Technical - Oak Beams
Wood is a hygroscopic substance.
Wood retains its hygroscopic characteristics after it is put into use.
It is then subjected to fluctuating humidity, the dominant factor in determining its Moisture Content (MC). These fluctuations may be more or less cyclical, such as daily changes or annual seasonal changes.
To minimize the changes in wood moisture content or the movement of wooden objects in service, wood is usually dried to a moisture content that is close to the average MC conditions to which it will be exposed. These conditions vary for interior uses compared with exterior uses in a given geographic location.
However, the MC is as low as 8 to 12% in dry centrally heated houses and offices or in permanently air-conditioned buildings. The primary reason for drying wood to a moisture content equivalent to its mean MC under use conditions is to minimize the dimensional changes (or movement) in the final product. This will always happen during the first few years of installation.
Types of Oak
We will concentrate on European Oak not American in this section
This is oak that has been recently felled and normally up to 6 months old. It is easier to work, although it contains a lot of moisture and over time, this will evaporate causing shrinkage and movement within the beam
Seasoned (Air Dried) Oak
These beams are normally a minimum of one year old although most of our stock are 3-7 years old. Although slightly more expensive you have the added benefits of buying a more stable oak beam with the additional characteristics of splits within the timber.
This timber will be slightly darker in colour as oak beams will naturally darken over time.
Kiln Dried Oak
This oak has been subjected to heat and reduces the moisture content (MC) down from an initial 70% MC to around 8-12% MC.
This oak is used for most internal oak items including oak floors, oak doors, furniture and mouldings.
Occaisionally we are asked for reclaimed oak beams and this depends on current stocks. We have a limited supply of reclaimed oak although we are now able to offer an aging service that creates a great old looking beam from Air Dried Oak.
We have examples at our showroom in Harrogate.
To the right are two pictures showing two methods of fixing an oak fireplace beam to a wall.
The actual construction of your wall may be different to that shown and you should seek the advice of your installer before completing any work.
Option 1 - The Builders or Restraint Strap
On the left hand side of the beam is a small section of builders strap, a galvanised piece of flat bar measuring approx 2.5mm x 30mm x 1000mm
This is screwed into the back of the beam allowing sufficient strap to extend top and bottom from the beam as shown.
Although some remedial work regarding plastering will need to be done, the beam is simply screwed to the wall through any of the holes available.
This option is best for walls that are waiting to be plastered and gives a good hold on the beam.
Option 2 - Screw and Plug
On the right hand side of the beam you notice 2 pre-drilled holes. These are counter sunk allowing a screw or frame fixing to be inserted into the beam.
Note: Mild steel and air dried oak do not mix. The screw or bolt should be stainless or passivated to ensure the two don't touch.
When the screw or fixing is in place the exposed head is hidden with a matching oak dowel (supplied).
This dowel can then be chiselled flat and waxed or left proud to create a feature.
This method uses 4 holes position approx 25mm to 50mm inset from the edges depending on the size of beam used.