Wood Finish Shelf Life: Can Stains and Finishes Go Bad?
Last summer, I helped clean out my great aunt’s garage. My grandfather was a woodworker, and apparently stashed some supplies back there before he passed away a decade or so ago. I found the treasures, but then had to wonder: do wood stains and finishes go bad?
Turns out, manufacturers publish Technical Data Sheets for each type of stain or finish, which lists the shelf life of the product. I pulled this information for each type of stain or finish. Here’s a summary of what I found:
|Traditional Oil-Based Stain||3 Years|
|Gel Stain||3 Years|
|Oil-Based Stain + Poly||5 Years|
|Water-Based Stain + Poly||3 Years|
|Water-Based Polyurethane||3 Years|
|Oil Based Polyurethane||3 Years|
|Wood Conditioner||3 Years|
|Shellac Sealcoat||3 Years|
Manufacturers typically suggest a 3 year shelf life for wood stains and finishes. However, that time frame is simply an estimate; when stored in a temperature-regulated environment and air in the can is minimized, wood stains and finishes can last much longer.
Lets chat a little about where those numbers came from, as well as what other features you should be taking into consideration to determine if your wood finishing products are still good to use!
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How to Find the Shelf Life Of Your Specific Wood Stain or Finish
The recommended shelf life of wood stain and finishing products can typically be found on the Technical Data Sheet (TDS) for the product. I recommend starting here for determining if your wood stain or finish is still good, although it shouldn’t be the only thing you consider!
Manufacturers Varathane and General Finishes both post the TDS on their website for every product they sell.
Here’s where you can find that on Varathane’s product page:
General Finishes has a single page that links all of the TDS pages. You can find that page here.
While I can find the Safety Data Sheets (SDS) for Minwax’s products on their website, that is unfortunately not the same as the TDS. I don’t believe they have the TDS posted, and therefore, I couldn’t pull shelf life estimates for Minwax’s products.
If possible, I recommend pulling the TDS for the product you’re specifically looking for information on. While a 3 year shelf life is standard for most wood stains and finishes, some products have different recommendations.
Also note that the recommended shelf life is only one piece of the “is this product bad?” puzzle. Don’t throw your product away just because it’s more than 3 years old! Often times, stains and finishes last well over the manufacturer’s predicted shelf life.
How to Tell If Your Wood Stain Is Bad
While manufacturers indicate that wood stain has a 3 year shelf life, keep in mind that they benefit from you throwing away a product and having to purchase it again.
I have stains in my basement that are 6+ years old. I used one last week with no problems.
There is no reason to throw away a wood stain unless you’ve confirmed it’s gone bad.
So then, how can you tell if a wood stain has gone bad?
Open the stain. Does it look normal? Some signs it may be off include the following:
Change In Texture
A change in texture is the biggest visible sign that something has gone wrong. Traditional wood stain should still be a liquid. Gel stain should still be a pudding-like texture.
Any indication that the stain has separated, turned stringy, dried up, or had any other change in texture is a sign that it’s gone bad.
Note that pigments sinking to the bottom of the can is normal, and doesn’t indicate that the stain as expired. In that case, it just needs to be stirred.
Oil-based wood stain should still smell like wood stain. If it doesn’t smell right, something is wrong.
Water-based wood stains, on the other hand, shouldn’t have a strong smell. If they do, that’s an indication that something has gone bad.
If you’re still worried your wood stain is bad, there’s one final test you can do.
Stir the stain to mix up any pigments that sunk to the bottom of the can, then grab some scrap wood and apply the stain to the wood. Let it soak in for about 5 minutes, then wipe any excess stain off the rag.
Let the stain dry for 24 hours. At this point, is the stain actually dry? Does the wood feel wet, or does the stain come off on your hand when you wipe your hand on the wood? If the stain is dry, then it’s still good to use!
If the wood stain didn’t dry properly, that’s a huge problem, and it’s time to throw your stain away.
How to Tell If Your Wood Finish Is Bad
Wood stains are all formulated somewhat similarly. There’s some pigment or dye, and it’s suspended with a binder that’s either water or oil-based.
Different types of wood finishes, on the other hand, aren’t really similar at all. As a result, I’m going to break this into a couple sections, one for each type of wood finish.
Oil-Based Polyurethane and Other Varnishes*
Oil-based polyurethane begins to dry as soon as it’s exposed to air. As a result, if you have a half-used can of polyurethane sitting around, it’s likely that the top layer of the can began to dry.
This is perfectly normal! Scrape the dried layer off, and you should find some nice useable liquid underneath. This is not an indication that the polyurethane has gone bad.
The best way to tell if polyurethane has gone bad is by testing the dry time on glass, laminate, or a piece of scrap wood. Apply the the polyurethane to the material, and allow it to dry for 24 hours. If it’s hard to the touch after 24 hours, it’s good to use.
*Note: Oil-based polyurethane is technically a type of varnish. Whatever rules apply for polyurethane can typically be extended to other varnishes, like Arm-R-Seal, Waterlox, and Tung Oil Finish.
I love using dewaxed shellac because it’s super easy to use. However, there’s one danger to shellac: the shelf life.
Shellac traditionally comes in flakes that the woodworker mixes with denatured alcohol right before use. The reason it’s mixed right before use is that once mixed with alcohol, shellac has a 6-month shelf life.
And unfortunately, there’s no visible sign that the shellac is bad. It looks the same. It smells the same. But chemically, the alcohol has broken down the shellac too much, and when applied to your piece, it will never, ever dry.
If you’re ever in the situation where you’ve applied bad shellac to your piece, luckily it’s easy to clean up. Dip a rag in denatured alcohol, and rub the rag on the shellac. This will dissolve and wipe up the product.
To avoid using bad shellac, test the shellac on some scrap wood before you start. Allow it to dry for an hour. Is it dry? Are there weird blotches? If it’s dried properly and there aren’t any strange marks, your shellac is still good, and you can apply it to your piece.
Premixed shellac is a little different. Zinsser sells all three lines of premixed shellac that are on the market. They use a long-lasting resin so that the shellac has a longer shelf life.
You can pull the TDS for your product from Rustoleum’s website, but last I checked, the recommended shelf life was 3 years.
If you’re worried your shellac has gone bad, the same test that I described above works for premixed shellac too!
Good news – lacquer doesn’t really go bad! The bad news? It’s typically a poor finish choice for most home hobbyists (check out my full post on choosing a finish for all the reasons why.)
The only thing that can happen to lacquer, is if it’s exposed to air for too long, it will turn thick and gloppy. This is really obvious, and at that point, it’s time to throw the lacquer away.
Water based polyurethane doesn’t really have any special quirks like some of the other finishes. It does have a shelf life, though, so if you’ve had it for over the recommended three years, test it before use.
Like the other finishes, you can test water-based polyurethane by applying some of the finish to a piece of scrap wood. Water-based polyurethane typically dries within two hours. If it’s dry within two hours, it’s probably still good.
If your test polyurethane isn’t dry within two hours, first check the weather. Is it a humid day? That can slow down dry-time too.
But if it’s a neutral day, and your polyurethane is taking longer than two hours to dry, that’s a sign that it’s gone bad, and you should purchase a new can.
Extending the Life of Your Wood Stains and Finishes
Air is the primary enemy of every wood finishing product. In addition to oxygen, which dries out many products, air brings bacteria and moisture, which can make wood stains and finishes go bad.
Additionally, extreme temperatures can freeze or vaporize product, which leads to it separating or otherwise changing texture. This also causes the wood stain or finish to go bad.
Obviously, if you want to make your woods stains and finishes last longer, we need to avoid air and extreme temperatures. Here are a few ideas:
Get Rid Of The Air
Now, woodworkers have invented some very fancy products for eliminating air in opened cans of stain or finish. Bloxygen is an inert air that is added to your can of finish in order to block oxygen from reaching the finish.
Bloxygen is cool and all, but honestly? It just seems complicated. How do I keep air from entering the can as I’m adding the Bloxygen? Maybe I’m over thinking this.
But there’s an easier solution anyway, so I’m happy to pass on the Bloxygen.
Grab some marbles. Dust them off if they somehow mysteriously became covered in sawdust. Drop them in your finish, until the finish reaches the top of the can.
Now there’s no room for air in the can. Magic.
Be sure to fully seal your can lid, or else all your marble work will have gone to waste.
And if you don’t have a mallet, get one. I spent years hammering can lids back in place, only to ultimately realize that hammers can bend the lid so that it doesn’t secure properly. Wooden mallets are the way to go.
Pro Tip: As you’re tapping the lid back into place with the mallet, cover the lid and can with a rag or paper towel. That way, if any stain or finish splashes out, it hits the rag, and not you and your clothing.
Store Stains and Finishes in a Temperature Controlled Location
This one sounds obvious, given what I said above about extreme temperatures affecting stains and finishes. But, raise your hand if you’re guilty of storing finishes in the garage. (*Raises hand*)
Wood stains and finishes shouldn’t be stored in garages, because most garages aren’t temperature-controlled locations.
If you have a basement, that’s a much better option. If you don’t have a basement, is there a closet in the house that could hold your stains and finishes?
For the record, my stains and finishes are now stored in the lower level of my house, and not the garage.
Throwing Out Wood Stains and Finishes That Have Gone Bad
If you’ve determined your stain or finish has bit the dust, I’ve got bad news. Not only is your product worthless, but it’s also going to be difficult to throw away.
Wood stains and finishes are considered hazardous materials. If you’re throwing away product that’s still good, it’s not that hard to dispose of. Paint the stain or finish onto some cardboard, let it dry, and then it’s no longer considered hazardous.
But if your wood stain or finish has gone bad, then it probably won’t dry either. And in a liquid state, stains and finishes are hazardous materials, and cannot simply be thrown in the trash.
Instead, they have to be disposed of at hazardous waste disposal centers. Sometimes this costs money, sometimes it’s free; it all depends on your local municipality.
So, in order to throw away bad wood stains and finishes, you’ll need to research your local hazardous waste disposal center, and find out their policies.
Check your city’s website as well; I’ve lived in places that have semi-annual hazardous waste drop-off days, which make disposing of hazardous waste at least a little easier.