Replies

1. 
   MikeHennessy | Nov 06, 2006 07:02pm | #1

   Your theory sounds right. Now, what's the question?

   Mike Hennessy
   Pittsburgh, PA

1. 
   rick12 | Nov 06, 2006 08:17pm | #2

   Mike, thanks for your reply.  I didn't know whether the cupping resulted from moisture from above (spilt water) or whether it was resulting from moisture from below(high humidity).

1. 
   MikeHennessy | Nov 06, 2006 08:36pm | #3

   Moisture expands the wood. A board cups with the concave side to the dry environment. In your case, from your description, the bottoms are the convex side, i.e., the side with more moisture.

   Mike HennessyPittsburgh, PA

2. 
   user-211435 | Nov 07, 2006 06:52am | #4

   If the boards are cupped, the moisture probably came from below as the bottom has expanded.

   There is one other possibility though, but it's a long-shot.

   It is possible that when the home was being built that the decking was dry.  It could have even been rained on enough to swell a bit.  Then the sun came out and dried up all the rain, and the intsy bitsy spider...opps, wrong story!

   Then the sun came out and dried the top of the boards so they shrank.  But unfortunately, when these boards were wet, really wet from the rain, the wood on the top actually became compressed since all of the water was on the top and the bottoms wouldn't give.  Some of the wood fibers became crushed.  So when everything eventually dried completely, the top is cupped because of the wood that was crushed a bit by this compression is now a bit narrower than the bottoms of the boards.

   I know it sounds like a weird theory, but it is a common occurence on outside decks built with 2 x 6 deck boards.

   You should get a moisture meter and make sure the boards have the same moisture top and bottom.  If they are the same, it doesn't matter why they are cupped.  If you want to, you could have them sanded flat again.  If the bottom has more moisture than the top, you need to fix the problem.  

   Hal

   http://www.rivercitywoodworks.com

   PS   Did I tell you that I was a home builder for many years?