I made a little meditation stool prototype in pine. The dry fit was good, but some swelling during glue up made the through tenon too tight leading to splitting one side. At that point, I was about to take everything apart so that a new side could be cut, but it is my understanding that, once PVA glue has penetrated a joint, you really cannot reglue without scraping back to fresh wood. That’s not possible with housings and through tenons, so I decided to leave it together and accept the crack. (That is, in some bizarrely profound way, appropriate for a meditation stool.)
My question is whether this is a correct understanding of PVA glue?
If so, my slow meandering towards hide glue is going to become a sprint with nearly total abandonment of PVA. Hide glue can be reversed and, I believe, reactivated with nearly full strength. So, had this been made with hide glue, I could have disassembled, fixed things, and moved on. This prototype illustrated that, with PVA, the project can be lost entirely.
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I am not sure that’s entirely correct. If the PVA glue has not yet cured, you should be able to remove it with a wet rag, a chisel, or some sandpaper, depending upon how much it has started to harden. To get the best glue joint, you should sand it down to fresh wood, but I don’t believe that it is absolutely necessary if sanding it down completely is impractical. Just a bit of sandpaper in the mortise or tenon (depending upon which you are keeping) should be all you need. I agree that once completely cured, removing enough of the PVA from the joint without damaging the underlying wood will be a real pain, and may not be practical in some cases.
Also, if you are making a new side anyway, you could always cut the new mortise to match the dimensions of the freshly sanded tenon.
I’m also not sure it’s correct to say that cured hide glue can be “reactivated”. Cured hide glue can be reversed with heat and moisture, but once loosened it should be removed if possible. It is more forgiving in that hide glue will bond to a thin layer of hide glue on an existing joint, but even so it will work better on bare wood.
Where dried PVA can pose a problem is with finishes. Even a thin layer can prevent some finishes from penetrating, and sanding it all away can be difficult. Hide glue is more forgiving in that respect. Also, hide glue is more easily reversed after it cures.
Like everything, whether you use PVA, hot hide glue, or liquid hide glue, each type of glue has its benefits and tradeoffs.
@AWESOMEOPOSSUM74 Thanks for the critique. Feedback like that is always helpful. In this case, there’s a reason for what you’re seeing- It is a kneeling stool. When in use, the stool is between the ankles, maybe nearly touching them, and the knees are on the ground. The seat is 14″ wide, several inches narrower than a typical chair. If you spread the legs, then it is two wide for the ankles.
The reason it’s a prototype was to play with these dimensions, especially height and angle.
I thought an angle would be necessary, too, which is why this is a prototype. I placed a bit of scrap wood on top of a rigid ball, about 6 or 7 inches in diameter and sat on it with a large piece of cardboard underneath. My wife then marked the location of my knees, ankles, etc., and measured the angle of the plank. Surprisingly, it was pretty much level. Nevertheless, I expected to need to add some slope after using it, but so far it has been fine for kneeling. Time will tell.
I have rescued loose joints in the past by always having a piece of offcut available to take a few shavings from. If a tenon is loose, take a couple shavings, glue them om the tenon. No one will ever see.
A similar thing applies to dovetails. We would all love to have our dovetail joints come in perfect every time, but, if you do end up with a gap, having a thick shaving to fill a gap does keep a project running, and is very hard to spot. You will know it’s there, but no one else will, and after a year, I bet even you won’t be able to spot it.
Your grasp of PVA glue and it’s non-reversibility is spot on.
The issue with your joint swelling/splitting is one problem,and the advantage that hide glue gives, is that it would prevent the second issue you are having with removal of the adhesive on the joint. Both PVA and hide glue (being water based) will swell a joint somewhat, but hide glue is infinitely reversible. More importantly, it will stick to itself after re-activation, whereas PVA does not.
I have found that using PVA is great for certain items I will never want to take apart again (like a laminated wooden plane body).
Furniture joints are another matter entirely, and using hide glue allows for repairs, as well as corrections should a joint go wonky.
@manic thanks for your thoughts. I’m headed the same route as you- A mixture of PVA and hot hide glue depending upon the task. I just bought an electric glue pot with lid. Do you know what would be the minimum size batch of glue that can be made? It’s a 1 qt Hold Heet pot. Although glue can be reheated many times, why push my luck, so I’d like to make small batches that only need a few reheats before being used up. Any idea?
Unfortunately I do not have any first hand experience with the hold-heet glue pots, although I would love to own one at some point in the future.
I have seen youtube videos of people preparing a smaller batch of glue in a glass baby food container or small mason jar and heating it in that type of unit, but you may have to surround it in a bit of water to prevent the glass from getting too hot.
If you are concerned about making too much at once, you can always pour any unused glue (after the initial preparation) into cheap plastic ice cube trays, let it cool to room temp, and then stick it in the freezer. It allows you to just take a few cubes out when needed and re-heat them. To my knowledge, a freeze-thaw cycle does not affect hide glue’s performance, only overheating does.
On a side note, http://oldbrownglue.com contains lots of information on the preparation & use of traditional hide glue. I have used the bottled glue they sell, but prefer using the traditional stuff, so I’m not making any type of endorsement of their products.
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