / fungus on it in a matter of days. (I have never seen plywood just melt like that before.)
So I am looking into alternative materials.
So far my research suggests that white oak is the best for rot and weather resistance. But it is costly and hard to find in wider sizes. I would be doing glue ups for some of the parts (more labor) and doing traditional carpentry for most of the build, as opposed to cutting out all the parts with the XC. (Having the XC cut everything and just doing final assembly was a big appeal to this project for me) And that still would not eliminate warping and cupping of the wood due to moisture.
The outdoor rated plywood that I have found is expensive and has a horrible surface. (I want something furniture grade)
HDPE is what professional playground equipment is made of but it is significantly more expensive! $200 to $400 a sheet.
I came across some composite decking material at Lowes. The Choice Decking has a 11.25" wide trim board that will work for some of my designs. It is fairly flexible, but most of the equipment is small so material flex should not be an issue. (and in areas where it is, I can look into reinforcing it somehow)
I do need to find out if anyone makes it in a wider size, say 14"~24"?
If no one makes a wider board, I want to see if multiple boards can be glued to gather to make a glue up panel?
I am going to attempt to carve some of it this weekend. It is a plastic wood fiber blend so I will try my plywood settings with it first and see how it goes?
I may try some 3d carvings on the scrap just to see how it works out too. 
Has anyone had any experience with this material before? Cutting, carving, gluing?
I’ve carved composite decking material before. A friend of mine finished putting in a deck and gave me his cutoffs. I am not so sure about the trim boards though. Could you provide a link so I know exactly what material you are talking about?
Composite decking material (this stuff) behaves like a hard plastic that doesn’t melt at high RPMs. I haven’t had any significant trouble cutting, carving, or gluing with Titebond II.
Two minor things:
- it is difficult to finish as the surface fuzzes a bit from the material used as a resin filler. A sealer is required to get a smooth finish. Cut/milled surfaces of this material soak up finish like end-grain.
- The chips resist breaking up. Strings of this stuff will wrap around the bit shaft and accumulate. I’ve only used this in small carvings… pocketing and profiling operations over less than 12 square inches, but I suspect that for a larger carve you’ll need to pause and clean the accumulated junk off the bit.
The black portions of this box prototype I made is composite decking material:
If you are going to glue up panels of this stuff, you should use dowels or biscuits to reinforce the edges. Personally, I would just apply it like decking material and avoid the extra work - this would provides better drainage.
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Here is a link to the deck board at Lowe’s.
It is more like a plank of wood - as opposed to the 2x4 style of the deck planks.
I did a quick test carve on a composite plank.
It carved just fine with my 1/4 downcut bit and plywood settings. Good chips and a smooth cut. It did get a bit warm to the touch but not hot enough to cause any issues. I think I can cut much more aggressively. I will have to experiment and see if I can up the settings
It will work well for my application. Only a couple of designs need a wider plank. I may try to get clever and redesign them so they fit together from smaller pieces rather than mess around with glue ups. unless I can find a really effective glue.
Nice chips and a clean cut
There are a little bit of fuzzies on the bottom edge. But they sand off easily.
(I will give my compression bit a try and see how that works.)
A dry fit of the finish build. It looks good and best of all should be weather proof:
A close up of the wood grain detail:
A close up of the edge:
It is significantly heaver than wood, about 3 times? But will be perfect for this application.
(I have another project to make weather proof transport boxes. I think this will be too heavy for that application)
The original prototypes were put together with pocket screws. But the final version needs to use traditional screws with screw holes and countersinks cut by the machine to save labor. The challenge will be that my 1/8" downcut bit only cuts to 1/2" thick. So I need to source a longer 1/8 downcut bit, or do the screw holes with a different bit from the profile cuts. Ideally, I want one bit for the whole job to save labor
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Yeah I was afraid of that. This stuff is mostly recycled HDPE - which is resistant to most paints and glues.
Heat welding is supposed to work.
It looks like if you heat treat it with flame first you can get some epoxies to work well. 
It looks like liquid nails makes a version for composite decking as well.
I did a 3D carve with the composite decking this weekend.
I used my fast “pine” settings. It carved easily, with nice chips no dust. It reminds me of milling wax.
The final carve did have a little bit of fuzzes left on it, but most of these came away just by rubbing it with a cloth.
This stuff carves really well. I wish it came in wider sheets, I could use it for more outdoor projects.
As it is I think I will be using it a lot more for outdoor projects. 
(Up until now cedar fence planks have been my go to material)
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Have you considered using marine grade plywood. We use it for boats, kayaks and canoes, so with a proper sealant it should last a long time.
I looked into it but cost and availability was an issue. Cheaper than HDPE but not cheaper than using white oak.
