greybeard
Herd Master
The usual reason for PT warping on deck rails relates to the selection of the individual boards being used, more true if it's pine. Avoid any board with a big knot or grain oddity in it, especially if the knot is within 2' or so of an end. It's guaranteed to curl up or outward if there is a knot near the end..the wood dries out more in the less dense section and the more dense section of the knotted area does not. Sealing it as quickly as possible after building and keeping it sealed helps, but can't completely offset the effects of knots and grain variations. Be very selective when choosing boards for deck railings, looking at each side of the board.
On vertical sections (vertical supports) it is not so evident, but any board installed flat and horizontal will go thru dry/wet cycles as humidity and rain comes, followed by sunny days. For horizontal runs, if it's in the budget, buy premium PT lumber, not the generic pt stuff right off the rack at Lowes or Home Depot. More expensive, but the treatment from the plant lasts much longer. I like to use pt lumber that is rated for below ground on my railings.
http://www.buellinspections.com/not-all-pressure-treated-lumber-is-created-equal/
On vertical sections (vertical supports) it is not so evident, but any board installed flat and horizontal will go thru dry/wet cycles as humidity and rain comes, followed by sunny days. For horizontal runs, if it's in the budget, buy premium PT lumber, not the generic pt stuff right off the rack at Lowes or Home Depot. More expensive, but the treatment from the plant lasts much longer. I like to use pt lumber that is rated for below ground on my railings.
http://www.buellinspections.com/not-all-pressure-treated-lumber-is-created-equal/
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