GLUE GRADE SELECTION
The proper choice and selection of the hide glue adhesive for the specific application greatly simplifies all gluing and provides fast, efficient operation at maximum economy with consistently strong joints. For most adhesive applications, it is desirable to use grades #135 through #379. For general repair work, grades #135 through #251 are commonly used as the lower ratio of water to glue (versus higher gel strength grades) permits depositing more glue (higher solids) with adequate open time. Glue makes the bond, not water.
For assembly and edge-gluing there are three major groups of hide glue, all providing a wide margin of safety factor and a tensile strength far greater than that of wood itself, and differing principally only in inherent strength, elasticity, and shock-resistant properties.
- For maximum strength and shock resistance
Jelly strength grades testing 315-379 grams
- For average strength and shock resistance
Jelly strength grades testing 192-315 grams
- For non-critical strength and shock resistance
Jelly strength grades testing 135-192 grams
For soft porous woods, principally the conifers, a fairly heavy-bodied adhesive is employed; for dense, non-porous woods, such as maple, birch, and some of the oaks, a moderately thin-bodied adhesive is desirable. This variation in the glue concentration of a given test grade of glue directly leads to consistent gluing results through
- control of the thickness of spread of the adhesive,
- degree of penetration into the wood and proper anchorage of the adhesive,
- holding of the adhesive film at the joint,
- desired speed of set and length of tack of the adhesive at the joint face.
The following table gives average formulations for the various test grades of glue for assembly gluing where wood and room temperatures are in the range of 74-80o F.
Typical Water to Glue Ratios
|Glue Grade (Test in Grams)||Porous Woods (Weight, Water to Glue)||Non-Porous Woods (Weight, Water to Glue)|
|379||3 – 1||3 ¼ – 1|
|347||2 ¾ – 1||3 – 1|
|315||2 ½ – 1||2 ¾ – 1|
|283||2 ¼ – 1||2 ½ – 1|
|251||2 ¼ – 1||2 ½ – 1|
|222||2 – 1||2 ¼ – 1|
|192||1 ¾ – 1||2 – 1|
|164||1 ½ – 1||1 ¾ – 1|
|135||1 ¼ – 1||1 ½ – 1|
The preparation of the warm hide glue adhesive solution follows the standard procedures previously described. The glue is maintained at 135o to 145o F and applied at this temperature for best results.
The following table gives typical viscosity values for solutions based on the percentage of glue content.
Approximate Viscosity in Centipoises at 140o F for
Dry Glues of Given Grade Test and Millipoise Value
|% Glue Content||High Gel 379 Gram 131 mps||Medium Gel 251 gram 92 mps||Low Gel 135 gram 58 mps|
|30||420 }||225 }||69|
|35||1060}||490 }||160 }|
Depending on the tack and set desired, the typical viscosity during use will be 150-500 cps. Rarely would it be over 1000 cps. The three } values are the typical ranges that would be employed for each grade 135, 251, 379. For production-line edge-gluing, where speed of operation is an economic factor, the fast setting properties of a warm hide glue adhesive film with resultant immediate tackiness, holding of the adhesive at the joint face, control of bleeding-in of the adhesive, and fast development of initial joint strength are factors of great value that are unique with hide glue. Considerable latitude in the speed of set and corresponding length of tack is possible with hide glues. For slower speeds of set the lower-testing grades may be employed, or the ratio of water to glue may be increased for the specific glue.