Demolishing a wall the right way

It is important to take professional advice before demolishing a loadbearing masonry wall and to understand many of the variations you may come across. Using the consultant’s report and the evidence of your own inspection, you should already have obtained a suitable support or lintel— in the case of a cavity wall you will need two—to take the weight above the wall and decided how this is to be inserted.

Except where your support is to rest on piers , the next stage is to work out what temporary supports you need while demolishing the wall: it is absolutely essential to collect everything together before you start work.

Temporary supports

The temporary supports most often used for this kind of work are expandable steel props, commonly known in the UK as Acrow props. These are available for hire quite cheaply and can be adjusted to fit the heights of most domestic rooms. To spread the load on the props—both top and bottom—you also need a number of wooden planks. These must be at least 200mm wide by 50mm thick and should preferably stretch the length of the wall you are working on. Scaffold boards can be hired for this pur pose if you have no suitable timber; double them up if necessary to obtain the minimum thickness.

In certain cases you may also require a supply of needles -1.5m lengths of sturdy 100mm x 75mm timber. You can either cut these yourself or hire them along with the props and scaffold boards.

Erecting temporary supports

Ceiling supports

Where the wall to be demolished is non-continuous but takes the weight of the floor above, erect a row of temporary props on each side of the wall and tighten them hard against the ceiling.

Before you make any attempt to set up the temporary support, make sure that your permanent support or lintel is in place on the floor underneath where it is to go. And as the work proceeds, make certain that access for raising the support is unobstructed by props. Non-continuous wall: Where the wall to be demolished does not continue upwards but merely supports the floor above, temporarily supporting the latter is relatively straightforward. Simply assemble two rows of adjustable steel props and planks, parallel to each other on both sides of the wall. The rows must be 0.6m away from the wall and the props themselves 1.2m apart.

Continuous wall: You need to employ a different approach where the wall continues into an upper storey: if you supported only the floor, the upper wall would collapse during demolition. Support for the wall is provided by the timber needles. These are inserted through holes cut in the wall just above the line of the lintel and are themselves supported at both ends by props and planks.

The holes for the needles should all run along the same course of brickwork at intervals of about 1m, and should be about the size of one brick. Where necessary, strip away plaster from the wall with a club hammer and bolster so that you can plan the hole cutting properly.

Start the holes from one side of the wall, again using the hammer and bolster and making sure that you are wearing safety glasses or goggles. If you are dealing with a cavity wall, or one that is particularly thick, use a large masonry bit to drill through to the other side and then finish the cutting from there.

Finally, slide the needles through the holes in the wall until they pro- trude by equal amounts on both sides. Erect props and planks at both ends of the needles then tighten the props slowly and by equal amounts until the timber is pushed hard against the brickwork. Do not overtighten the props—they are there to support, not to lift—and make very sure that the needles remain horizontal.

Cutting out

With the temporary supports in position, you are ready to cut a slot in the wall to take the lintel or support. But before doing so, check that there are no power lines or service pipes running across the wall under the plaster. These, together with any power sockets, must be rerouted before demolition can proceed.

Once this is done, mark out the proposed position of the lintel with a spirit level, plumbline and chalk. The hole should be fractionally larger all round than the proposed support so that the latter can be fitted comfort- ably into place once you have cut away the brickwork.

Use the club hammer and bolster to cut away the bricks and be sure to wear goggles or safety glasses. Try to remove only a few at a time and avoid using brute force if possible as this is likely only to break away or loosen bricks accidentally.

If a brick proves difficult to move, drill a number of holes in the mortar around it using a masonry bit. It should then be possible to remove the brick with the hammer and bolster. As you progress, try to control your chisel blows and angle them into the wall so that you disturb no more masonry than is necessary.

Where your proposed support is to rest in the adjacent walls rather than simply on the ends of the wall you are demolishing , cut into these to the required depth once you have finished the rest of the slot. If one or both are cavity walls, take care not to let debris fall between the leaves as this may stick to the wall ties allowing damp to bridge the gap.

As the support will be longer than the wall you are demolishing, it may be necessary to cut extra masonry out of the side walls so that you can twist it into position. But if the wall is external, you may find it easier to feed through the support from the outside and then gently ease it into its eventual resting place. This, of course, means cutting a larger slot on the outside of the wall.

Once the slot for the support is finished and you have smoothed out the cut edges as far as possible, check that the sides are completely vertical with a plumbline and rebuild any brickwork which is loose or broken. Finally, check the dimensions carefully to make sure that the hole is the correct size to receive the lintel.

Inserting the support

The method you use to bed the support into position depends on whether you are using a lintel or a rolled steel joist. Lintels: These must be lifted and twisted, slid or fed carefully into position. Because of the weight of the lintel and the need to position it accurately, it is essential to have several people to help you do this.

Lay a bed of fairly dry 1:3 mortar on all parts of the lintel that are likely to come into contact with the wall above the opening before you slide it into its final resting place. Before you go any further, make sure »*5* 7b that the lintel lies exactly as specified in the plans.

The next step is to cut away more holes underneath the lintel and insert two or more needles—with props —so that you can jack it up against the wall above. Pack any gaps above the lintel with mortar before you do this, and make sure that the lintel remains horizontal at all times.

Then, with the lintel forced upwards by the needles, pack the gaps underneath both supporting ends with pieces of slate tapped firmly into place with a hammer. Finally, point all around the cracks between the lintel and brickwork with mortar ready for replastering.

Rolled steel joists: These are not bedded in cement but instead set on ‘pads’ of natural stone or pre-cast concrete. Pads are available at most large builder’s merchants and are usually sold along with the joist. Depending on the size of the joist, they should be at least 50-70mm thick and long and wide enough to guarantee good support at both ends. The pads must rest on a firm, level base and this may involve renewing or adding to the brickwork piers which support them. ‘Use a trowel to spread an even bed of 1:3 mortar below the pads and leave this to set for at least 48 hours so that there is no risk of movement. Then lift the joist into place with the help of your assistants and position it accurately. Gaps around the outside of the joist should be packed with slate and pointed in a similar way to the pre-stressed lintel.

Removing the props

Do not be in a hurry to remove the temporary supports—they are best left where they are for at least another two days so that the bedding around the lintel or joist can harden fully. When you do remove them, bring down the weight on the support gradually by loosening off the props a little at a time. And while you are taking the props away, look carefully at the area around the top of the support to make sure that it is not suffering from any undue stress.

Finishing a rolled steel joist

Because of their shape, rolled steel joists do not look particularly attractive when left uncovered. In most cases, the easiest way to improve their appearance is by covering them with a shell of plasterboard.

In order to do this, you need to make up wooden noggins to act as supports for the board. Cut these fractionally longer than the distance between the upper and lower lips of the joist then tap them into place at 300mm intervals.

Most joints protrude slightly from the wall surface, which makes it difficult to cover them neatly. But with care, a piece of plasterboard can be made to ‘bend’ around the three protruding sides.

The length of plasterboard needed for this will be determined by the length of the joist plus a slight overlay at each end. But to find the width, measure the widths of the protruding sides, add these together and then add a further overlap allowance of 600mm.

Lay the plasterboard face downwards on a flat surface and transfer these measurements to the material; then, using a sharp handyman’s knife and a steel straightedge, cut through the cardboard backing and separate.

Next turn the material over so that the face is uppermost and mark pencil lines across the material corresponding to the top, bottom and side edges of the joist. Use the steel straightedge and knife to score along these lines, but make sure that you cut through only the paper face and do not damage the plasterboard itself. Because the backing is made of a much stronger material than the face, you find that you can then wrap the sheet around the joist.

Hammer flat-headed galvanized nails through the plasterboard to the noggins below to fix the covering in position. The surrounding area can then be skimmed flat with a layer of fresh plaster.

Making good the floor

How you make good the floor depends on whether your floor is suspended or solid, and if the former is the case, on which way the joists run. Suspended floor: Where the floor joists run at right-angles to the wall you are demolishing, they will either be supported on sleeper walls running parallel to it or on the wall itself by means of hangers or ledgers.

In the first case, demolish the wall down to below the level of the joists and fit new lengths of joist between the sleeper walls in the newly-adjoining rooms. These should rest securely on the base of the old wall and be skew-nailed to the joists that are already in place.

If the wall itself supports the joists, demolish only as far as just below the floorboards. Where the wall is external, you can then arrange to fit a suitable hearth and step. But if it is internal, arrange for short lengths of joist-size timber—noggins—to rest on notches cut into the base of the wall and extend underneath the floorboards on both sides of the gap. Once you have nailed the noggins to the existing floorboards, they will make suitable supports for the additional boarding that will be required for you to cover the hole.

Where the joists run parallel, demolish the wall below the level of the boards. This will leave you with a gap—ragged because the existing floorboards are certain to be staggered. If the floorboards are not to show, it may be possible to cut them back to—and over the middle of—the nearest joists. You can then fit boarding—such as flooring grade chipboard —across the gap. However, if you want the floor completely floorboarded, you have no choice but to take up the existing ones and stagger them in a different way so that when relaid they span the gap.

In both cases, carefully level the base of the demolished wall to just below floorboard level so that it acts as an extra ‘joist’ to support the boards over the gap. If this proves impossible, demolish it a little further, fit an extra joist on top and secure this at the adjacent walls.

Where the wall is external, use the remainder of it as a base for your hearth or step. To bridge the rest of the gap you again may have to take up some or all of the existing boards and relay them in a different pattern. Solid-floor: Here, the procedure is much simpler in that you do not have to arrange for supports—simply demolish down to the base level of the oversite concrete, then carefully pour in fresh concrete to fill the hole.

The only difficulties you may encounter are where it is necessary to disturb a damp-proof membrane

I located below the surface screed. In this case it may be necessary to break up more of the floor so that you expose the existing DPM and fit a strip of the same material over the gap before you concrete over. The new section of the DPM should fold back twice.

Where the problems are more complex, it is likely that your architect or surveyor will have allowed for and dealt with them in his specification. If not consult your building inspector.

Making good the piers

The first job is to firmly mortar in place all loose and suspect brickwork. Where bricks have broken badly, giving a ragged vertical edge to your piers, cut them out entirely, and replace them with neatly cut ones.

Then replaster each side of the pier separately, nailing wooden guide battens to the vertical edges to give you something to plaster up to, and to help get corners neat.

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