Knots in timber are one of those things everyone sees, but many people have no idea about. Essentially, what a knot is is the base of a branch. What happens is that as the tree grows, branches sprout and crowding occurs in a way that makes it difficult for itself to grow; so much so that all its rings of growth are compressed into one lumpish trunk. Those branch bases appear as knots when the tree is sawn into boards.

That is partly why knots can differ so very much. Some are small, tight; others are large, dark, or even cracked. It comes down to what type of tree it was, how quickly it grew, and where in the trunk that board came from. For Timber Frame Construction, visit https://merlintimberframe.co.uk

When knots are a good thing

Knots, of course, are part of the charm in many projects. This could refer to rustic shelving and exposed beams, garden structures, or flooring that has ‘character’, for example. Knotting can add texture and create the look of timber being less uniform (i.e., more natural) with tight, sound knots.

When knots can be a problem

Knots weaken timber; they interrupt the straight grain needed for wood strength. They can lead to problems more likely when:

They’re quite large (especially at board edges)

They are “dead” or loose

They are cracked

The timber is structural (ie, joists, rafters, or studwork).

What to do about it

A knotting solution or a stain-blocking primer should be used on painted woodwork. Use graded timber (such as C16/C24) for structural jobs and steer clear of boards with large knots in areas where high stress is anticipated.

Knots are not inherently “bad” – you just need the correct board for the required task.