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Old 07-27-2009, 10:44 PM   #1
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Any way to flatten cupped pressure treated wood?


I'm doing some repairs to the deck on my house. I cut some 2X10 pressure treated boards and fastened them as a skirt around the edge of the deck. So far I have cut three boards, and they met at goofy angles (one was 17, the other was 52) so it was tricky getting them to line up, but they looked all right when I was done.

I went away on vacation and when I came back, the skirt didn't look as good as I remembered. I took a straight edge to the boards and found that in just two weeks they had severely cupped, causing noticable gaps where the boards joined together. I know for a fact the boards were nice and flat when I fastened them to the deck because I spent a good deal of time hand picking each board.

Because of the odd angles, I can't flip the boards around and screw them back in place.

Is there anything I can do to try to flatten out the cupping?

Should I take these boards back to Lowe's? (sorry, no pics yet to show how bad they are)

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Old 07-28-2009, 12:38 AM   #2
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Any way to flatten cupped pressure treated wood?


No point in taking them back, what you're experiencing is not uncommon and has more to do with the species of lumber (southern yellow pine in this case). SYP is known for its tendency to "move". Gotta properly secure it in place from day one.

Short of drawing it in with lag screws or ledgerlocks, there isn't much you can do about the cupping.

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Old 07-28-2009, 12:49 AM   #3
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Any way to flatten cupped pressure treated wood?


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Originally Posted by thekctermite View Post
No point in taking them back, what you're experiencing is not uncommon and has more to do with the species of lumber (southern yellow pine in this case). SYP is known for its tendency to "move". Gotta properly secure it in place from day one.

Short of drawing it in with lag screws or ledgerlocks, there isn't much you can do about the cupping.
I fastened them in the same day I cut them, using deck screws placed about 2" from the top and bottom edges, and about 6-8" apart from each other, horizontally. Would using more screws help?

I've never worked with ledger locks. Are they expensive?

What exactly causes the boards to cup like that? Is it from moisture finding a way inside the boards through the screw holes?
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Old 07-28-2009, 02:20 PM   #4
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Any way to flatten cupped pressure treated wood?


http://www.fpl.fs.fed.us/documnts/fplrn/fplrn226.pdf

http://wiki.elearning.ubc.ca/ViewHere

http://www.fastenmaster.com/Files/Fa...erLok%20SS.pdf Box stores carry them. Be safe, G
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Old 07-28-2009, 02:27 PM   #5
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Any way to flatten cupped pressure treated wood?


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Originally Posted by spaceman spif View Post
What exactly causes the boards to cup like that? Is it from moisture finding a way inside the boards through the screw holes?
The moisture content of basic treated lumber is about 30%, more or less. If the wood is maked KD it has been kiln-dried, and that helps make it a bit more stable...Pretty rare to find KD treated lumber at the average yard. Nothing to do with the screw holes.

The cupping also has a lot to do with where the board was cut from the tree. If it has the center of the growth rings it was cut from the dead center of the log, and that'll be a bit less prone to cupping. If it is cut offset from the center of the log the tendency is for the wood to cup toward what used to be the tree's center.

Like I said, aside from knowing what you're doing when selecting lumber there isn't much you can do about it. The forces in that wood are incredibly strong and treated SYP is generally a crumby deck material if you want it to look good for too long. Much better to go with treated SYP for the structure and use cedar or another nicer decking material for the exposed parts.
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Old 07-28-2009, 11:13 PM   #6
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Any way to flatten cupped pressure treated wood?


Some great info from you guys - thanks!

And now for a surprise...I went to Lowe's tonight to select some hardware for this project and when I talked to the guy at the counter about what happened with the treated wood I got from their store, he told me to bring it in and they would exchange it for free!! Sweet!

I've already selected one replacement piece, and it's definitely cut from across the center of the tree, so any warpage should be at a minimum. I'm thinking this time around of using carriage bolts to hold it in instead of screws. I'm using carriage bolts because the head of the bolt will be sticking out in an area where my chunklets will be playing and I don't want them scraping against the corners of a hex head.
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Old 07-29-2009, 10:04 AM   #7
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Any way to flatten cupped pressure treated wood?


All of the above given advice is true in regards to using Pressure Treated Southern Yellow Pine as decking material, although it is the most popular in this area. Depending on the area where you live, as to how much hot weather you have, it will dry out fast and twist badly. As far as using carriage bolts, or any other type of bolt, when I build decks in this area I do use carriage bolts for the main structure of the deck. BUT I always counterbore the hole for the bolt so the head is not exposed at all. Beside being a bit safer, I think it looks better than a bolt head sticking out. Having Lowe's, or any other lumber supplier, take back twisted PT SYP after it has been installed and warped surprises, no--shocks me, to say the least. The Lowe's/Home Depot in our area goes so far as to tell customers they cannot "cull" lumber in the store. I seem to have a hearing problem when they start that. Thanks, David
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Old 07-30-2009, 01:43 AM   #8
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Any way to flatten cupped pressure treated wood?


I live in Ohio, so I get hot summers, cold winters, and rain in the spring, so this deck will see it all.

I talked to another guy who builds decks around here, and he suggested I use "timber lock" wood screws. He told me I'd need a corded drill to work with those. Anyone use them? How many amps will I need for the drill? Any suggestions on which brand of drill? I've had good luck with DeWalt power tools so far.
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Old 07-30-2009, 12:14 PM   #9
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Any way to flatten cupped pressure treated wood?


Timber locks are pretty much the same thing as ledger locks. I'd get a 1/2" drill for sure, just to have the flexibility to use 1/2" bits for other tasks. The average homeowner-sized drill may lack the guts to drive a screw like that home. The DeWalt DW235G would be a good choice since you're a DeWalt guy.
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Old 07-31-2009, 02:12 AM   #10
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Any way to flatten cupped pressure treated wood?


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Originally Posted by Thurman View Post
...they cannot "cull" lumber in the store...
What does that mean ?

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Old 07-31-2009, 08:21 AM   #11
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Any way to flatten cupped pressure treated wood?


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Originally Posted by iMisspell View Post
What does that mean ?

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They don't want you to pick through the lumber to get the ones that aren't twisted or have a bad crown to them.

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Old 07-31-2009, 02:36 PM   #12
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Any way to flatten cupped pressure treated wood?


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Originally Posted by Gary_602z View Post
They don't want you to pick through the lumber to get the ones that aren't twisted or have a bad crown to them.

Gary
Actually they will let you do that. Sort of. The first time I started culling the boards, some workers yelled at me to stop and chased me through the store. I hid inside a garden tub display until they passed me by.

So later on, I sent one of my kids over to the paint section and told them to "accidentally" start knocking down the cans of paint, sent another to the plumbing section to use one of the display toilets, and sent my boys off to hijack a forklift and take it on a joyride.

While the employees were busy chasing my kids, I had plenty of time to cull all the lumber I needed.
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Old 07-31-2009, 04:38 PM   #13
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Any way to flatten cupped pressure treated wood?


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Originally Posted by spaceman spif View Post
Actually they will let you do that. Sort of. The first time I started culling the boards, some workers yelled at me to stop and chased me through the store. I hid inside a garden tub display until they passed me by.

So later on, I sent one of my kids over to the paint section and told them to "accidentally" start knocking down the cans of paint, sent another to the plumbing section to use one of the display toilets, and sent my boys off to hijack a forklift and take it on a joyride.

While the employees were busy chasing my kids, I had plenty of time to cull all the lumber I needed.
You're a strange duck, spaceman!
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Old 07-31-2009, 05:05 PM   #14
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Any way to flatten cupped pressure treated wood?


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Originally Posted by thekctermite View Post
You're a strange duck, spaceman!
Strange, yes. But irresponsible?? No! I made sure that my 5 year old buckled his seat belt before he drove the fork lift!

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