A Perfect Case
If an imperfect door casing is the main reason for problems when fitting a new door, then it goes without saying that almost all of these problems would be eliminated if the casing was fitted perfectly.
This section covers everything that you would want to know about the installation of a door casing into different types of openings. It is important that you ensure that each step that you complete is correct before proceeding to the next stage.
Irrespective of the type of opening that you're fitting to, door casings are fixed at three points per jamb; bottom, middle and top. It follows then, that if you are fitting to brickwork these three points would correspond to brickwork joints, where some form of timber would be inserted. Two bricks up from the floor would be about 150 mm, determines the bottom point, the same applies for the top. The centre would be in between the two.
If fixing to timber stud Partition, you should still maintain these same fixing points even though there are no joints, so to maintain a professional standard.
In new property where brick or blockwork is used, timber 'pads' are placed dry into the brickwork joints as the walls are being built at the door and window openings. Different to timber plugs which are driven into the joints, 'Pads' are square pieces of softwood timber, manufactured to the same width as the brickwork and the thickness of mortar joints.
They are placed in position with the grain running the width of the brick, it's this that makes the 'pad' an excellent form of grip for the nails, because the nail is not driven into the end grain as with the plug, so that in use, the nail expands the pad in thickness, which increases its hold between the brickwork courses.
The Right Size
If you are building the wall that the casing will fit into, or having the wall built for you, it would be an advantage to have the size of the opening made exactly to the size of the door casing. This would eliminate the need for any packing pieces to compensate for any size difference. However, a word of warning, if you choose this method, you must make sure that the proposed brickwork opening is perfect, otherwise you could end up with major problems. If the brickwork is not running 'true' (in any way) and the casing is a tight fit, you will not be able to make any adjustments to the casing so as to correct it. Therefore, if you suspect that this may apply, make the opening wider, sufficient to allow space for casing adjustment.
A way of overcoming problems of this type is to 'prop' the door casing (that has been prepared as described 'Features') up in the proposed opening before any bricklaying work commences, ensuring that the jambs are plumb and the head level. The brickwork would then be built around it. The disadvantage with this option is that the door casing is subject to damage and distortion by the subsequent wall building.
Alternatively and a better method, is to use a timber frame 'blank', made up of cheap timber such as 75 mm x 50 mm scant. This frame would be identical in size to the door casing, becoming a substitute or pattern door casing that can be used again and again, useful if you intend installing a number of door casings. This frame is removed when the brickwork has been formed, ready for the door casing to be installed.
The advantage here is that this framework is much sturdier than the door casing and less likely to alter in size due to any pressures that could be imposed upon it from external sources.
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