Watch Luke test the integrity of a PVA glue repair of broken timber
Wooden furniture can break in all kinds of ways, but one of the most common is a break along the grain of the timber. Wood can be imagined as a bundle of fibres all stretching in the same direction and bonded with lignin. This is often what we refer to as the ‘grain’ of the timber, and because of this wood acts differently depending on which way the grain is facing. Wood is strongest when the grain is aligned with the length of the timber, and wood breaks most commonly along the grain, or between the fibres.
When this happens, you might be uncertain of how to fix it in a way that will be strong enough. If the break was in the leg of a chair for instance, you might worry that just gluing it back together won’t hold and that the timber will break again along the glue joint. We have seen many occasions where people will add nails or screws or brackets to a break in hopes of securing it, but more often than not this is unnecessary and can cause more damage further down the line.
To prove this, we have been doing a test in our Furniture Repair classes for years where we break a piece of timber, glue it back together, then break it again. If the glue has cured properly, the wood always breaks somewhere else. Watch the video to see Luke do the test and also accidentally break my beaker in the process.
Here are some things to consider if you are going to do a similar repair:
We are going to be talking more about glue choices in the future, but for now, know that the glue Luke uses PVA wood glue (polyvinyl acetate) which is a very common glue for timber. We recommend this for home repair as it is easy to use and commonly available. It also washes up easily with water.
This sort of glue works really well on a break that goes along the grain, or when gluing two timbers together side to side, but as Luke mentions in the clip, it doesn’t hold nearly as well at the end of a board, so pay attention to grain!
TIGHTNESS OF JOINT
We will mention this again and again, but for this to work the timber has to be glued up very tightly. You don’t want the glue to be filling a gap, as the glue isn’t strong enough on it’s own to do that. This works if the glue can soak into both sides and the timber is touching along the whole joint.
The last thing to mention is time. The glue is pretty solid after a few hours, but we always recommend leaving things 24 hours when possible.
And that’s it! Enjoy woodworking and try not to break any glassware!