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Do Knots in Cedar Cause Structural Weakness?

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Forum topic by Furnitude posted 07-25-2012 08:55 PM 1547 views 0 times favorited 11 replies Add to Favorites Watch
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Furnitude

346 posts in 2229 days


07-25-2012 08:55 PM

I’m making a set of Adirondack chairs and this is my first time to really use Western Red Cedar. If you look at the crude drawing, I’ve tried to show the location of a knot in one of the boards I’m going to use for arms. Will a knot in this location cause structural weakness? Thanks for any comments.

-- Mitch, http://furnitude.blogspot.com Also blog at http://www.craftsy.com/blog/author/mitch-roberson/


11 replies so far

View Ryan Haasen's profile

Ryan Haasen

362 posts in 1123 days


#1 posted 07-25-2012 09:49 PM

Yes, I think it will, especially if it has a hollow spot.

-- Ryan

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Doss

779 posts in 987 days


#2 posted 07-25-2012 09:50 PM

Yes. If the knot is that circle and it takes up that much space, it’s going to be a problem. The knots usually fall out of WRC.

If the wood were really thick and the knot pretty shallow, possibly not. But, it looks like, in this case, that it’s going to be an issue if it gets any load applied to it.

-- "Well, at least we can still use it as firewood... maybe." - Doss

View Blackie_'s profile

Blackie_

3595 posts in 1235 days


#3 posted 07-25-2012 11:17 PM

I’m curious if CA wouldn’t solve that problem, I know it would keep the knot from falling out. One other thing you might try is making a western sawdust paste using wood glue and fill in the voids also blending.

-- Randy - If I'm not on LJ's then I'm making Saw Dust. Please feel free to visit my store location at http://www.facebook.com/randy.blackstock.custom.wood.designs

View gfadvm's profile

gfadvm

11366 posts in 1412 days


#4 posted 07-26-2012 01:59 AM

I learned the hard way that knots at stress points are the weak link and will fail in a load bearing situation. In my tall chairs of recycled Doug Fir, I have learned to avoid putting knots in the legs or seat slats. I’m referring to full thickness knots of significant diameter (3/4-1”).

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

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Arlin Eastman

2213 posts in 1284 days


#5 posted 07-26-2012 02:04 AM

It will cause a weak point, however, I do know of several guys that have drilled them out and put in epoxy in the hole with some ceder dust.

Arlin

-- It is always the right time, to do the right thing.

View Bearpie's profile

Bearpie

2591 posts in 1740 days


#6 posted 07-26-2012 02:53 AM

Yes, definitely it will weaken the area. could you possibly switch the board around and put the knot on the wider part of the board?

-- Erwin, Jacksonville, FL

View MonteCristo's profile

MonteCristo

2098 posts in 911 days


#7 posted 07-26-2012 03:39 AM

Curious that someone in Tennessee is using Western Red Cedar (WRC) which is native to my neck of the woods. This wood is weak structurally to begin with, which makes it even more important that a knot like the one you show should be avoided.

In case you aren’t familiar with WRC, it is very easy to crush so cutting motises and the like requires really sharp tooling. It is quite rot resistant but that comes at a price – depending on who you talk to it’s dust is toxic to very toxic. Some people out here even get an alergic reaction just handling it, although that is pretty unusual. Old growth WRC is a much better wood than second growth stuff, much deeper color to the heart wood and very stable with fine annual rings. Much more rot resistant too I suspect than second growth.

-- Dwight - "Free legal advice available - contact Dewey, Cheetam & Howe""

View bondogaposis's profile

bondogaposis

2696 posts in 1074 days


#8 posted 07-26-2012 03:56 AM

I would be looking for another piece of wood for that.

-- Bondo Gaposis

View rrdesigns's profile

rrdesigns

502 posts in 1908 days


#9 posted 07-26-2012 04:01 AM

And some ears, legs and a tail and you can use that piece for an elephant. Waste knot want knot.

-- Beth, Oklahoma, Rambling Road Designs

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tomd

1788 posts in 2493 days


#10 posted 07-26-2012 04:21 AM

I would be leary of using it.

-- Tom D

View woodtools's profile

woodtools

21 posts in 1011 days


#11 posted 07-26-2012 05:22 AM

A western red cedar knot as you display in the drawing has no structural value. If you were to think about your adirondack chair arm as having a hole in it the size of the knot, you will answer your own question. As with western red cedar, used in outdoor applications, the knot as described will fall out in 8-12 months
Good luckwith what will be a beautiful piece of outdoor furniture.

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