Knocking a hole in a wall

Checking for es cab

If there is a power socket on the wall in which you intend to make an opening, there is a possibility that the cable may be routed across the proposed site of the hole.

Before starting any demolition work, check that the way is clear or you may sever a cable.

First, turn off the mains supply— and leave it off, even after you have established the direction of the cable.

Then, carefully chisel away the plaster from a small area around the power socket until you can see which direction the cable takes. Normally cables go up or down— rarely straight across the wall. If a cable is routed across your proposed opening, it must be rerouted before any demolition takes place. This will probably require a longer cable which should be carefully installed.

In some older houses, gas pipes may also be set into the walls. The procedure for establishing their direction is the same as for power cables.

Home improvements can often be made just as easily by demolishing bricks and mortar as they can by building up. Knocking a small hole through a wall is a good way to master the basic techniques—and makes space for a serving hatch, window or two-way bookshelf.

Demolishing masonry normally entails using supports—temporary ones as you do the work and permanent ones afterwards, to keep the wall structurally sound. For holes under 1.5m wide, only simple supports are needed. Demolishing larger holes— and complete walls—calls for more complex supports and is covered further on in the course.

External walls, and most internal walls, take the weight of the structure above them. When a hole is knocked through, this weight can bear down on the space and cause the structure to collapse.

This is prevented by installing a lintel—a beam of concrete, galvanized steel or wood—over the hole.

The lintel must be strong enough to take the place of the missing masonry. In the case of a small hole up to 450mm wide, a strong wooden frame built into it may be sufficient—the top of the frame acts as the lintel. Such a frame may also suffice where the wall is simply a dividing wall and does not bear the weight of any structure above it.

Checking the wall

To find out if the wall in question is masonry or timber framed, tap it sharply with your fist. A brick wall gives out a dull, solid sound whereas a stud wall sounds loud and hollow. If you are in any doubt, cut a test hole within the area of the proposed opening in the wall.

If the wall is a non-loadbearing one, it usually ends slightly above the ceiling level. However, if it continues on an upstairs floor, it is loadbearing. It is also loadbearing if struts which help support the roof rest on it, or if the wall supports the ceiling joists of the room itself.

In all cases, check out the wall by looking into the roof space or, in the case of a two-storey house, by checking on the direction of the floorboard-ing above. When the floorboards lie in the same direction as the wall the joists below are being supported by that wall.

Choice of lintels

Lintels come in a variety of types. If you are knocking through an exterior wall in a house with a solid wall of standard 225mm brickwork, the easiest to use is a pre-stressed concrete lintel 220mm wide and at least 65mm thick (depending on the width of the opening). You set it flush with the outside edge of the opening so that the concrete is visible.

In newer houses with a cavity wall —two layers of leaves of 112mm brickwork with an air space between—a proprietary steel lintel is better.

For an interior wall of single skin brickwork, a timber or concrete lintel 100mm x 75mm thick will suffice for small openings.

Lintels come in different thicknesses for different loadings. Since the right size to use depends not just on the width you are spanning but also on what is above it—right up to the roof—most Building Regulations do not specify sizes for particular jobs.

Only an engineer can calculate the loadings accurately but your Building Inspector will advise you on the safest lintel to use if you show him an accurate drawing of the wall.

Whichever size you buy, the lintel must be at least 305mm longer than the opening you wish to span, so that it has an adequate grip or bearing on either side.

Selecting a site

When selecting an exact site for the hole, bear in mind that it should be at least two bricks’ length from any angle in the wall—such as a corner. Any closer than this and you may weaken the structure.

Temporary supports

A brick wall is exceptionally stable within certain limits—even with a hole in it. If you go carefully, you can cut an opening up to lm wide in sound brickwork without any temporary support at all. Most of the bricks over the opening will just hang there during the time it takes to insert the lintel.

However, for a wider opening you should start by cutting only the slot for the lintel , at the same time supporting the wall above with lengths of timber known as needles. When the lintel is in place and the mortar around it has hardened, you can cut away the brickwork below it.

Needles are made from lengths of 100mm x 75mm timber and for a 1-1.5m hole, two only will be needed. The needles are inserted through holes in the wall immediately above the proposed position of the lintel and then propped on either side with Acrow props (jack posts) to carry the weight of the whole wall down to the floor or ground. Lengths of timber—at least 200mm x 50mm—are placed between the supports and the ground to spread the weight over a greater area.

You can hire both the needles and the steel supports from larger hire shops. Before you start to erect them, get your lintel into position at the foot of the wall—you may not have the room to manoeuvre it in later.

Cut the 100mm x 75mm holes for the needles with a club hammer and plugging chisel or cold chisel. Work from both sides of the wall if necessary and keep the holes as rectangular in section as possible, so the needles lie fiat. Having wedged them through the wall, erect supports on both sides.

Marking the cutting area

Having selected the approximate position of the hole, take its overall measurements and transfer these to the wall.

Assuming that the wall is still plastered or rendered, you must now chip away this layer to reveal the brickwork underneath. Use a club hammer and bolster, keeping at least half a brick’s length inside the marked lines.’

When the brickwork in the centre of the cutting area is exposed, you can tell—without removing all the plaster—whether or not your proposed cutting edges correspond with vertical and horizontal joints. Do this by measuring from an exposed joint to the marked edge. If the proposed edges do not line up with any joints, move the markings of the cutting area over until they do. This keeps the number of bricks to be cut from the opening to a minimum. Check the joints for level and plumb.

The position of the lintel must also be marked, directly above the top cutting line.

A certain amount of wall vibration is inevitable at the cutting-out stage and you will certainly create thick clouds of dust. Because of this, it is a good idea to remove all breakables from the vicinity and to remove or cover up furniture.

Cutting out the opening

The secret of demolishing brickwork is to work carefully and steadily, removing only a little at a time. Start with a vertical joint in the middle of the cutting area and drive in a plugging chisel with a mallet. Loosen the mortar around one brick and try to ease it out. If it will not move, smash it out.

After you have removed one or two bricks in this way, you can exchange the plugging chisel for the bolster. By driving it into the mortar joints, you should be able to lever bricks away rather than have to smash them out. Continue using the plugging chisel on vertical joints.

Enlarging the opening is a gradual, careful process and only small sections of masonry should be knocked out at a time. Too big a ‘bite’ with the chisel will result in uncontrolled cracking and possible major structural damage—so be careful.

Chisel cuts about 20mm.apart should be completed step-by-step fashion. By angling the chisel blows into the line of the wall outside the cutting area, the blows are absorbed by the wall bulk and the vibration shock is lessened. This helps reduce the chance of uncontrolled cracking.

When the wall is hit at right-angles none of the vibration is absorbed and there may be loosening of nearby fittings, such as wall cupboards.

You should continue chiselling until you have cut the slot for the lintel.

Inserting the lintel

Make the bedding mortar for your lintel from three parts of soft sand to one of Portland cement with just enough water to make it workable. Slide the lintel into place and let the mortar under it harden overnight before you proceed. Check that the lintel is plumb and level , before the mortar dries—then you can cut the rest of the opening .

If the space is deeper than a normal joint (10-15mm), reinforce it by driving in bits of slate, knocking off the projecting pieces with a hammer when the mortar has dried . Fill the space above the lintel with the same mortar, pushed well into the gap.

Cutting the main hole

The plaster must be gradually stripped back to the line of the final cut and cut neatly with the bolster. A neat job at this stage reduces the amount of making-good needed when the framework is installed .

In a solid wall you must cut off all the half- and quarter-bricks that project into the opening. Tap them firmly on top with the hammer and bolster, then a bit harder from the face side to cut them off squarely.

In an outside cavity wall, the procedure is slightly different. Square off the opening in the outside leaf as you would for a solid wall. But do not cut off the protruding bricks or blocks on the inner leaf—they will be needed to close the cavity later.

Openings in stud partition walls

The first step in making an opening in a stud partition wall is to find the studs. Bang on the wall with your fist; where you hear a ‘solid’ sound there will be a stud.

The next step is to site the opening so that you will do as little damage as possible to the plasterboard (wall-board). You will anyway have to cut the opening over-depth so that you can nail the timber lintel to the studs on either side. Try, by siting the opening neatly between two existing studs, to avoid having to cut over-width as well —otherwise you will have a lot of plasterboard patches to fit.

Mark out the proposed opening, plus the depth of the lintel and bottom bearer , in the same way as for a masonry wall. Cut the plasterboard on one side with a handyman’s knife and steel rule. Then poke a nail through the wall, at each of the four corners, to show where to cut the other side.

Next, saw through the middle stud or studs at the top and bottom. To help keep your saw cut straight, use a pencil and try-square to mark right round the studs, and saw alternately from each of the four edges.

Skew-nail the lintel to the studs on either side of the opening, and nail in the bottom bearer. You may also need vertical packing pieces between the lintel and bearer, to give you nailing positions for the plasterboard patches around the opening.

When you cut and fit the plasterboard patches, try to have a dead straight ‘factory’ edge where a patch meets an existing sheet of plasterboard. This will make stopping and levelling easier after you have nailed it on.

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