Hide glue: zero open time?

[Bill Hicklin]

WTF?

I use HHG only sometimes, for certain joints (neck/body, bridge, fingerboard) but go with AR the rest of the time so I don't often fire up my Proctor-Silex "glue pot", and I'm still using the same can of Behlen's hide glue I bought sometime in Nineties.

But today something bizarre happened- even though I had a solid reading of 148 F (glue, not water bath), the glue was already gumming up before I even finished applying it! Needless to say, the joint failed, and I can't for the life of me figure out what went wrong (except, possibly, not using enough water with this batch).

Any ideas?

[Peter Wilcox]

Cold ambient temperature? Did you heat the wood before applying, if cold? Maybe old glue could cause this - I don't know.

[Barry Daniels]

I would add some water and reheat. If that works, well then there's your problem.

[Alan Carruth]

Hide glue gets thicker as it ages, which speeds up the gel. This also makes it weaker.

Most proteins start to denature rapidly at around 140 F. That's why you try to heat things up to that temperature range fairly quickly when you cook them; above that point bacteria have a hard time surviving for any length of time. Heating it to 145F, as it says on the can, will more or less prevent mold and bacteria from getting going in it, but it also breaks down the glue pretty quickly.

Hotter glue is thinner, of course, and takes longer to gel, all else equal. If you mix it in the proportions that the can says to you might well need to get it that hot to thin it out enough to work well. The question is why you need to make it that thick in the first place.

What counts in the joint, as far as I can tell, is how much glue ends up between the pieces of wood when it's dry. Ideally you want very little: just enough to be sure that there's some in between the highest points of a surface that's irregular at some scale. That would argue for mixing the glue rather thin, with more water. OTOH, if you mix it that thin it's possible to end up with a 'starved' joint by over heating or over clamping. I know there are people who don't believe in starved joints, but they just haven't made one yet.

Clamps are used to pull the parts in and expel excess glue. You use heavy clamping pressure when the parts are not well fitted (or warped, as might happen in case work) or the glue is unavoidably thick. When the parts fit well you can use other means, such as rubbing the pieces together, to work out the excess glue, and dispense with clamps entirely. I use such rubbed joints all the time for violin and archtop plate joins, and have had very little trouble. This doe not leave a thick glue line when properly done; in fact, it can be nearly invisible. There are poeple who use rub joints to attach bridges: I have not tried it yet.

We tend to work with thin pieces and make them fit properly, so heavy clamping pressure is not really necessary or appropriate in general. In that case, mixing the glue thinner works better, and with more water in the mix you don't need to heat it up as much to get the proper consistency or a long enough work time. So long as you keep the glue refrigerated when not in use, and mix smal batches that you can use up before they mold the lower temperature is not a problem.

I usually mix by eye. I put in glue to half fill a baby food jar, or a little less, and add cold water to fill the jar. This is allowed to soak until the glue takes up the water, and then heated slowly to my working temperature of about 120F. Some people say that you get a stronger joint if you then refrigerate the glue, and only use it after reheating. Works for me.

[Dennis Weaver]

This is what I do but I am not well experienced-

I put one part granules and two parts water in a can or wherever for at least a few hours or until overnight if I don't need to glue yet.

I heat until the 150 degree area. Stewart MacDonald guy says you can heat higher and my pot will heat higher fast with the lid on it. Hold Heet glue pot now instead of pot of water on stove.

Consistency- It should run off the brush in a stream, not like water but like a stream sort of.

If I am gluing a part on I heat it up a little first to give more glue time.

If scared the joint didn't work put a heat gun or something on it after- til you see a little liquid glue emerge in case it gelled up and got cold and didn't work.

Interesting how some like drips but not streams. Interesting old and new (probably an error on new label) LMI Glue instructions. (See two images below) I switched to Behlen's anyhow.

I don't do reheated glue but probably could. Well maybe reheat the same day. Jose Oribe in his book said he threw away the unused glue at the end of each day.

I know when kept on heat it loses moisture and needs water added. Prob. best to pull plug when you got the immediate gluing done.

Any comments on my procedure? It is still being learned here! I have yet to glue binding on with it! I need time with that and use rubber bands and Titebond.

[Bill Hicklin]

Must have had it too thick- I did as Barry suggested, added more water and reheated, and it was fine the second time round. My tipoff the first time should have been that it was more like corn syrup in consistency, rather than runny and drippy (I usually make rather a mess with the stuff).

I think my mistake was letting it soak in an uncovered jar-- too much water evaporated.

[Dennis Weaver]

I think my mistake was letting it soak in an uncovered jar-- too much water evaporated.

Thanks for the idea of covering the jar.

[Todd Stock]

The higher the gram strength of the glue, the higher the gel temp, and once hide gels, there is no hope of squeezing hard enough to thin the glue line enough to avoid a weak joint. The solution is to keep the glue above the gel temp (about 95 degrees F for 192g and about 115 F for 315g) until pressure is applied to close the joint. The best strategy is to work very quickly, allowing the glue (at about 145 F out of the pot) to locally warm the work enough (glue dumps heat into work) to keep it above gel temp. That strategy is also the most challenging for newer hide glue users or for work where several surfaces need to be joined and aligned during a complex joint closure (e.g., neck block on a cutaway guitar).

Some other strategies are:

- Warm the components prior to glue-up: This adds heat to the joint as the components cool to keep the glue line above gel temp longer. A Salton plate warmer (us greybeards will recall them from 1950's/1960's pot lucks) available on Ebay for bargain prices) works well, or even a foil-lined box with incandescent light bulb warmer can be used to warm parts. Avoid over-warming...you want 180 degrees or less for bridges (hotter risks cooking resins out), neck blocks, etc., and keep in mind that the larger and denser a component is, the longer the joint will remain above gel temp.

- Add heat after assembly: For braces, linings, and other assemblies where a heat gun will be effective in re-warming the glue line, gentle heating applied with a heat gun or good-quality hair dryer extends gel time, or can rewarm a joint which has gelled to liquid. This technique is particularly valuable with linings, where reverse kerf lining in particular can be difficult to wet out, place, and clamp before the glue gels. I use modified wooden spring-type clothes pins to clamp, then rewarm with a heat gun...when I see squeeze-out, I clean up with popsicle stick glue cleaner and paper towel dampened with 140 F water.

Both strategies - adding heat to components prior to glue-up and adding heat after - become less important as speed and accuracy are developed, or where the workshop can be kept at a higher temp. On some jobs, I always warm things - neck and tail blocks, bridges, and fretboards always seem to do better if they are pre-warmed, and as I always use 315g on bridges, the 5-7 minutes of open time I see with a 160 degree rosewood or ebony bridge allows me to get both primary and secondary clamps on the joint well before it cools to 115 F.

Finally - think about using a heat gun prior to glue-up to bring plates and other larger assemblies up to a temp above the gel point of the glue...especially when operating in a cool shop. I keep a heat gun at hand when doing any glue work - helps when you realize that the back graft is 1/16" shy of clearing the neck block during a box close...

[Randy Roberts]

I've found one or two 500 watt shop lights on stands to be invaluable in both pre-warming the parts, and the immediate work area whenever using HHG.
Cheap point and read laser temp. sensors from Cen-Tek and others, available at Harbor Fright,etc. are quick and remarkably accurate, and also have been very useful.

I'll second Todd's suggestion of post warming with hot air gun for thin material glue ups like linings. I have glued up 3 ply solid linings several times by applying the HHG to the entire lining, then fitting the lining to the side (obviously the HHG has gelled before this is completed), clamping, and then warming with the gun. As the glue and wood reaches liquefying temperature, it's very obvious, as the HHG squeezes out allowing the clamping pressure to squeeze the wood surfaces into good contact. I would not expect this to be a good idea with thicker parts, as getting uniform warming to the deepest areas would be unpredictable, but for linings, etc. it seems to work well, and takes the time pressure out of the equation.