– Step 1: Before you patch a cement floor
– Step 2: Clean the floor
– Step 3: Apply an adhesion primer
– Step 4: Prepare the fibre patching mortar
– Step 5: Pour the patching mortar onto the cement floor
– Step 6: Case 1: Spread the self-levelling mortar
– Step 6: Case 2: Smooth the levelling mortar
– Step 7: For a 2nd layer of levelling mortar
Levelling a cement floor consists of balancing the foundation of an entire room before covering it, such as carpeting, tiles, linoleum, etc.
– If the defects of flatness (holes, cracks, hollows, etc.) are very localized, it is not necessary to level the floor, and it is enough to fill the gaps with mortar glue or cement.
– If your floor is uneven over a large area, levelling is required.
If the floor is heated, turn off the heat at least one day before levelling.
Turn off the radiators.
Do not apply patching mortar to a frozen floor.
1. Before levelling the cement floor
Assess the flatness of the floor
How do you know if your floor needs patching? Several techniques:
– Put your eye to the floor and look. Repeat the operation in several places in the room, taking distance. If you see only a few irregularities, try to remove them with a spatula.
– Place a 2-meter-long ruler at different points on the floor. If the unevenness is never more than 7 mm under the ruler, you do not need to level the floor. It is sufficient to fill the most critical holes and cracks.
Levelling is only for floors with irregularities greater than 7 mm on large surfaces.
Choose the suitable mortar to level your floor.
Depending on the unevenness of the cement floor, a professional can choose between self-levelling or levelling mortar:
– For a floor with flatness defects of less than 1 cm, use self-levelling mortar.
– For a floor with significant unevenness (indentations greater than 1 cm), use a levelling mortar.
2. Clean the floor
– Smooth out the roughness of the cement floor with a sanding stone.
– Clean the floor:
◦ With a brush to remove anything that sticks out or snags.
◦ With a vacuum cleaner to rid it of dust.
◦ With a solvent and rag for glue marks and grease stains.
– If necessary, dry the floor with a fan heater.
– Treat the floor for moisture if needed. Never scrape a wet floor.
3. Apply an adhesion primer
Bonding primer is a liquid that allows the floor covering or patching mortar to adhere to the surface.
Once the cement floor is clean, dry and free of unevenness, apply the bonding primer.
– Protect the bottom of the walls with tape.
– The primer is applied like an undercoat of paint, using a roller or a brush.
– Start away from the door, and finish at the door so that you can leave the room.
– After applying the primer, allow it to dry for the time indicated on the package. Some adhesion primers are coloured and turn white when dry.
4. Prepare the fibre-reinforced patching mortar
Screed mortar comes in powder form for mixing with water.
There are two types of patching mortar, self-levelling mortar and levelling mortar. The preparation is the same for both mortars:
– Calculate the surface area of your room to determine the amount of levelling mortar to prepare, based on the desired thickness:
◦ a few millimetres for self-levelling mortar;
◦ 1 cm for levelling mortar.
– Observe the proportions of water and powder indicated on the package.
– Mix the mortar and water using an electric mixer or drill equipped with a mixing whisk. Set the mixer or drill to a slow speed.
– The resulting mixture should be smooth and fluid without being too liquid.
– Let stand for 2 minutes.
5. Pour the patching mortar onto the cement floor
Once the mixture is ready, pour it onto the floor in successive zones.
When pouring the patching mortar, remember to finish at the door!
You will then need to spread it. The technique is different for different types of patching mortar.
6. Case 1: Spreading self-levelling mortar
Self-levelling patching mortar is an easy way to level a floor; it is prepared the same way as levelling mortar but is easier to apply. Self-levelling patching mortar spreads by itself.
Once the self-levelling mortar is poured:
– Using a smoothing trowel, spread the mortar over the entire surface. The paste spreads easily when it is fluid enough.
– Make vertical movements from left to right and then from right to left to spread the mortar properly. The goal is to obtain a 3 mm thick layer.
– Let it dry for about half a day, and the mortar should not be exposed to drafts or heat.
– Wait 3 days before laying a floor covering.
Tip: If the surface shows slight unevenness after drying, sand the floor; if the unevenness is significant, apply a second coat of levelling mortar.
6. Case 2: Smoothing the levelling mortar
The levelling mortar is applied in much the same way as the self-levelling mortar: it allows the levelling of a floor with hollows or a significant unevenness (deviations of more than 2 cm).
Once the levelling mortar is poured:
– Pull the mortar with an iron rule to spread it in a layer of about 1cm. Make movements from right to left and left to right, and pull towards you.
– Smooth with the smoothing trowel and let dry.
– You can lay a floor covering after 3 days.
Levelling mortar does not spread as quickly as self-levelling mortar, so do not hesitate to apply two coats on a floor with too many defects.
7. For a 2nd layer of levelling mortar
If you decide to apply a second layer of levelling mortar, smooth the first layer and let it dry for 3 hours before applying the second layer.
How to apply the second layer of levelling mortar:
– Prepare and pour a second coat.
– Pull with the iron ruler to spread the mortar evenly in a layer of about 1 cm. The two superimposed layers should not exceed 3 cm in thickness.
– Smooth carefully with a smoothing trowel and let dry.
– Wait 3 days before laying a floor covering.
Materials needed to level a cement floor
Drill with mixing whip
Aluminum ruler 2 m
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