Minwax Wood Hardener

[---k---]

Minwax High Performance Wood Hardener:



Approximately $9/can at Home Depot.

http://minwax.com/products/wood_maintenance_and_repair/high_performance_wood_hardener.html

Minwax High Performance Wood Hardener is a quick-drying liquid formulated to strengthen and reinforce decayed or rotting wood. Minwax® High Performance Wood is made up of solvents that carry resin deep into the pores of the wood where they evaporate and leave behind hardened resin resulting in hardened wood.

Directions:
1. Completely remove decayed and very soft, crumbly wood until you reach reasonably sound wood. Wood should be dry, free from dirt, grease, oil and loose paint particles. 2. Shake can well; apply Minwax® High Performance Wood Hardener with a disposable bristle brush to the softened wood to completely saturate the area. 3. For strength, apply several coats in quick succession until a shiny surface appearance is obtained. 4. Allow to harden for 2-4 hours before filling void with Minwax® High Performance Wood Filler. 5. Sand, paint, or stain if desired.

Ever since I saw this product in Home Depot a couple of years ago, I've wonder how it would work on MDF. Well, this past weekend I set out to find out.

Not super scientific, but I took four scraps of 3/4" thick MDF that I had in my garage. Two were the light brown MDF from Home Depot and two were from the darker brown MDF from Lowes. The samples were approximately 3" wide by 9" long. I set aside one sample from each brand to be used as a control. Then I prepared the two remaining samples by applying several coats of the Minwax Wood Hardener. I poured about 1/2" into a small plastic cup and just kept applying the wood hardener to all sides until it was gone. I didn't really put much effort into making sure that each side got the exact same amount. The wood hardener went on quickly and appeared to be absorbed rapidly into the surface. It took probably 15 minutes to apply. I may have been able to apply more and have it absorbed.

After allowing the samples to dry about 4 hours, the surface became very hard. Trying to bend the samples, the untreated samples feel like they bend very slightly, while the treated samples feel much stiffer and can't be bent.

I then cut the samples in half and trimmed the edges to view the wood hardener penetration. You could easily see the color change where the wood hardener penetrated. The penetration appeared to be very uniform in depth and measured approximately 1/8". I'm not sure if it is just the difference in the original color of the MDF, but the wood hardener appears to have penetrated the lighter MDF from Home Depot more thoroughly.

Four Samples
Dark MDF Control, Dark MDF Treated, Light MDF Control, Light MDF Treated



Dark MDF Treated, Inside Faces



Light MDF Treated, Inside Faces



Based on what I've seen, it appears that Minwax Wood Hardener is cheap, easy to apply, and can significantly increase the stiffness and strength of MDF. I can only see this as a good thing for building speakers as we try to stiffen up boxes to reduce resonances. It probably is also a good product to seal the MDF for painting or whatever.

Tomorrow, I'm going to call a testing lab that I work with a lot and see if they'll do me a favor and break these samples. I would love to have real test results. I'll also probably do some experiments with my three surrounds currently in production to see how it takes paint and such.

[Dennis H]

Seems like I recall Shinobiwan using the UK equivalent of that to seal endgrain before painting. Looks like it would also be good for strengthening screw holes.

[Bill Schneider]

Two questions... did you see any dimensional changes in your treated samples? IOW, did they grow a few thousandths in thickness? I've seen changes in MDF treated liberally with de-waxed shellac. In one instance, the biscuits 1/4" below the surface of a joint didn't swell as much as the adjacent MDF, and it required additional sanding to smooth out their "ghost".

Second, do you know what the solvent is?

[---k---]

I didn't visually notice any dimension changes. I would need some calipers to actually measure the change if there was any. I also don't know what the solvent is - only that it is known by the State of California to cause birth defect.

That is interesting that it could cause the wood to swell. That is why I post here. I guess I'll test that prior to liberally applying to a completed speaker box.

I still think it would be an excellent cheap tweak. Much more effective than most of the other crap people try. At least that is my hope. Hopefully, I'll be able to get the guys at the testing lab to prove me right.

[Bent]

If it only causes birth defects in the state of California, then I should be safe.

[jbateman]

I used the stuff before, in an attempt to seal end-grain mdf where it butted against the smooth face. This was done so that paint would go on evenly and not show the seam.

It takes very many applications to reach the point of getting a smooth, hard surface. At that point, it doesn't sand so easily anymore. It's more like hard plastic than mdf.

Useful...but not a perfect solution.

[---k---]

You're right about the end grain. The cut surfaces on my samples still feel "furry" after a few coats. Since it penetrate the wood so easily, the product is beneath the surface. I'm not sure if it is the right product to make the end grain smooth.

I'm looking at it more for strength. When I see some of the crazy extremes some people around the net go to to reduce resonance in their boxes, I thought this would be something that might actually work, be very cheap, and not add any weight or size. I think it holds promise here. It will also be helpful to reduce damage corners from dropping.

[Brandon B]

Based on what I've seen, it appears that Minwax Wood Hardener is cheap, easy to apply, and can significantly increase the stiffness and strength of MDF. I can only see this as a good thing for building speakers as we try to stiffen up boxes to reduce resonances.

In hardening and making MDF more rigid, you are also making it less "dead", and hence more prone to resonance, not less, I would think. The reason plain hardwood is not a good idea. Stiffening an enclosure moves its resonance up in frequency, rather than eliminating it.

It would make it a better material structurally though, so potentially a worthwhile compromise.

[Johnloudb]

In hardening and making MDF more rigid, you are also making it less "dead", and hence more prone to resonance, not less, I would think. The reason plain hardwood is not a good idea. Stiffening an enclosure moves its resonance up in frequency, rather than eliminating it.

It would make it a better material structurally though, so potentially a worthwhile compromise.

That's the whole point - to raise the resonance up in frequency where it can easily be deadened by poly fill and other box deadening methods. Reinforcing a box does the same thing. You want raise the resonance above where the woofer interacts with the box. Some one can explain this better, I'm sure, but raising the resonance frequency is what you want to do.

[---k---]

Yeah, stiffer moves it up further. We're starting with a pretty dense, material, so I'm not worried about it.

I talked to the testing lab today. They said that they would break them, but my samples were too short. So, I have to cut some more. I may throw in some ply. I'm just worried about abusing the freebe and sending them too many samples.

[Martyn]

Breaking them isn't going to tell you very much. It's the possible change in stiffness that you're after, i.e. how much force it takes to produce a given deflection (or vice versa which is probably easier to measure).

It would be interesting to compare MDF with plywood, but unless your samples are dimensionally identical (including thickness) you're going to have to do some math to adjust for the differences. If you have access to a planer, just plane all your samples to the same thickness and rip them to the same width.

Martyn

[Winter]

Good idea in principle. I hope it works. Basically a form of constrained layer construction. Stiffer outer walls with a damped more pliable inner layer. The stiffer outer walls reduce the amplitude of the wall vibration movement and move the wall vibration frequencies higher. In general, higher frequencies are easier to damp, which the more pliable inner layer would be better able to do.

[---k---]

Breaking them isn't going to tell you very much. It's the possible change in stiffness that you're after, i.e. how much force it takes to produce a given deflection (or vice versa which is probably easier to measure).

Martyn

While I would love to get a load deflection curve from them, that is a lot more work for the testing lab. If I were paying them, that would be a different story.

That said, I can just feel that the stiffness has increased. If we look at it from a logical standpoint, stiffness is just the ratio of stress versus strain. If we know the force to break them, we can determine the bending stress. We won't know stain, but the treatment is going to make it more brittle and stain less. Just holding the stain constant and increasing the stress will increase the stiffness; reducing the strain will just make the stiffness sky rocket.

I'm also not sure that this has any similarities to constrained layer dampening. Its a bit more straightforward than that.

Please don't make me break out my mechanics of materials text book.

[Winter]

The relative stiffness increase can be measured at home. Support the two ends of the specimen, deflect the mid-section down with a fish scale or other device while measuring the deflection. As the stress/strain curve is probably not linear and may differ in shape (one may show a more plastic curve than the other), the failure stress load may not be as precise an indicator.

As can be seen by the cross section of the MDF saturated with the hardener, three layers are present. Whether the differences in stiffness and dampening between the layers are great enough to be beneficial as a mild form of constrained layer construction is questionable, but worth testing. Any one with a accelerometer and an impact hammer? I am involved with operating equipment vibration analysis at work, but we do not have the impact testing equipment.

[cobblepots]

The relative stiffness increase can be measured at home. Support the two ends of the specimen, deflect the mid-section down with a fish scale or other device while measuring the deflection. As the stress/strain curve is probably not linear and may differ in shape (one may show a more plastic curve than the other), the failure stress load may not be as precise an indicator.

As can be seen by the cross section of the MDF saturated with the hardener, three layers are present. Whether the differences in stiffness and dampening between the layers are great enough to be beneficial as a mild form of constrained layer construction is questionable, but worth testing. Any one with a accelerometer and an impact hammer? I am involved with operating equipment vibration analysis at work, but we do not have the impact testing equipment.

Might not even need to be that elaborate. A more visual measurement could be used as a quick and dirty approach. Just construct a simple pendulum out of scrap wood with a pointed object on the end. If the pendulum is clamped to a table and the MDF to a stable 90 degree panel, the pendulum can be swung for a know height (maybe use marker as an indicator of angle) and let go to strike the panel. repeated tests should give some sort of indication on if the hardener does anything.

Simulink can be used with an AVI file to analyize velocity at impact as well. to get a more accurate result. You'll know the mass, lever arm length, and velocity at impact so energy calculations should be a breeze.

[---k---]

Well boys, it is 9$ a can and you probably have scraps of MDF in your garage. I suggest you start experimenting!

[bobhowell]

I have used it for several applications over the years, mostly to firm up soft spots in wood to extend usability.

It is very strong and will dissolve many plastics.

[Johnloudb]

Ryan,
I suggest a knuckle tap approach. Fix the treated MDF in a vise as well as an untreated MDF board and tap on them. Listen for a change in resonance. Or are you primarily interested in the increased strength?

And, I will do this myself - when I get a chance. It sounds like an effective treatment from your description. Thanks for the tip! :T

[JonP]

Interesting experiments...

Like has been said, you should be able to kludge up a jig to hold the strips, and press or pull with a weight or scale at a repeatable point, such that you could get good meaningful info on deflection/force.

I've seen and wondered about the stuff myself. Never tried it. Would be interesting to compare it with Shellac (Zinnser Sanding Sealer) for the strength/bending change tests, as well as the depth of penetration and size expansion effects.

Can't compare the two directly, but my experience with Shellac soaked MDF is that it doesn't become more difficult to sand, if anything it gets easier. The combo grinds down to a nice powder. Never cut thin strips like you did to feel the stiffness, but it does seem to harden the surface a lot.

Another thing, Shellac is almost universally compatible with other finishes.

If you're feeling inspired, try the Sanding Sealer cut 1:1 with alcohol, (2lb cut to 1lb cut) as well as straight. I usually use it diluted and it really soaks in. If I want to add more substance I change later layers to straight 2lb.

Once I went totally crazy and just kept going on a veneer finish, umpteen layers of sealer Shellac and it looked pretty good. Took a long time, I could have made a piano finish by the time I was done, and Shellac is a pretty fragile finish, but it looked pretty good. :roll:

[---k---]

Finally getting to use my Master's Degree in Structural Engineering from one of the nations top 10 Universities to build speakers! I was able to roughly calculate that to break my small samples in a simple 3-point bending rig would take about 200# to break and would deflect 0.08". (Lots of assumptions)

I weigh a little over 200 pounds , so I can generate that. Quick test, I set up each sample up in a 3-point bending on my office desk and leaned on the ends until it broke. The untreated sample broke with just before I was able to put my full body weight on them. The treated samples took my fully body weight and a little bit of a bounce to break them. It was pretty convincing to me and my co-worker who walked in that it took more force to break the treated samples. My guess is that the force was increased about 50%.

There appeared to be a somewhat consistent pattern in the failure plane, but really too few were tested to say for sure (and the testing wasn't exactly scientific). They all broke in bending, with the fracture plane being jagged interlocking fingers - a combined tensile and horizontal shear failure mode. But, in the treated samples, the jagged planes were much deeper and less frequent. This indicates that the treated samples were able to generate higher tensile stresses before failure.

Obviously the deflection is too small to measure. But again the treated samples felt like they didn't deflect as much as the untreated. Deflection is linearly related to stiffness and stiffness is linearly related to strength. So, just increasing the bending stress alone should increase the stiffness and reduce the deflection.

Very convincing that the strength and stiffness is increased.

I'm hoping to cut some new samples this weekend that the testing lab can break. I don't want to send them too many, so I may just do the dark MDF and then throw in some birch ply. The ply is up in the air, because the layers are thinner than 1/8", so how much can it penetrate before it hits a glue layer? Ply may not benefit nearly as much.

[djn04]

I was going to use this on the inside of the cabinet to seal it as well. Is there any chance this could damage the drivers over time if I seal the inside?

Thanks

[RobP]

I wonder about what solvent they use, just curious if over time it could break down the glue that bonds the MDF particles together.

[ThomasW]

I was going to use this on the inside of the cabinet to seal it as well. Is there any chance this could damage the drivers over time if I seal the inside?

I imagine the solvents are so volatile they're long gone after it's dry.

I wonder about what solvent they use, just curious if over time it could break down the glue that bonds the MDF particles together.

That would sort of be antithetical given the product's name...

[---k---]

According to the MSDS sheet:

http://www.hardwarestore.com/media/msds/268532.pdf

It looks like it is 25% of the solid product suspended in 72% Acetone and 3% Methanol.

My experience was that it dried very quickly.

Googling a little shows that people building model rockets use this stuff to stiffen cardboard and wood. Knife and pen makers are also using it. Some suggest thinning it with more Acetone and heating to promote penetration. Several websites discussed soaking the wood in it to get 100% penetration.

I don't think it will hurt a glue joint, but not sure. If you apply this stuff prior to glue up, then you'll probably have to use epoxy for the joints - wood glue would no longer work.

[JonP]

Alright... good quick and dirty testing... I like it. Interesting that it does add that much strength, I'd have guessed much less.

On the solvent, Acetone can attack a lot of plastics and possibly glues, I have no idea what it will or won't do to wood glue, or speaker glues. OTOH, it extremely volitile, and should evaporate pretty thouroghly, given the chance.

Not to... well maybe yes to, harp on Shellac, the alcohol solvent is probably less harmful, not quite as low boiling but still pretty easily evaporated. If you do send samples, I'd be highly interested in how it does.

Baltic Birch... I wonder how deep of penetration you'd get with just a coat or two. The wood will be so much more dense and less porous than MDF, I'd think it might end up so thin of a layer that it wouldn't make much difference. But testing will tell...

[RobP]

That would sort of be antithetical given the product's name...

possibly, but I wouldn't want to lay faith in just a name. :W

I was talking with a couple of gents at Woodcraft today about this stuff and one guy said that he uses it on his MDF jigs to make them hold up longer, he said that he never had had any separation issues as long as he has been using it.

[JohnA]

If you would like to try something a lot better than the Minwax wood hardener, there is also a penetrating epoxy based solution called CPES (you can also get it under another name of MultiWoodPrime) that will soak in even quite a bit deeper due to the much longer cure time for it. Although it also is quite a bit more costly at $36 quart, than the Minwax is a $9 a pint. I have used both, in fact I have used about 12 gallons of the CPES so far on some restoration on a porch I'm still working on (trust me it's a big job) and the CPES is a lot better in how it soaks in deeper than the Minwax, and it's very possibly also more stable over a long period of time than the Minwax is.

But be warned though, if you are going to try it indoors, the cold weather formula is the one recommended for indoor use. They do not recommend the warm weather formula for indoor use as the warm weather formula has a very very strong smell that lasts until it's almost fully cured. Also the warm weather version also takes longer to cure, but because of that the warm weather formula also has the potential to soak in deeper than the cold weather formula. Although the cold weather formula in some cases, could also set up too fast and not soak in as deep as the warm weather formula if it's used in higher temperature ranges.

http://www.smithandcompany.org/CPES/index.html

http://www.smithandcompany.org/mwp/index.html

http://www.star-distributing.com/smith/products.html

I don't sell the stuff or have any affiliation with it or anyone that sells it. I've only used it extensively, along with some of their thicker epoxy products used for laminating/reinforcing, and the stuff works and has saved me a lot of expense of having to replace quite a bit of wood that was starting to get soft and porous. Using this I was able to stabilize it, restore the strength to it and in some cases even increase it over what it was even when the wood was in good condition, and I only added new wood reinforcements where it was structurally needed. Not to mention it saved me even way more in labor time so far, by not having to spend days tearing down the entire porch and then totally rebuilding it with all new wood.

[---k---]

Prior to applying to a speaker, I was planning on doing a some testing to see what it might do to a glue going, etc. But, I had another case of cabin fever today and wanted to accomplish more than just "testing". So, out came the three 1/2 finished speaker boxes for my rear and the paint brush.

My speaker boxes are done, except for gluing the baffles on. Once the baffles are on, it will be a lot more difficult to apply the hardener to the inside. So, I masked off the edge where the baffle mates up. I also masked about 1/4" of the inside face around the baffle edge. I wanted to make sure the hardener would not interfere with gluing the baffle on with regular old wood glue.

I used up about 3/4 of the can applying it to the inside. I'm not sure how much penetration it is going to have. 1 can seems like it would go a long way, but man, the MDF just soaks it up. It actually seemed thin. If I had more and it was free, I would have used more. I'll get one more can for the exterior of the thee boxes - that should be enough.

So far, I don't see any ill effects of using it. Without the front on, it is hard to do the knuckle test to see it made any difference. I'll be able to judge better when I do the exterior.

Unfortunately, I'm not going to be able to get samples tested at the lab for free. So, I'm going to let it go for now. Maybe some day I'll do a more formal test myself. With the load so small, I could probably do it myself. If I use a little longer sample, I can get the breaking load down to 30 - 50 lbs range. Then load it with a bucket and sand. Just pour sand in until it breaks. Then weigh the bucket. Pretty easy.

Funny thing, I pour the hardener into a plastic cup and was applying it. About 5 minutes in, the hardener spilled out the bottom of the cup. It had eaten though the plastic cup. I got an old ugly coffee cup to complete the job. But, just a word of warning, use a glass container when applying.

[atm98]

If you would like to try something a lot better than the Minwax wood hardener, there is also a penetrating epoxy based solution

I use a lot of epoxy. Mostly for more industrial applications. Sandblasting steel and coating with epoxy is a favorite trick as mine since it prevents rust like galvanizing or powder coating. Two weeks ago I covered the plywood floor of a trailer with epoxy. Seemed to soak in nicely. However after the first coat you are more likely to build up the outer layer then absorb into the wood. For more play time or more "soaking" I use less hardener.

Also, epoxy claims to be 50x harder then urethane. FWIW

[bobhowell]

I used this stuff on some window molding in a Florida beach house. The sun, over twenty years, turned the wood to mush. Applied it from a plastic cup too with same mess. Sun destroyed it, also, in 2 yrs. I have used it on spalted(rotten ) patches of wood, in woodworking projects, to restore strength, and save a project, turned bowls, mostly. I normally use thin super glue, but Woodhardner is better for big areas, as it is cheaper.

I just put supper glue on the baffel of a Zaph HiVi b3s speaker, where I had relived too much of the backside and created a weak spot at the screw hole.

Fixing mistakes is where you will find this stuff a lifesaver. After Hours on a baffle and a miscalculation on router setup might ruin your masterpiece, but for Woodhardner.

You might need this as you try some of Zaph's waveguide ideas, or fancy tricks for doing away with the tweeter flange to get closer driver spacing.

Be nice to know how it compares with thin super glue.

Another trick to add to the woodworker's bag.

[brianpowers27]

Great testing premise

This is a great testing premise. I would love to see the hardened material tested with an accelerometer vs the equivalent non-hardened box. This should reveal whether or not the hypothesis of a stiffer outer box increases the resonance.

P.S. Do you think that a MDF box covered in undiluted wood glue would be stronger than it's untreated counterpart?

[---k---]

I would love to test with an accelerometer also, but unless someone comes forward with the means, it isn't happening. I'm satisfied with understanding the relationship between strength, stiffness and deflection.

I don't think undiluted wood glue would do much. It isn't going to penetrate the like the wood hardener. It would be much like paint. Anyone is welcome to prove me wrong.

[brianpowers27]

I found this article informative. It is a brief discussion of this product. It also mentions some solvent based based hardener products that the author feels do a better job.
(http://makezine.com/pub/tool/Minwax_..._Wood_Hardener)

[bobhowell]

I would love to test with an accelerometer also, but unless someone comes forward with the means, it isn't happening. I'm satisfied with understanding the relationship between strength, stiffness and deflection.

I don't think undiluted wood glue would do much. It isn't going to penetrate the like the wood hardener. It would be much like paint. Anyone is welcome to prove me wrong.

Super glue comes in 3 formulas, thick,med . and thin. The thin soaks right into MDF, like Wood Hardner.

[liasom]

I Made Homebrew Wood Hardener

I use the Minwax stuff to harden templates that I make for use with my router. So, I was telling my Dad about the Minwax product yesterday. He's a retired Pharmacist. He told me that in the old days they used to make something similar to this to plasticize paper labels. They wrote on the labels with a wax pencil. This way they could easily change pricing and inventory on their stock in the pharmacy. They would post a sign advertising 50% off on a new toothbrush if you traded in your old one. I suppose the price was right, because then they would dissolve many old toothbrush handles in acetone to make a plasticizing agent. That got me thinking.

SO, I did research, read the MSDS for the Minwax product which basically gave its composition, and researched how acetone will dissolve certain plastics and what types. Here's what I've come up with.

NOTE: acetone is nasty stuff. Before you try this (if you want to try this) go to the web to read ALL the safety data you can find regarding handling, toxicity, AND volatility (especially when combined with other chemicals). There's a good Wikipedia entry on acetone, others I'm sure.

Polycarbonate (id code 7 plastic) will dissolve in acetone. I had a busted amber colored turn signal lens from my truck in the recycle bin and thought that it was probably polycarbonate, or very similar plastic, so I dissolved it in acetone. Took overnight in a glass jar to dissolve a 1" square sized chunk of the lens in about two ounces of acetone. Got outdoors in good ventilation and painted it on some porous wood (fir I think) and...voila! Homebrew wood hardener.

From what I can tell the homebrew stuff seems to perform very similar to the Minwax product. Even tried it on a business card. Dries hard. Turned that sucker into a piece of plastic. Although now it IS tinted yellow because of the original lens color.

Provided there's access to polycarbonate for free (like, a friend in the auto body repair shop) a gallon of this homebrew stuff could be made for basically the cost of the acetone. Far less expensive than the Minwax product.

[JonMarsh]

If you would like to try something a lot better than the Minwax wood hardener, there is also a penetrating epoxy based solution called CPES (you can also get it under another name of MultiWoodPrime) that will soak in even quite a bit deeper due to the much longer cure time for it. Although it also is quite a bit more costly at $36 quart, than the Minwax is a $9 a pint. I have used both, in fact I have used about 12 gallons of the CPES so far on some restoration on a porch I'm still working on (trust me it's a big job) and the CPES is a lot better in how it soaks in deeper than the Minwax, and it's very possibly also more stable over a long period of time than the Minwax is.

But be warned though, if you are going to try it indoors, the cold weather formula is the one recommended for indoor use. They do not recommend the warm weather formula for indoor use as the warm weather formula has a very very strong smell that lasts until it's almost fully cured. Also the warm weather version also takes longer to cure, but because of that the warm weather formula also has the potential to soak in deeper than the cold weather formula. Although the cold weather formula in some cases, could also set up too fast and not soak in as deep as the warm weather formula if it's used in higher temperature ranges.

http://www.smithandcompany.org/CPES/index.html

http://www.smithandcompany.org/mwp/index.html

http://www.star-distributing.com/smith/products.html

I don't sell the stuff or have any affiliation with it or anyone that sells it. I've only used it extensively, along with some of their thicker epoxy products used for laminating/reinforcing, and the stuff works and has saved me a lot of expense of having to replace quite a bit of wood that was starting to get soft and porous. Using this I was able to stabilize it, restore the strength to it and in some cases even increase it over what it was even when the wood was in good condition, and I only added new wood reinforcements where it was structurally needed. Not to mention it saved me even way more in labor time so far, by not having to spend days tearing down the entire porch and then totally rebuilding it with all new wood.

Shiny! Some very other interesting products in that last link, like the hardwood and tropical wood epoxy glues! I have just been using marine epoxy with good results, but this may be even better!

Layup and laminating epoxy might be overkill for my sheet layup and construction for cabinet walls, but I'm going to check it out.

And yesterday I just ordered 10 of my favorite squeegee's, because I found the Mfr on the internet!

Thanks for posting this, John!

[---k---]

Provided there's access to polycarbonate for free (like, a friend in the auto body repair shop) a gallon of this homebrew stuff could be made for basically the cost of the acetone. Far less expensive than the Minwax product.

Interesting. I'll have to start going through my recycling bin.
Thanks.

[liasom]

Or you could melt down the canopy from an F-22 Raptor... :E hmmm... I wonder if they have well equipped wood shops in federal prisons.

[JonP]

Cool idea, the homemade wood hardener. Hmmm... polycarbonate isn't the only thing Acetone will dissolve... I remember pouring some in a Styrofoam cup long ago, with dramatic results. Or "desults"? Probably a few others might work as well.

A place like McMaster-Carr would be a source for plastic stock of various kinds, wonder how much clear polycarbonate stock costs per cubic inch...

[savage25xtreme]

in college one of my design projects was making an injection molding of some lego like blocks for making robots, we bought 5 pound sacks of polyethylene and polycarbonate grindings and they were less than 10 dollars a bag IIRC. I tried searching for granular polycarbonate and didn't find much though. Maybe I can find where we bought that if I dig out my old notebooks.

[liasom]

I used the turn signal lens (polycarbonate?) because it is a hard and dense plastic and it was available for free. I thought that those qualities would be the among the ones that would be desirable. Not sure of other plastics, I will probably stick with this.

One other important quality was how the stuff dried. So, I had a small amount left over from the first test batch and poured it into a shallow tray made from a piece of aluminum foil. At first (about 8 hours of drying) it was still gel-like, but I peeled it free of the foil so it could dry completely. Next day, after much of the acetone had evaporated, the residue was hard and minimally flexible. There are bubbles in the residue. I suspect that is because it was 97 degrees here during the initial drying. Today, I snapped off a piece to see how brittle it was and was pleased that it broke cleanly with no crumbling.

To compare the two, I'm still waiting for a sample of the Minwax product to dry and that has been three days now...it seems to dry much slower. But it has been cooler than 97 degrees.

As you can tell there's no scientific method going on here, I'm only seeking the most frugal product that I think will work to increase the stiffness and strength of an enclosure. For the heck of it I'm making up a new batch to test on some MDF like Ryan did. I plan to include a test on glue joints using two brands of PVA glue I have on hand to see if there is any reaction or change there.

[BigguyZ]

I'm looking at doing a MDF stacked lam for a build of 4T's... and although I don't think I'd use this on the outside to smooth the surface (which will be all furry end grain), this might be good for the inside of the cabinet.

Anyone have ideas on what to use for the outside? I'm going to veneer, but I'm worried that all end grain will soak up the glue so much that it won't provide a good bond...

If anyone wants a good source for polycarbinate or plexi- make nice with your local hardware store. If they have plexi for windows, they probably won't give it a second thought to give you the scraps. I now have more plexi than I could ever dissolve in acetone...

Also, someone mentioned styrofoam and acetone. When I have a build-up of styrofoam from packages and such, I'll get a gallon of acetone and melt it down in a bucket. I've had massive amounts of foam melt down almost to nothing. Then let the acetone evaporate, and you'll have a mass of plastic to throw away instead. If you live in the city and have limited space in your garbage, this is really helpful.

[liasom]

I haven't had time to do all tests I plan yet, but can give a quick summary of the first round on two glues. I dried a couple of samples of the two glues I had on hand, Elmer's Glue-All and Elmer's Carpenter's Wood Glue. According to their individual MSDS both of these are PVAC based adhesives. The samples are approximately 1" x 1/2" and are approximately 1/16" thick. Just squeezed some out on a piece of flexible plastic to dry.

After they were fully dry, like 48 hours, the Glue-All was fairly transparent and somewhat flexible. The Carpenter's Wood Glue was slightly more opaque and relatively stiff.

I placed both glue samples into some acetone for about a minute and then removed them and placed them on a paper towel to dry. The results were not good for either. Both samples are now completely opaque and both are very flexible. Almost rubbery. They compress. They stretch. They retain much of their original size and shape, but they have both been radically changed by the acetone.

I do have some samples of MDF glued up from some scraps using butt joints. Someday soon I will get to that and paint on both the Minwax and the Homebrew Wood Hardener. Painting it on vs. immersion may be different? It will be interesting to see what the joints are like after.

Makes me wonder what acetone might do to the adhesives used to manufacture both mdf and plywood.

[---k---]

There should be no worries about using a moderate amount of Wood Hardener on a completed speaker. I used almost 1 can on each of my completed In-Khans-Neatos, applying about 4 - 5 rapid coats, inside and out, (around the driver holes even more) with a brush. It seemed to improve the knock test slightly. It also made the edges much more durable while dragging them in and out of my house, which was very helpful. I was happy with the results and think it was worth the minimal cost. But, I do wonder if it would have just been better to use the expensive birch plywood. The edges were still a little fuzzy and soaked up the paint - where I used a LOT of wood hardener, it was better.

I didn't see any adverse effect on my Tightbond 3 glue joints. None at all. The boxes are rock solid. Maybe if I wood have soaked the speaker in Wood Hardener, it would have been a problem. But with only 1/16" - 1/8" of penetration, I don't think enough of the acetone gets to the glue before it gasses off. You said you let it soak for about a minute or so - big difference.

[liasom]

The edges were still a little fuzzy and soaked up the paint - where I used a LOT of wood hardener, it was better.

With homebrew you could have a larger amount of plastic dissolved in the solution and more solids might penetrate down into the edges. The batch I have now is far more viscous than the Minwax. Maybe a small batch of a more viscous solution to pre-treat edges with?

I'm looking at doing a MDF stacked lam for a build of 4T's... and although I don't think I'd use this on the outside to smooth the surface (which will be all furry end grain), this might be good for the inside of the cabinet.

Lots of time and work involved in that stacked lam project. I know there are many techniques to deal with the edges of MDF. If using any acetone based stuff I'd do a test sample just to examine my glue joints. Someday I'll get this all done and report back, but FYI I soaked a piece of MDF in this homebrew stuff. The result on the edges were that they dried/cured relatively hard, but not as hard as the faces. Only thing I can think of that might be a problem is high speed sanding (belt sander?) that generates too much heat. The plastic solids would likely be a problem then.

I didn't see any adverse effect on my Tightbond 3 glue joints. None at all. The boxes are rock solid. Maybe if I wood have soaked the speaker in Wood Hardener, it would have been a problem. But with only 1/16" - 1/8" of penetration, I don't think enough of the acetone gets to the glue before it gasses off. You said you let it soak for about a minute or so - big difference.

Yes, a big difference. I just wanted to see what would happen to the glue I had on hand when it was exposed to pure acetone. At least I have an idea now what the worst case result would be for the two glues I used. The joint tests I'll do will use both the homebrew and the Minwax and will be brushed on not soaked. Also Titebond III may react very differently.

"Rock solid" boxes. I like the sound of that.