This post provides an overview of the formaldehyde and formaldehyde-free glues used in plywood.
I look at the offgassing levels and rates of formaldehyde in various types of plywood so that you can choose the lowest VOC option and minimize offgassing in the home.
There are non-toxic plywoods as well as non-toxic alternatives to plywood listed here.
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What is Plywood?
Plywood is an engineered wood product made up of thin layers of wood called “plies” glued together. Each layer is laid with the grain running in the opposite direction to the previous layer.
Where is Plywood Used in a House?
- Often used as sheathing on the exterior of the wood framing of a house
- Often used as roof decking
- Often used as subflooring
- Often used as the boxes of cabinets, and as structure inside sofas and other furniture
- Sometimes used as an underlayment or the structure of countertops
- Sometimes (rarely) used as interior walls
Myths About Plywood
That it offgasses forever
Plywood made with phenol-formaldehyde rapidly reaches non-detectible levels. Plywood made with urea-formaldehyde offgasses for longer, but it is up to 60% of the way there in 30 days. Plywood made from urea-formaldehyde is generally avoidable (and should be avoided in my opinion).
That it is high in formaldehyde
Plywood made with phenol-formaldehyde is not high in formaldehyde since it rapidly reaches non-detectable levels. Interior furniture grade plywood (which can be made with urea-formaldehyde) needs to come in at 0.05 parts per million formaldehyde.
That it is toxic
Plywood made from phenol-formaldehyde is not technically toxic. Plywood made from urea-formaldehyde is also technically not considered toxic at 0.05 parts per million formaldehyde. But those with compromised detox systems can find this level to be toxic to them. Whether it’s toxic or not very much depends on how much plywood is in the room, the size of the room, airflow in the room, and the person that is being exposed to it.
Which Chemicals Offgas from Plywood
Overview of the Adhesives Used in Plywood
Phenol-Formaldehyde (PF) (aka phenolic glue) – Most of the plywood I see now is made with phenol-formaldehyde. The offgassing is much lower and in many products comes to a complete cure in a short amount of time.
Urea-Formaldehyde (UF) – This is the type of formaldehyde that offgasses at higher levels and for longer. When you think of furniture or flooring that is offgassing for many years it was likely made with urea-formaldehyde. The offgassing rate of UF plywood varies by the exact formula (also some companies use heat to accelerate the offgassing) – it can vary from 15-60% offgassed in 30 days (source). Remember the offgassing is on an exponential curve.
Melamine-Urea Formaldehyde (MUF) – This is a urea-formaldehyde glue modified with melamine and PVA. It gives the plywood more water resistance and is usually only used for exterior door skin, marine plywood, and concrete formwork plywood. Adding melamine reduces the formaldehyde offgassing levels (source).
No added Urea Formaldehyde (NAUF), this almost always means PF is used.
No Added Formaldehyde (NAF), this means that no formaldehyde is added to the product – the glue used does not contain formaldehyde. They cannot be labeled “formaldehyde-free” because wood naturally contains formaldehyde. No added formaldehyde plywood is made with “soy-based” glue.
Soy-Based Glue – Soy-based glue is not just one formulation. They use soy protein mixed with polyamidoamine-epichlorohydrin (PAE), isocyanates, and aldehydes. (From the co-inventor of the adhesive for Purebond Plywood). This one is called soy-PAE. A similar type of soy-based glue that may be used to replace formaldehyde in MDF and particleboard is an amine-epichlorohydrin adduct/soy protein/isocyanate (source).
Types of Plywood and Their Glues
Structural plywood is softwood plywood (SWPW) and it is used for roof sheathing, subfloors, and roof decking.
This type of plywood is made with phenol-formaldehyde as the binder/glue (3.5% formaldehyde to be exact). Phenol formaldehyde is the least toxic type as it offgases less than urea-formaldehyde and it off-gases faster.
Formaldehyde levels in freshly produced plywood start out below 0.1 parts per million (ppm). But “emissions rapidly approached zero as the panels aged. In fact, the levels were so low and so close to the ‘background’ levels in the test chamber that it was not possible to measure them accurately” according to the American Plywood Association.
While the APA would not say exactly when the PF levels approached zero (or close to it), I do think that a few weeks is more than adequate for most people.
For most people, exterior plywood in a build will be sufficiently offgassed by the time the building is complete.
Testing Your Reactions
If you are extremely sensitive you should test out plywood when new, after a few weeks, and after 2-3 months of airing. You should also compare that to OSB, to see which is better for your health (I certainly prefer plywood to OSB). The extremely sensitive can often pick up the residual odor of the plywood glue even after the point where it’s undetectable by any instrument. It also becomes difficult to tell where the formaldehyde from the glues ends and the natural level of formaldehyde in the wood starts if you are sensitized to it.
Marine-Grade Plywood Glues
In the US, the marine-grade plywood I’ve seen is made with phenol-formaldehyde, but it can also be made with melamine-urea formaldehyde.
This is not a specific type of plywood in Canada.
Pressure-Treated Plywood Additives
Pressure-treated plywood is commonly treated with alkaline copper quaternary (i.e. copper and quaternary ammonia) (ACQ).
Copper Azole (CBA) is another type, which contains copper, tebuconazole, and possibly boric acid.
Though some wood is still treated with chromated copper arsenate (CCA), this is rare nowadays and it’s definitely not often used in residential buildings.
Product Certification Levels for Formaldehyde
CARB II – Formaldehyde Levels CARB II is a standard set by California for products sold there, but when it comes to common building materials like plywood, all major manufactures tend to comply with California’s standards.
Products that fall under this standard include hardwood plywood, medium-density fiberboard, and particleboard – these are pressed wood products sold for interior use.
It does not regulate exterior sheathing products like structural plywood (softwood plywood) and OSB.
(The allowable limits for TSCA Title VI are the same as CARB).
CARB II Formaldehyde Limits Are: Hardwood Plywood 0.05 ppm (parts per million.
The CARB II limit is the same as the GreenGuard limit (not Gold).
Furniture Grade Plywood
Interior grades of plywood can be made with urea-formaldehyde as the adhesive. Urea-formaldehyde (UF) offgasses more and for longer. Now phenol-formaldehyde (PF) is more standard, but I still see some SDS sheets showing urea-formaldehyde.
Interior plywood is often called furniture grade or hardwood plywood. You will want to make sure your furniture is made with PF or NAF glues, not UF.
1. Purebond Plywood by Columbia Forest Products is a no added formaldehyde plywood (NAF). It is made with a soy-based glue.
When folks talk about formaldehyde-free plywood, this is the one they are usually referring to.
Their adhesive is partially proprietary, but they claim it is “soy-based”. The full Declare label is here but this doesn’t tell us much about what it will offgas in the end, only what went into it.
I have seen extremely chemically sensitive folks react to this brand of plywood so I would make sure to test it out yourself before using it. I do think the odor is extremely mild and unoffensive.
Purebond plywood is intended for interior uses like furniture and cabinets (here are some cabinet makers who use Purebond). It is not structural and it is not made to hold up to high humidity or moisture. Some folks are using this as sheathing and roof decking which is a very bad idea.
You can buy it at Home Depot.
2. SoyStrong Hardwood Plywood is another brand of formaldehyde-free plywood made with a soy-based glue.
You can buy it at Lowes.
How to Offgas Plywood & Seal in the Formaldehyde
1. Give it Time to Air Out
Stack your plywood in a garage or covered area in a way that allows each piece to have some airflow.
Time, heat, and air are the main ways to allow any material to offgas.
2. Seal it
Whether you should seal your plywood partially depends on where it will be going.
If it’s on the interior of your home, then no problem, seal away.
Exterior applications, like wall sheathing and roof decking, are trickier. Wood naturally has the ability to absorb and release moisture. Stopping that natural process could cause problems.
To seal plywood there are a few ways you could go, but the two main options are AFM Safeseal which is a clear acrylic-based coating that helps to block and seal in formaldehyde, or shellac which is an alcohol-based natural wax coating. Shellac does a slightly better job at sealing.
Alternatives to Plywood, Which Are Less Toxic?
1. Formaldehyde-free plywood is a good non-toxic alternative to regular plywood in most interior applications and in furniture.
2. OSB is often used in place of plywood in structural applications. I don’t consider OSB to be less toxic, as it has higher offgassing and takes longer to come to completion but it’s possible that it works better for some people since the glues are different.
3. XPS foam can replace plywood as wall sheathing (but it’s probably not a good idea in most situations).
4. MgO board can sometimes be used as the subfloor and other sheathings (and I even used it for cabinet boxes and countertop underlayment).
5. Solid wood can replace plywood in some applications, like purlins or skip sheathing on a roof, in subflooring and sheathing, and for cabinet boxes and most furniture.
6. Georgia-Pacific DensGlass can replace plywood sheathing in some areas.
7. Cement board is sometimes used as sheathing, especially in tropical areas. Another concrete-based board, USG Structural Panel, is a thick and very strong board, it is sometimes used on foundation walls when the framing is metal.
8. Drywall is generally zero-VOC so it is technically less toxic than plywood but there are not many instances where they are interchangeable. If plywood is an option for your walls then you may prefer to use drywall.
Corinne Segura is a Building Biologist Practitioner with 8 years of experience helping others create healthy homes.
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