Sealing Plywood to Slow Down Formaldehyde Emissions
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Here's an extended discussion of whether, and how, to seal plywood in order to reduce the emissions of formaldehyde (or whether to purchase a different type of plywood instead). December 27, 2010
Question
I'm getting ready to build some cabinet bases for my own kitchen and I'm using 3/4" birch plywood. I'm wondering what anyone would recommend as a sealer for the plywood as I'm concerned about the formaldehyde outgassing.
Forum Responses
(Cabinetmaking Forum)
From contributor D:
I use 3/4" American maple plywood prefinished both sides. I figure the cost of the plywood is offset by me not having to do the finishing myself.
From contributor F:
You could buy a formaldehyde free plywood. If you already have the wood, cabinets are typically sprayed with lacquer or conversion varnish, though I doubt this will stop the formaldehyde from off-gassing. Pre-finished plywood is the way to go in my opinion as well.
From contributor M:
Get a cabinetmaker if you're worried about formaldehyde. You'll get more exposure building your kitchen than in ten years of living with the off-gassing.
From the original questioner:
The wood is already purchased and the formaldehyde free was way too expensive. Telling me to get a cabinet maker is not helpful. I'm hoping someone has an opinion of a sealer for material that is already purchased. This is a prototype for a job that is coming up toward the end of the fall.
From the original questioner:
Where we are, the cost of the formaldehyde free was 35-45 % higher and the plywood isn't truly formaldehyde free. There's just no added urea formaldehyde so a sealer seemed to make much more sense. The consensus was also that that the urea free products haven't been out long enough to know whether the laminate holds together under heavy use in a kitchen.
From contributor B:
To my knowledge the off gassing occurs from the core, not through the face veneers. That said if you treated any cut edges you will do more. Just out of curiosity, are you using China ply? If so the toxic levels are way too high in many cases, domestic made plywood will surely contain fewer levels.
From the original questioner:
The plywood we have is 3/4 birch made in New York. That's good to know about the cut edges. I guess what I'm getting at is that, according to the vendors we spoke with, buying the formaldehyde free wasn't worth any extra money because there is no true formaldehyde free plywood. We were hoping to minimize any out-gassing but it sounds like maybe it isn't really a huge issue.
From contributor K:
If you want to be 100% green build with 100% solid wood. I have seen a kitchen built with 100% solid black walnut. That's everything sides, backs, drawers. I saw it ten years after it was installed no issues, no splitting, no cracking, and it looked just like the day it was installed. The lumber was air dried in a garage attic for four years (upstate New York). It can be done but I don't think money can be made that way.
From the original questioner:
For sure it would be great to use solid wood but the reality is, it isn't going to happen. Where we live, green is a marketing tool, not a true philosophy so any thing is better than nothing.
From the original questioner:
The pollutants are inherent in the laminating process. The dealer we were talking to is a knowledgeable, reputable dealer. We're happy with what we have for plywood, just wanted to know about sealing it.
From contributor V:
Are we talking about cabinet bases or base cabinets? There's a big difference.
From the original questioner:
I should've said carcasses maybe. There are going to be upper and lower cabinets. These are the actually bodies of the cabinets.
From contributor D:
If it is a real issue for you, the best approach is to use the best material. Talk to another supplier. "Inherent in the laminating process" means they are using urea based resins that contain formaldehyde.
Just about any exterior grade panel will not because they have to use a different type of adhesive. This is probably what you are being priced. Vesta core melamine (flakeboard product I believe) is also made without ureas. Purebond ply (Columbia) uses a soy based adhesive. This is what we use and have found the difference (cost) to be not so great as you have described.
CV and lacquer based finishes contain formaldehyde. Poly does not. Chemcraft (Sadolin) have a good waterborne polyurethane floor finish that should not add to the off gassing. I'm not sure about vinyl based finishes. The premise of your question (that you can seal it in) is incorrect but to reduce it or slow it down, you could simply edgeband all sides. The off-gassing does not go on forever so you have to ask yourself are you better off with a higher level for a short term or a lower level for a longer time.
From contributor K:
You can't seal it off. Even if you could, if it couldn't off-gas, it would just degrade. Your sealer will also off-gas. In addition you are worrying too much about this. The only way this would be a problem is if the home where the cabinets are located in was hermetically sealed and the doors/windows were never opened. Most homes circa mid-1990's-forward have central-air, and the air is routinely replaced and filtered.
From contributor F:
Put the plywood in room or garage, gradually raise the heat to 95 degrees, leave at that level for three days and gradually bring it down to normal temperature. This will cook most of the formaldehyde out. You can also call a pallet manufacturer that does certified pallets and ask them if they will bake your plywood. This may cause checking in the faced but you can patch before you finish. This is the technique that was used years ago before everyone figure out it damaged the materials, mostly from rapid heat up and rapid cool down. Banding the edges will help with the off-gassing.
From the original questioner:
Thanks everyone for the input. The NAUF plywood was approximately $1000 more than the non NAUF and this was priced at more than one supplier. That $1000 represents the floor budget. We understand completely that there is a decision to be made regarding the lesser of evils. The original question, which has been thoroughly answered, was what product to use to seal a traditional plywood. The plywood in question is a US product so the contaminants found in Chinese plywood weren't ever a concern. I think perhaps, in light of the fact that we're expecting a baby in the spring, maybe I have been overly concerned. I do want to be able to give my customers informed, responsible answers and you have all given me info that will allow that.
From contributor V:
Now I’m really curious. What did you pay per sheet for the 3/4" domestic birch plywood and what were you getting quoted per sheet on the NAUF plywood?
From Gene Wengert, forum technical advisor:
The idea of sealing in the formaldehyde is indeed bogus. This gas will come out of the wood (or adhesive) over time as there is no perfect sealer. No commercial finish will seal the wood or stop it; some finishes might slow it down, but over 20 years, the excess formaldehyde will leave the wood. Any effective finish must be quite thick and without any holes big enough for a formaldehyde molecule to get through - that is small.
Even if a finish did seal the wood perfectly and prevented this gas from leaving, assuming the finish was applied thick enough and continuously, the finish would have to cover the entire piece including the edges, and any holes drilled in the pieces, perfectly. Of course, then what would happen when the wood moves (summer to winter) when the interior RH changes? Will the finish crack microscopically?
From the original questioner:
40 sheets of plywood, we paid $44 per sheet and the NAUF was $65-$71 per sheet depending on vendors. We paid more for the American plywood than we would've the Chinese which was in the $20 range. It is a fairly large kitchen but the wood is being used for some built-ins in the nursery too.
From contributor V:
For that quantity of plywood, my price for 3/4" Columbia PureBond, prefinished maple two side, would be $65.60 per sheet (quoted two months ago). Unfinished PureBond would be similar to what you paid. I’m a small shop that doesn’t use a lot of material, so I don’t have special high volume pricing. Are you sure that they were quoting both products unfinished?
From contributor K:
I would suggest contacting your supplier and switching out the batch for pre-finished. If the kitchen is that big (40 sheets, even with built-ins), do you know how long that will take you to finish that many cabinet carcasses? Even if you spray the initial coats as sheets, you are talking at least two days and a lot of extra unnecessary work. Add to this, there would be easily over $200+ for finishing materials, and this does not include your labor. While it may seem like you are saving money doing the finishing yourself, believe me, it is costing you money. Realize that while you are working on finishing these carcasses, you are not able to work on regular work. It is just not worth it, which is why the majority of shops buy pre-finished.
From the original questioner:
As I've stated, the material is purchased. We shopped it quite a bit, were comfortable with the price we got for the material I wanted. It's already cut, ready to be sealed and assembled.
From contributor V:
I believe that you did get a good price for the material that you purchased. My issue is what your supplier told you about the NAUF plywood and the price that they quoted you. It’s been my experience that some salesmen will tell you anything to get a sale. Now I don’t know your location, so who knows, maybe there really is that big of a price difference, but I can tell you one thing for sure, multiple people here have said that there isn’t that big of a difference in price in their market. So in the future you may want to shop around a little more to see if you can get a better price for the NAUF plywood if that is what the job calls for.
From Gene Wengert, forum technical advisor:
You cannot seal in the formaldehyde, which is what I said. I did say that coatings can reduce the rate of emission. I did not say that sealing will not reduce emissions.
Sometimes one bit of misinformation can get spread to many others. The EPA indeed has it correct when they say a coating "might reduce" emissions (referring to the rate of emissions), but over a long time period, the total emitted will not change. The US CPSC is again referring to the rate and not the total emitted and they also indicate that uncoated has the "potential" to release more, implying that it is not for certain.
From a technical viewpoint, the movement of formaldehyde through a film is controlled by Fick's Law. In addition to the gradient of the chemical and the vapor resistance of the film, temperature also plays a role, as well as the thickness and integrity of the film.
The good news is that all the cancer studies that show a correlation (not cause and effect) between exposure to formaldehyde and cancer are for people with a high exposure level (such as workers in funeral homes and people working with the adhesives that use formaldehyde as a catalyst). Even the rat studies that showed a link between formaldehyde and nasal cancer were for very high exposure levels. In fact, smokers and people exposed to tailpipe exhaust get much more formaldehyde exposure than the wood products will be releasing in this case.
