Intro: Resin Stabilizing Wood
Good evening denizens of the internet! Epicfail48 here, and today I'm going to walk you through how to resin stabilize wood in a home workshop. "But wait", i can hear you say, "what the merry devil is resin stabilization, and why would i want to in my shop?". Good question!
First, some background. Wood, as you may know, is a natural material, and wood moves, which you may not know. Difference in humidity and temperature can cause wood to expand or contract, changing sizes and even warping. What causes this is water absorbing into the wood, causing expansion, or water being lost from the wood, causing contraction. This can be a problem for you if you want to use wood for something requiring tight tolerances, like making a pen, or for use as the handle scales on a knife (my personal favorite use). You could get the handles fitted nice and perfectly on a humid day, then as soon as the air drys a little, the handle scales no longer fit the knife quite as nice, or the pen binds up. In other words, disaster!
This brings us to the process of resin stabilization. The process entails a drying process to get rid of all the moisture in the wood, putting the now bone-dry wood into a vacuum chamber to remove all the air, then introducing an acrylic resin into the wood, to occupy all the little nooks and crannys that water can absorb into in the cells of the wood. The end result is a piece of wood that no longer moves with changes in humidity, i.e the dimensions are stable (hence the name!).
Stabilization brings a host of other benefits too. In addition to the aforementioned movement issues, stabilization is also used on punky, spalted or soft woods to strengthen them; the acrylic resin adds a lot of strength to the wood itself. Now, it wont turn Balsa into Maple, but it will make a soft wood like Chestnut plenty hard enough for use in a heavy use role, like a knife handle. Stabilized woods are also generally easier to machine, more resistant to rot, and don't require finishing. They also take a very lovely polish. Best of all, despite the acrylic resin penetrating the wood, it still feels like wood in the hand, not plastic!
Sound awesome to you? Sweet, lets see how to make some!
Step 1: Step 1 - Git Yer Materials
So, first off you need to gather your materials and tools, otherwise you wont get much done. First, the software:
1. Wood. Yes, this one is painfully obvious, i know, but if i didn't list it I'm sure someone would forget. Now, stabilizing works well on a lot of woods, but there are some things to watch out for; this doesn't work with wood that have a high natural oil content (most exotics like rosewood and cocobolo, or oily domestics like teak), and extremely dense woods don't seem to let the resin penetrate well enough. Anything harder or denser than hard maple i wouldn't recommend trying. Here ill be using a selection of Sassafras, American Chestnut, Spalted Maple, Spalted Basswood, Beech and Walnut.
2. Stabilizing resin. There's a few to choose from here. I'm using Cactus Juice, a pre-catalyzed heat-activated acrylic resin. This is my favorite, and I highly recommend it, it works well and TurnTex Woodworks is fantastic to work with. Stick-Fast resin is another I've heard works well, and would be easily substituted in this guide. Id stay away from the more improvised solutions that are recommended online, like Minwax Wood Hardener, or the oft-recommended plexiglass dissolved in acetone. Neither are meant for this process, both are highly flammable and both will (not can, will) destroy your vacuum pump. Whatever you go with, you'll need enough to completely fill your vacuum chamber, plus a little more
That's all for the software (materials), onto the hardware. Now, i usually try to stay away from recommending specialized equipment, but for this, its necessary:
1. Toaster Oven. You'll need this to dry the wood before stabilizing, as well as curing the resin after infusing it into the wood. Nothing in this is particularly toxic, so your kitchen oven would work as well, but toaster ovens are cheap and generally have better heat control.
2. Vacuum Pump. This is completely necessary. Get the best you can, two-stage if you can swing it, you need to pull as deep a vacuum as humanly possible. An electric rotary vane pump like this will work well. You can find used HVAC service pumps on ebay as well, if you want a better price. A venturi pump hooked to an air compressor will technically work, but the length of time youll need to run it can strain your compressor. Dont even try those hand pumped brake bleeder things, they wont work for this, and you do not want to know how i know that.
3. Vacuum Chamber. You can build or buy these. I chose to build mine, and ill give you a quick run down in the next step. If you decide youd rather buy yours, here again TurnTex Woodworks is an excellent resource. At first glance the price seems high, but you get extremely solid build quality with an excellent company backing the work
4. 1 Gallon Freezer Bags. Youll see why these are needed
Got all your stuff? Good, on to the next step!
Step 2: Step 2 - Make a Vacuum Chamber (optional)
Alright, this is a quick and dirty rundown of how i built my chamber. Its really simple and completely thrown together, but has been serving me well for quite some time. My setup is a 2 part design, a chamber where the wood to be stabilized will chill in the resin, and a secondary overflow chamber that mitigates the risk of my vacuum pump sucking up resin (read: bad thing happens). So, first, a shopping list:
1. 2 Mason jars with lids - Yes, this is perfectly safe to use. Mason jars are actually meant to stand up to vacuum pressures, that's what the process of canning entails. Mine has been through hundreds of cycles and hasn't grenaded
2. (5) 1/4" barbed hose to 1/4 MPT connectors
3. (1) 1/4" barb to 1/4 FPT connector
3. (3) 1/4" FPT pipe caps
4. (1) 1/4" brass pipe tee
5. (2) 1/4" brass ball valve
6. (5) hose clamps
7. 1/4" tubing, im using vinyl here
8. PTFE Thread tape, dont want any leaks
9. Silicon Caulking, also to seal leaks
You'll also need a drill with a 1/2" bit. Betcha didn't notice one of those numbers repeated.
So, first up, put a few holes in the lids of the mason jars, 2 holes in one and 1 in the other. After that, assemble everything as indicated by the pictures. Really, they explain a lot more than anything i can type.
Now, a few things to note with this setup:
1. The 2 chamber design will prevent the resin from getting to the pump if it foams up, more on that later. You can get away with just the stabilizing chamber, but i don't recommend it
2. Use as much hose as you can between the vacuum pump and the valve setup, this mitigates risk to the pump if something should go wrong
3. The valve setup is important, it will allow you to keep a vacuum in the chamber setup while shutting off the pump, as well as reintroduce air to the system. It also allows for control of how fast the chamber is de- and re-pressurized
4. Do everything you can to make the system air-tight. Caulk all joints, thread tape all pipe connections, use hose clamps to attach the hose to the barb fittings
It shouldnt take much work to get your setup looking like mine, its just screwing things together. The only challenging part is attaching the hose to the vacuum pump, but since there are so many different pumps and ways to attach the hose its pointless for me to try to list them all here. I replaced the flared fitting in mine with a barbed fitting and attached the hose to that, you may have to do different. Once your chamber setup is all built, lets move on to the fun stuff!
Step 3: Step 3 - Preparing the Wood
Alrighty, now its time to get down to business and get the wood prepped to go in the vacuum chamber. The first thing you want to do is take your pieces of wood close to whatever the finished size you need. After all, you dont want to waste the time and materials stabilizing a 3"x4"x5" block of wood if you're going to cut it down to a 1" cube after the fact. Im stabilizing this batch for use as knife scales, so i machine my bricks and blocks down to roughly 1.5"x4.5x1/4", leaving everything a little oversized. That's just what works for me. Remember, you want to make yours as small as possible, but leave a little extra in case anything warps during drying.
Speaking of drying, lets talk about that! Before going into the resin, the wood needs to be as close to 0% moisture as you can possibly get it. The dryer the wood is, the more the resin will penetrate and the better the final results will be. If the wood is too wet, the stabilization process will fail, so take this part seriously. Also note, when i say moisture, its not anything that will even feel wet, what I'm talking about here is water that's actually trapped in the cells of the wood that we need to get rid of.
Now, the drying process it pretty simple, stick the wood in your toaster oven at 250f and leave it there for as long as possible. In my case, i left my scales cooking for about 8 hours. Overkill? Yeah, maybe, but better than underkill. Thicker pieces will require longer drying times, so the thicker the piece, the longer you want to leave it in there. I recommend a minimum of 2 hours, but again, as long as possible. Once you thing the pieces are dry enough, toss em in a zip-top freezer bag and let them cool to room temperature. Quick tip, if you see and condensation on the inside of the bag, the blanks aren't dry enough, pop em back in the heat until the bag stays clear. Make sure your blanks are in a sealed container to cool, if you just leave them on the counter the blanks will actually absorb moisture from the air, defeating the purpose of drying them
Now, the wood im using is already pretty dry to start with, so i cut my pieces pretty close to what i wanted the final dimension to be. If your pieces aren't quite so dry, they could warp as they dry in the oven, so for the first few batches you do i recommend leaving them fairly oversized.
Alrighty, once your blanks are nice and dry, mosey on over to the next step!
Step 4: Step 4 - Vacuuming
Wood nice and cool? Are you sure? Remember, the resin were using is heat-activated, so if the wood is still hot when you put it in, the resin will activate on the surface and prevent any more absorption, so make sure its cool. You're sure? Really? Wait a little long to be sure, then come back.
Okay, now that the wood is sufficiently cool and dry, time to actually make with the stabilization! Here again the pictures explain a lot, so check those for more details. First things first, take the lids off both the jars, make sure they're clean and empty. Now, place the wood blanks in one of the jars. This will be the stabilization chamber, it gets the lid with 1 hose. Once the wood blanks are in the jar, find some way to prevent them from floating. Ive found that a round cut of chicken wire does a pretty good job, just bend it so that it forces the wood down against the bottom of the jar. Once that's done, take your cactus juice and fill the jar about 3/4 of the way full. Place the lid on it and set aside.
Now, take the remaining jar and fill it no more than 1/2 way up with the resin, then screw on the remaining lid. This will be the reservoir, and it serves 2 purposes. For one, the air space at the top of the jar will keep the pump from sucking up liquid. The second purpose it serves is to keep the stabilizing chamber filled with resin, more on that in a minute. Make sure the lies are hooked up correctly, and the pickup hose in the reservoir reaches to the bottom of the jar.
Once you have that done, time to put the spurs to it. Adjust the valves to that the valve going to open air is completely closed, and the valve going to the chambers is all the way open, then turn on your vacuum pump.
Got kinda foamy, didn't it?
Now, just let it run until you stop seeing air bubbles come up through the resin. Keep an eye on the hose between the valves and the chambers, make sure no resin is getting sucked up. If it is, quickly open the valve going to open air to release the vacuum, don't let the pump suck up the resin. The massive foaming subsides pretty quick, after that its pretty much set and forget. Again, just let the pump run until there aren't any bubbles, this could take anywhere from 30 minutes to several hours, depending on the thickness of the blank. Don't rush this, it takes time.
Once the bubbles stop, its time to shut off the pump. Don't just flip the switch though, you'll kill your pump. Instead, close the valve leading to the chambers, then open the valve leading to open air. Once the pump is pulling air, shut it off. Now, slowly open the valve leading to the chamber. You'll hear a big "whooosssshhhh" as air rushes back into the system, and the increase in pressure will force the resin in the reservoir into the stabilizing chamber, fully filling it up. Neat, huh? That pressure is actually the magic to this process, now atmospheric pressure will force the resin into all the tiny little nooks and cranny in the wood that water and air used to occupy, all you have to do is wait.
How long should you wait? Here again it depends, the rule of thumb is let the blanks soak for twice as long as the vacuum was running, i.e if your pump was running for 4 hours, let the blanks soak for 8. Personally, i like tripling that amount of time, (2 hours vacuuming, 6 hours soak), and i always soak for at least 12 hours. Too much time cant hurt, but too little can. You also want to make sure that no part of the blanks are exposed to air, everything should be covered in the resin. The 2 chamber design should ensure that, but it never hurts to keep an eye out. If any part of the blanks is exposed to air, start the vacuum process over.
Once everything is nice and soaked, join me at the next step!
Step 5: Step 5 - Bake to Perfection
Shockingly, that title isnt sarcasm.
Assuming youve let your blanks soak long enough, theyre now completely saturated with an acrylic resin, but that resin still needs to cure. To do this, you need to expose it to heat, 200f in this case. Here again we use the toaster oven. You can either wrap your blanks in foil and bake them, or do as i am and place them all on a wire rack. Wrapping the blanks cuts down on the smoke generated but tends to leave excess resin dried on the surface, the wire rack will let the excess run off but can put off a bit of smoke. Both work equally well. The key things here are time and temperature, the core of your blank HAS to reach 200f. Set your oven for 200f, pop everything in and wait a few hours. Too much time wont hurt anything, but take the blanks out too soon and theyre ruined. Im doing 1/4 thick handle scales here, so i left mine cooking for about 2.5 hours. Thicker pieces will take longer, and again, you cant rush this. Leave them cooking overnight if you can manage, you wont hurt them as long as the temperature stays at about 200f.
Once the blanks are finished baking, set them aside to cool
Step 6: Step 6 - Youre Done
At this point, congrats, your wood is officially stabilized and subject to all the benefits that process entails! Clean off the excess resin and see what youve got!
Huh, it still looks like plain old wood. Guess that was pointless. Oh well, see you next time
Step 7: The Stinger
Please, did you really think id leave it like that? One of the biggest benefits to stabilized wood is that it looks like wood, it feels like wood, but the finished product is a wonderful hybrid. I knocked together a knife using some of the Sassafras i stabilized. Before stabilization, this was a wood i would've never used on a knife handle, it was far too soft, subject to far too much movement, hard to work with on account of the splintery grain, really just completely unsuitable for this application.
After the stabilization process, however, the wood is much harder (i can no longer dent it with a fingernail), much more resistant to rot, more durable, easier to work with and a perfect fit against the tang of the knife, a fit it'll keep. The best part is there's no finish on this knife, no oils or varnishes needed. The acrylic that's now embedded in the very fibers of the wood allow the wood itself to take a very high polish, so it even looks better. The best part? It still doesn't feel like plastic, it still feels like wood. Smells like it too, Sassafras smells just like root beer. The second knife pictures has much the same success story, the wood itself was too soft, too unstable, not durable enough, etc. The only redeeming factor it had was it was pretty. After stabilization though, it's perfect for a knife handle
So, now you know how the process is done, go out and salvage that piece of good looking scrap you wanted to make into a pen, but set aside because it wouldn't stand up to the lathe. The sky's the limit, and stabilized wood is really a fantastic material to have, plus doing it yourself beats the commercial prices