Decking: Bark-side up or down?
Up until today, everything I’ve ever read or heard said to put bark-side up on a deck decking. But they never say why. It seemed wrong to me because putting bark-side up will tend to cup concave on the top, trapping water. I assumed the reason for this was so that the water did not run in an get trapped in the annual rings like a bowl. Then today, I see a recommendation to put bark side down so the crown is convex.
So, which is right, does it matter, and why?
Replies
Bark side up for decking - "outside of the tree to the weather" - that's how I do it with any wood exposed to weather on one side only.
Don't really know the physics or biology behind it but, whenever I see boards - decking or siding which has cupped - they always seem to have been nailed with the "inside of the tree to the weather".
Incidently, I think you have confused convex and concave in the OP - assuming you are viewing from the topp - a deck board which has cupped and the resulting board is higher at the edges than the center would be concave, convex would have the center higher than the edges.
Go with the advice which you have heard prior to today - bark side up and you will be happy with the results!
Good luck,
Jim
Never underestimate the value of a sharp pencil or good light.
P.S.: There is a school of thought which says to set decking boards with the "best side up" - this can be very tempting since if there is any wane present, it will always be on the side which should be up. Some folks have been known to install best side up - get paid and disappear before anything cups. Selection and grade of the decking lumber can eliminate this problem.
No, I think I was correct in my OP. Wood shrinks more along the rings than along the radius, so the rings tend to "flatten" as the wood dries.You only need to look at split firewood to see there's always a pie-shaped wedge split. If wood shrank the same in both directions (radial and tangential), there would be no split (circumference = diameter * Pi)
I don't think it makes that much difference unless you are using green wood or really full wet PT which I never do.But bark side down if I did
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I think this is gonna be like attic venting - There never will be a consensus.
A father can give his son homes and riches, but only the Lord can give them understanding wives. [Proverbs 19:14]
You may be right!!
Had this argument WAY too many times!
Anyway, my conclusion-
Bark down, unless I don't like that face, then, nice side up.
Wood cups any which way it feels like, so make it pretty.
On the contrary, the concensus seems to be that boards should be screwed to allow one to periodically flip them over!
The hell with it!!
Poured concrete from now on!!
or maybe just pith on it?
Yet another explanation
Yes, intersesting, although I don't think I'll be using those techniques on my deck! :)
Are you trying to say that attic venting increased cupping or decreases it..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Depends on if they stick frame the house or use trusses.(-:
Q: Why do drivers' education classes in redneck schools use the car only on Mondays, Wednesdays, and Fridays?
A: Because on Tuesday and Thursday, the sex education class uses it.
It increases it from an A cup to a C cup.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
The natural boards are often pretty flat, but I've heard you can get some synthetics with increased cuppage.
Did you transpose a couple of letters there??
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
It was supposed to be a witty response to your post. ;)
As was mine ;)
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
OK -- I think I finally got it! Cuppage often temporarily lowers my IQ like that. ;)
You just weren't keeping abreast of the banter.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Come on guys! Let's not get into a thing where you're going #### for tat with these puns.
Edit: Incredibly, the moderator replaced the word t_t with ####. I guess they didn't want this discussion to get out of hand. What are the standards? I'm groping in the dark here.
Edited 6/1/2007 10:23 am ET by Mudslinger
Hey, how many times do I have to tell you to keep your hands to yourself?!
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
I'm groping in the dark here.
I'm reporting this to the moderator.
That wasn't the moderator; it was Prospero's automatic censoring software (the 'kill-list' is, admittedly, under the SYSOP's control, of course).
If you want to write the word which sounds like tee eye tee, you've got to spell it correctly: Teat. That is actually the proper spelling (check a good dictionary if you don't believe me)...and it is pronounced with a short i sound.
Ohhhh, the useful information that clutters up my organic data-base....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Thanks, Dinosaur. I talked with you concerning mortar a while back. How did your bread oven turn out?
That job got 'snowed out' last fall and put over till the spring...and it is now no. 2 on the list. I oughta get to it in about a month or two, LOL.
I'm gonna have to go look over the posts on that subject again. I've forgotten everything you tried to teach me by now. CRAFTS again, dammit.
Any chance you're gonna be here for the Fest in August?
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Dinosaur, Unfortunately, I won't be able to make the fest. What does "CRAFTS" mean? I can't figure that one out.
Can't Remember A Flippin' Thing.
Or something like that. I can't really remember....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
so, then, does TitForTat work?
Not one that'll get my blood up tho.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Personally, I reject deck boards that still have bark attached.
:)
"Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
The cover of this book shows which way boards will warp.
View Image
"Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Edited 5/30/2007 9:22 pm ET by FastEddie
Here is a good visual on this subject:http://individualfurniture.com/maker/Wood-Movement.htm
FWIW, I think the cupping is nearly a random process.
On my own house, I installed about eight treads on some steps. If there was any existing cupping, I put it down as to not trap water.
After several months, half the boards were still cupped in the down direction, the other half were cupping in the up direction.
At this point, I looked at the grain orientation. As luck would have it, I had installed exactly half of the boards "bark up", the other half "bark down". And guess what? The offending boards were: half "bark up", half "bark down". Thus, the grain orientation literally showed no difference in its directional tendency to cup.
I then removed the offending boards, flipped them over, and reinstalled them.
After another several months, two of the boards from the bad batch actually reversed back into cupping up again! One was "bark up", the other "bark down". Again, no statistical difference.
I don't know what to conclude from my little science project other than to use CVG! ;)
Hello Ragnar17
Cupping, as explained by others in this post, is a function of how the wood fibers expand and contract with moisture and how they are laid out in the board. Flat sawn lumber will always cup the same way, with the heart side concave, when the moisture is equal throughout the board. Sometimes when you get the wood, it is not equally dry on both sides. this will make it cup the other way temporarily sometimes. When it dries it will cup the same as always- heart up. Hope this helps. RZ
RZ,
Thanks for the explanation. I guess the only challenge is figuring out how to develop an installation system so that my stair treads don't cup the wrong way when it rains!
yep - just visualize that the curved rings want to straighten out."...an open mind is a powerful thing. The ability to listen to others is invaluable."
Jim Blodgett
The US Forest Lab's say to put best side up.
That with a deck board you are always going to have a big moisture difference between the top side and the botton side. When you get rain the top side get moist. After a time period the moisture equalizes. Then later when the sun beats down on it the top will dry out first.
Thus you always have cupping in both directions regardless of how the boards are laid.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I look at the decking which almost always has begun to cup. The side which has begun to cup up goes up. If no cup is noticeable, I go with the best side.
The side of the decking that is up will dry faster and will cause a cup. If time allows the boards can be stickered and allowed to dry before installing.
Dave Otto -- Otto Construction -- PA
Yes - I've tried this way and that way and read this and that.... Then a carp told me "look at the board and which ever side is already cupped will probably continue to do so or get worse so put that side down. If there is no cup, put either the bark side up or the pretty side." Done it that way ever since.
The thing is that it really doesn't matter that much because the top of the boards will always dry faster, and therefore shrink and cup, so your are hosed no matter what you do...
I don't know where you've been reading advice to put the 'bark-side up' on deck boards, but it's dead wrong.
Most natural softwood decking is not fully seasoned, which means it will continue to shrink after you nail it down. The last thing any sane carpenter would want to do would be to lay the boards so they trap and hold rainwater, thus encouraging rot, staining, and early failure. Instead, you want to lay them so they shed water--and leave enough space between boards so the shed water can drain well, too.
Wood shrinks much more cross-grain as it dries than it does in length. This is because each fibre--think of a fibre as a strand of wood running along the length of the board--will get skinnier as it loses cellular water. As they get skinnier, they scrunch up closer to each other...and the board shrinks tangentally (which is to say, around the circumference; parallel to the run of the fibres).
But since the number of fibres per circumferential inch remains more or less constant, there are obviously more fibres per growth ring for those larger rings toward the outside of the tree--and the more fibres there are in a ring, the more that ring will shrink as they dry.
So a slab-sawn board will cup away from the heart as it dries. Which is why you need to lay the deck boards HEART UP to prevent each board from becoming a water-trapping trough.
BTW, the way to solve this the expensive way is to use only CVG lumber. It will not cup; being vertical grain it will just shrink laterally in a uniform manner.
Dinosaur
How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....
I don't think it matters either way. If you lay a big imaginary piece of wood out in the sun, the top surface will dry first, causing the wood to cup (concave) and then catch water if it were to rain.
If you flip the big piece of wood over the other way and lay it in the sun, it will still cup. The side doesn't matter. Justin Fink - FHB Editorial
Your Friendly Neighborhood Remodelerator
Justin,
Your theory seems to be based on the behaviour of re-wetted, fully-seasoned lumber, but there is a huge difference between the effect of cellular water and environmental water on wood behaviour.
Wood loses its cellular water content (ie: the water which is actually contained within the cells making up the wood fibres) as it is seasoned or kiln-dried. Once that water has migrated through the cell walls and been evaporated out of the wood into the atmosphere, exposure of the wood to environmental water (rain, splashing, whatever) does not cause the cells to reabsorb water, especially through its face.* It is the loss of cellular water--and the consequent reduction in the diameters of the fibres themselves--which causes the board to shrink tangentially and cup away from the heart.
Environmental water is absorbed primarily into the spaces found between the individual fibres, and rarely goes deeper than a single growth ring (unless the board has been completely submerged for an extended period of time, like months or years). That surface, intra-fibral absorption can cause some temporary, minor warpage...but it will not change the permanent, dry shape of the fully seasoned board, to which it will always return once the environmental water has evaporated.
In addition, remember that when you lay partially seasoned boards heart up, they will cup downwards leaving a crowned top surface which will shed water naturally, thus minimising environmental water absorption (and any consequent temporary deformation). Contrariwise, if you lay the board heart down, they will tend to collect and hold environmental water and this will worsen the effect.
It does make a difference.
*--environmental water absorbed through unprotected end cuts can infiltrate the intra-cellular spaces within the fibres, but this is a slow process and is not an issue in decks unless the butt joints are so made as to collect and hold water.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Edited 5/31/2007 3:56 pm ET by Dinosaur
T.H.,
As the French Canadians say, "touche" - you make some really excellent points. I stand corrected, and nicely put!
Still...I'm not sure that "contrariwise" is a real word :)
EDIT: I just looked it up. touche once again!
Justin Fink - FHB Editorial
Your Friendly Neighborhood Remodelerator
Edited 5/31/2007 4:00 pm ET by JFink
LOL. In my first draft of that post, I used the word <skinnyfying> to describe the radial shrinking of each fibre as it lost water.
Then I thought better of it....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
There is no right answer.
You are right that the rings will want to flatten out, so if the bark side is up the boards would tend to cup on the top side. That is one justification for bark side down--to get boards that drain. Another benefit of barkside down is that knots will not fall out of their tapered knot holes.
On the other hand, barkside down (or pithside up--same thing) creates more problems with raised grain. When boards are planed the lighter-colored spring wood (between the dark rings gets squashed down between the hard, darker, late-wood. This happens on the side toward the inside of the tree (pith-side).
Exposed to moisture, the squashed springwood becomes larger than the planed down, dark rings...this is called "raised grain". This can lead to delamination, splinters, and a rough surface.
So, you can have cupped boards that "retain water" and drop knots or
boards with a tendency to have raised-grain, but that shed water and hold their knots...
...or you could use Trex ;o)
I did a little 10x10 deck off my sun room about 10 yrs ago, purposely installing about half the boards (5/4 x 6" PT) bark up and the other half bark down. The deck is on the sw side of the house and gets full sunlight from early afternoon on. There is no detectable cupping on any of the boards. Everything was fastened with 16P hot dipped galvy nails, 2 nails per joist. The recommended fasteners for todays PT are stainless. Screws might have good holding power, but don't think that ring shank SS nails have the same bite that a old good crusty HD spike would have. Others have detailed the theory, but in a properly fastened deck board, I don't haven't seen evidence that it matters.
Depends on the wood. My experience has been that cupping is worse bark side up, but if the wood is cut real close to the center you can end up with a notch on the "inside" side that is best kept down.
But either way you put the piece it will tend to cup (concave up) at some point in its weathering process. Further weathering usually causes it to flatten and possibly cup the opposite direction.
Hello
I have always put the "heart out" so that the wood, when it cups, will not hold water. I have done this with fences too-heart side out to the good side of the fence. That way when the boards cup, all the edges will not peel off the rails and they all will cup the same. Hope I haven't been doing this wrong for 20 years! I know that it looks better. Good luck. RZ
I tend to do heart side up for the same reasons as the others. If the board is quartersawn, or very close to it, then I go for the prettier side up. Heart center flatsawn boards get culled. They tend to shell out as they age - ugh.
Bill