For a long-lasting joint that won’t come apart one needs to know how to correctly apply glue. Glue is strong, irrespective of whether it is hide glue, white, yellow or fish glue they’re all stronger than the wood itself. While yellow is commonly known for its gap filling properties it’s actually not entirely true. No glue is a gap filler, for a successful join each joint must be a friction fit with no gaps.
The practice of edge gluing two or more boards to form a panel or a table top has been in practice for several thousand years. Sprung joints aren’t new either and is still widely practiced. The idea of a sprung joint is to form a slight hollow in the middle of the board’s edge so as to apply pressure on the ends to keep them tightly closed during seasonal changes. That’s the idea and it works, but I’ve also edge glued without a sprung joint and as long as the two edges are perfectly straight making perfect gap free contact works just as well. For the sake of time and efficiency sprung joints are a better alternative.
Friction fit joinery
Mortise and tenons including dovetails should be a friction fit requiring only moderate hand pressure. To ensure everything comes together perfectly prior glue up a quick rehearsal is recommended. Some woodworkers like Rob Cosman are confident enough that he never does a test fit of his dovetails as he believes with each fit your loosening the joint which is true, but it is better to side with caution than to find out later you’re not so good after all. No pun intended.
Clamps should only be used to hold a joint together while the glue is drying. If you find that you’re using a lot of clamping pressure to force the joints to close, then you need to reexamine your joinery as to why this is happening prior to glue up. During glue up sometimes you get what is known as glue freeze and usually a light tap with a mallet will remedy this problem.
Best glue up methods
The best form of glue up is bonding long grain to long grain, end grain absorbs too much glue starving the joints creating a weaker bond. Many modern-day furniture and kitchens are made from MDF and Chipboard, applying glue to either end grain or its edges is like not applying any glue at all as the wood (lets humour the mass manufacturers and call it wood) absorbs all the glue so they rely on dowels to keep them together. This too isn’t a good practice either as your relying on tiny little sticks stuck in tiny little holes to hold everything together. For mitre joints you have to apply glue to end grain and there is a little trick that works very well. You allow the end grain to absorb the glue, then you apply some more and allow it to dry enough to form a film then apply some more, clamp it and leave it to set over night. I’ve done this using hide glue as a test and I gave up trying to break it apart so it works.
Don’t be overly concerned on what type of glue works the best, they all work equally well as they’re all stronger than the wood itself. Usually, the company that spends the most on advertising gets the biggest exposure but that’s as far as it goes.
I’m a big advocate for hide glue and have recently become equally enthusiastic about fish glue. I’m a traditionalist in one respect I like to practice ancient methods but I also have a slightly different outlook on these matters to other people. I build by hand while others use machinery, I am of the opinion due to the current rise of automation that in 50 years time there will only be a handful of people building anything by hand, and in 100 years time there will be nothing built by hand. So, my work will be far more valuable after I’m long gone than a piece made by anyone using machinery. If for any reason my work needs to be repaired, I know that the glue I used which is hide glue or fish glue can be reversed, repaired and re glued, while others cannot and most probably no one will ever bother. So, I feel it’s an obligation upon me to owe it to conservationists to continue with this practice of using animal protein glues in all my builds.
Glue is readily available in all stores and is inexpensive other than hide glue. PVA glue has a shelf life of up to 12 months while liquid hide is two years, the granules if keep out of direct sunlight are indefinite and fish glue is advertised as a two-year shelf life but if kept out of direct sunlight in a cool dark spot can run into a number of years. No matter what type of glue you use make sure it’s fresh, there’s no point in using glue that’s gone off and ruining your hard work. I always make a fresh batch of hide glue if I’m going to use it that day and if there’s anything left over, I throw it away. This may sound like wastage but comparing to the price of timber it’s a small price to pay.
Irrespective of what type of glue you use the work needs to be warm, yes you read that right, even if you’re using PVA. In the past their labels read room temperature above 32f and others have read above 65F for a strong bond. I haven’t seen this labeled for a long time on bottles but none the less whether or not they choose to label or omit it nothing has changed. Glues usually takes 12 hours to set but in colder conditions you need to allow 24 hours to pass before you do any work with it. With hide glue I will always allow 24 hours to pass and the same applies to Fish glue. I guess the only real issue I have with fish glue is that the glue line reactivates immediately if your hands are damp. I’ve noticed this the other day after using my waterstones. As my hands were damp from being in contact with water, I felt immediate tackiness on the glue line. This isn’t a problem as the water didn’t penetrate to break the bond, but I wouldn’t glue up a tabletop with it. Spills and general cleaning will leave a tacky surface and that isn’t a good thing.
When applying glue to joinery apply a thin amount and spread it over both surfaces. On edge gluing apply an even thinner coat and use either your finger to spread it, roller or brush even a stick will do the job. Don’t apply so little to where you will starve the join but enough to end up with a small bead of squeeze out when you clamp it. If you apply too much glue not only, will it be messy and drip all over your clamps and bench top but it will be too slippery and you will have alignment issues. Allow an hour to pass before cleaning up, some manufacturers state 30 mins minimum but I always allow an hour. Use a chisel if you’re using PVA and a damp cloth if using hide glue, with hide glue you can wait the full 24 hrs. Unlike PVA glue if left will not affect your finishes but water will clean it all off not so with PVA.