LumberJocks

methods of work #43: Making liquid hide glue

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Blog entry by Loren posted 05-21-2018 11:27 PM 615 reads 1 time favorited 4 comments Add to Favorites Watch
« Part 42: Cutting dovetails using a bow saw part 1 Part 43 of methods of work series no next part

I’ve been running tests for veneering with liquid hide glue I make myself from granules. I’ve also used hot hide glue for veneering and I like it a lot but its short working time imposes some limits. Liquid hide glue can be made by adding other stuff to hide glue and cooking it. I used salt.

One recipe I tried involved 2 parts glue, 3 parts water and 1 part salt. This recipe didn’t work out very well for veneering, though the glue produced has some useful characteristics. It is fluid, even runny at room temperature and it has a high initial tack so the veneer doesn’t shift around. Unfortunately it also soaks into the veneer excessively and causes excessive veneer expansion which results in adhesion problems away from the edges. It didn’t cure well in the press though perhaps I pressed it too long resulting in dry edges and a wet center. I think it would be a good glue for rubbed joints. The recipe I followed suggested adding salt after letting the mixture gel overnight and this also caused problems because the salt crystals didn’t dissolve thoroughly after being cooked for two hours twice over and cooled in the refrigerator in between. I strained the salt crystals after the second cooling.

The second liquid hide glue recipe I tried worked better for veneering. It uses a lot less salt and I dissolved the salt in hot water first. I added the hide glue to the water which is a mistake. It’s better to add the water to the hide glue because any moisture in the jar will cause glue crystals to stick to the sides where they won’t dissolve and will either have to be wiped out or pushed down into the water with a rubber scraper. Pouring the crystals into the center of the jar using a funnel may also prevent any from sticking to the sides.

The second recipe produces a thicker glue that is not usable at room temperature. It can be made liquid by placing the jar in a hot tap water bath for a couple of minutes. The recipe is 1/2 cup hide glue granules, 2 tsp salt, and 1/2 cup water. After the mixture sits overnight the glue was cooked (like hot hide glue) for 2 hours and then cooled in the refrigerator and cooked again afterwards to dissolve any remaining crystals.

The second glue worked well for adhering veneer to MDF in a screw press. I tried overnight pressing and a 3 hour press time and both test pieces showed good adhesion.

The salt acts as a preservative and it stands to reason that adding more salt makes the shelf life longer in addition to decreasing its working temperature.



4 comments so far

View Rich's profile

Rich

3880 posts in 790 days


#1 posted 05-22-2018 12:30 AM

I like your blog series. Very informative. I’ve been making my own LHG for a couple of years now. You’re wasting your time with salt. Here’s a tip: look at a bottle of Old Brown Glue or check Patrick's web site. Ingredients are hydroyized collagen and urea. You want to be using urea, not salt. There’s a world of difference in the results.

The trick is getting the right viscosity at your working temperature. I like it to be about the same as PVA glue. Of course as it gets warmer, the glue gets thinner. I did two blog posts here and here (the second one shows my setup for cooking the glue) on my efforts to alter the recipe for the warmer summer months here in Tucson, however, in the long run I find it’s more practical to regulate the working temperature of the glue than to mess with the recipe. I keep mine in the fridge and put it in a container of water to get it ready to use.

You got the cooking process right. Two hours at 140º, into the fridge overnight and then two more hours at 140º. The temperature is pretty important.

Beyond that, all that’s left is getting the recipe right. Glue, urea and water — but in what amounts? That’s the fun part.

P.S. For veneering, one trick is to put the bottle in very warm water. It will get almost as

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View woodbutcherbynight's profile

woodbutcherbynight

5697 posts in 2609 days


#2 posted 05-22-2018 03:57 AM

Okay so what kind of urea? In diesel engines they are using pig urea as a additive for emissions reasons. Who came up with that I have no idea.

Can I just pee in a bottle, boil it off a bit and that works? My wife has alot of cats, bet with some work I can get them to pee in a collector.

-- Live to tell the stories, they sound better that way.

View Rich's profile

Rich

3880 posts in 790 days


#3 posted 05-22-2018 04:10 AM


Okay so what kind of urea? In diesel engines they are using pig urea as a additive for emissions reasons. Who came up with that I have no idea.

- woodbutcherbynight

LOL. OK, one of the stories about how liquid hide glue was discovered was that a disgruntled apprentice peed in his master’s hot glue pot in an act of rebellion. Is it true? Who knows? Probably not.

Here’s the urea you’re looking for though: https://www.amazon.com/gp/product/B00H9U3FJM

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View Loren's profile

Loren

10477 posts in 3848 days


#4 posted 05-22-2018 04:52 PM

Thiourea can be used as well.

I found this somewhat scientific guide to adding “gel suppressants” to hide glue to extend its open time. In the case of veneering I want it to gel, which means that it has to be heated at least a little so it gels when it cools. The curing comes from air exposure while the gel holds it in place after removal from the press.

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