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Forum topic by mikeber posted 01-20-2022 10:17 PM 693 views 0 times favorited 23 replies Add to Favorites Watch
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mikeber

78 posts in 2319 days


01-20-2022 10:17 PM

Topic tags/keywords: question plywood standards

Maybe this topic had been discussed before, but I couldn’t find a direct answer.
My question is about the manufacturing standards for plywood. In almost all cases plywood thickness comes rated as a rounded number: 1/4”. 1/2”, 3/4”…But in reality all of them are significantly thinner. For example the 1/4” is 5mm, while the 3/4” is only 18mm thick. That is a significant difference. Therefore my question is why?
And, is there any kind of plywood that is made true to the advertised size and if so, who sells it?
​Also, there doesn’t seem to be a standard about the number of ply for any thickness. At least it’s never specified in stores and lumberyards.


23 replies so far

View CaptainKlutz's profile

CaptainKlutz

5613 posts in 2954 days


#1 posted 01-20-2022 10:38 PM

There are many plywood standards. Some published by mfg, and others published by national organizations founded by government(s). Most align with standards from APA – The Engineered Wood Association. NIST co-publishes APA voluntary standard for Structural Plywood used by most USA mfg.
Believe most recent version is PS 1-19?
https://apawood-europe.org/wp-content/uploads/2021/07/PS1-19.pdf

There are also an APA-ANSI standard for plywood that are referenced by NBC/UBC that all 50 US states use as basis for state building codes. Don’t have those links handy.

PS – Do not confuse big box store marketing/measurements to have any resemblance to national standards used by commercial builders and/or national building code (NBC). It is pure marketing BS.
Need to learn to read and understand the grade codes and stamps directly on plywood to know what you are really getting.

Best Luck.

-- If it wasn't for bad luck, I wouldn't have no luck at all, Doom, despair, agony on me… - Albert King - Born Under a Bad Sign released 1967

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mikeber

78 posts in 2319 days


#2 posted 01-20-2022 11:47 PM

It’s not limited to Big Box stores. Lumberyards, websites, vendors, Amazon, all refer to plywood in minimal terms. The only commonly published details are the “thickness” (which is way off) and wood species (but just the exterior face). The consumer is supposed to guess or assume every other detail. Coincidently, if you bother asking, most retail workers have no clue.

View AlaskaGuy's profile

AlaskaGuy

6876 posts in 3768 days


#3 posted 01-21-2022 12:00 AM

Lol, I don’t think there are any standards that anyone follows anymore.

-- Alaskan's for Global warming!

View bigblockyeti's profile

bigblockyeti

8530 posts in 3180 days


#4 posted 01-21-2022 02:53 AM

I think that Lowe’s and HD do note the actual thickness of OSB and plywood as they were well sued for not selling a 2×4 that was actually 2” x 4” some time ago. If memory serves me correctly, they list the thickness to three decimal places, not that wood ever holds to that precision but at least they’re doing what the attorneys told them to.

-- “I never in my life thought I would have to say this, but the proper role of government is not to fund the distribution of crack pipes,” Lauren Boebert

View Lazyman's profile

Lazyman

9602 posts in 2847 days


#5 posted 01-21-2022 03:51 AM

Just like how 2-by lumber is before planing(i.e. rough dimensions), a friend of mine who was the timber procurement forester at a plywood mill told me that the thickness measurement on plywood is the thickness before sanding. Since you cannot really buy plywood that hasn’t been sanded on at least one side, that is sort of BS IMO but that is the practice. Baltic birch PW doesn’t seem to suffer from this and if you can make it exactly a target dimension, there really is no valid reason why they don’t make it so that it is exactly 3/4” after sanding for example.

I wonder when the US manufactures started doing this. I bought some really nice, old sheets of plywood at an estate sale that was exactly 3/4” thick.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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TopamaxSurvivor

24619 posts in 5135 days


#6 posted 01-21-2022 06:49 AM

I remember 2×4s losing the second quarter inch. I’m surprised they haven’t lost a 3rd quarter by now. Plywood has done well. Only lost one ply in most cases ;-))

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Gene Howe's profile

Gene Howe

12609 posts in 4888 days


#7 posted 01-21-2022 09:44 AM

It’s been over a year since my last purchase but, Baltic Birch plywood has always been true to the marked dimension.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

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mikeber

78 posts in 2319 days


#8 posted 01-21-2022 06:49 PM

Thanks for the info! That’s what I was looking for! In another thread someone mentioned a true to size plywood, but couldn’t remember which was it.

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Kudzupatch

395 posts in 2668 days


#9 posted 01-21-2022 06:53 PM

There are standards but correct me if you KNOW otherwise, There is no one enforcing them. I think it is voluntary thing.

-- Jeff Horton * Kudzu Craft skin boats* www.kudzucraft.com

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mikeber

78 posts in 2319 days


#10 posted 01-21-2022 08:46 PM

There are a few standards but compliance is voluntary. The problem is not so much with standards, but the lack of information provided to customers. Sellers need to specify precisely what wood had being used, if finished or unfinished, number of layers (ply), their thickness and what these layers are made of.

Like with so many items in woodworking, details are hidden, confusion is common, buzzwords and slogans rule.

Here is a characteristic discussion I had a few months ago with a seller:

Sir I said, your prices are much higher than other retailers.

His response: our plywood is of better quality and much stronger! Well, can you tell me how? What lumber is it made of and how many layers are there? His response: It is very strong! Just look at it! That’s when I figured that these people are clueless.

For sellers it’s a win win situation: confusions rules! Customers can’t compare between products and reveal they are paying unnecessarily high prices. The retailer doesn’t have to educate their employees. Ignorance is bliss.

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bondogaposis

6183 posts in 3811 days


#11 posted 01-21-2022 09:06 PM

It is my pet peeve. There is no valid reason that plywood should have a nominal and an actual thickness. It is a manufactured product and they could make it any thickness they want. It wasn’t all that many years ago when plywood was true thickness. It doesn’t mean much for construction sheeting, but they should give us cabinet makers a break. It is like they hate their customers. MDF, and particle board come in true thickness, why not plywood? 3/4” Pre-finished, birch ply at Home Depot is .703” thick. What the heck kind of number is that?

-- Bondo Gaposis

View Underdog's profile

Underdog

1908 posts in 3495 days


#12 posted 01-21-2022 09:27 PM



It is my pet peeve. There is no valid reason that plywood should have a nominal and an actual thickness. It is a manufactured product and they could make it any thickness they want. It wasn t all that many years ago when plywood was true thickness. It doesn t mean much for construction sheeting, but they should give us cabinet makers a break. It is like they hate their customers. MDF, and particle board come in true thickness, why not plywood? 3/4” Pre-finished, birch ply at Home Depot is .703” thick. What the heck kind of number is that?

- bondogaposis


It’s the bane of our existence isn’t it?. Plywood thickness varies from manufacturer to manufacturer, and batch to batch. As a CNC guy, and a cabinet vision design engineer who works in .001” precision all the time, it drives me a bit nutz.

-- Jim, Georgia, USA

View mikeber's profile

mikeber

78 posts in 2319 days


#13 posted 01-21-2022 09:35 PM

They can make it ANY thickness they choose, but they can’t sell it with wrong information like calling 18mm – 3/4” ! You can’t do that.

Also, since their product doesn’t meet any standard, it is their responsibility to publish all data including the total thickness in mm (if they manufactured it so) number of layers, thickness of the core, material used for the core. You can’t say- “that’s 3/4” plywood and is very strong” when it’s actually 18mm.

View bigblockyeti's profile

bigblockyeti

8530 posts in 3180 days


#14 posted 01-21-2022 10:22 PM

Here’s a pic of OSB at Lowe’s and last time I checked 0.406” isn’t the same as 7/16” but that doesn’t keep them from false advertising. Perhaps a fresh dose of lawsuits would help?

The $27.05 price isn’t for three sheets like it used to be, that’s only for one sheet!

-- “I never in my life thought I would have to say this, but the proper role of government is not to fund the distribution of crack pipes,” Lauren Boebert

View splintergroup's profile

splintergroup

6950 posts in 2682 days


#15 posted 01-21-2022 11:44 PM

A nearby supplier has 3/4” AA plywood with veneer over thin (1/8”) mdf and a wood ply stack core. Exactly 3/4”. The same ply without the mdf is the typical “whatever” dimension.

Their BB ply (Russian or Finnish) is quite variable. 1/2” is usually undersized by 0.050 +/- 0.025”. Probably is really metric, but the variability can be an issue when I’m mixing cutoffs for a project.

This is all one of the reasons I’ll never buy a “plywood” dado bit for the router. They are sold as undersized to properly fit the undersized plywood being sold. Too much variability to be of use for a single pass dado.

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