PRO-GLUE veneer bond
tips.
Urea Formaldehyde glues have been used since 1942, and
was formulated during WWII for gluing wooden PT boats together. Urea Resins
have a few variations such as dry powder mixed with water, liquid resin with
powdered catalyst, or two liquids that are mixed together. All these glues
have different working properties and are suited for different applications
and different working conditions. Urea Formaldehyde Glues generally have
ridged glue lines, are waterproof, and extremely tough glues that are
permanent bonds, and are relatively easy to use. The fact that they dry so
hard makes them ideal for laminations, veneer work or other applications
that require a rigid a tough glue bond. Large manufactures of plywood and
veneered panels use Urea glues, with and without heated presses. The
addition of heat can dramatically accelerate the cure time, so most
production plants have hot presses that will cure a Urea glue in 5 minutes
or less. Given the cost of a hot press, the formulation of Liquid urea
Pro-Glue was designed to be suitable for vacuum or cold pressing as well.
We have found that this liquid resin with powdered catalyst is the best for
laminations, where the ability to alter the mixtures to suit the particular
lamination need is very desirerable. One of the many features of the liquid
Pro-Glue is a different colored catalyst that can create almost invisible
seams, when the glue color can be matched to the surrounding wood. Woods
such as maple have always been a problem since squeeze through and slightly
open seams become visible with most Ureas or Polyurethane or PVA glues. The
white hardener is the whitest that we have found, making it ideal for
lighter colored woods, and the dark is very suitable for darker woods.
Mixing the two colors will yield different shades of tan, or you can darken
the glue with the addition of an aniline dye that can be mixed into the
liquid before the hardener is added. You will find the Pro-Glue is a little
thicker than other Liquid Ureas, due to the fact that no solvents are added.
The type of alcohol that is added to other Ureas is strong in odor, tends to
darken the glue line, has a strong odor, and will eventually no longer be
allowed in certain states due to its high level of toxicity. The solvents
are usually added to enhance spreadability, penetration, and quicker mixing
of the two components. We have found that mixing Pro-Glue might take a
little longer, and you will occasionally need to apply a thin wet primer
coat over the substrate first, and re-rollering
out a second coat before clamping. I find that an inexpensive, disposable
black foam paint roller or a close cropped carpet roller or a velvet roller
to apply this glue work best. Even after scuff sanding, be aware that
fish-eye or spotting during the rollering out of the glue is caused by
traces of oil, wax, dirt or very dense material and can be usually overcome
by this second application of glue. If the problem remains chronic add a
little (never more than 5%) white PVA glue to enhance spreadability. The
glues pot life can be extended or shortened by the amount of hardener that
you add, but here is the funny thing about that, to EXTEND the pot life, ADD
more hardener, or reduce the amount of liquid resin when mixing. To shorten
the pot and cure time add less than the recommended ratio to achieve this.
There are dried urea crystals in the hardener, which will change the
catalyst to resin ratio, making it an Inverse hardener. Do not add
or subtract more than 20% (by weight) hardener with the resin, or the bond
may be affected. Overall, I have found the glue to work quite well, and I
now use it in creating much of my veneer work in my shop.
In case of eye contact, immediately flush with water. Wash with warm soapy
water in case of skin contact. Use adequate ventilation when mixing and
applying glue.
This product contains formaldehyde, and acid base catalyst that may cause
allergic skin reaction or eye irritation. Harmful if ingested, inhaled or is
absorbed through skin.
Pro-glue is a liquid urea resin that is mixed with a powdered 'inverse
catalyst' hardening agent, creating a hard permanent glue bond well suited
for veneering and laminations. The light and dark powder can be used
separately or blended to tint the glue for approximating different shades of
the wood, making seams, and any bleed-through on thin veneer invisible. Urea
resin bleed through on veneer sands off easily, and will not affect
finishing. Custom glue colors can be created by mixing aniline dye into the
resin prior to mixing it with the powder.
The _ gall resin package is mixed with powder:
One packet (a) of powder to one cup (8 fl.oz) of liquid resin, or 10% powder
to 100% liquid resin by weight.
When the shop temperature is above 75° f. You can use less resin (down to
6.5 fl.oz resin) per packet of powder to extend pot and open face time. The
spread rate is about 10 to 15 square feet per cup of resin depending on the
core absorption rate, temperature and the amount of glue needed to load the
roller. Mix with a wisk or glue mixer for 2-3 minutes until powder is
completely dissolved.
Be sure that the core material is free of dust, burnish marks or waxy
residue. It is a good idea to lightly scuff sand the core with 100 grit
sandpaper to remove any impurities from the surface before applying the
glue.
The mixed adhesive is applied with a brush, notched spreader, or best with a
foam paint roller or a close cropped carpet roller or a velvet roller to
apply. Porous surfaces will need more coats after a few minutes to resemble
a 'good coat of paint' coverage.
Before gluing a large project, run a test sample to determine proper mixture
ratio, core absorption, spreading technique and cure time. Be sure that the
adhesive is spread with an even uniform layer and has no dry spots or fish
eyes. A second application will usually overcome fish eyes, and adding up to
5% pva (white glue) into the resin mixture can aid in spreading the resin if
problems persist.
Clamping pressure needs to be applied while glue is still 'wet'. The room or
wood temperatures should be at or above 70° f so proper curing will take
place. Cover the project with an electric blanket (add a packing blanket on
top) if temperatures drop below 70° f (21° c).
The clamping time varies, depending on the temperature of the room, glue,
wood, the mix ratio, whether you are doing flat panel work, curved or bent
laminations.
Severely bent laminations will require a longer clamp time to avoid joint
creep or spring back.
A small amount of mixed glue placed in a ziploc bag or cup can test clamping
time. When the glue has cured to the consistency of hard rubber, or, can be
removed from the cup or ziploc bag in one piece, clamps can be removed and
the project set aside 12 to 24 hours to fully cure before machining.
Typical clamping times are:
10 hours 65°
7 hours 70°
6 hours 75°
4 hours 85°
2 hours 95°
Applying too much or to little glue, improper ratio, surface contaminations,
low temperature and inadequate clamping pressure can cause delaminations.
For minor veneer bubbles or delaminations, inject polyurethane glue into
delaminated area and clamp for 6 hours. This will fix most problem areas,
and should not affect sanding and finishing.
Pro-glue / veneer bond should be kept closed, stored in its original
container and kept in a cool dry area. Resin stored at 70° f degrees is good
for 6 months and refrigerated resin (40° f) has a potential shelf life of
3-5 years.
More than 70° f will greatly reduce shelf life. Lumpy, thick or discolored
resin should not be used. Catalyst has 10year shelf life if kept dry.
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