Thread: Questions about Hide Glue

Hi Silent...wondering where you bought you glue from ?

This is after a couple of days. It was quite hard to break apart but the glue failed not the wood (which is cherry).

Is this what you would expect or what am I doing wrong?

I would have expected to see torn wood fibres.

1. Where did you purchase the glue? - There are many different strengths of HG, the poorer often being sold by less reputable establishments.
2. Did it smell oddly sweet, or slightly rancid? - If the pearls smelled 'off', the glue could be old stock.
3. What temperature did you heat it to? - If the glue was over heated, it would have lost some strength.
4. How runny was the glue when you applied it? - If the glue was too dilute, it would have lost some strength.
5. Did you clamp the pieces of cherry, or was it just a rubbed joint? - If the joint wasn't clamped or rubbed sufficiently, the joint could contain too much glue which is not optimal.

Originally Posted by Woodwould

I would have expected to see torn wood fibres.

1. Where did you purchase the glue? - There are many different strengths of HG, the poorer often being sold by less reputable establishments.
2. Did it smell oddly sweet, or slightly rancid? - If the pearls smelled 'off', the glue could be old stock.
3. What temperature did you heat it to? - If the glue was over heated, it would have lost some strength.
4. How runny was the glue when you applied it? - If the glue was too dilute, it would have lost some strength.
5. Did you clamp the pieces of cherry, or was it just a rubbed joint? - If the joint wasn't clamped or rubbed sufficiently, the joint could contain too much glue which is not optimal.

Thanks for the response:

1. The glue is newly purchased U Beaut Pearl Hide Glue

2. Very slight leather smell, neither sweet or rancid

3. Heated in a wax pot at setting 4. It was newly mixed I set the pot at 4 and used the glue as soon as it got to temperature.

4. Consistency of warm treacle

5. It was just a rubbed joint. I used lots of glue and rubbed it well.

I was also surprised that it took so long to set, It was rubbery for a few hours and I could have pulled it apart quite easily. I expected it to achieve a reasonable strength within a few minutes.

I'm heating it up again now and I'll have another go. The glue has been in the fridge in the meantime (which wasn't real popular with SWMBO).

I'm guessing the problem may be in the temperature of your glue. Have you tested the actual temperature of the glue whan at 'setting 4'?

It would pay to borrow SWMBO's jam thermometer or buy one of the cheap digital culinary ones off eBay to graduate the temperature of your wax pot accurately.

Incidently, I recently passed on a photo of the dial setting of my wax pot to someone else with an identical pot and after many frustrating days of mucking about with it, their dial setting ended up being significantly different.

I have huge respect for Neil (U-Beaut), but i don't concur with his temperature recommendations (unless he sells some sort of HG I haven't come across before). HG should not be heated above 60° C (140° F); it degrades fairly rapidly once heated above this figure. Actually, it would be interesting to know what gram strength Neil's HG is for the record too.

I just tried again at setting 5 and I can rub the surplus glue off the wood with my finger as if it were candle wax, that's after half an hour or so. The glue in the pot had a 'skin' on top that I stirred in before I used it, so I don't think it is too hot.

I don't have a thermometer. Is it so critical? I thought in the old days the glue pot just lived on the workshop stove with occasional top ups of water or glue as necessary.

it just occurred to me that my mercury room temperature thermometer can handle that. The glue is at 70 C.

It all sounds OK. I think we need to establish what strength of glue it is.

Yes, in the old days, I kept my glue hot on a stove, but it took me a while to learn the best position on the stove so the heat of the glue didn't fluctuate too much with the ferocity of the combustion within the stove.

Colour and consistency are the clues to optimal glue condition which are learned with time.

How quickly should it go hard? That's what puzzles me. The surplus glue on the sample I glued a couple of hours ago by now is still rubbery, about the strength and consistency of a jelly baby.

HG sets in two ways; it initially gels as it cools down (its major asset in woodworking), and then it dries by absorption of its moisture by the surrounding wood. If it's a thick glue joint, then it will take some time to fully dry. The moisture content of the wood should be taken into consideration too.

Depending on what I'm working on, I sometimes unclamp edge-glued boards etc. within twenty minutes, but I wouldn't think of working them until the following day. Ditto M&T joints; I often unclamp a chair after thirty minutes to an hour, just so I can use the clamps to glue-up another chair, but I'll ensure the first chair is sitting perfectly level and square and I won't touch it again until the following day.

HG never fully hardens (unless it's been centrally heated) which is what gives it such longevity - its MC is at equilibrium with the surrounding wood.

I can't give you a definitive answer to your drying question, but HG doesn't go off like PVA, yet it's workable within a reasonable period of time.

Originally Posted by Woodwould

HG sets in two ways; it initially gels as it cools down (its major asset in woodworking)

Why is that the 'major asset'?

If it is disturbed whilst setting does it re-bond, or is it like normal glues that are useless if they are moved between going off and setting?

It sounds like my sample is behaving pretty much as you'd expect. The squeeze out is rubbery but the bits in close contact to the wood are fairly hard. Maybe because the cherry is quite hard and the tight grain doesn't absorb moisture too well the glue is failing rather than the wood.

Thanks for spending so much time on this, I suspect a few people are curious about HG and will be interested. I have a table base ready to glue up and I'm wondering whether to use HG or stick with the tried and trusty until I get a bit more confidence.

The trouble with PVA and other glues is they aren't sticky. HG is exceedingly sticky and moments after application, it gels, thus providing a degree of hold until it dries and attains full strength. It's a huge asset which no doubt you will appreciate in due time.

Once HG cools and gels, there's no point trying to bring two surfaces together to form a joint. If this happens, just wipe it off with a hot cloth and start again.

I think you may be expecting HG to perform as PVA etc., but I would certainly recommend it for your table if it's something you care about and have put precious time into making.

I first started using HG about 2 years ago. Up until then I had used PVA exclusively. As I worked more and more with fine woods I found the problems of PVA, lack of taking some finishes and inability to easily repair and take apart, were more and more troublesome. I use two different strengths of HG, 192 and 251. I don't use the pearl or flakes or anything other than high quality gram strength labeled HG from a reputable source. I don't want to talk about how I learned that!! I Some of the other things I had to learn the hard way:

1. Don't heat HG over 240F.
2. Don't dilute it too much for use on wood, using the watery stuff on paper is fine.
3. If the squeeze out looks like cottage cheese when I first apply the clamps it was probably too cool when I clamped.
4 Squeeze out is best removed after the HG has gelled because then it rubs off like rubber cememt.
5. I mix the 251 at 7 parts glue to 1 part urea (I measure by dry volume rather than by weight, which many say is wrong) so I get plenty of working time. I just cover the dry mix of HG and urea with water and let it set in the refrig for a couple of hours before the first heat. I mix up about 8 ounces at a time in a glass jar. I mix the 192 with water only, it doesn't gel as quickly and I use it to veneer.
6. After the glue is heated to 240F, I adjust the mix by adding water to get the proper consistency, i.e. it runs off the brush nice and fluid and creates a 6 to 8 inch tall steam above the pot.
7. I stir the glue with the brush each time before I apply it.
8. I cover the glass jar with a screw on lid after each use and store it in the refrig until the next use, if I notice mold or a "funny smell" I pitch it. I have kept it for nearly a year this way.
9. End grain and burned long grain don't make for strong joints.
8. I keep a lid on the pot so I don't have to add water as often in the day.

Originally Posted by BilWil

1. Don't heat HG over 240F.

I presume that's a typo and you meant 140F?

Originally Posted by BilWil

5. I mix the 251 at 7 parts glue to 1 part urea (I measure by dry volume rather than by weight, which many say is wrong) so I get plenty of working time. I just cover the dry mix of HG and urea with water and let it set in the refrig for a couple of hours before the first heat. I mix up about 8 ounces at a time in a glass jar. I mix the 192 with water only, it doesn't gel as quickly and I use it to veneer.

192 gram glue by its nature has a naturally longer open time than 152, but is somewhat weaker. By adding urea to the 152 to extend the open time, you also decrease its strength, so you probably end up with weaker glue than 192.