There are many references to the fact that using a fire pit on a composite deck can damage the deck, but we could not find any test results that show exactly what using a fire pit on a composite deck will actually do. So we conducted tests of our own on two very different days. We are not a certified testing facility, and our test was probably not strictly scientific. We bought composite deck boards at Home Depot, placed them under a fire pit, and burned a vigorous fire for over an hour. And of course, we did not place a DeckProtect under the fire pit.
The fire pit for the test (shown at left photographed unused in our studio) was a very typical fire pit we purchased at Home Depot for $89. The feet raise the fire pit bowl about 5 inches above the surface.
Also at Home Depot we purchased Veranda® composite deck boards for the test. Veranda is similar to other brands, but may not be exactly the same as other brands. It is made of “80% pre- and post-consumer recycled wood and polyethylene.”
The polyethylene is a very thin layer about 1/32″ thick that has the color and texture. It is this layer that is most vulnerable to heat damage.
Again, our tests were less than strictly scientific. There are so many variables, I am not sure how a controlled and measured test would be done. Obviously, there is a big difference between a cold day and a very warm day. Heat of the fire is a factor. We used hardwood logs and got a brisk fire going. Duration of the fire would be a factor. There are several other variables including the space between the fire bowl and the deck, whether or not there is a breeze that would replace hot air under the fire pit with cooler air. The cumulative effect of using a fire pit more than once on the same section of your deck is something our tests did not address. Some composite decking has a polyethylene layer, as in our experiment, and some brands have polypropylene or poly vinyl chloride. Melting temperatures vary, not just between different types of plastic but within each type with different formulations.
Therefore we do not pretend that our test is somehow definitive. We wanted to see for ourselves what a fire pit will do to a composite deck and share what we found with our readers.