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Are the gaps in decking boards (PT or composite) *REALLY* necessary?

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Are the gaps in decking boards (PT or composite) *REALLY* necessary? Thomas G. Marshall 04-25-2008
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Posted by Thomas G. Marshall on April 25, 2008, 10:43 am

I've spoken to a number of people who have put composite decks in and they
followed the manufacturers suggestions carefully and ended up with boards
that just "seem" too far apart. A friend of mine has these large gaps
around his posts that I'm not particularly fond of.

And two of these people say they've never seen the boards expand nor shrink
the way the manufacturer warned. I'm not sure of the brands.

But this reminds me of something a construction guy told me once about PT (I
know, a different issue): "Don't ever listen to the advice about keeping the
boards a nail width apart....they will dry and shrink on their own". The
only reason I mention this is because I would like to know to what degree
such rules of thumb (PT or composite) are real, or just passed along advice
that never really applies.

For example, has anyone seen trouble with compostite decking boards placed
flush (say, in the summer)?

Thanks!






Posted by Wilson on April 25, 2008, 10:47 am
sometime in the recent past Thomas G. Marshall posted this:
> I've spoken to a number of people who have put composite decks in and they
> followed the manufacturers suggestions carefully and ended up with boards
> that just "seem" too far apart. A friend of mine has these large gaps
> around his posts that I'm not particularly fond of.
>
> And two of these people say they've never seen the boards expand nor shrink
> the way the manufacturer warned. I'm not sure of the brands.
>
> But this reminds me of something a construction guy told me once about PT (I
> know, a different issue): "Don't ever listen to the advice about keeping the
> boards a nail width apart....they will dry and shrink on their own".
But if already well dried, they will expand on their own too.
The
> only reason I mention this is because I would like to know to what degree
> such rules of thumb (PT or composite) are real, or just passed along advice
> that never really applies.
>
> For example, has anyone seen trouble with compostite decking boards placed
> flush (say, in the summer)?
All materials expand and contract. Without spaces, dirt will still find its
way in and then stay there, water will puddle and possibly freeze. Sometimes
'been doing it that way forever' has a real reason. Just my 2 cents.
>
> Thanks!
>
>
>
>
>


--
Wilson N45 W67

Posted by Dioclese on April 25, 2008, 10:53 am
>
> I've spoken to a number of people who have put composite decks in and they
> followed the manufacturers suggestions carefully and ended up with boards
> that just "seem" too far apart. A friend of mine has these large gaps
> around his posts that I'm not particularly fond of.
>
> And two of these people say they've never seen the boards expand nor
> shrink the way the manufacturer warned. I'm not sure of the brands.
>
> But this reminds me of something a construction guy told me once about PT
> (I know, a different issue): "Don't ever listen to the advice about
> keeping the boards a nail width apart....they will dry and shrink on their
> own". The only reason I mention this is because I would like to know to
> what degree such rules of thumb (PT or composite) are real, or just passed
> along advice that never really applies.
>
> For example, has anyone seen trouble with compostite decking boards placed
> flush (say, in the summer)?
>
> Thanks!

Don't know anything about composite.

Treated lumber, like any other lumber, absorbs water. In that process, it
expands. As an example, treated lumber placed immediately next to the next
deck plank sequentially may buckle. This is because the board expands and
may cup either way as well as a result. There is no room for expansion.
Would suspect that composite may have the same property if it absorbs water
as well.
--
Dave

Hypocrisy. Big SUV, filament lights on all night. You think your neighbor
should be changiing to compact fluorescent light bulbs and driving the
hybrid.



Posted by Thomas G. Marshall on April 26, 2008, 5:39 am
Dioclese said something like:
> "Thomas G. Marshall"

...[snip]...

>> For example, has anyone seen trouble with compostite decking boards
>> placed flush (say, in the summer)?
>>
>> Thanks!
>
> Don't know anything about composite.
>
> Treated lumber, like any other lumber, absorbs water. In that
> process, it expands. As an example, treated lumber placed
> immediately next to the next deck plank sequentially may buckle. This is
> because the board expands and may cup either way as well as a
> result. There is no room for expansion. Would suspect that composite
> may have the same property if it absorbs water as well.

Ok. Hmmmm....my side porch (uncovered, and just a landing for steps leading
into the house, perhaps 5' x 7', is covered with 5/4 PT untreated, and it
was placed tight and never buckled. I'm not saying that this is the rule,
I'm just adding it as empiracle evidence that's made me start to wonder...



Posted by Edwin Pawlowski on April 26, 2008, 7:52 am

"Thomas G. Marshall"
> Ok. Hmmmm....my side porch (uncovered, and just a landing for steps
> leading into the house, perhaps 5' x 7', is covered with 5/4 PT untreated,
> and it was placed tight and never buckled. I'm not saying that this is
> the rule, I'm just adding it as empiracle evidence that's made me start to
> wonder...

PT is wood. Composites are a mix of wood sawdust and plastics. The movement
will be different so you are comparing different physical properties. With
wood, most of the expansion occurs in one dimension, the board width. With
plastics, it will occur equally in all dimensions.

Other factors are the temperature and humidity swings where you reside and
that of others who may take your empirical evidence and apply it to their
situation that may differ greatly.



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