Decks, Patios, Porches and Docks - new composite on top of old PT ???
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BetsyK
09-16-09, 05:39 PM
Hi,
This is the first time I have posted on this forum. I have been reading other posts and have not seen this situation discussed. We need to replace our old PT decking but my husband would like to keep the old and lay new composite on top. This will give added strength, but the deck is not under a roof, gets sun from morning to evening and of course, all other weather conditions apply. I am worried about mold, freeze/thaw, and the different expansion and contraction of these diverse materials. It would be easier not to remove the old decking, but is it a good idea? The joists are 16 inches, the deck is 12X24. The composite, Elements, is 3/4 inch thick, will it flex on 16 inch joists?
Thanks for educating me.
BetsyK
This is the first time I have posted on this forum. I have been reading other posts and have not seen this situation discussed. We need to replace our old PT decking but my husband would like to keep the old and lay new composite on top. This will give added strength, but the deck is not under a roof, gets sun from morning to evening and of course, all other weather conditions apply. I am worried about mold, freeze/thaw, and the different expansion and contraction of these diverse materials. It would be easier not to remove the old decking, but is it a good idea? The joists are 16 inches, the deck is 12X24. The composite, Elements, is 3/4 inch thick, will it flex on 16 inch joists?
Thanks for educating me.
BetsyK
getzjd1
09-16-09, 06:51 PM
According to the installation manual for Elements, http://www.elementsdecking.com/pdfs/installation.pdf 16" OC is what they recommend.
I see no reason why one would want to attempt to install composite decking on top of old decking. You will most definitely have a mold/moisture issue between the two boards. Not to mention risk the new screws not completely grabbing the old wood and loosening over time.
Assuming your josts are of sufficient size for the span, then you should not exxperience flexing. What size are your joists? What is the span between beams?
I see no reason why one would want to attempt to install composite decking on top of old decking. You will most definitely have a mold/moisture issue between the two boards. Not to mention risk the new screws not completely grabbing the old wood and loosening over time.
Assuming your josts are of sufficient size for the span, then you should not exxperience flexing. What size are your joists? What is the span between beams?
lefty
09-16-09, 08:52 PM
BetsyK,
Welcome to the forums
NO, NO, NO, NO, NO. Did I mention "NO!!"
Have hubby tear off the old decking, install joists between each of the existing joists to reduce the span of the deck boards, and THEN install the composite.
As getzjd1 mentioned, the trapped moisture will be an issue, the inability of the screws to hold will be an issue, and (what he or she didn't mention) the difference of the expansion and contraction rates of the wood and the composite will be a killer. Wood reacts to moisture. (It swells in the winter when it's wet.) Composites react to temperature (they swell in the summer when it's warm.) Guess what -- the wood is doing exactly the OPPOSITE of what a composite does in the summer and the winter.
I'm sure that hubby is thinking that it's a cheap fix up front -- and it is. But JUST WAIT UNTIL NEXT YEAR!!!
Welcome to the forums
NO, NO, NO, NO, NO. Did I mention "NO!!"
Have hubby tear off the old decking, install joists between each of the existing joists to reduce the span of the deck boards, and THEN install the composite.
As getzjd1 mentioned, the trapped moisture will be an issue, the inability of the screws to hold will be an issue, and (what he or she didn't mention) the difference of the expansion and contraction rates of the wood and the composite will be a killer. Wood reacts to moisture. (It swells in the winter when it's wet.) Composites react to temperature (they swell in the summer when it's warm.) Guess what -- the wood is doing exactly the OPPOSITE of what a composite does in the summer and the winter.
I'm sure that hubby is thinking that it's a cheap fix up front -- and it is. But JUST WAIT UNTIL NEXT YEAR!!!
BetsyK
09-16-09, 09:49 PM
getzj1, lefty,
Thank you so much for the quick education. I needed to know right away because my husband is ready to act "right now !". It looks like you both have saved us much time and $$$. He read your responses and has changed his mind. Finding this forum was just what I needed.
Again,
Thank You.
BetsyK
Thank you so much for the quick education. I needed to know right away because my husband is ready to act "right now !". It looks like you both have saved us much time and $$$. He read your responses and has changed his mind. Finding this forum was just what I needed.
Again,
Thank You.
BetsyK