Has anyone build anything using 'synthetic decking' material?

[e100]

It appears to be some kind of wood and plastic composite that is popular for outdoor use because of it's resistance to insect damage.

Is it like Tufnol (cotton/phenolic resin).
Does it have grain (like wood).
Is it dimensionally stable?
Is it fire retardant?

[ataradov]

I've seen some version of it used and I was not impressed. I don't know what Tufnol is, but the stuff I've seen had structure like pressure formed plastic or shredded paper/cardboard. It has no grain, the texture outside if formed by the mold.

My understating is that it is dimensionally stable, which is one of the biggest advantages. No idea about it being fire retardant.

One thing that really SUCKS about it is that you have to mount it using their hardware. It is extremely crumbly, it will not hold a screw. The boards can be cut to length and that's as much handling as you can do with them . Fixing them in place would require special brackets.

Based on what I've seen, I personally would avoid that stuff, unless there is some breakthrough in quality and mechanical  properties.

[jpanhalt]

I agree on what I have seen of such composite decking but have not used it.  I believe it is made using recycled plastic and wood in the US.  Home Depot sells a brand called Fiberon (https://www.homedepot.com/p/Fiberon-ArmorGuard-15-16-in-x-5-1-4-in-x-16-ft-Brazilian-Walnut-Grooved-Edge-Capped-Composite-Decking-Board-BRDVCG-BW-16/202594367 ).  It is about $4.50/bf (board foot).  Pressure treated SYP (yellow pine) is cheaper, more structural, perhaps less attractive, and subject to mold and rot over a long time.  I prefer cedar or redwood for decks.  Redwood is now quite expensive.

A PVC material is available for trim.  One brand in the US is Azek:
https://www.lowes.com/pl/Azek--PVC-trim-boards-Lumber-composites-Building-supplies/2820601687039?refinement=4294744980

PVC is non-structural.   It can be machined to various profiles like "brick molding" (with appropriate cutters) and can be solvent welded to an extent; however, the welded seams do telegraph through any finish applied.  Latex paints must be used.  I did a couple of rotted window sills more than 10 years ago, and it has held up well.  Price is not really an advantage.  It is about $8/bf (i.e., a piece 9-1/4" x 0.75" x 8ft -- nominal 1x10x 96 -- is $53).  It's main advantage is no dry rot.  I have also used Azek as a base for indoor projects much as one might use PVC plumbing for stands and such.

[Jester]

I installed a deck at home using solid  “TREX” 25 years ago and it more or less looks like new. There is nothing crumbly about the TREX I used. It’s made of sawdust and recycled plastic bags. I think it will last 100 years.

I’m doing the deck at the cottage next, other than a pressure wash every once in a while, zero maintenance.

[aargee]

I've used it to make a deck, it works fine for that intended use, no painting/oiling and the finish still looks 'like new' after two years.
I have noticed that large lengths can exhibit plastic deformation when stored vertically (or possibly used this way), not surprising considering what it is made of.

[Gregg]

A neighbor used it on their boat dock.  The biggest downside is that when the sun shines on it it can get too hot to walk on barefoot.

[cdev]

Many of these wood substitute products dramatically lose strength if they are soaked for any length of time, in other words, immersed in water. A good example is houses that fronted on beachfront during Hurricane Sandy. There was a kind of failure where suddenly the walls of the lower part of a house that were made with this stuff would lose lateral strength and the house would fall onto often backwards, into their foundations, inward. Entire blocks in San Francisco and a row of identical Craftsman cottages, small homes, on the coast near Santa Cruz, closer to the Loma Prieta quake, did that.
Its a real problem in areas prone to soil liquefaction.

 This failure mode of housing resembles something I had seen a lot in California during the two large earthquakes I have lived through. There it had not gotten wet, it was just the huge strain put on it when the earth became liquid like. Just remember to replace it completely if it ever gets soaked. even if it looks okay. One cant prevent earthquakes, they just happen. I hope that its clear that I am talking about two unrelated phenomena, simply because the aftermath of both look similar.

Just keep it dry.. if it ever gets wet its never as strong after that ..
Also these products are much more prone to getting moldy if they get wet for any length of time than wood. Wood is much more resistant to mold than wood substitute products.

The web site buildingscience.com is a very good resource for info on this phenomenon. I live in an old house that does not use that stuff and thats what I prefer. They outvent formaldehyde if they get wet too. And it irritates the eyes as well as being unhealthy.

Many new buildings make extensive use of these products and smell so much that I cant spend a lot of time in them. It makes me sick. Its some kind of vascular spasm in my brain that reliably, without fail, gives me a nasty migraine headache.