Indy Total Construction

A solid floor often consists of concrete rag that has been laid on top of a layer of hardcore in the ground. This is then covered by a damp-proof membrane, which may in turn be protected by a thin layer of mortar called a screed which is leveled out arid topped by the flooring. But not all solid floors are laid directly on top of the ground.

You may find solid floors in flats and houses, at first floor level and above, as an alternative to framed floors which are supported by beams and structural walls and are usually floorboards mounted on joists.

How are solid floors constructed? You’ll only find the concrete floor surface laid directly on the soil in the oldest houses. And even then you’re more likely to find a heavy concrete slab beneath the surface flooring. If your floor is old, it will probably consist of hardcore with up to 150mm (6in) of concrete on top.

Surface finish, such as a 25mm (1 in) terrazzo screed, quarry tiles, floorboards on slim joists or wooden block flooring like parquet. Was then laid on top.

With this older style of construction little consideration was given to rising damp. Parquet blocks were sometimes bedded in bitumen, but only if the surface of the floor came below soil level would any systematic damp-proofing be used. In that eventuality, the structural slab was covered with asphalt, which was in turn covered with a further 75mm (3in) of concrete.

The design of a modern solid floor slabs allows for a much more rigorous approach to damp proofing. A 100mm (4in) structural slab is laid over a damp-proof membrane that protects the walls as well in order to provide complete protection. On top of the structural slab may come a mortar screed suitable for carpet or vinyl laying or a direct surface finish? Damp proofing is vital because although well-laid concrete. Basically water proof, it still may allow damaging water vapor to pass through without the membrane.

Cracks are the most common fault in solid floors – and are usually due to drying shrinkage or thermal movement. But, provided the cracks are no wider than 6mm (I/4in), you can repair them quite easily yourself. Minor surface damage such as roughness and unevenness is also simply repaired.

If, however: the cracks are wider than 6rnm (‘/4in), that means that something more serious is wrong with your floor – probably a crack going all the way through the slab as well as the screening – so you should call in a builder or surveyor to advise you. A still more worrying problem, especially in a direct-to-earth floor, is rising damp. If a damp-proof membrane already exists and there is still evidence of damp, the damp is likely to be localized: the result of a small break in the membrane.

This may show up only after the old porous floor surface has been replaced with some more modern flooring. The original surface would have let damp through, so avoiding damage, but as the modern ones don’t let water vapor evaporate. It tends to build up underneath and attack both the adhesive and the flooring.

So. If you are going to fit new flooring on an old solid floor, first of all check that it’s damp proof (see Ready Reference). If you do have damp. Then you can put up with your existing flooring: replace it with a new flooring of the same

All you do is slightly widen the crack by using a club hammer and cold chisel, going down to a depth of 12mm (1/2in), undercutting the surrounding floor a little. This is very important as it allows the mortar to get a much better grip on the surface than it would if you were attempting to fill a crack with smooth, feathered edges.

Clean out any dust or debris before brushing on a coat of PVA adhesive, smoothing in the mortar with a small trowel and finishing it off level with the surrounding floor. The chances are that the crack will open up again at some stage. Especially if the floor on one side of it has pushed either up above or down below the rest. The only really permanent solution is to have the floor completely replaced before you lay your new floor surface.

Inserting a damp-proof membrane the simplest way to do this is to remove the skirting boards and strip off the plaster on the walls to a point 50mm (2in) above the wall’s damp-proof course. If at this stage you find your walls don’t have a damp-proof course. It is advisable to get one put in before going any further.

Various forms of damp-proof membrane are used, ranging from thick polythene (often known as ’1000 – gauge’ or ‘sheet 1000′), PVC, butyl rubber or polyisobutylene for large scale work (where the sheets are loose laid or bonded to the structural slab with water-resistant adhesive), to bitumen emulsion for smaller scale jobs.

These sealants are sprayed or painted on the slab in two coats. With the second one being brushed at right angles to the first to prevent thin spots and pin holes where damp could come through. To protect your room completely against rising damp you should link the membrane into the damp-proof course.

This is easy if the dip is above the floor, but it is possible that it’ll be below the level of your floor. If that’s the case then you will have to dig a small channel round the floor so you can gain access – Then all you do is paint bitumen. Either up or down the wall or fit the poly-sheets with more water resistant aches.

Some solid floors are not laid direct. Some of them are cast in situ around reinforcing steel and some are precast concrete floorboards that are locked together_ others, which are made of hollow terracotta blocks that are linked together with Meta Rods and that have the gaps filled in with concrete, are also technically known as solid floors.

You can create a damp-proof membrane by using two coats of bitumen emulsion and applying them over the concrete slab and the exposed brickwork. The second coat should be brushed on at right angles to the first.

The first job is to remove the old floor and dig out the ground below to at least 12in below the final floor level. Lever up an old wooden floor and saw through the joists for easy removal. Then demolish the dwarf walls. Break up a concrete floor: the best way is with a rented jack hammer. Keep the rubble for use as a bed for the concrete later. Wear stout boots, thick gloves, overalls and safety goggles.

Find the flashing in the walls; it may be a layer of slate or bitumen, or one or two courses of engineering bricks. If necessary, chip away the plaster to find it.

If the floor in the next room is of suspended wood, lay plastic drain pipes between any airbricks and the inter-connecting door threshold, setting them in place with bits of stone or brick: this is vital to provide ventilation throughout the floor. Build a retaining wall across the threshold with concrete building blocks.

Next make up some datum pegs from 2 x tin sawn softwood marked with the depths of the bed and concrete subfloor layers: 6in and 4in respectively. Cut a point on one end of the pegs then drive a peg into the ground near a given reference point, to indicate the surface of the floor. Drive the other pegs in at 3ft intervals, checking that their tops are level with the first.

Put down the brick and stone bed, leveling it with the marks on the pegs and compacting it well with a purpose-made tamper. Spread a layer of damp builder’s sand over the top to fill any voids.

The concrete for the subfloor should be of 1 part cement: 21/2 parts concreting sand: 4 parts gravel.

Lay the concrete so that it is level with the tops of the pegs, tamping it down well and drawing a stout batten across the tops of the pegs to level it. Fill any hollows with more concrete then tamp again.

When the concrete has cured, lay the cleavage membrane. With bitumen emulsion apply about three coats, taking it up the wall to the flashing. If plastic sheet is used, tack it to the walls above the flashing. Fold the corners and overlap the sheets by 8 to 12in, sealing the join with building adhesive.

Use 1 x 2in battens to divide the floor into 3ft wide bays for the finishing screed. Set them in place with dabs of mortar, level if necessary by packing offcuts underneath: check with a spirit level.

Fill the bays with a 3:1 mortar mix and draw it off level with a straight-edged batten held across the tops of the dividing battens. When two bays have been completed, lift out the batten in between and fill the resulting slot with mortar. Then trowel both bays smooth with a metal trowel. When the mortar has stiffened, give it a final polish with a wetted trowel.

While the upper floors of a house will always be constructed of wood, the ground floor may be made of wood or it may be of solid concrete.

All wood floors are based on the same method of construction with minor differences. They all have a supporting framework of wooden beams called joists onto which are nailed wooden boards or plywood panels and may have a plain or decorative finish.

The joists of wooden ground floors are supported at their end — and sometimes at one or two points in between — or additional wood beams known as “wall plates”. These, in turn rest on the tops of low brick “sleeper” walls.

These are not solid, but are laid in honeycomb fashion with spaces between the bricks to allow the air to circulate below the floor to prevent condensation and rot forming. For the same reason, vents are usually fitted at the base of the external walls and must always be kept clear. Slates or strips of flexible flashing material are laid between the wall plates and sleeper walls to prevent damp attacking the wood.

Sometimes the joists are laid on top of individual bricks set on the ground. Upstairs, the joists are also supported by wall plates but these are held by metal brackets called joist hangers, which are cemented into the walls. Sometimes the joist ends may be set in sockets between the bricks, with a metal plate below to spread the load through the wall.

Most modern houses have solid ground floors. These comprise of a layer of compacted gravel on top of which is a 4in layer of concrete called the subfloor. A damp-proof membrane bitumen or thick plastic is laid next and is carried up and down the wall to link with the flashing around the base of the house.

A thin layer of mortar can be laid on top of the membrane which will provide a level surface for most types of flooring.

Over the years a wooden floor can suffer considerably from wear and tear. The joists may warp or sag, boards may shrink to open up gaps through which draughts whistle, or they may become loose or damaged. The whole structure may be further weakened by woodworm or rot. Fortunately, many of the minor problems can be cured easily, although serious rot or insect attack may mean complete replacement and should be dealt with by a specialist.

Probably the most common fault with a wooden floor is creaking floorboards due to the fixings working loose. The cure is simple: either drive the nails back in or replace them with longer nails or screws. Punch nail heads below the surface and countersink the screw heads.

Gaps of less than 1/tin can be filled with papier-mdché, which you can make yourself. Half fill a bucket with small pieces of torn, soft white paper, gradually adding boiling water while you pound the paper into a thick paste. Allow it to cool and stir in enough cellulose wallpaper paste to make a thick mixture. Add wood stain to match the color of the boards.

When the papier-mâché is quite cold, force it between the boards with a filling knife, leaving it slightly proud of the surface. Leave it for at least 48 hours then sand smooth.

Fill wider gaps with softwood fillets: cut the fillets fractionally wider than the gaps they are to fill, using a backsaw. The fillets should be fractionally deeper than the floorboards: that is, about lin. Plane the fillets so that they taper slightly at the bottom then tap them into the gaps with a hammer and block of wood. Use a plane to shave the top edges of the fillets flush with the tops of the floorboards. Make sure the ends of fillets meet on a joist: secure them to the joists with brads.

Damaged boards

Damaged sections of boards should be cut out and replaced, or a new board fitted if the damage is substantial. First check that there are no pipes or cables running below the damaged section, otherwise you will have to remove the entire board in case you cut into them by accident.

To cut out a section of board, first find the edges of the joists at each end. Do this by sliding a knife blade along the gap between the boards. If the boards are tongued-and-grooved, you will have to cut through the tongues by drilling a starting hole and using a keyhole saw or with a circular saw set to the depth of the board.

Drill a starting hole for the saw just in from the edge of each joist and cut through the board at each end in line with the joist edges.

Lift out the damaged section; if it is nailed to intermediate joists, lever it free using a masonry chisel and a stout length of wood. Lever the board upwards at the fixings with a chisel until you have lifted the end enough to be able to slide the wood below it, while resting it on the tops of the boards on each side. Pushing down on the end of the board will spring the fixings from the joist. Continue in this fashion until you have freed the board. A complete floorboard can be removed in the same way.

Screw or nail lengths of 2in sq batten to the sides of the joists flush with the undersides of the old boards. Then nail a new section of floorboard to the tops of the battens.

Sagging joists

On wide, unsupported spans, the joists may sag in the centre of the floor, giving it a slightly “dished” surface. To overcome this, add packing pieces to the tops of the affected joists.

Lift the floorboards and place a straightedge across the joists at several points. Measure any gap between the tops of the joints and the straightedge and use the measurements to mark out lengths of softwood batten. These must be the same width as the joists. Plane the battens to size and nail them to the tops of the affected joists. Finally, re-lay the floorboards.