Stress-Free Glue Ups:
John Lloyd has top tips for stress-free glue-ups to avoid sticky fingers
A little while ago in ‘Our correspondent’ I had a look at the psychological turmoil that tends to accompany the process of applying glue to pieces of wood, so now it’s time for some more information on glues and some foolproof, sanity preserving strategies for calm, considered and, dare I say it, enjoyable gluing.
When you’re thinking about glue, bear in mind that even the most exotic formulation is likely to only represent a small proportion of the overall material costs for any project, it is also the vital thing that’s going to hold all of those lovingly hand-crafted pieces of wood together. So don’t be seduced by that 50 litre bargain buy, quite apart from anything else, glues have a shelf life, and some of them are remarkably short, so as a general rule, buy the right glue for the job, even if it’s expensive, preferably in smallish quantities. With this in mind, it’s a good plan to add a date to the container as it comes into the workshop, read the label and check for a ‘use by’ date or guidance on life expectancy, it’s usually somewhere between three months and two years! If you’re unsure whether the glue you have is still going to cut the mustard, you could always do a test glue-up on a couple of pieces of scrap, just prepare the surfaces, glue and cramp, then try to split the joint along the glue line with a chisel; if it makes a clean break right along the glue line, the glue has failed, what you want to see is a nasty splintered mess where the wood breaks around the glue line – as it says on the bottle, the glue should be ‘Stronger than the wood itself’. If in any doubt, bin it and buy some more, the prospect of glue failure is just way too traumatic to even contemplate.
You may have your favourite, general purpose glue that you’ve used for years, you might enjoy the clinical precision of weighing, combined with the ‘custard making’ process, required to prepare a ‘UF’ glue like Cascamite, you might even be seduced by the romance of mixing and heating animal glue, all of these options have their place, but remember, there’s actually a reason, beyond the commercial appetites of marketing departments, that there are so many different types of glue. Some glues are better at doing things than others, they have various properties, they might be water based or solvent based, there will be wildly different open times and set times, some will be gap filling, others will creep, temperature sensitivity can be vitally important, ‘White’ and ‘Yellow’ glues generally don’t like the cold but set worryingly quickly when it’s hot, some are only for internal use while others will happily resist the rigours of an Arctic, seawater environment.
There’s a D1 to D4 ‘Durability’ classification, indicating how waterproof a glue is, but I find that other properties that are signified by this classification are more important to me as a furniture maker. If I want a glue to allow a little ‘creep’ or ‘give’ in a joint, I will opt for a D1, but for a stiffer joint, a cross-linking D3 glue would be good. But for any external work, if I really want to avoid sleepless nights, I would use a completely reliable boatbuilding glue like West System epoxy, not a D4 PVA.
I will often use two or three different types of glue for any given making project. Choice of glue might take into account things like, ambient temperature, PVAs just don’t work when it gets cold and set way too fast when it’s hot but otherwise they’re very user-friendly for many unchallenging glue-ups.
A complex assembly needs a glue with a long open time – maybe a UF or even fish glue. A tightly curved lamination in solid wood needs something completely reliable that sets like concrete, perhaps a boatbuilding glue, like West System epoxy.
As new glues come along I occasionally change my preferences for specific gluing challenges. For a long time I just used Cascamite when laminating strips of solid wood, this is a glue that has endured a bit of an identity crisis changing from ‘Cascamite’ to ‘Extramite’ to ‘Polymite’ and back to ‘Cascamite’ again, another fine piece of work by the marketing department. UF glues don’t ‘creep’ and are strong enough to hold boats together so they must be the perfect choice for laminating chair legs mustn’t they? But UF glues aren’t good for your skin, the powdered glue and the water need weighing accurately, there’s always the chance of mixing too much or, worse, too little and if moisture has got into the powder while it’s being stored it won’t set properly, in short, it’s a great glue that’s very strong and has a reasonably long open time but it has a long set time and can be a little bit of a pain. Recently we’ve been trying Titebond ‘Extend’ for solid wood laminating with excellent results. I wouldn’t use it for laminates under large amounts of tension or general gluing duties around the workshop, it’s just a bit ‘gloopy’, but for general laminating, and if you need a bit more time, this is pre-mixed, water washable, stress-free happiness in a bottle.
Another excellent UF glue is the version that’s a pre-mixed resin with a powder hardener. It’s an expensive glue with a short shelf life, but it’s possible to control the set time with the quantity of hardener used, and it doesn’t add any water to the surfaces being glued, this can be a huge benefit if you want to avoid problems with wood expanding during the gluing process, perhaps when assembling and pressing very thin laminates, it’s still water washable though, making it really user friendly.
Epoxy is an impressively muscular glue, but accurate mixing, long set times, unpleasant fumes and the risk of causing skin problems mean that this is not a glue that I would want to be using on a daily basis, but for a mighty glue that can fill gaps and maintain its remarkable strength across the glue line, this can sometimes be the only real choice.
Polyurethane is another glue that I find is not particularly pleasant to use, famous for the ‘black finger’ effect although this can be avoided by wearing gloves or can be removed with acetone. Generally it doesn’t mind the cold or the wet, so sometimes it’s appropriate, but it always needs cramping because it foams and expands as it cures.
At the end of the day, the easy glue choice is always going to be a ‘PVA’, whether it’s a ‘white glue’ or a Titebond aliphatic resin, but don’t turn your back on the other glues, and don’t be frightened to use several different glues on one project, an informed, considered glue choice will often be the key to controlling stress levels.
Having chosen your glue, you need to consider getting it onto the wood with some degree of control. How much glue? First, take your guidance from the label on the bottle, the people who make the glue generally know most about how it should be used, if they suggest a ‘heavy spread on one surface’ it’s probably unwise to think that you know better. However, if there’s no instruction to the contrary I will generally go for a reasonable spread of glue on both surfaces – the last thing I want is glue starvation, I always want to see that comforting line of glue squeeze-out along the joint. Moving with calm, but swift, precision is what you’re after and the correct choice of applicator will help with this endeavour. For small areas I quite like those little disposable brushes that come all the way from Taiwan, but the bristles, which are far too long and floppy, need a trim with a pair of scissors to stiffen them up. If you know anyone in the medical profession, see if they can supply some tongue depressors, the plastic ones are best but they seem to have mainly switched to wood, NHS cost-cutting seems to even be affecting the woodworking industry now! Gluing biscuits, obviously not the chocolate variety, can be a bit of a time-consuming fiddle. A Lamello dispenser will get the glue into the slots quickly and efficiently, although Swiss engineering does come at a price. For larger areas, a roller is a great option, the cheapest of these will be a small roller with a gloss-paint, foam sleeve, or there are rubber rollers with gravity feed hoppers. Don’t even think about the Lamello pressurised system unless you’ve just won the lottery though.
With the glue and applicator selected, all we’ll need is a cunning plan for stress-free cramping.