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I've noticed on most of our balconies and decks, the top plate on the railing has warped a great deal over the years. This is worst at the corners, where the wood pulls away from the 45 degree cut there. On our solid railings it allowed a lot of moisture in, and you can see the water damage. But even the sides of the top plates sometimes pull up, leaving gaps where moisture can get in.
I replaced a section of top plate on a rail, but after one year the sides are already pulling up a bit, creating small gaps in the sealant.
Is there any way to prevent these top plates from cupping and pulling away from each other?

Thanks
 

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I've noticed on most of our balconies and decks, the top plate on the railing has warped a great deal over the years. This is worst at the corners, where the wood pulls away from the 45 degree cut there. On our solid railings it allowed a lot of moisture in, and you can see the water damage. But even the sides of the top plates sometimes pull up, leaving gaps where moisture can get in.
I replaced a section of top plate on a rail, but after one year the sides are already pulling up a bit, creating small gaps in the sealant.
Is there any way to prevent these top plates from cupping and pulling away from each other?

Thanks
Pick out dry wood for the railings. If the suppliers around you always have "wet" wood, buy the railing pieces long before you build the deck, stabilize them so they won't warp and let them dry out
 

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Anytime you install a board flat for a cap, expect warping. Boards need two nails across their width to hold them in check. On a rail (1-1/2") with pickets (1-1/2"), you have only 3" minus the edge = 2" nail spacing in the center of a 2x6 isn't enough to control warping. Using one nail is even worse, just asking for cupping as the board's edges will move and cup upwards. If the cap is installed level, the water sits and soaks in to the top face, promoting warping, cupping, and twisting. Just butting a miter joint (with a nail or two) and expecting caulking to seal it is asking for trouble. Glue and biscuit-join the miters, pitch the level board for water, design the cap for two nails with additional 2x under (or other means). Seal/water-proof the top, leaving the bottom face to air dry the wood, if it does get wet. If not b.j. the miters, fasten them both to a single piece of wood eliminating any additional movement from seasonal changes and weather. Seal the end-grain leaving a gap for backer rod under the caulking to create an "hour-glass" shape to optimize movement; http://www.coastalcontractor.net/article/117.html

http://docs.google.com/viewer?a=v&q...Qhob1z&sig=AHIEtbSStI_KRvAh59zqX1IjstvXQPNoxA

Gary
 
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