From episodes of This Old House to shop classes in school, we saw, heard about, and employed biscuit joinery as part of our woodworking education on joining two pieces of wood together.
It’s a quick and easy way to glue together those two pieces and ensure proper alignment. They also add a measure of strength to the joinery not found in butt joints or miter joints.
But are they always the right choice for joining those pieces of wood together? Are there advantages and disadvantages of biscuit joints to be considered?
What Is A Biscuit Joint?
A tool known as a biscuit joiner is used to cut a small crescent-shaped hole in opposite sides of two pieces of wood. Then, glue is applied into the holes, and a wafer of dried, compressed wood is inserted into them. The wafers are made to expand when wet, and the glue provides that moisture to help them fill the space tightly and form a solid joint.
This technique, developed in the 1950s, aligns the two pieces of wood and provides a relatively tight connection to hold everything together. For joints that will experience torture such as undue torquing, though, that connection might not be able to stand.
As to what size biscuit you should use, it depends on the two pieces of wood to be joined. Generally speaking, you should use the largest biscuit possible so as to provide the greatest surface area for the glue to work its magic.
Biscuits generally come in three sizes:
- #0: 5/8 inch by 1 3/4 inches.
- #10: 3/4 inch by 2 1/8 inches.
- #20: 1 inch by 2 3/8 inches.
So, the #20 would be the first choice for most joinery unless you are working with narrower materials. In those cases, use the largest that fits from the three generally available sizes. By the way, you can buy biscuits in bags of up to 75 pieces.
You might also be wondering how far apart biscuits should be, and again that depends on the size of the wood you are working with for the joinery. Generally speaking, you will want to space your biscuits at about 6 inches along the span.
Are There Any Challenges to Using a Biscuit Joiner?
While This Old House certainly made biscuits well known and biscuit joiners a popular home workshop tool, there are some challenges to their use.
If your project is a new table, and you are joining multiple pieces of dimensional lumber for the tabletop, biscuit joinery might be a good choice. You can afford a little leeway in the measurements along the running dimension because you can always square off the ends after the glue dries.
But, if your project can’t afford that leeway, then measurement along the running dimension becomes critical for proper alignment. Biscuits do help with a good alignment, but only if you’ve measured carefully. The biscuit joiner cuts need to be precise for that to happen.
Pocket screw joinery does not require such measurement precision for a good alignment result, and like biscuit joinery, it is also invisible in the finished joint. Dado joints also require accurate measurements but are often used on internal joints of boxes, desks, and other enclosed wood constructions.
It is an understatement to say that a mortise and tenon joint is stronger than a biscuit joint, as the mortise and tenon joint is the strongest of joints in woodworking. But, biscuit joinery does have its place in the home workshop.
What Are The advantages of a Biscuit Joint?
Biscuit joinery has some clear advantages over other methods on the right projects. Again, while stronger than a butt joint or a miter joint, there are other methods that might be preferred. We’ll get to those in a minute.
- The biscuit joint is quick and easy, assuming you have the biscuit joiner in your workshop. Careful measurement, quick cut, a little glue, a couple of clamps, and the task is done.
The careful measurement ensures proper alignment of the pieces being joined, and the glue provides the moisture a biscuit needs in order to expand. That expansion in the cut secures the joint tightly, and assuming the joint will not be heavily tested or tortured, it will hold.
If your project is small, and the piece you are making will not undergo great stress, a biscuit joint will serve you well.
- Biscuits are inexpensive and pre-made, thus making them very easy to work with on your project.
In bags of up to 75 pieces, they are a cheap inventory item at under $7 per bag at the large DIY stores and online retailers.
What Are The Disadvantages of a Biscuit Joint?
We’ve already suggested the need for accurate measurements when using biscuit joints, and some may consider this one of its disadvantages. But the arguments against the use of biscuit joints come into focus with comparisons.
Biscuit joints do not stand up well against other joinery methods. We won’t spend any time comparing with mortise and tenon joints because all other joinery methods pale in comparison when measuring strength.
But, as an example, the use of dowels as opposed to biscuits is a step up in strength. Many argue that biscuits are suitable only for alignment, and that may be true. We would suggest ease and speed to that argument.
In wood joint torture tests, biscuits do not withstand much. Biscuits, for example, do not penetrate deeply into the woods being joined, whereas dowel depth can be extended simply by drilling deeper into the wood. The biscuit strength comes from its expansion and glue; dowel strength comes from penetration depth, the tensile strength of the solid wood dowel, and glue.
Dowel joinery takes more time, but it has an advantage over biscuits for the extra strength of the joint created. It also does not require a special tool for the task; it’s likely your wood workshop already has a power drill and bits.
Can You Biscuit Joint Plywood?
The short answer is yes. The biscuit joiner will give you a clean and invisible cut; the biscuits will expand inside the hole with the moisture of the glue, and the plywood will hold.
Although MDF is not as dense or strong as wood or plywood, you can also use a biscuit joint to bring two pieces together. The same dynamic is in play; clean and invisible cut and biscuit expansion.
Can You Use Biscuits For Solid Wood Edge Joints?
We now know that biscuits can be used to join plywood. And, biscuits can be an excellent choice for joining solid wood edging to sheet pieces.
Biscuits are used, too, for straightening bowed boards. Measurements become increasingly important in joining a bowed board to a straight board, or even two bowed boards, and a little extra pressure is required to push the bow down to insert and join the biscuits.
But, it can be a useful joinery choice.
Typical Biscuit Joint Uses
Biscuit joints are easy to make, assuming you have a biscuit joiner, and they are easy to employ in your woodworking projects. The uses for biscuit joints include:
- Joining sheets of plywood, particle board, and medium-density fiberboard;
- Joining lumber into tabletops;
- When joining workpieces in 90 degree angles (yes, mitered biscuit joints are a thing);
In actuality, biscuit joints can be used for pretty much any joinery task. It’s more about the strength needed for the joint – – its purpose, size, and use. As we often say in our posts, the right tool for the right job, and in joinery, it’s the right joint method for the right job.
For a project that will not be tortured or put to a strength test, biscuit joinery is a good choice – – easy and quick in creating a well-aligned joint.