Adhesives can be used in the initial construction of joints -making joints in wood, for instance – or for repairing things as well as for fixing things like tiles, wallpaper and carpet.
When you use an adhesive in constructional work, choose one which has been specifically formulated for the job. For example, when you make woodworking joints which will have to withstand very wet conditions, you should use an exterior woodworking adhesive rather than the normal PVA type.
When you use an adhesive for repairing things you may not always be able to find one which has been specifically formulated for the materials being joined. As a result glues used in repair work are less likely to give such good results, but, again, modern adhesives can be very good.
Adhesives have a number of specific advantages over other methods of fixing:
- there is no need to make holes for fixings – this is time-consuming and can weaken the materials being joined
- when using adhesive for joining wood there is no need to learn how to make complicated joints
- adhesives can be used to fix fragile things which might be damaged by other methods of fixing
- it is possible to use adhesives in awkward positions where there is insufficient access for screwing and nailing
- mechanical fixings are often difficult to hide successfully, whereas glued joints can be almost invisible.
- But gluing has its disadvantages too:
- although using adhesive is quick and easy, it may take a long time to set properly – often things which have been glued are too delicate to move or use for over 24 hours
- it is not easy to dismantle a glued joint
- some kinds of wood joint, particularly butt joints involving end grain wood, are unlikely to be very strong
- some adhesives will not stand large variations in temperature and humidity without weakening.
Using adhesives
Before using adhesive, read any instructions and precautions which come with it. With most types, once you open the container the adhesive inside starts to deteriorate slowly.
Epoxy adhesives – which you have to mix – have a limited life before they set too hard to use. Fast-setting (often advertised as five-minute) epoxy adhesives have to be used immediately, but ordinary ones generally remain usable for one to two hours. Powder and water-mix casein adhesives should stay usable for three to four hours. With many contact adhesives, once the surfaces are put together they cannot be adjusted.
Where possible, always allow a minimum of 24 hours before putting any load on a joint. Allow even longer if you are working under low temperatures or damp conditions. The following hints apply to most adhesives:
- always make sure that the surfaces to be joined are clean and dry. Grease must be avoided – use a solvent degrcasing agent if any is present. Any wood stored outside should be brought into the house and allowed to stand for at least two days
- clean off any old adhesive by sanding or scraping with a knife
- support the glued joint until it is dry. If possible clamp the joint
- where possible, use adhesives (and allow glued joints to dry) in warm dry conditions – not in a damp cold shed
- always spread the adhesive as evenly as possible over the entire surface to be joined not just a blob here and there
- never use your finger to spread adhesive: use a wooden spatula instead
some adhesives are difficult to remove from skin (like contacts), some irritate (like two-part acrylics) and some are dangerous (like cyanoacrylates)
- never use too much adhesive a thin film gives a stronger bond than a thick one
- when gluing the end grain of wood, spread the adhesive on to both surfaces, allow it to dry and then spread on a second coat for making the joint. Any sanding, sawing or planing should be done immediately before gluing, particularly on oily woods such as teak. If you want to treat wood with preservative, do it two days before gluing. If the wood is already treated with preservative, sand it down immediately before gluing
- in damp conditions, use special exterior adhesives for wood and cither epoxy or cyanoacrylatc adhesive for other materials. Pre-condition woodwork by leaving it for a few days in the damp environment before gluing
- if it has to withstand high temperatures in use, choose an epoxy or acrylic adhesive others may soften when heated. With epoxics and natural glues, the warmer the temperature, the faster they will set and the stronger the bond will be. The converse holds at low temperatures and some may not set properly. Epoxy and contact adhesives will not set at high temperatures
- avoid using woodworking and contact adhesives for making joints which are likely to be under permanent load
- avoid trying to fill gaps with adhesives. If you have to, use epoxies rather than two-part acrylics and PVA adhesives.