Timber is very rarely used in its natural state. When it’s alive, it has natural defences but once it is cut down, decay to the environment sets in. There’s also aesthetics to consider, varnish, paint, oils etc are all widely used to both preserve and change the appearance of the wood.
In this guide we will discuss the popular methods of preparing the wood for the next phase of its life.
As with many things in life, preparation of the wood is key to the final outcome of any project. From a fine cabinet to the garden shed, the end product is more affected by the preparation stage than any other.
Acclimatisation of the timber
A tree spends its life minding its own business until someone comes along and chops it, or some of it, down or off. The resulting piece of timber no longer has the benefit of being managed by a living organism so it needs to be cared for in other ways. Apart from structure, the wood’s main function is to move moisture around the tree so it will retain this property when it’s in use.
Generally lumber is rough sawn into convenient dimensions and stacked outdoors or in a warehouse. Either way it is unlikely that the environment it is used to will be the same as the one it will be kept in once it is the finished product.
- Store the wood for a week or two in a warm dry space
- Place spacers between the individual pieces to allow airflow
- Check the moisture levels – aim for 6 to 9%
Milling step
Most woodworking projects require wood that is S4S or Surfaced on 4 Sides. It can be purchased this way or, if you are starting with raw lumber, it will need to be prepared. It is usual practice to follow a 6 step process to ensure each of the 6 faces are at 90 degrees to each other.
- Face jointing to provide the first flat face
- Thicknessing, second face is planed parallel to the first
- Edge jointing, an edge is made 90 degrees to the faces
- Ripping to width, second edge is sawn parallel to the other
- Squaring one end, an end is cut 90 degrees to the faces and edges
- Cutting to length, a final cut is made to the final required dimension
Regarding the thickness, always leave 1 or 2 mm until the next day to allow the wood to relax.
Managing defects and grain
Before you jump in, carefully study the wood to decide how to best utilize it bearing in mind the function of the intended result.
Check the ends of your boards for cracks (the cracks are also known as “checking”). These cracks can occur because the ends dry faster than the middle. Cutting off the first 5-10cm will indicate if the board is solid.
Knots can give the wood character but can be sources of weakness. If your wood has a beautiful but loose knot, fill the voids with a two-part clear epoxy. This stabilizes the wood and prevents the knot from falling out later.
For most projects, try to orient the grain patterns so they look continuous, this is called “grain matching” and distinguishes fine furniture from DIY projects.
Surface preparation
Once the wood is the size and shape that you want it, the final refinement is needed to prepare it for the time it will spend as the finished product in the environment that it was intended for.
The finish you intend to use plays a large part in how fine a surface you need. A thick coat of paint or varnish is a lot more forgiving than a light penetrating oil. Here are instructions for getting a professional finish, depending on your aspirations you might decide to pull back early.
- Sand with a course paper – 80 grit, then gradually reduce to 120, 150 and finally 180 or 220 grit
- If you plan to use a water-based finish, wipe the bare wood with a damp cloth, this expands the wood fibers, making the surface feel fuzzy
- Dry, then lightly sand with your finest grit again
- Wiping the wood with denatured alcohol or mineral spirits will reveal any hidden glue spots or sanding scratches that would be highlighted (and ruined) by a stain or oil finish
Cleaning and tack-off
The final step is to eliminate all the dust because the last thing you need getting in the finish is any sawdust. Thoroughly vacuum clean the whole area and follow up with a tack cloth or a microfiber cloth dampened with a bit of alcohol.
