Can Biscuits Telegraph Through the Wood Surface?

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Duration: 2:48

Woodworkers have said that biscuits shouldn’t be used in thin wood (½” or less thick) because when the biscuit swells with moisture from the glue it’ll exert enough force that the shape of the biscuit will telegraph through the surface of the wood. Fact, or fiction? Let’s find out.

How biscuits work

You’ve probably noticed that when you insert a dry biscuit into a biscuit slot it’s kinda loose in the slot. You don’t get a good fit between the biscuit and the slot until you add glue. Moisture from the glue causes the biscuit to swell and fill the slot.

How the experiment was done

This was a simple test. The question was, will biscuits swell and telegraph through the surface when used in thin wood, so let’s grab some thin stock. Three species were used; pine, cedar and red oak. Pine and cedar were very intentional choices because they’re relatively soft woods. You would think that if a biscuit can make wood move, it’s more likely to happen in soft woods than hard woods.

How thin?

The six boards used were planed to just under ½”. This thickness is generally called out as the minimum for biscuits, the point at which telegraphing starts.

And so…

In the end, no change was seen in the surface of any of these boards. Even the soft woods, the pine and cedar, showed no indication that biscuits were in the seams.

Biscuit joiners are great tools

Biscuit joints and biscuit joiners are great, and can add a lot to your woodworking. They really simplify joinery. There are lots of great ways to use these joints.

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