What’s your all’s experience with thermal movement along the length of PVC based synthetic decking?
I recently installed a product that’s new to this area called Millenium decking. It’s very similar to Deck Lok (FHB#172 p. 47) except that it has some wood flour in the mix – not 100% pvc. The joint is different but also a tight interlock.
This installation was for a client’s 2nd floor balcony with joists running out from the house (decking // to the structure) at about 50′ length. Max length on this product is 20′, so I’ve got 2 joints in the field per row. I installed at about 25 degrees C (80ish) with tight butt joints and came back in the morning at about 10C (50ish) to see all the butts showing 3/16 gap.
Question is – is the client going to call me in January when it’s 40below and tell me about the 5/8 gap or in July when it’s 105 and tell me about the buckles? The manufacturer says no, that the stuff reaches its “expansive limits” within about 20 degrees C and doesn’t move much after that. I might have been born at night, but it wasn’t last night and that story seems a little suspicious to me.
I’d appreciate your all’s experience and maybe what you did to solve any problems.
thanks,
Jeff
Replies
Greetings ap,
This post, in response to your question, will bump the thread through the 'recent discussion' listing again.
Perhaps it will catch someones attention that can help you with advice.
Cheers
sleeps till noon but before it's dark...
thanks rez,i think twice through the discussion loop without much comment answers my question. It turns out that i WAS actually born last night, since I believed the spin and installed it the way i did. now it's a high end job with one very low-end, very visible detail. :(jeff
we learn, we live, we roam, we die.
be living
sleeps till noon but before it's dark...
Sorry, no direct experience with this material.
However, I think the chemists / physicists would be interested in just how a material will only expand / contract within a 20 degree range and then magically stop. Is that a +10 and -10 = 20 degree range or a +20 and -20 = 40 degree range?
Never heard of an "expansive limit" -- maybe that's like Z-7 ( the exclusive secret ingredient only in Pennzoil! ) - try to find it on a periodic table.
Jim
Never underestimate the value of a sharp pencil or good light.
i've never used any interlock decking.. but we have done a lot of Trex..
and a lot of PVC trim ( Koma...... Azek )
they all have very large coefficients of expansion... and every installation has to take this into account
some products more than others..
with Trex you have to gap the boards 3/8" below 40 deg and 1/4" above 40 deg
think he was talking butt joints, could you half lap them so the joint wasn't open through to the joists?
The nice thing about Trex is that you have space between anyway for those nice little thingamabobs to slide into the grooves, so if you get a little bit of long-wise contraction it's just one more gap among lots of other ones. This stuff is a tight fit so they really show and it's tech sheet rates it for only 1.5mm between -30C and +30C, which is pretty amazing for PVC. Evidently too amazing. Yeah, I was talking butt joints and the opening to the joists (which are cca treated) is a concern but not a huge one. the half lap idea is an interesting one but you'd have to be awful determined to make that work. as someone said in another discussion, one man's milking is another man's careful attention to detail. jeff