I hope this isn’t a dumb question, but here goes. I just started my screen porch addition yesterday and noticed that the 2x12s used on the existing deck are actually 11-1/8″ wide. The new 2x12s I just bought are 11-1/2 (which is what I thought all 2x12s were). The existing 6×6 posts are 5-1/2 square, new ones are 5-3/4. Luckily I noticed these differences before I did too much cutting.
So the question is, are the size differences due to shrinkage? Can I really expect almost a half-inch of shrinkage across the width of my 2x12s? The existing deck is about 4 years old. Or maybe it’s a grade thing–my new lumber is all #2, and I don’t know what grade the existing lumber is–are sizes slightly different across lumber grades? Can anyone explain this? Thanks!
Mike Powell
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Just ask George on Seinfeld about "shrinkage", evidently it can be a "big" problem but is usually a "little" problem (;-0.
I did my deck on diagonal, it was really wild seeing how some shrunk in length while almost all did cross-grain.
If my math serves well 3/8 out of 11.5 is a little less than 3%. Most PT is pretty well still soaked when delivered here.
It is a fact of physics that wooddoes not shrink in length. There are a number of things like diagianl with certain fastening that can make it appear to have done so, but it will not.
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Paul, cut 45's on two 5/4 x 6 pressure treated decking and cap the top corner of the deck rail. What will happen?A great place for Information, Comraderie, and a sucker punch.
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It will shrink in width such that the short side of the 45 shrinks towards the long point. The two long points are in contact so it cannot shrink the other way. The direction the shrinkage occcours opens a gap wider at the short sides making it ook like it shrunk in length.
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>> cut 45's on two 5/4 x 6 pressure treated decking and cap the top corner of the deck rail. What will happen? << I think you know, but for everyone else:
This is why I never join 45 degree miters to form a right angle using PT lumber. See attached pic. No, this is not my work, however The miters were cut tight when the PT decking was installed. Pretty - HU?
The boards don't shrink in length, but rather in width which I guess essentially transforms your 45 degree cuts into 46 or 47 degrees. If you put a spline board between the 2 miters, it makes the problem 1/2 as noticeable, but it still is not acceptable to me.
The second pic shows butt cut deck boards - a better way to do it.
We do a lot of 45° deck joints like that with IPE`.because it is a far more stable wood, the joints don't show that kind of shrinkage. One of the many advantages of using good wood!
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Wow - I wasn't gonna say anything but now that you responded, I think you get the prize for the most responses to a single thread!!! :-)
Regarding using Ipe, there is an article in the current JLC basically saying that high end remodeling is where the money is. I didn't read the article since I have little interest in remodeling, but it made me think of some of you guys. I have a lot of respect that you all that have built your businesses to the point where you only service the high end customers who can afford stuff like Ipe, etc.
Q - I guess Ipe is kiln dried? It looks like it is....
Back to PT lumber, I like using KDAT (re-dried) PT lumber, which mitigates quite a bit of these shrinkage problems.
Shoot, Mr. P holds the record for mosts posts, period!Looked to me like some wanted to split hairs with Mr. P over language and other issues and Mr. P knew damn well he was right, so he provided more info to support what he said. (and I agree with him)
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Shoot, Mr. P holds the record for mosts posts, period!
and all this on dial up!Treat every person you meet like you will know them the rest of your life - you just might!
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Here is that board I was talking about. One shows a slice I stuck in there after it was put down, the second one is the other end. This particular board just seemed to shrink more than the others. Like I said it was cut a little short but no where near this much.
Missed the second pix.
It looks to me like three things are at play there.One is that whatever it is fastened to iunder it seems to have shrunk or movedAnother is that it has shunk in the direction away from the cut and the board next to it - see th elarger gap thereThird is that as you mentioned, it was ut short to begin with. There is no way any piece of lumber shrinks this much in length.Thge second photo on the opposite side shows that the outrig board is shrinking and possibly puilling AWAY from the rest of the bunch
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I am sure the rim/picture frame boards did shrink a little width wise (picture exaggerates it a little) but that one deck board did go more than the others. That slice was pretty tight when it was dropped in. The board was not over 1/4 shorter that the others. You can see the diagonal variation you and others described with most of them.
The rim/frame bd is attached to the same joists as the deck board so I would not think it is pulling away as your second issue offers and had it shrunk it would have pulled them closer.
Bob
If it is a fact of physics that wood does not shrink in length - could you please explain what causes the gaps at the but joints of my oak hardwood floor?
The joints are pretty tight in the humid summer, but, they can open up to an eighth inch or more in the dry winter.
Any thoughts what might cause this? I always attributed it shrinkage.
You have all male boards.. .they swell in the summer when the girls boards aren't wearing as much due to the heat.
that's good - better than I can do
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Here is my understanding of wood shrinkage in the long orientation.It would be more correct if I were to say that wood CELLS don't shrink noticeably in thier length. A hunk of wood is made of individual wod cells which are like long strings of spaghetti noodles, all running pretty much the same direction, but winding and twisting over each other. the pattern they use in tieing themselves together as they grow is partly determined by species and partly by environment.These cells can be ccompared to ballons or bladders full of moisture. As wood ages and stabilizes, the it looses water initially from between cells and later from within those cells.Since there might be a hundred or a thousand times as many laps between sides of the cells across the width of the grain as along the length, that is where shrinkage occours. But there are a few places where the twisting of the grain gives us some laps between cells in the long direction, so yes there is a little bit of shrinkage in the length, but for purposes of carpentry, it does not exist because it is so slight as to be un measureable. You can take a ten foot post and check its length under load in support of a structure with a laser or a tape over the years aND NEVER FIND MORE THAN 1/64" change. I have done this myself.I wonder if the fact it is under load forces those minor changes in MC to force the swelling of cells to perform in the tangenital direction while perhaps a piece of flooring might make a minor change in length since there is no load forcing it. But I really do think that wood does not move enough to be noticeable in it's length based on my own experiences with it, so there may be other factors allowing pieces to move. The ONLY times I have seen flooring butt joints to open is when the stucture under it allows excessive deflextion. The other expalnation might be that the species and grade has an abnormal amt of gross grain and twist grain through each piece creating a situation where there are a large numeber of wood cells lying perpendicular or nearly perp to the length of the piece.
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Here are some pertinent linkshttp://www.woodkit.net/articles.php?ai=80http://www.woodbin.com/calcs/shrinkulator.htmhttp://www.woodweb.com/cgi-bin/calculators/calc.pl?calculator=shrinkage
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Wood does shrink along its length, but about 1/100th as much as it does across its width.
I would not argue with the master but tomorrow I will try to remember to shoot a picture of one of my deck boards. I would agree that a diagonal cut would make it appear so. This particular one was cut with about 1/4" gap when screwed down next to the picture frame rim. My guys on the project were not perfectly accurate but pretty good.
It went to about 3/4" in a short period, I cut a filler and it still has a pretty good gap after 8 yrs. The rest do not. Must have been cut on the dark of the moon or something.
Maybe hillbilly physics is different (:-).
A 2x12 is milled on the saw to close to 2" x 12"
Then it is kiln dried and planed to 19% surface moisture and about 1-1/2" x 11-1/2" more or less. It still may be greater than 19% moisture content (MC) in the middle of the board.
Then it is taken into a vat where liquid chemical is driven into the wood under pressure ( thus the name Pressure Treated) so if you buy shortly after treatment process the wood has swelled up again with all that injected liquid. We call it "pond dried"
In six months to a year, it will again shrink down to about 1-1/2" x 11-1/2" and can easily be 11-1/4" in a year.
next stpe in your education - do you realize that the PT of today is a different chemical than a few years ago and needs fasterners to be SS?
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"A 2x12 is milled on the saw to close to 2" x 12""That might have been back when Adam was still personally planting the trees.But all of the references that I have seen is that nominala 2by lumber is 1/2 under up to 8" and then 3/4" for dry.Specifically 2*12 is 11 1/4 dry, 11 1/2 wet.http://justwoodworking.com/charts/standard_lumber.php
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Thanks for all the replies.
With this cold snap we're having I think I saw a lot more than 3% "shrinkage" yesterday...
Reaad what I said aagain. You missed it
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> A 2x12 is milled on the saw to close to 2" x 12"Not a good way to put it. When the rough-cut board comes off the saw, it's 2" x 12". Then it's milled and polished. That takes off 1/2".George Patterson, Patterson Handyman Service
That was the old days. Now they come off the saw closer to 1-5/8 x 11-1/2. Least that's what I've heard.
Never heard of the boards being polished either, but it can be tough to get a grip on them sometimes. Do they wax them too?
No, they aren't supposed to be waxed. The whole idea behind it is to remove rough edges to reduce fire risks. Seems to me that waxing would increase the fire risk again.When I lived in Georgia, you could go to the mills and buy lumber straight from the saw. That's been 30 years, so maybe they have reduced the dimensions. I don't see how they could reduce it to 1 5/8" and still wind up with a finished product 1 1/2" thick, though. When I feed rough material through a planer, it usually takes at least 1/4" off just getting the mill marks out.George Patterson, Patterson Handyman Service
Some woods like SYP will seem waxed sometimes beccause the planer blades beat the resin in the wood into a waxy finish with the heat and friction
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How close depemnds on the mill amnd the tolerances of the machinery they use. new thin kerf machines and laser guidance helps reduce waste in more modern mills, but you know as well as I do how many older mills there are.The fact that PT is sometimes 11-7/8" on delevery tells me that was never milled to 11-1/2"
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OK, it is SAWN to 2x12 before milling on the planer.howzat?
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5/4 decking is really becoming a problem, always has been, but heard more shrinkage since new process? Anyway, lumber does shrink in length, we always butt joints tight, come back 6 months later and find as much as 3/8-1/2 gaps, have had shearing of deck screws a couple of times.
Main problem with irregular width of joists is when they are placed over a beam, not so bad in hangers on ledger but still we almost allways run joists thru table saw to make them all one width, but even then they will still dry and shrink differently depending...
Now handrails... Still using pt but so bad that allmost to the point of using composite for railings, balusters. Id'e be willling to pay more for dried pt just for the handnrail material.
PT lumber does shrink in width, and when you first buy it it is often still wet with the treating chemicals so it is swollen. It will shrink in width as it dries.
Also though framing lumber is of nominal size. Around here, the kiln dried 2x4s and 2x6s we get tend to be pretty uniform in size: 1.5"x3.5" and 1.5"x5.5" although the 2x6s can vary some. With 2x8s, 2x10s and 2x12s they can vary in width quite a bit: for example a 2x12 can be anywhere between 11 1/4 to 11 1/2. So the larger sized lumber in not real uniform in size, although generally, you can expect lumber from the same "bunk" to be of the same size.
To my knowledge, grade has nothing to do with it, although 99% of the framing lumber we get is #2 including PT framing lumber. Yes I can get some #1 PT deck boards, but I don't see that they shrink any less (or more),
Matt, thanks for the detailed reply. If I'm reading all this right, it sounds like I should expect my 11 1/2" boards to shrink as they dry, but maybe not all the way down to 11 1/8" to match the existing boards. Maybe they came from a smaller bunk, or maybe as BillHartmann pointed out, they were just originally finished to 11 1/4. I won't have anyplace where a new board will butt into an existing one, so it shouldn't be too noticeable anyway.
I did a wood basement, the .60 CCA stuff. The PT boards were so wet that water would fly when i chopped them. After drying thoroughly, the 2x6 studs varied 3/8" plus/minus, so i had to fur the walls flat.
My experienc is that non-PT lumber is 1/2" smaller than its nominal dimensions up to a 2x8, from 8" upward it is 3/4" smaller--e.g. a 2x6 is 1-1/2" by 5-1/2", but a 2x8 is 1-1/2" by 7-1/4". I think this is standard in the industry. But with PT, all bets are off--I've had 2x8's measure anywhere from 1-1/4" to 1-5/8" thick by 7-1/4" to 7-5/8" wide. Then when they dry they shrink--usually across the width. Most PT I buy is so wet that when I pound a nail into it, the treatment literally sprays out, so I would plan that it will shrink perhaps a quarter inch in width as it dries out. Like someone else said, wood doesn't shrink (at least not that you can measure) lengthwise.