I want to glue some PT boards together to make a deck for a swim platform
and have them very waterproof. Will biscuits swell properly with urethane
I have a large bottle of TitebondII, but don't think it is sufficiently
waterproof for this application.
(If not, maybe I will try that glue-joint router bit I have never used...)
Although it's not PT, I made a picnic table out of cedar 3 years ago. I
used biscuits and Gorilla Glue, there has been no problems at all. It
sits outside all year, everything from snow to the hot sun here. I'm
not sure if PT acts differently than cedar when it comes to biscuits,
though. Mark L.
I constructed a deck storage box (24 x 48) about 4 years
ago and used poly glue for the M/T lid and for the butt joints
on the box. I stained it with semi-transparent (Behr)
No problems so far - joints still tight (allowing for the
P/T wood shrinkage factor).
It is not adjacent to the pool, so not soaked daily. I cover it woth a
tarp during the snowy months, but not during the rainy spring/
No, they don't swell at all -- but they don't really need to, either. The
urethane glue forms a pretty strong bond. In any event, the principal benefit
of biscuits is to aid in alignment of the joint, and not to add strength: the
strength comes from the glue bond between the edges of the boards.
I have my doubts that *any* glue is going to work for long in this
application. No finish short of total encasement in Lucite is going to make
your platform waterproof. After a few years/months/weeks/days (depending on
where you live), the UV in sunlight will have degraded any finish you put on.
The platform will be exposed to repeated soaking and drying cycles, hence
repeated swelling and shrinking cycles, and the glue joints will eventually
break. Further, the PT lumber is going to twist and warp as it dries, too. IMO
you can count yourself lucky if any glue survives two years in this use.
Doug Miller (alphageek-at-milmac-dot-com)
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on second thought, i think i would consider using cedar and shiplap the
joints. if you prefinished the boards, you could add a bead of clear caulk
in the shiplap during assembly. I'm uncertain as to why you need a
watertight deck, but water has to go somewhere. You may be able to cut a
channel in the deck or slope it in the direction you want the water to go.
In any case, keep in mind that galvanized fasteners will stain cedar (and
redwood for that matter) so another metal fastener, such as stainless steel
, would make a better choice. I built many decks and have not yet been
challenged with making one watertight, but i do know the characteristics
of PT. I can say for sure it has a tremendous shrinkage rate, and easily
checks, making way for splinters in your feet. I've used 2x6 tongue and
groove and some of the boards shunk so much the tongue and groove were
barely touching each other after time even with 3 16d twistie nails per row!
You could leave the boards out in the sun for some time until they dry out
for use, but they have a tendency to twist and bow as they dry (about 1/3 of
them would be useless and have to be returned for straight ones) I
personally don't recommend PT to finish a deck for these reasons. PT is
fine for the framing though. If cost is not a problem, you also may want
to consider vinyl (hate so suggest this on a WW forum, but vinyl can be far
superior to wood in some cases) please keep us informed as to your choice
and how it turns out. -dave
I've used the PU glue with biscuits for some gates and arbors a few
years ago and they have held up fine. Don't know if it is really
necessary, but I dunked the biscuits in water before inserting in the
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