- Q.I am having a problem
that’s not uncommon in my area (north-central Florida). I
recently built a nice custom deck for a customer who
wouldn’t accept pressure-treated wood because of its
appearance. I used kiln-dried southern pine 5/4x6. We primed
all sides of the boards with oil-based primer before
installation, then applied three coats of oilbased enamel when
the deck was in place. We ran the boards perpendicular to the
house, and sloped the deck so that water would drain away from
Still, some boards are rotting at the ends, where stairs
join the deck (there’s a decorative bullnose nailed to
the edge of the deck there). What’s causing the
A.Paul Fisette responds: I understand your
client’s reluctance to use treated boards in a beautiful
custom project. But the problem is caused by using untreated
wood in an exposed location.
Your choices for installing and finishing the deck boards
were sound ones. But the end grain of the wood is absorptive,
like a sponge. Water is splashing off the stairs onto the ends
of the boards, soaking in, and encouraging rot. Unfortunately,
no paint job can stop that.
The bullnose over the ends of the boards makes matters
worse: It lets water seep in, but then blocks it from
The only thing you should have done differently is to use
pressure-treated southern pine. To prevent shrinking,
cracking, and cupping, use "kiln-dried after treatment" (KDAT)
deck boards and have the boards additionally treated with a
water repellent at the treating facility.
You could also use a naturally decay-resistant wood species
(redwood or cedar), if you can accept the fact that those are
relatively soft woods for decking.
Paul Fisette teaches wood science at the University of