Internal corners are dealt with in a different way to external ones, and internal mitres are rarely used as the inevitable shrinkage of the timber would open up the joint. The preferred method used to bring skirting boards around an internal corner is to use the 'scribed' joint. A scribed joint is where the skirting is cut to follow its own pattern shape (its profile).
Before any cuts can be made to shape the skirting, the profile will need to highlighted. Though there are a number of methods that can be used to do this, the best option is to make a vertical cut at 45 degrees to the skirting board as shown in plan view in Fig 9, which when cut will clearly highlight the front view profile as shown in Fig 10.
This profile will need to be cut out, and two different types of saws will be required, the tenon saw, and a Coping Saw. The bottom section straight cut of the profile can be cut using the tenon saw, while the molded section will require a coping saw. The two adjoining pieces of skirting board can now be brought together, as shown in Fig 13.
Traditionally, skirting boards were fixed directly into timber plugs that were driven into the vertical joints of the brickwork at 450mm centres, which is part of the 'First fix' process in the construction of new houses. All the plugs are left long, so that they could be cut to a 'true line', to the thickness of the base coat of the plaster 'browning', and the plasterer would use this 'line', as well as the outer edges of the door casings as a guide for the base coat plaster. The skirting board would then be nailed to the plugs, and the plasterer would then plaster 'skim' the wall and up to the skirting board, (and architraves) producing a perfect finish between the two. An alternative method based on the same principle is to use timber 'Grounds', where lengths of rough saw timber is fixed to the wall, and packed out at points to produce a true line.
In the situation where the wall has been plastered prior to any plugs or grounds being fitted, the skirting board will need to be fitted directly onto the plaster, and fixed to the base material. Though this is common practice today, especially in realms of renovation and repair work, it is not an ideal situation, because the skirting is fitted onto a surface that may not be perfectly flat, which very often results in the joint between the two having to be filled to hide any imperfections. Another problem often encountered using this method, is that a 90 degree brickwork corner that has been plastered before the skirting is fixed, is very often altered as a result of the plasterer not having a guide to work to, where as the same un-plastered corner would be a right angle.
The type of fixing used for fixing skirting is dependant on the base material that it is being fixed to. Timber grounds, and plugs, as well as the light weight blocks and stud partitioning, is nailed directly though the face of the board into either the blocks, or into timber using 65 mm lost head nails, where as brickwork and certain types of clinker block would require fixing by using screws and plugs.