Before fitting a door into an opening in a stud or brick wall, you need to fit a door lining. The door lining gives you something to firmly affix the hinges to, as well as forming a cleaner finish to the inside of the opening. You can build a lining from individual lengths of timber, but it is easier to buy a door lining kit. These kits usually contain three pieces of timber, with slots pre-cut in the head section. The kit might also contain a number of wooden or plastic wedges, used for holding the lining in place.
If you have created a new doorway in a wall, you should have taken the standard size of a door and the thickness of the door lining into account when planning the size of the opening. If you have not, you could be faced with the prospect of having a non-standard sized door made for you, which will be expensive.
Step 1 – Constructing the frame
Lay out the three sections of the lining kit on the floor. If your kit has pre-cut grooves cut into the head section, make sure that the two uprights are slotted into them. If needed, lightly tap the uprights into the grooves using a mallet. There will be excess timber on the head section, overhanging the uprights. This can be trimmed off later.
Drill through the head section, into the top of each upright, creating two screw holes an equal distance apart. Fix the sections together using appropriate wood screws (the longer, the better). Once it feels solid, you can trim off the excess timber on the head section.
Step 2 – Make the frame rigid
Cut three lengths of timber batten long enough to sit across the frame at its widest point. Now, using a carpenters square (cheaply bought from most DIY stores, and very useful to have) make sure that the frame is square. To do this, make one upright square with the head section and lay the batten across the corner (to create a triangle). Nail it in place to hold the angle. Trim off any excess that overlaps the frame, and then repeat the process for the other angle. This should make the frame fairly solid, but you can make it even more so by nailing the third batten straight across the two uprights, near the bottom.
Step 3 – Fitting the door lining
Measure each side of the opening in your wall and transfer those measurements onto each upright of the frame. Trim the uprights as required. Your door lining should now be ready to slot into the opening. It is very unlikely that it will be a perfect fit, so you may have to use small wedges of wood knocked into the gaps to hold the lining more firmly in place. Tap the wedges in lightly, so as not to distort the shape of the lining, and check regularly with a spirit level to make sure the frame is still upright.
Once the lining is tightly fitted into the opening, you can start to fix it in place with screws. Using the appropriate screws for the material the wall is made from (timber stud, bricks or blocks), screw through the lining and into the wall. You should aim to use at least five screws in each upright (spread out at regular intervals) and a couple in the head section. Remember that these screws need to withstand the constant opening and closing of the door once it is fitted.
Once the lining is screwed into place, trim off any excess material from the wedges so that they are flush with the wall and lining. The gap will eventually be covered by the architrave, but it won’t hurt to fill it with a bead of appropriate sealant.