Gluing
Today there is a huge variety of chemical glues available, some for general purpose bonding others for specific types of bonding.
In the restoration of antique and valuable furniture however these products are rarely used as a professional restorer will undoubtedly rely on natural glues, especially animal glue, a glue type already used by the late Renaissance that ensures a good bond for both the gluing of joints as well as veneer.
The only drawback of this glue is the poor resistance to humidity (hot and humid), which often causes the detachment of pieces.
Following is a list of the most used glues with their most important characteristics.
[bullet_list icon=”play” indent=”10px” style=””]
- Colla Animal (or carpenter’s glue or hide glue) – as stated above is a glue of animal origin, can be found in the form of beads, tablets and powder, it is sensitive to humidity and heat, but it has the advantage of being reversible in fact pieces can simply be heated to cause them to disengage.
(Reversibility is a very important feature in restoration).
As it is not a ready to use glue it is necessary to prepare it first by “cooking it” in a double boiler, proceed as follows:
- Place a few spoonfuls of glue beads in a small pan (not made of iron), covered with water and let stand for 7-8 hours. At this point if the glue has absorbed part of the water and is softened, it is ready to be dissolved in a double boiler (if the glue is not in beads but in tablet, it will need to be crushed and put in place in the pan according to the amount required, the rest of the procedure is identical to the glue in beads).
- Take a large enough container to hold the pan, fill it with water and bring to a boil, then take the pot with glue and dip it in the bowl, wait until the glue melts. The glue should have a syrupy consistency, if too thick loosen it with a little water, if it is too runny, add a little glue.
- It is applied quickly, while still hot ( when cooled it loses some of its adhesive power), when using for veneering, the glue should be spread on, the plywood placed on top and any air bubbles eliminated by applying pressure to a flat piece of wood or metal and passing it over the veneer itself. The piece should then be placed in clamps. Drying time is about 24 hours.
- The heated glue can only be reused a few times, its adhesion decreases as it ages. This adhesive is of organic origin and consequently, over time it ” goes off” giving off a bad smell, so it is not advisable to prepare an excessive amount.
- Colla Vinyl (or white glue), is a white chemical glue which is quite dense. It is used at room temperature and once dried it becomes transparent. It can be used both for gluing joints and for veneers. Has a drying time ranging from 12 to 24 hours (depends very much on the ambient temperature), the bond is good and durablSome advantages of this glue is the absolute non-toxicity, ease to use and quite economical.
[/bullet_list]
Of the various types of PVA available a brief list of the most useful ones follows:
[bullet_list icon=”play” indent=”10px” style=””]
- Colla traditional vinyl, as mentioned above bonds well, but is sensitive to moisture, in fact it can be weakened by wetting it with water, for example, you can detach a glued piece by injecting hot water with a syringe.
- Colla Vinyl D3, is resistant to water while not losing any of its bonding strength, it is a suitable adhesive for outdoor use and for particularly humid environments.
- Colla Rapid vinyl, is used when rapid bonding is needed, it has a setting time that goes from 10 to 30 minutes (but the maximum grip is reached after about 12 hours).
[/bullet_list]
To get a good grip with these adhesives, it is best to spread the glue on both parts to be bonded.If desired it can be coloured with dyes for water based products:
[bullet_list icon=”play” indent=”10px” style=””]
- Contact Glue (e.g. Prittstick), fast-setting glue, good for bonding veneers on plastic or metal laminates, as well as for Veneering curved pieces. It has a very good grip and good resistance to moisture, it is diluted and cleaned with trichlorethylene. The glue is rubbed with a spatula onto both surfaces to be bonded which are then left to air for 5 – 10 minutes before proceeding with the gluing. It is important to position the pieces well before gluing, since once bonded it is difficult to detach them without damaging the pieces. Super glue or cyanoacrylate, adhesion occurs in a few seconds and it will bond almost anything including fingers. The grip is strong and durable. Suitable for small bonding (wood chips, pieces of plywood). It is useful to have in the workshop.
[/bullet_list]
