Hide Glue

3notes · #1 09-07-2020, 08:58 PM

I was watching a workshop by Dana Bourgeois on youtube. He mentioned that they bumped into a problem with hide glue. If I recall correctly he said the hide glue was failing on torrified(spell check) wood.

Anyone here had problems with hide glue.?? Curious to know.

John Arnold · #2 09-07-2020, 10:56 PM

The main issue with hot hide glue is the short open time. Once the glue is applied, you don't have much time to get it clamped before it gels. Heating the parts or the room helps extend the open time, but not by much.
Gluing torrefied wood with most any water based wood glue can be a problem, simply because torrefied wood is not very absorbent. Wood glue works by being absorbed into the wood; that is what facilitates the curing. Some have reported better results when gluing torrefied wood by clamping the joint for an extended period, up to 24 hours. With 'normal' wood, clamping for 30 minutes to an hour is usually sufficient, provided the parts fit well and don't require excessive pressure to make full contact.

3notes · #3 09-08-2020, 12:19 AM

Quote:

Originally Posted by John Arnold

The main issue with hot hide glue is the short open time. Once the glue is applied, you don't have much time to get it clamped before it gels. Heating the parts or the room helps extend the open time, but not by much.
Gluing torrefied wood with most any water based wood glue can be a problem, simply because torrefied wood is not very absorbent. Wood glue works by being absorbed into the wood; that is what facilitates the curing. Some have reported better results when gluing torrefied wood by clamping the joint for an extended period, up to 24 hours. With 'normal' wood, clamping for 30 minutes to an hour is usually sufficient, provided the parts fit well and don't require excessive pressure to make full contact.

Nice reply. Thanks.

redir · #4 09-08-2020, 08:40 AM

I've been working with Torrified tops lately and torrified braces too. For the bracing I use fish glue and clamp for 24 hours. Fish has a very long open time and a slow cure so I hypothesize that ling period of cure allows the glue to soak into the hydrophobic wood.

I use LMI yellow for the bridge and after a year so far no problem. On the last two I used HHG but I make it a semi-liquid hide glue with the addition of salt. This gives a longer open time. So far those have only been strung up for a few days now so it remains to be seen but I am confident based on some of the tests I have done.

Mr. Jelly · #5 09-08-2020, 09:36 AM

Gelatin or hide glue swells and becomes more liquid with more water. It adheres more as it dries out. The longer it is kept warm and in a liquid state the more it degrades. The protein chains break apart and it becomes weaker and weaker until it will not be sticky or set up at all. Once dried it can be put back into a liquid form by soaking it in water. Warm water or steam brings it into a liquid state faster than cold water. Once dried it is in a stable form that will last forever. I've seen dried gelatin peeled off concrete and take the concrete with it. I produced gelatin for thirty some years.

Alan Carruth · #6 09-08-2020, 01:12 PM

It may be an issue with 'surface energy'.

A lot of the strength of a glue bond is chemical. Back in WW 2 the Forest Products Lab did some work to address glue line failures in wooden aircraft structures. They found that they got stronger bonds when the surfaces were glued within 15 minutes of being worked.

When you remove material from a surface you are breaking chemical bonds; relatively weak ones, to be sure, but still... It can take some time for those open bond sites to pick up something that will make them whole again. Until they do those sites carry small electric charges.

Water is a polar molecule; one end is slightly electrically +, and the other end -. That's why water stays liquid and freezes at a much higher temperature than CO2: water molecules are attracted more to each other. They're also attracted to those open bond sites on freshly worked wood. If you spritz the surface with a light mist of water it will tend to spread out into a film on a freshly worked surface, as the water is attracted to the high 'surface energy' of the open bonds. On an older surface the water tends to bead up, and the angle that the edge of the water drop makes relative to the surface is a measure of the surface energy.

The heat treatment of Torrefaction makes chemical changes in the wood that seem to reduce it's natural surface energy. This would tend to produce weaker glue joints.

I once made a guitar with a mammoth ivory bridge. The information sheet that came with the blank talked about gluing issues in a way that suggested it might have naturally low surface energy. Sure enough, water beaded up on it. Scraping the surface raised the energy usefully, but it didn't stay high for long: I imagine most of the chemistry had already happened in the ground, and it was naturally unreactive, like a wax. When the time came I made sure to have fresh hide glue, warmed surfaces in a warm room, clamps all set up, and I gave everything a light scrape just before slapping on the glue. So far, so good...

I know it sounds 'new age', but it's real.

TomBeltran · #7 09-09-2020, 08:42 AM

Quote:

Originally Posted by Mr. Jelly

I've seen dried gelatin peeled off concrete and take the concrete with it. I produced gelatin for thirty some years.

I once bought a glue chip glass window, which is made by spreading HHG on sandblasted float glass. when the glue cools, it shrinks, pulling chips of glass with it. The treatment makes the window look like it is frosted. When the glass dealer told me how it was made, and I told him I used HHG all the time, he was amazed that it was still used in woodworking.

"They found that they got stronger bonds when the surfaces were glued within 15 minutes of being worked."

I had learned to scrape the wood just before gluing, but as Paul Harvey would say, this must be "the rest of the story." Very interesting Alan.