Q.  We are making some outdoor furniture and BBQ cabinets. The wood will likely get wet, even though we encourage the owner to cover the furniture items. Ideas?
A.  A few comments, but it would take a much longer document to cover all the details..
Virtually every species of wood prefers not getting wet.  Some begin to decay (also called rot) in a few days and some can withstand wetting without decay for many years.Tropical species seem more resistant than most U.S. species.
A list of naturally resistant species is summarized at
Note that black locust, red mulberry, and osage orange are the best in the U.S.  Foreign species that are really good are listed  as well in this publication, but many of these species are hard to find on the marketplace.


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Gene Wengert, aka The Wood Doctor, troubleshoots wood related problems, and explores lumber and veneer qualities and performance, species by species, in Wood Explorer, inside FDMC's Knowledge Center.

To understand all this, appreciate that decay fungi require four elements in order to be active—water (usually liquid), oxygen, warm temperatures (80 F is ideal), and food.  Eliminate one of the four and the decay process stops.
Consider eliminating food:  The food is part of the wood structure, so even early decay results in strength loss.  Some species however have natural fungicides within the wood; that is, these species poison the food supply for the fungus.  Some of these are very effective (strong) and some are weaker.  When the wood does not have enough natural poison, we add chemicals to increase the decay resistance.  A small amount of added chemical can extend the life of the wood to a century, which is oftentimes better than cutting another tree down every 10 years to make replacement furniture.  It is also better than having a leg begin to lose strength at it decays, breaking, and possibly injuring a person.
There are some indications that heating wood to around 300 F for a short period of time alters the chemical structure enough that the decay fungi no longer can use the wood as a food source.  There is also wood with acetic acid added that provides decay prevention (trade name Accoya).
Consider eliminating liquid moisture:  As far as I know, there is no finish or chemical that can be applied to wood to prevent the outside moisture (liquid) from getting into the wood eventually.  Wax is perhaps the best, nearly 100% perfect, chemical in this regard.
Other moisture issue:  All wood shrinks as it loses moisture and swells as it gains moisture.  Due to the grain, this swelling or shrinking can result in warp as well.  Teak is one of the lowest moving species, while oak and hickory move quite a bit.  Plywood moves less than solid wood.  MDF is also a small mover, except for the first time it gets wet, it moves a lot as the wood cells, which were compressed in manufacturing, spring back.


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