So you go to grab the wood glue from the shelf, only to find that last time, you accidently left the glue open. Maybe the glue is fine. Maybe it’s now a thick mess.
How would I know? Take a guess.
Whoops.
Good news! Thickened wood glue can be saved, and it’s actually pretty easy to save it.
Most wood glues can be thinned by adding up to 5% water by weight to the glue. Adding more than 5% water decreases the bond strength of the glue, leading to a weaker glue overall.
However, if you’re using a more unique type of wood glue, water might not be the right choice, so lets go a little deeper.
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How to Thin Different Types of Wood Glue
PVA Glue (Start here!)
By far, the most common type of wood glue is PVA glue. If your wood glue just vaguely titled “Wood Glue,” you’re almost certainly working with a PVA glue.
PVA glues are water-soluble, and can therefore be thinned with water, up to 5% weight.
Now, you could absolutely just add water slowly, stop when your glue meets the desired consistency, and bet that you won’t hit that 5% mark. Honestly, that will probably work.
But if you’re worried about going over the 5% mark (aka, you think like me,) then here’s the process I usually use.
My handy dandy kitchen scale comes in handy here, and I start by adding some “scrap tupperware” (is this a phrase?) and zeroing out the scale.
Then I add the entirety of the wood glue I’m trying to revive.
The final weight of the glue times 1.05 is the weight I can’t go over once I add water.
So if my glue is 5.32 ounces, when adding water I shouldn’t go over 5.32*1.05=5.58 ounces.
Then I slowly add the water, stirring each time I add more, and stopping when either the glue is thin enough, or I hit that predetermined weight.
Polyurethane Wood Glue
If you’re working with something titled “Polyurethane Glue” then you have a polyurethane glue. Duh.
The other “hidden” polyurethane glue is Gorilla Glue, which is the original polyurethane glue.
Just to be clear – the Gorilla Glue brand also sells a perfectly normal, PVA wood glue, which is titled “Wood Glue” or “Ultimate Wood Glue.”
But if you’re working with any of the original Gorilla Glues, than you have a polyurethane glue.
Regardless, you don’t want to add water to a polyurethane glue, since they’re not actually water-soluble. Water will ruin the glue, and you’ll have a sticky mess on your hands.
The official literature from Titebond recommends submerging the bottle of glue in warm water to thin it out. Gorilla Glue doesn’t have a specific recommendation, but the warm water idea is worth a try.
I also suspect mineral spirits/paint thinner can be used to thin polyurethane glue, since both clean up with the compound. However, I haven’t tried this, and I have no idea what effect this would have on the bond strength of the glue, so try at your own risk.
Epoxy Wood Glue
I’m not sure who’s over here trying to thin epoxy glue, because it usually comes in two parts that you mix together directly before applying.
Once the two parts are mixed together the epoxy has a short shelf life (usually between 5 minutes and an hour,) and once that shelf life is over, it’s hardened completely and the idea of thinning it is straight out.
But if you’re sitting in that short shelf life window, frantically googling how to thin epoxy wood glue, I’ve got you covered.
Epoxy wood glue usually cleans up with acetone. It thins with it too.
Once again, there is no official recommendation from the epoxy wood glue manufacturers on thinning the product, so be aware that you might be compromising the strength of the product.
Hide Glue
If you’re working with Hide Glue, you probably know it, since it says “Hide Glue” on the label.
Like polyurethane glue, Hide Glue can be thinned by submerging the bottle in warm water.
Other Magical Methods for Thinning Wood Glue
The above methods are what I usually go to, because they’re endorsed by the manufacturers, and they work.
But there are a couple other “word of mouth” methods out there that people swear by.
Vinegar
If for some reason you have no water, but you do have vinegar, a few drops of vinegar is said to thin PVA glues. Obviously, stir after adding drops, and add a few more if necessary.
People swear by this method, so it’s worth a shot. I’ve never tried it, but in an experiment I did messing around with different ways to remove dried wood glue, vinegar actually did something.
I’m not totally sure what the chemical reaction was there, but at the very least it turns dried wood glue white, so maybe it’ll thin thickened wood glue too.
Tap the Bottle
This method is harmless to try, and is certainly easier than adding water, so it’s worth testing before trying something more labor intensive.
Grab the bottle of glue, and tap it repeatedly against the countertop.
After 10 or so taps, check and see if the wood glue has thinned. Yes? You’re good to go! No? Try one of the methods above.
Why Your Wood Glue Thickened
Hopefully you know why your wood glue thickened, so you can avoid it in the future. In my case, it’s almost always because I forgot to close the top.
This happens a lot.
But there are reasons wood glue thickens other than air exposure. Here’s a non-comprehensive list:
- Freezing Temperatures
- Extreme Heat
- Expired (shelf life is generally 2 years in optimal conditions)
- Air Exposure
- Contamination from other products
When to Give Up On Your Thickened Wood Glue
If you’ve tried the above strategies, and your wood glue is too thick to use, it’s probably past saving.
Additionally, if it’s orange or stringy, it’s gone bad, and even if you manage to get it to a working consistency, it probably won’t do a great job of bonding your wood.
And if the glue has separated, that doesn’t necessarily mean it’s gone bad, but it could’ve. Shake the bottle and see if you can recombine the liquids. If not, toss the bottle and move on.
Finally, if a film has formed on the top of the glue, that’s a sign that you should throw it out. That said, I’ve been known to peel off the film and use the glue underneath and nobody’s died yet, but do this at your own risk.
The official recommendation is to toss.