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Gluing of wood implies permanently joining several workpieces to improve technical or optical properties.
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Term |
Definition | |
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period of maturing (swelling) |
1 period from mixing or stirring solid glues with the gluing liquid (also period from mixing the components of a multi-component glue) to reaching a workable condition | |
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solid content |
non-volatile portion of glues which remains after the volatilization of the solvents or which is forming during hardening by chemical conversion | |
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extenders |
substances which are added to glues to improve the joint stability or to lower the glue costs; they have a bonding power of their own | |
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fillers |
substances added to the glues to reduce the glue costs (no inherent bonding power) | |
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pot life |
period from preparing the glue mix or from taking the glue out of the packing to the time the glue remains workable | |
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waiting period |
period for keeping the parts to be joined at room temperature between glue spreading and applying pressure on the glued joints | |
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open waiting period |
time between glue spreading and putting the parts together |
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closed waiting period |
time between putting the parts together and loading the pressing facility | |
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gluing temperature |
according to the processing temperature we distinguish between: | |
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cold gluing at 10...30 °C |
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warm gluing at 30... <100 °C |
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hot gluing at a 100 °C |
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Property/Operation |
Glutin glue |
Casein glue |
PVA glue |
Urea-formaldehyde glue | |
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swelling period |
10...90 min |
30...60 min (period of maturing) | | | |
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melting temperature |
>30...40 °C | | | | |
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solid content |
20...50 % |
30...40 % |
» 50% |
60...70 % | |
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pH value |
5.5...9.0 |
10.0...14.0 |
4.0...5.0 |
7.0...8.0 | |
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moisture content of wood |
4...10 % |
4...10 % |
8...12% |
8...12 % | |
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pot life at 20 ºC | |
4...12h | |
according to the kind of glue and hardening from 30 min to several hours | |
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open waiting period at 20 °C | |
5...10 min |
5...30 min |
according to the kind of glue and hardening from 5 min to several hours | |
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spread |
150...170g/m2 |
180...250g/m2 |
150...220 g/m2 |
80...150 g/m2 | |
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pressure |
0.6...1.2 MPa |
0.5...1.0 MPa |
0.1...1.2 MPa |
0.6...2.0 MPa | |
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pressing temperature |
10...50 °C |
10...100°C |
20...50 °C |
20...90°C | |
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pressing time |
2...4 h |
cold 2...4 h |
10...60 min |
0.5...4h at 20°C | |
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storage ability |
dry rooms at 65 ± 5 % relative air humidity for prolonged storage |
4...6 months when kept airtight |
several months in tightly closed containers |
liquid: 3 months, powder: 12 months at 20 °C each |
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application |
construction of chests and frame furniture, assembly gluing, for veneering with warmed-up press plates |
making of joinery structural elements, repair work, for veneering |
in furniture construction, window, door and interior work, gluing wood and plastic material together, for veneering |
construction of furniture and frame furniture, interior work, construction of windows and doors, for veneering, for all kinds of repairs |
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Hints for use | |||||
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glue selection |
water-soluble warm gluing |
water-soluble cold or warm gluing |
water resistant cold or warm gluing |
like PVA glue | |
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glue preparation |
initial swelling, melting at = 70 °C; addition of water influences spread-ability |
dissolve powered glue in glass or porcelain vessels |
ready for use as delivered |
Either mix glue and hardener solution in the ratio specified or make both available in glass or porcelain vessels. | |
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preparation of the workpiece |
warm up the surfaces to be glued; warm up and wax the press plates when veneering on Oat workpieces |
for warm gluing like glutin glue; for cold gluing just lay out the work-pieces |
like casein glue |
like casein glue; make sure to label the vessels for glue and hardener (danger or mixing up) | |
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glue spreading |
by means of a brush or roll spread the glue rapidly, uniformly and thin on the two surfaces to be joined |
like glutin glue |
like glutin glue |
When applying the mixing technique, spread as described for glutin glue; otherwise coat one of the surfaces to be joined with glue, the other one with hardener. | |
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pressing of the glued joint |
join the parts coated with glue by means of a screw clamp; put flat parts together with the heated press plates into the hand screw press |
for warm gluing like for cold gluing press use cold press plates, |
glutin glue; plates are not if need be |
absolutely necessary, | |
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Kind of mistake |
Description of mistake |
Causes of mistake |
Elimination of mistake |
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glue bleed-through |
bleeding of the glue through the pores of the face veneer |
glue unsuitable or too thin, insufficient addition of filler or extender, thin or coarse-pored veneers, excessive pressure, excessive pressing temperature, moisture content of the wood too high |
If glutin glue is used, wash out with bronze wire brush and warm water (add oxalic acid, if required. Wash out PVA glue immediately after veneering, otherwise not possible any more. |
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discolouration |
colour changes caused by chemical processes between wood components and substances added to the wood during working |
wood with high content of tanning agents, hardener vapours, excessive pressing temperature |
Wash out iron discolourations (blue) with oxalic acid, eliminate discolourations to the red caused by high pressing temperatures by cooling the workpieces for several minutes after pressing. |
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visible and invisible bubbles and similar |
Poor gluing as bubble is visible immediately after pressing, invisible bubble is visible only after contact with moisture. |
insufficient or uneven glue spreading, insufficient pressure, exceeding of the open or closed waiting period, wood too dry, pressing times too short |
Cut open and glue again the - defective spots, if number and size of the poorly glued spots allow this. |
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uneven spots and similar |
thickness differences on the veneered workpiece |
uneven glue spreading, improperly made cores, joints in cross-band veneer, cross-band veneers or face veneers lying one above the other |
hardly possible |
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warping, distortion |
deformation of panel-shaped workpieces in the plane |
one-sided veneering of base material, different moisture of the coating material used |
hardly possible |
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marking of veneer joints | |
use of inaccurately joined veneers, poorly glued veneer joints, excessive veneer moisture |
hardly possible |
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loosening of the glued joint |
gluing destroyed or not achieved at all |
preheating temperature of the parts to be glued too high; misfitting of the parts glued; moisture differences of glued parts |
not possible |
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insufficient stability of the glued joint | |
gluing of uneven surfaces; gluing of dirty surfaces; use of dowels made of unsuitable wood, uneven glue spreading insufficient preheating of the surfaces to be glued |
not possible |
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marks |
base material shows through the covering material |
high pressures when gluing thin sheets on frame elements, use of highly viscous glues for gluing thin hygroscopic sheet materials on frame elements |
not possible |
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waviness of the surface |
deformation in the plane of sheet materials |
processing of improperly made sandwich panels with solid wood core, excessive pressure during processing of sandwich panels with hollow core |
not possible |
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