Can composite decking rot?
If you go to the composite manufacturer websites will tell you their products do not rot.
If you search on line and find home repair websites, or forum websites, you will read that there are complaints all over the country.
Personally I had never seen composite decking rot in any way, until this inspection. The listing information indicated that this was a Trex deck, but there are many imitators so we could not be certain. Still, it was composite material.
Walking under the deck and looking up I found that every board had some form of rot or fungus growing on it.
One problem I noticed immediately was that there was little to no separation between the decking boards.
Again, if you go to any of the websites, and to the installation guides, it says there must be space left between the boards so water can exit.
It also says that composite materials expand a lot with heat. What I gather from that is that during the summer each board would squish against the one next to it. Why wouldn't that crush the edges, and expose the insides to water intrusion?
The decking in the photo is a composite product - recycled plastic and various forms of cellulose.
It is said that the cellulose component approaches 50% of the composite material.
Cellulose has a high sugar content.
Fungus LOVES sugar!
There were many areas under this deck where a multiplicity of large, bulbous, fungal growths could be seen.
So the answer to the question in the title of this blog is YES.
The upper side of this deck had been recently painted. Perhaps that was done to make it look nicer, or perhaps to cover up black stains which had migrated to the upper side. There was visible damage up on that side as well. And walking on the deck it bounced a lot between joist supports.
Until this inspection I had never seen composite decking painted before either!
The various websites say its decking can be painted IF it is cleaned properly first (not pressure washed), and then a primer/sealer layer is put on under the paint!
Was that done here? I don't know.
My recommendation: like everything, proper installation of any product is essential. In this case it appeared that the installation at least had a role in the destruction of this material. If water can't be eliminated from anything it will sit and find a way in. When cellulose is included in any material - like composite decking or fiber cement siding - it will absorb that water and the water will encourage the amplification of microbial growth. Fungi is its own phylum! Fungi exists for a reason. Its purpose is to eat and destroy. If not we would be surrounded by and under tons of old, old everything! So don't let fungus eat your recycled deck!