drying treated lumber

hackberry jake · July 20, 2016, 05:49:13 PM

Does anybody else do this? Buy treated lumber for a project and air dry it just to minimise shrinking and bowing? I've done it with success for trailer decking, but never for a house deck rebuild. I watching a video about a month ago that explained how to build a long lasting deck. The main point was, you don't want fasteners to hold anything up. You just want the fasteners to hold it together. So the lower 2X10s will be set into the upright 4X4s. And the 2X6 deck joists will sit on top of the 2X10s. And the decking will sit on top of those 2X6s. It made sense to me because I've seen three decks collapse due to the fasteners slipping out. I've never seen one break due to lumber strength. The longer lumber on the bottom is soft maple. Just needed somewhere to put the treated pine and soft maple is my lowest selling lumber so , I thought it'd be a good place to put it.

WDH · July 20, 2016, 09:11:48 PM

Beautifully stickered. You will make the cover of "Good Stickering" magazine ;D.

scleigh · July 20, 2016, 10:25:13 PM

And the stickers are grooved for better air flow and less sticker stain. Somewhere redoaks just shed a tear :D

GeneWengert-WoodDoc · July 21, 2016, 07:28:51 AM

A little technical info. The weakest fasteners is one putt into wet wood that then dries. This is why we generally use metal hangers when building a deck...to avoid the fastener issue. The fasteners for hangers are loaded in sideways shear rather than withdrawal, which means much higher strength.

The strength of a fastener depends on the wood density, plus depth of penetration and diameter of the fastener. Screws are generally much stronger than smooth shank nails. If not too close, two fasteners are twice as strong as one. Coated nails are stronger than smooth.

With treated wood, we need to use special fasteners--special metal or coated--to avoid rapid deterioration.

Most deck failure is because someone did not follow the code requirements for a deck...fastening or sizes of structural pieces. The treatment must be ccorrrrecct...some places have incorrect chemical levels and penetration.

Some places kiln dry after treatment, KDAT. Controls shrinkage and the treatment works better.

bluthum · July 21, 2016, 12:45:52 PM

Doc, with all due respect I say the statement that "generally screws are stronger than nails" is a bit misleading. Withdrawal strength of course but shear is not so much. In the carpentry world I see frequent [though declining] misuse of screws by the misinformed. Drywall type screws especially are not very strong. As for the green "deck screws" nobody seems to know but I have suspicions. The only sure enough structurally rated screws are premium priced so often don't get used where they should. Most deck failures are from grievously poorly built jobs, which are not uncommon.

Back to the thread I would not think that the drying set up shown would result in straight boards given my respect for the ability of KDSYP to warp but I will be happy to be surprised otherwise.

69bronco · July 21, 2016, 08:05:14 PM

Used to do a lot of decks 20-30 yrs back. Best way to keep PT stable back then was get it screwed together asap. Unless things have changed PT was mostly cut from plantation pecker poles. Unstable to say the least, maybe you should reverse your stack so PT is on the bottom or at least put a couple rachet straps on it. Just my 2cents, good luck.

Chop Shop · July 22, 2016, 04:55:28 AM

PT is GARBAGE.

Its inferior wood to begin with and then its pumped full of HORRIBLE chemicals.

I will never build a deck with it or deck a trailer with it. It rots out trailers and screws/nails/fasteners because its so corrosive.

I would rather paint, stain or seal untreated wood instead.

xlogger · July 22, 2016, 05:45:49 AM

I just rebuilt a deck on a rental, the 8/4 PT boards where cheaper than the 5/4. Wonder why?

GeneWengert-WoodDoc · July 22, 2016, 07:24:58 AM

I did say generally screws are stronger, and that is true. Certainly, if the screws are smaller diameter than nails, they will not be as strong in shear. If the screws are driven so their heads are way under the surface, they are weak. Nails in a deck will pop up with wetting and drying and become weak in shear and withdrawal; so, all in all, screws are better.

Note that with a proper treater, the wood is graded after drying and then is treated. So, the grade is the dry, pretreated grade. The treatment adds water, so the wood is dried again.

Here is the big issue...some wood is treated before much drying and is not graded before drying. It has a counterfeit grade and treatment. The treatment called "treating to refusal" is bogus. It is cheap and there is not enough chemical and the wood warps after treatment. As a result, we see the complaints mentioned in some of the previous postings.

longtime lurker · July 24, 2016, 09:07:22 AM

Treatment has no negative effect on lumber stability or quality whatsoever.

It has a huge effect on lumber durability.

But treating bad boards just turns them into long lasting bad boards.

Depending on the treatment solution used it may decrease the lifespan of fastenings. The solution is to use galvanized fastenings or stainless / copper / etc. cheap and nasty electroplated fasteners won't cut it, though I'm not always certain if cheap ones fail sooner then they would in untreated lumber or if it's a case of treated lumber lasting long enough to outlive them.

hackberry jake · July 24, 2016, 09:18:44 AM

Quote from: xlogger on July 22, 2016, 05:45:49 AM
I just rebuilt a deck on a rental, the 8/4 PT boards where cheaper than the 5/4. Wonder why?

I saw that the 1X6s were the same price as 2X6s as well. I chose to use 2X6s for the decking. I put a bunch of heavy gearboxes on top of the stack to help weigh it down.

GeneWengert-WoodDoc · July 26, 2016, 07:07:08 AM

When building a deck, oftentimes we use a treated product called 5/4 radius edged decking lumber. This material is more expensive than 4/4, 5/4 and 8/4 because it is graded for both strength and for appearance. Other products are graded for strength alone or for appearance.

hackberry jake · July 27, 2016, 04:24:59 AM

Another difference I saw was surface finish. The 5/4 boards were pretty smooth and the 2X6s look like they were shot through a 4 head molder with a cannon. One pass through the planer should make everything right .

GeneWengert-WoodDoc · July 28, 2016, 12:02:11 AM

Planing treated lumber is not a good idea, as the highest concentration of chemical is on the outside...the chips are a pollutant that need special disposal and the fine dust should not be breathed, so a mask is needed and the dust bag should also be disposed of properly.

Incidentally, if you hold a piece flat during drying and that piece wanted to warp, it will try to warp when it gets wet and then dries and gets wet, etc. So, it might be better, especially with SYP, to let it warp when drying (and not use weights) and then discard or remanufacture those warped pieces.

petefrom bearswamp · July 28, 2016, 07:42:14 AM

I stickered my PT 2x 22 years ago for my deck for 2 months..
2x10 Joists end nailed against the house, on top of 2x10 double brg beams on the outside ends, bearing beams rabbeted in to the pt posts.
Decking screwed in with the best available at the time.
We get up to 4 feet of snow on it and my hot tub weighs about 2400 pounds.
No issues at all, YET.
My friend/builder says the new stuff is crap, the stuff is typically very rapid growth SYP.
I agree with the pecker pole observation.

GeneWengert-WoodDoc · July 28, 2016, 02:54:38 PM

It is interesting that GA is the #1 forest products state with more SYP forests. But when you go to the store to buy 2x material, over 80% is Canadian SPF. Houses are built with SPF and not SYP as it Is very hard to get SYP lumber, except for structural grades for trusses and rafters and for treated grades. It used to be that over 50% of SYP lumber was treated.

It would be interesting to hear why the present day SYP is crap. Certainly, the grades and adherence to them has not changed, so perhaps he is comparing two different grades of SYP. Or perhaps air dried from the past with KD today. Or perhaps SYP is compared to today's SPF. Overall, SYP is the strongest pine, even with lower grade material. So, perhaps he is referring to straightness. SYP is kiln dried to around 16-19% MC, but when stored in a retail warehouse, the wood can dry to under 10% MC and warp after grading. The old "outside" warehousing of construction wood is indeed a good idea.

Regarding the density of SYP, there are three density breakdown of several construction grades...for example, No.2 Dense, No.2 and No.2 nondense. Higher density means slower growth so more rings per inch, four. The slower the growth, The stronger for softwoods.

WDH · July 28, 2016, 10:04:13 PM

Slower growth in SYP gives you a higher proportion of the denser latewood (the dark part of the growth ring) relative to the less dense earlywood (the light colored part of the growth ring).

The majority of SYP lumber is from faster growing plantations. When I first started in Forestry, there was much more natural pine timber being harvested than plantations, but that has all changed over the last 35 years.

The average rotation age for SYP plantations is about 28 - 30 years of age. It is projected to be 25 years by 2025.

petefrom bearswamp · July 29, 2016, 06:43:56 AM

I have seen SYP 2x4s and 6s here with 3 rings per inch, very weak in shear and side stress in my opinion.
Danny what diameter will these tress be at 28 yrs?

Ianab · July 29, 2016, 07:16:23 AM

:D Three rings per inch would be a bit slow growing locally.

The main problem isn't the spacing of the growth rings, it's the "juvenile" wood. This is wood that's laid down in the first few years of growth. Maybe 10 or so depending on the species. This wood is weaker, more prone to spiral grain and longitudinal shrinkage. All bad things if you want strong straight wood.

The problem with fast growing trees is that you have large central area of that juvenile wood. Locally you can get up to 1" growth rings on a good site. But that means that after 10 years you have a 20" tree that is pretty much all juvenile wood. After that the tree lays down better quality wood.

Much of the local research has been to develop genetically "better" trees, and using cuttings or clones to grow seedlings with less juvenile wood. By growing a cutting of a tree you have a plant that "thinks" it much older than a seedling, and it grows in a different way.

Locally you might be expecting 36" + butt logs in 25 years.

WDH · July 29, 2016, 07:47:52 AM

The 28 year rotation will yield DBH's of 12" to 15". Stand average would be closer to 13" to 14".

Ian is spot on. Most modern 2x4's and 2x6's are sawn from the juvenile core of the plantation trees.

GeneWengert-WoodDoc · July 29, 2016, 06:30:46 PM

Almost all of the research in the USA on SYP seedlings and genetics is based on volume per year, not lumber quality, as the future seems to be heavily into chips for pulp, various flake boards and similar, and energy. Plus studying and modifying genetics for lumber production takes many years (20+) for the results to seen. The cost of private research that will payback initially in over 20 years is hard to justify; public research is directed at "more important issues" than sawmill profits.

Back when we made SYP plywood, the veneer cores (4" diameter) were often sawn into 2x4s. Profits for these SYP 2x4s were darn small, due to warp (twist especially) and due to the market shunning as nailing was so difficult. Profits when sawing were better than energy, at the time.

The good news was that drying at 230 F and hotter softened the wood enough so that twisting was reduced with proper stacking and with low final MCs. If the MC was too high, the pieces dried after kiln drying and did twist. Many operations found that letting the MC adjust while still stickered in a stack was important for straighter lumber.

hackberry jake · August 17, 2016, 07:24:02 AM

The lumber wasn't as dry as it could've been, but much lighter than when I bought it. The 2X2 spindles were super lightweight. I'm assuming because they had more surface area they dried quicker. Those things are pretty bad about bowing as they dry. I got some decorative blocks for the first step since this picture was taken.