Concrete screed flooring

The best way to repair an old uneven or decayed wooden floor on the ground is to replace it with a concrete floor covered with a screed layer. Such a floor will be dry thanks to waterproofing with a polyethylene membrane (below), even and durable and is an ideal base for laying ceramic or stone tiles, as well as subfloors made of chipboard..

The construction of such a floor requires careful planning. The total thickness of the multi-layer concrete floor will be at least 25 mm, so make sure that the passage in doorways is not restricted or the volume of the room is not reduced. Pipes and cables running under the floor must be either insulated or covered with covers. It is necessary to provide ventilation of plank floors in adjacent rooms if it is disturbed as a result of laying a concrete floor. To do this, use plastic pipes with a diameter of 100 mm, installed in concrete, connect the ventilation holes in the inner walls with the ventilation holes in the outer walls..

Prepare all necessary materials before starting work. Usually, all the necessary materials can be purchased at a building materials store, but sometimes you have to purchase gravel directly from a company that is engaged in quarrying. To estimate the required amount of cubic meters of concrete, screed and gravel, it is necessary to multiply the area of ​​the room by the thickness of each layer. Order a concrete mix in the ratio: 1 part of cement, 2 parts of sand and 3 parts of crushed stone or gravel, or 1 part of cement to 6 parts of a ready-made mixture of 20 mm crushed stone with sand. For the screed, order a mixture of 3 parts of acute-angled sand with 1 part of cement. Remember, cement must be stored dry..

For mixing large quantities of concrete, rent an electric or diesel mixer. To prepare the first batch, fill the mixer with approximately two-thirds of the dry components in the appropriate proportion, mix them dry and then gradually add water until plastic, measuring its volume. When preparing subsequent batches, first pour water (the volume is already known), and then pour dry ingredients into it.

Wear gloves to avoid skin irritation. If concrete gets in your eyes, rinse immediately with cold water and see a doctor immediately. At the end of the work, rinse the mixer thoroughly with water and remove all concrete splashes from the skin. To speed up the placing of the concrete, have two assistants prepare the concrete and bring it to the placement room. Divide the room into strips about 1 m wide. Start with the strip farthest from the doors and work your way towards the doors. After the concrete has been wet for two weeks, lay a screed layer on the floor. A properly arranged concrete floor does not require any maintenance. However, if the old screed is cracked or a new screed needs to be laid on the old concrete floor, you can break the old screed layer with a jackhammer and then put a new screed. If there are signs of dampness of the old concrete floor due to a violation of waterproofing, place a new polyethylene membrane on the concrete and lay a screed layer 50-65 mm thick on it.

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Anatomy of a concrete floor. A hard concrete floor is built over the ground from several layers of different materials. On a crushed stone or gravel base, usually from 100 to 160 mm thick, a layer of sand or screening is laid, which protects the waterproofing membrane and provides an even surface for laying the next layer – concrete of the same thickness as the gravel layer.

The concrete surface is covered with a layer of slurry to ensure a strong bond with the top layer of the screed, at least 40 mm thick. The edges of the film are raised to the walls above the concrete layer to ensure good waterproofing of the floor.

Laying the floor on the ground

1. Marking floor and concrete levels. Remove debris (paper, wood chips, pieces of plaster) from the ground and protect the cables and pipes under the floor by insulating or laying them in gutters.

Set the level of the finished floor to the level of the doorway so that it corresponds to the level of the floor in the adjacent room, and make a mark on the wall at a height of 1 m from this level. Draw a solid (beacon) line at this level throughout the room. At a distance of 1 m from it, draw a line of the surface of the clean floor. At the doorway and in each corner of the room, measure the thickness of the screed layer from the floor level and hammer nails into the walls at this level. Pull a cord between the nails to indicate the level of the concrete base. In a room with plastered walls, remove the plaster 25 mm above floor level before drawing the floor line and installing the cords..

2. Laying gravel. Drive wooden pegs into the ground along the walls in rows going through the center of the room at 1m intervals so that their top is 100mm (concrete layer thickness) below the cords. Start backfilling with gravel against the wall opposite the doorway by tamping large stones with a sledgehammer. Compact gravel with a tamper – metal plate with wooden handles.

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The surface of the compacted layer must be flush with the top of the pegs. Remove sharp stones from the surface, as they can damage the plastic wrap. Check the levelness of the gravel layer by placing a long ruler on the pegs and adjust where necessary. Remove the pegs and fill in where they were with gravel.

3. Laying a layer of sand. Spade a layer of sand with with sharp-angled grains on a layer of gravel, then smooth out its surface with the back of a shovel. Tamp the sand surface with a wooden rammer.

4. Laying the waterproofing membrane. Place a 250 micron thick plastic wrap on top of the sand layer, raising it on the inner walls just above the level of the finished floor, and on the outer walls above the level of waterproofing of the walls. Carefully wrap the film in the corners of the room.

Smooth out any folds in the film and place the edge under the cords that mark the concrete level. If several rows of film are used to make the membrane, lay them overlapping and cover them with thick PVC adhesive tape.

5. Placement of concrete. Divide the room into strips about 1 m wide using slats 1.5 to 2 m long and 50 mm wide. The top surface of the slats should be flush with the cords stretched along the walls. Remove the cords after installing the slats. To protect the plastic wrap while you work, lay the boards up to the center of the first strip you will be placing the concrete on. Place the concrete starting at the corner farthest from the door and leveling it with a shovel so that it is just above the level of the wooden battens.

6. Leveling concrete. Level the concrete with a rule-rail with a section of 100 by 60 mm and a length of about 1.2 m, moving it along the demarcation rails and towards yourself. Continue placing and leveling the concrete as shown, removing the battens between the strips and filling in the concrete in the gaps after removing the battens..

After laying each strip, cover it with damp bags or plastic wrap and allow to cure and harden for about 4 weeks. During this time, constantly moisten the concrete surface with water.

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Screed laying

1. Application of slurry. Rinse the floor with warm water to remove debris from the surface.

Prepare a screed mix using the same technology as concrete, then from cement and water prepare a little slurry with the consistency of sour cream, adding the appropriate binder during preparation in the proportion recommended by its manufacturer. Starting from where you started placing the concrete, spread a layer of cement paste about one square meter with a wide brush. meter of concrete.

2. Installation of lighthouse rails. Place two parallel, 100 mm wide screed strips on the cement-lined concrete floor. Lay one of the strips at a distance of 75 mm from the wall, the other at a distance of about one meter from the first. On each strip of the screed, lay 1 meter wooden lighthouses with a section of 75 by 37 mm. Use a hammer, spirit level and a ruler to make the slats level and level with the finished floor line.

3. Laying the screed. Check the consistency of the screed by kneading it in your hand. If it is not moist enough and does not keep its shape, add water. Use a shovel to place the screed on the part of the floor covered with cement paste and level it so that it is just above the lighthouse battens. Level the screed using the rule strip you used to level the concrete. If you get an uneven surface, add some mortar to the grooves and repeat the procedure. Remove the rail that is next to the wall and fill its place with a screed.

4. Leveling the surface. Smooth the surface of the screed with light circular motions with a trowel or special steel float. After smoothing, apply the slurry to the next square meter of the floor, lay the screed and flatten it so that the joint between the two areas is invisible. Install the screed throughout the room in the same order in which you placed the concrete.

As you progress, remove the lighthouse rails and fill the free joints with a screed. Leave the screed to harden overnight, then spray with water, keeping the surface moist for two to three days. The floor can be walked on after 24 hours, but you should wait at least two weeks before tiling, carpet, or subfloor chipboard.

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