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Why does plywood have little eyeballs on it?

J

Jhill

Diamond Member
I see a lot of peices of plywood with little eyeball shaped markings on them. They also look like footballs. Does anyone know why it has this?
 
Originally posted by: BingBongWongFooey
Yeah, it's called a knot, it's where a branch used to be before you murdered the tree! 😉
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I thought that also but the markings are always the same size and they are in a perfect shape so I didn't think it was a branch.
 
Originally posted by: Jhill
Originally posted by: BingBongWongFooey
Yeah, it's called a knot, it's where a branch used to be before you murdered the tree! 😉
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I thought that also but the markings are always the same size and they are in a perfect shape so I didn't think it was a branch.
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they might have been put on artificially to give the impression that its a real tree.
 
They cut that shape to fix a knot. Then the replace it with a little piece of wood to make it smooth..
 
That means you bought BC or better plywood. This is going to go way more into depth then you could ever want.

Plywood is made from a tree obviously. 4' wide trees are not in abundance. What they do, is take a tree, and "unwrap it" so you get a piece of flexable wood about 1/16" thick. Now, everywhere there is a branch, you end up with what is called a "knot" in the wood. When they glue the plywood together, these knots can fall out, and leave a hole. This is fine for some grades. (see next paragraph) I bet you bought BC plywood.

There are 4 main grades of plywood. A B C and D.

D = Construction grade. It has 90% the streanth of AB or BC, but doesnt look as good. knots are not patched, and regularly fall out. It is also not sanded.
C = Kinda decent. Knots are not allowed to fall out, they must remain in the plywood. ( I think 1 or 2 are allowed, not 100% sure) Mild sanding is done.
B = Good. Knots are patched, meaning the knot is cut out, and a patch is put in its place. these are usually football shaped for better adheasion. 4 patches are allowed, no more (usually)
A = no patches or knots. Sanded, and looks awesome.

Now, these are "side codes". So when you order "BC" one side is B, one is C. This is the most "normal" plywood. CD (also called CDX) is construction grade, one side C, one D. Looks like crap, but is cheap and strong. This is what your roof and walls are made out of. If you have a plywood floor, it is BC, but most flors nowadays are chipboard.

You can tell them apart real easy @ the store by the end markings: black = CDX. Green = BC. Red = AC. These colors are in bands. the more there is, the thicker the plywood. 5 lines = 3/4" thick, 4 = 5/8", 3 = 1/2 (if one color is white, or different from the others, it is 4 ply 1/2" which can be required for roofing instead of regular 3 ply.) 2 = 3/8"

There are 2 major kinds of plywood. Regular and water treated. Regular still has waterproof glue, but water treated is green like a decking board. this is for the ultimate in water and rotting resting. Commonly used in boats and shed floors. It is copper chromium arsinide treated. (CCA) usually.

That should be all you ever need to know about plywood 🙂
 
Not all plywood has waterproof glue. Maybe slightly water resistant, but it will delaminate if in any kind of prolonged contact with moisture.

The X at the end of the grade code denotes that the plywood is suitable for exterior use. If it doesnt have the X dont get it wet.

 
Originally posted by: Sluggo
Not all plywood has waterproof glue. Maybe slightly water resistant, but it will delaminate if in any kind of prolonged contact with moisture.

The X at the end of the grade code denotes that the plywood is suitable for exterior use. If it doesnt have the X dont get it wet.
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The X means it can stay exposed without a cover, and can just be left bare. it does not have to have the X for exterior. Plywood stopped having an interior/exterior grade about 10 years ago. You can use wither outside, as long as they are painted or covered in some way. If you submerge it, it will rot. It will not however delaminate alltogether. At least for a long ass time. The green plywood is usually just a piece of regular old plywoord that had the CCA preservitive injected into it (using LARGE amounts of water). That is why if you look at some inferior greenboard that was not glued gorrectly, the top and bottom layers can crinkle.

The venders that supply all the lumber yards areound here in the midwest use waterproof glue. It is urethane baised. it will not deteriorate in water. The wood however can.
 
They probably changed all the glue stuff after I learned what it was for, my Dad taught me this stuff about 30 years ago.

I remember when they came out with waferboard (or flakeboard/chipboard depending on where you live) everyone was so amazed at how it dont come apart when wet. I assume thats when they changed the glues to the more advanced glue.
 
there is interior and exterior grades of chip board, mdf, and particleboard. Tust not plywood. At least not what is available in mass quantities. you may be able to s/o it or something.
 
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