Cracks in pressure treated posts (4x4s, 6x6s) - DIY Chatroom

Deck · 05-15-2008, 12:45 AM

Two months ago I bought many pressure treated posts from Home Depot. I bought more than I needed because I knew that they would shrink, and with this could come warping or cracking.

The posts were spaced above the concrete and apart from each other in my garage, in low humidity.

Recently, I've been examining the wood as I've been using it (or marking it for return). Today though, I decided to re-examine all the wood after I noticed a 1/4" crack in a 6x6x8' running about half the entire length. You could see in. I didn't take any pictures today, but I wish I did.

I would say about 25% of the pressure treated posts I had left did not have serious (1/8" ? ) cracking. The rest did. The 6x6 is an extreme example, and no other piece had such a wide or long crack.

So my question is this. WTF? Is it just me? I've googled and I see other people have problems with cracks in posts, but how did this happen? There was no sun, and a dehumidifier so the moisture was controlled. What if I had installed those posts right when I bought them? What then? I'd be screwed.

I exchanged the posts this evening. I was told the posts I brought back will be spray-painted? and will be clearanced.

The new posts I need to use fairly soon. They are still pretty heavy. Do you guys think it would be OK to leave them in the sun to dry out? Putting them inside doesn't seem to make a difference.

Thanks

**thekctermite** · 05-15-2008, 12:58 AM

Your treated posts are Southern Yellow Pine, which is strong, but generally unstable. It is prone to twisting, cracking, and checking.

To make matters worse, the ACQ treatment is waterborne. They jam a considerable amount of water into the wood during the treatment process...Hence the weight of treated lumber. The post you bought are probably not KDAT (kiln dried after treatment) to 19% moisture content, so their water content is in excess of 19%....Probably in excess of 30% realistically. KDAT ACQ treated lumber is typically available at good lumber yards, but not home centers. Might be worth looking into. The process of the moisture being naturally expelled from the wood causes it to kind of go crazy.

The joke on jobsites is that if you have a bundle of Southern Yellow Pine boards, don't break the bands on the bundle that hold all the boards tightly together until you're ready to nail them into place.

Putting them out in the sun to dry out is the absolute worst thing you can do. They'll certainly develop the checking you're experiencing, and will also probably start twisting and bending. The best thing is to find a shady space outside and let them dry out that way for a few days. The ambient air will bring them down to 15 or 20% moisture content in no time, depending on the humidity.

If you ask me, the Home Depot is pretty nice to take them back. Unfortunately, it is a characteristic of the product.

Deck · 05-15-2008, 01:15 AM

Once again you come to the rescue! I'll change the configuration tomorrow morning so they aren't exposed to the sun. Thanks

**thekctermite** · 05-15-2008, 10:00 AM

Just understand that even when you do everything you can to let them slowly dry out, there is a very good chance that they'll still check. Wood can be unpredictable that way.

I cut corbels and brackets out of cedar timbers with a huge band saw as a side business. I was cutting a relatively wet beam, and had already finished about 15 corbels one day. I was putting them in the bed of my truck after I finished each one. I happened to turn the saw off for a break and instantly heard the sound of wood cracking or breaking...I looked at my corbels sitting in the hot truck bed and realized that they were all cracked in a matter of minutes. That was about $300 down the drain. Lesson learned!

Deck · 05-15-2008, 10:31 PM

ouch!

I should note that I buy plenty of pressure-treated wood from Home Depot that does not crack -- usually 2x's.
The only pieces to really crack on me are the posts.

And speaking of that... today I examined one of the 6x6 posts I installed two weeks ago. It looked fine when installed: dry, no warping, no cracks.

Today I see cracks starting to develop. Here are two pictures:

I'm not sure why these pictures came out blurry. Anyway.. I predrilled for the fastener's required 10d HDG nails using a 3/32 bit. The crack is not by the nail hole but close.

How can I prevent further cracks, and how can I prevent that crack from becoming wider? I don't want another gap on my hands like that other 6x6. Is it too early to seal/stain/etc ? I've had the wood for about two months. If sealing is the way to go, any recommendation as to brands?

Thanks

**thekctermite** · 05-15-2008, 10:50 PM

There's absolutely nothing you can do. Nothing you can apply to the wood. Sorry, but that is the nature of this type of wood. You're just going to have to accept it or find an alternative product.

Deck · 05-15-2008, 11:55 PM

Well it isn't as big a deal with the 4x4s because they're to support the joists to the upper landing for the dog ramp thing I'm making. But the 6x6's are absolutely required to support the deck. Is there any way to tell from the pics if this is going to become a problem structurally? Do I need to monitor with a caliper or something?

I don't understand how all these contractors at HD are buying up this wood if it has this problem. BTW the specific type sold at the HDs around me is Prowood Micro. I checked the Prowood website, and they sell a KDAT ACQ type, but not in NY.

Also, I read this link, in which some claim that the second KDAT drying warps the wood. Perhaps I'm misinterpreting it though. kctermite, if you could weigh in on this I'd appreciate it. Thanks again.

**thekctermite** · 05-16-2008, 12:45 AM

The process of kiln drying doesn't cause treated lumber to warp. It actually is a controlled removal of the moisture as opposed to installing it wet and letting mother nature do it.

This isn't a Home Depot problem. It is a lumber-in-general problem.
Remember what I said about Southern Yellow Pine? It does this. Fact of life.

Structurally, it won't be an issue. Even if the post were to split in half lengthwise, you still have the same amount of lumber in compression under the load at the bearing point, so the structure isn't weakened all that much. You'll see no ill effects.

I sure do like your attention to detail, but jeez you're thinking too hard!

bofusmosby · 05-16-2008, 12:57 AM

I have been told that these cracks do not really cause a structural problem. As stated, its the nature of the beast. You might want to wrap the 6 x 6 posts with thin boards. End, or should I say butt joint them around the posts. At least then, these splits will not be seen. If you have a lot of them to do, it may be too much work and wood, but if you only have a few, no big deal. As a matter of fact, I too have a 6 x 6 post (about 10 years old) that has a number of splits. because of the way it looks, I was going to fill the splits with polyurothane glue, and wrap mine. Probably use some 1" X s. The post will appear larger (7" X 7"), but with me, that is not an issue. Just a thought.

Bofus