Size
First calculate the size of the opening that you need. Doors come in a variety of widths so it is wise to work around the width of the door that you intend to buy. You will need to add around 50mm to the width and 25mm to the height to accommodate the frame.
Equipment
Here are the parts and tools you’ll need:
- 1 x steel reinforced concrete lintel at least 225mm longer than the width of the opening you need to make. An example can be found here
- Some slate. A broken up slate floor tile will do. An example can be found here
- A bag of sand
- A bag of cement
- Some mortar plasticiser
- 2 x Acrow Props. Acrow props come in different heights. For a standard door, you will need size/number 1 props. You can pick these up cheap from most hire shops
- 2 x Strong Boy attachments for the Acrow Props . You can pick these up cheap from most hire shops
- 1 x scaffold board, at long enough to span the width of your opening. Failing a scaffold board, a sturdy plank of wood will do
- Concrete saw, Stihl or similar. Failing that, a large angle grinder may do
- Lump hammer
- Brick bolster chisel
- A mortar gun. Not strictly necessary but it’ll make the job a lot easier
- 2KG SDS drill (roto-stop) with wide (40-80mm) chisel attachment. Not strictly necessary but it makes plaster removal a lot quicker
Method
First mark out the opening for the door. Mark out a rectangle above this roughly 2 bricks high and as long as the lintel. Example below:
Door Marking Example
Cut the plaster around the lines with an angle grinder or brick bolster and remove all of the plaster. You will also need to remove the skirting board, if applicable.
Drill the corners of your marking all the way through the wall with a small masonry drill bit. Join up the drill holes with a pencil and remove the plaster on the other side of the wall also. Again, you will also need to remove skirting board if applicable.
Using a 12mm drill bit, drill out slots in the mortar approximately equidistant from the edges of the proposed placement of the lintel with no more than a 600mm gap between the centres of the slots. The slots should be in the mortar line one brick above the proposed lintel placement and should go all the way through the wall. Example below, slots are blue:
Strong Boy Slots
Insert the Strong Boy attachments into the holes and tighten the Acrow Props under them, as pictured below. The base of the Acrow Props should rest on the scaffold board. This is important so as to spread the load, especially on wooden suspended floors.
Strong Boys In – Right prop isn’t in the right place yet
Now you can safely remove the row of bricks for the lintel. Do this by drilling out the mortar with a 12mm drill bit and then knocking out the bricks with a lump hammer. It’s possible that the row above will also drop out, if the mortar is old and weak. Don’t worry too much about this. In the image above, we’ve tried to keep it all roughly in place.
Bricks Removed For Lintel
Now you can insert the lintel and any bricks that have erroneously fallen out. Pack it with small slips of slate to get the spacing correct. Fill the gaps with mortar, using the mortar gun. Mortar should be 3 parts sand, 1 part cement, a small amount of plasticiser and enough water to make a thick paste.
Lintel in Place
You’ll now need to wait for the mortar to set. This will take about 12-24 hours. Once it has, remove the props.
You can now cut down the sides of the opening using the concrete saw. Warning – this will make a lot of dust.
Once the cuts are made, remove the top layer of bricks by drilling out the mortar with a 12mm drill bit and knocking them out. Once the top layer is out, the rest should come out without too much trouble. Remove all the bricks down to just below the floor level.
Opening Cut
The opening can now be framed, plastered and have the door installed.