# Pressure treated lumber question **URL:** \ **Category:** Factual Questions\ **Created:** [May 5, 2001, 4:29am UTC](https://boards.straightdope.com/t/pressure-treated-lumber-question/64415 "2001-05-05T04:29:39Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![dewt](https://avatars.discourse-cdn.com/v4/letter/d/9dc877/32.png) [@dewt](https://boards.straightdope.com/u/dewt)\ **Post date:** [May 5, 2001, 4:29am UTC](https://boards.straightdope.com/t/pressure-treated-lumber-question/64415/1 "2001-05-05T04:29:39Z")
I’ve been building fences for about 15 yrs. Over the last say, 3 yrs or so, I’ve noticed that the 4x4 posts have a tendency to crack and twist. Sometimes very badly. I know that this is caused by the drying process, and excessive sun exposure on one side can make it even worse. My question is this: what the heck can I do about this? Logic dictates that some sort of sealant, (Thompsons Water Seal, for example) might help, but I’ve also been told that one should let the wood weather for a year before going that route. Hmmmm. ---
**Author:** ![dp](https://avatars.discourse-cdn.com/v4/letter/d/ecd19e/32.png) [@dp](https://boards.straightdope.com/u/dp)\ **Post date:** [May 5, 2001, 5:04am UTC](https://boards.straightdope.com/t/pressure-treated-lumber-question/64415/2 "2001-05-05T05:04:52Z")
IMHO most cracking and twisting comes from the tree or part of the tree that the post was sawed from. Crooked,twisted trees make crooked or twisted posts. Select post from the bins more carefully. Pick smooth, knotless, straight posts. Check both of the ends of the posts for the growth rings, this can indicate if the post was cut from a straight tree. Find a different manufacturer of treated posts. ---
**Author:** ![GrizzRich](https://avatars.discourse-cdn.com/v4/letter/g/7ba0ec/32.png) [@GrizzRich](https://boards.straightdope.com/u/GrizzRich)\ **Post date:** [May 5, 2001, 5:07am UTC](https://boards.straightdope.com/t/pressure-treated-lumber-question/64415/3 "2001-05-05T05:07:21Z")
I’d but on a few coats of oil stain, to help saturate the wood to avoid checking. ---
**Author:** ![yamo](https://avatars.discourse-cdn.com/v4/letter/y/ecae2f/32.png) [@yamo](https://boards.straightdope.com/u/yamo)\ **Post date:** [May 5, 2001, 6:50am UTC](https://boards.straightdope.com/t/pressure-treated-lumber-question/64415/4 "2001-05-05T06:50:39Z")
how about steel bands? ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 5, 2001, 8:45am UTC](https://boards.straightdope.com/t/pressure-treated-lumber-question/64415/5 "2001-05-05T08:45:44Z")
Whenever I use lumber for an outdoor project, I always smear some 2-part epoxy on each end-grain surface; this prevents the wood from soaking up water through the end-grains. I’m not sure if this will keep your 4 x 4’s from twisting, but at-the-very-least it should keep the wood from rotting. ---
**Author:** ![Astroboy14](https://avatars.discourse-cdn.com/v4/letter/a/df705f/32.png) [@Astroboy14](https://boards.straightdope.com/u/Astroboy14)\ **Post date:** [May 5, 2001, 12:31pm UTC](https://boards.straightdope.com/t/pressure-treated-lumber-question/64415/6 "2001-05-05T12:31:42Z")
_Disclaimer: my memories of this are about 20 years old!_ Before reading any farther, realized that “green”=unseasoned wood; while green=green color… In high school, I had a part-time job at a pressure treating plant… we treated everything from 1X1 fence posts to 8X8 beams with CCA (um… chromium cubris asrsenide? Something like that! It included chrome, copper, and arsenic, anyways… it was colored green, FWIW.) The pressure treating of this lumber was to retard/prevent rotting of the wood. And it was of questionable efficacy. The deal was (is?) that lumber is treated in this way: the lumber is inserted into a vaccuum chamber, the air is sucked out (making a fairly hard vaccuum), the chemical bath is inserted (while maintaining the vaccuum by sucking out the displaced air that remains), the vaccuum is released. Theoretically, this forces the vaccuum-compressed cells of the wood to suck in the chemicals… In reality, this works well for _seasoned_ lumber. For _unseasoned_(“green”) lumber, however, it does nothing more than staining the outer layer green, while the core of the lumber gets nothing… We mostly (at our plant) treated “green” (unseasoned) lumber, and I’d be willing to bet that most lumber-treatment plants do the same thing! It’s not cost-effective to let lumber season before treatment… at the time, this didn’t bother me; now it does! But there ya have it! A small (in diameter) piece of lumber (maybe up to a 2X4) gets treated well, but a large (in diamter) non-seasoned piece gets a superficial green coating that does nothing to prevent rotting (due to cracking and twisting as it dries, or seasons). My (largely uneducated) guess is that you are buying lumber that has been treated while still “green”, and therefore twists and cracks as it seasons. I would advise checking the treated lumber you are buying by cutting a sample piece or two in half. Look at the cut surface… does the green coloring go deep into the core, or does it just sink in a little bit? That will tell you if it was treated while “green” (only a little penetration) or while seasoned (deep penetration). My guess is that you are buying “green” wood (IE: it has not dried out fully yet), and it is splitting and twisting as it dries… ---
**Author:** ![Turbo\_Dog](https://avatars.discourse-cdn.com/v4/letter/t/ce73a5/32.png) [@Turbo\_Dog](https://boards.straightdope.com/u/Turbo_Dog)\ **Post date:** [May 5, 2001, 12:57pm UTC](https://boards.straightdope.com/t/pressure-treated-lumber-question/64415/7 "2001-05-05T12:57:57Z")
My guess is that your posts weren’t fully seasoned. It is getting harder all the time to find really good wood. Today if you want really long lasting wood, kiln dried and treated is the only way to go, like what is used in playgrounds and stuff. It’s just expensive for fencing. As long as your posts are still solid though, wait for a good dry spell and then put some sort of sealant on them, especially in the cracks. As others have mentioned, for future posts, spend time being picky. Look at the grain and ends of each post. Stay away from knots and wavy grain, open grain, and look for even the slightest bit of warping and twisting. And irregularity will only get worse in the weather. Also consider steel if the fencing is “work” fencing.