Gap is too allow the wood to swell and shrink.I woul dhave at least a
little gap to allow for swelling and to let rain and dew drain off. A
little air gap may also help the wood dry out faster which might be
less swelling. Screws would be less likely to pull out. Use either
galvanized screws or outdoor treated wood screws that seem to be
powder coated with a weather resistant coating.

On 5 Mar 2007 02:56:00 -0800, "Tim_Mac" wrote:

hi folks
first post. i've read a lot of the posts here about wood movement and
understand that this needs to be taken into account especially in
respect to the width aspect. i have a question on how much spacing is
recommended between seat slats on a garden bench. the plans are
online at http://www.buildeazy.com/seat.html
i have all the wood cut, and when i did a trial fitting i found it
more aesthetically pleasing with the seat slats positioned tight
together. the design recommends a 1cm gap. the plans use 2x4 inch
unspecified exterior wood, i chose 6x1.5 inch mahogany (couldn't get
2x4). the climate is dublin = generally mild, not too hot, or cold,
or humid.
the reason i ask is because the instructions with the plans are just
to nail the planks in to the perpendicular seat supports. surely this
wouldn't be great for tolerating wood movement? i.e. if the wood gets
wider with humidity, it will be pulling the nails out sideways. i
intend to use three 100mm screws to give extra strength to fixing the
planks to the seat supports, since the piece will be extremely heavy
and people will invariably try and lift/move the bench by the slats.
i wouldn't trust nails to hold it together well over time.
since i've spent a few quid on the wood, there's no point risking
damage to the wood just because it would look nice to have the boards
together. but i'm wondering what's the expert opinion? on other
benches, i sometimes found a 1cm gap slightly uncomfortable for
sitting on for long-ish periods of time, especially on the back if
it's sunny, no t-shirt etc.,
aesthetically (and for comfort) i would prefer no gap, but then as
necessary i would hope for a smaller gap than the recommended 1cm.
any ideas? not using any glue or anything, just bolts for the stress
points, and screws to fix the slats. my main worry is that even
putting 3 screws down across a 6 inch board could be too restrictive
for the wood movement, but i have no hands-on experience with it so
don't know if i'm making too big a deal out of it.

many thanks in advance.
tim