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                              Construction Glues
Strong, water-resistant casein glue, which produces joints as strong as or stronger
than most of the common species of wood, is made from skim milk and common
chemicals. Casein glue joints are water-resistant but not waterproof. They will
withstand occasional soaking, but if soaked and dried, they will fail.
                             Tools and Materials
Mixer: paddle and bowl of wood, iron, or other material that won't be corroded
by the alkali in the glue.
Scale or balance
Skim milk
Hydrated lime, [CA(OH).sub.2], also known as slaked lime. This should be a good quality
lime: high in calcium and low in magnesia.
Silicate of soda, also called "waterglass" or sodium silicate. The preferred solution
should have a density of about 40 degrees Baume (Density 1.38) with a ratio of
silica to soda of approximately 3.25 to 1.
Cupric chloride, [CuCl.sub.2] (cupric sulfate, [CuSO.sub.4], also called "blue vitreol" can be
Wire screen or 20-mesh sieve with 0.033" (0.84mm) openings
Cloth for squeezing moisture out of curds
Making Casein Powder
Casein powder is made from skim milk by the following steps:
o    Let the milk sour naturally or sour it by slowly adding dilute hydrochloric or
     sulfuric acid until curds form. The milk will separate into curd and whey.
o    Drain the whey off. Wash the curd by adding water and draining it off.
o    Press the curd in a cloth to remove most of the moisture.
o    Break the curd into small particles and spread it out to dry.
o    Grind the dry curd to a powder and pass it through a 20-mesh screen.
Mixing Casein Glue
                                       Proportions for Glue
Formula 11 (not restricted by patent), U.S. Forest Products Laboratory
                                                   Parts by Weight
Casein (powder)                                           100
Water                                                 150 to 250
Hydrated Lime (powder)                                  20 to 30
Water                                                      100
Silicate of soda (solution)                                 70
Cupric chloride (powder)                                 2 to 3
Water                                                   30 to 50
If hydrated lime is not available, quicklime (CaO) can be used in the following
A mixture of 15.1 parts CaO and 104.9 parts water by weight can be substituted
for 20 hydrated lime and 100 water.
A mixture of 23.5 CaO and 106.5 water can substitute for 30 hydrated lime and
100 water.
When CaO is added to the water, it must be stirred for 15 minutes to get a
uniform slurry.
The bowl and paddle for mixing casein glue should be made of wood, iron, or
some other material that will not be corroded by the alkali in the glue and can
be cleaned easily. All the ingredients should be weighed rather than measured by
volume so that the proportions will be accurate. It is especially important not to
use too much water.
o    Put the casein and water in the mixing bowl and mix them well enough to
     distribute the water throughout the casein. If the casein used has been
     ground to pass through a 20-mesh screen, let it soak in the water for 15 to
     30 minutes before going on to the next step. The soaking period can be
     reduced if the casein is ground more finely.
o    Mix the hydrated lime and water in a separate container.
o    Dissolve the cupric chloride in water in a separate container and add it,
     while stirring, to the moistened casein.
o    Immediately pour the hydrated lime-water mixture into the casein mixture.
     When casein and lime are mixed, large lumps form at first but they break up
     rapidly and finally disappear. The solution becomes somewhat thinner.
     Thorough stirring is very important at this point.
o    About a minute after the lime is mixed with the casein, the glue begins to
     thicken. Add the silicate of soda at this time.
o    The glue will thicken momentarily, but continue stirring the mixture until
     the glue is free of lumps. This should take no longer than 20 minutes.
     If the glue is a little too thick, a small amount of water can be added. If it
     is too thin, start the whole process over again, using a smaller proportion of
Using Casein Glue
The working life of glue is the length of time it stays fluid enough to be
workable. The silicate of soda extends this time. The glue produced by the
formula used here will be usable for more than 7 hours at temperatures between
21C and 24C (70F and 75F). Working life will be shorter at higher temperatures.
Casein glue is fluid enough to be spread by a roll spreader or by hand with a
brush or scraper. Very heavy spreads are wasteful because excess glue will be
squeezed from the bond. Very light spreads can produce weak joints. A suggested
minimum is 29.5 kilograms (65 pounds) of wet glue per 92.8 square meters (1,000
square feet) of glue-joint area.
To obtain good contact between wooden members of a joint, apply pressure while
the glue is still wet. There is not much drying before 15 or 20 minutes. Under
ordinary circumstances, a pressure of 105,450 to 140,600 kilograms per square
meter (150 to 200 pounds per square inch) will give good results.
If casein glue joints are exposed for long periods to conditions that favor the
growth of molds, they will eventually fail. The joints will be permanent only if
the moisture content of the wood is not greater than 18 to 20 percent for long
or repeated periods.
Dry casein can be kept for a long time in a cool, dry place.
Casein Glues: Their Manufacture, Preparation, and Application. Madison, Wisconsin:
Forest Products Laboratory, Forest Service, U.S. Department of Agriculture.
Dr. Louis Navias, VITA Volunteer, Schenectady, New York
Cold liquid glue can be made from the heads, skins, and skeletal wastes of cod,
haddock, mackerel, hake, and pollack. A great advantage of liquid fish glue is
that it remains in liquid form and consequently has an almost permanent working
life. An advantage of using it to make wood joints is that it sets slowly and
therefore penetrates further than other glues before hardening.
Since liquid fish glues are not very water-resistant, a casein or other glue should
be used where water-resistance is needed. Thick fish glues produce stronger joints
than thin solutions.
                              Tools and Materials
Fish heads, skins, and skeletal waste
Large pan for washing fish parts
Steam bath or double boiler
Paddle for stirring
Filter, such as cheese cloth
To make the glue:
o   Wash the fish material thoroughly to remove blood, dirt and salt. If salted
    fish are used, wash them in running water for 12 hours.
o   Once the material is washed and drained, put it into a large container, cover
    it with water, and cook it slowly at a low temperature, about 60 [degrees] C 140 [degrees] F).
    Cooking in an open pot helps to eliminate unpleasant odors in the glue. A
    steam bath or double boiler should be set up so that live steam surrounds
    the pot. Stir the contents occasionally. The length of the cooking period
    varies with the kind of fish material used.
o   Let the cooked mixture settle. Skim off and discard the grease. Pour the
    remaining contents of the pot onto a filter.
o   Concentrate the filtered fluid by slow heating to the desired thickness. This
    is the glue; it can be stored in convenient containers.
o   Take the fish material remaining on the filter and cook it again to extract
    more glue, then repeat the filtering and concentrating.
Encyclopedia of Chemical Technology.
Paul I. Smith. Glue and Gelatine, Chemical Publishing Co., Inc., 1943.
Thomas D. Perry. Modern Wood Adhesives. Pitman Publishing Co., 1944.