Preparing Surfaces For Microcement

The following guidelines are for the attention of main contractors, builders, architects and clients who are responsible for preparing/specifying surfaces for microcement.  Please read them carefully as early in the build as possible. To see more background see our Microcement guide.

Well Consolidated

The surface should be well consolidated, so that no further settlement or movement is anticipated.  As with tiling, movement in the sub floor will cause cracks to appear in the surface.

Cracks in the microcement due to unconsolidated surfaces are the responsibility of the contractor who laid the sub floor not the applicator of the microcement.

Whilst microcement is very hard, it should be considered as a topping compound only.  It is the responsibility contractor who laid the substrate that the materials used are fit for purpose.

We can fill cracks and gaps that have appeared in the surface during settlement of less that 5mm wide.  Cracks that are larger than 5mm must be filled by the contractor who laid the floor in advance of microcement installations taking place.

Subfloors must be dried in accordance with manufacturers recommendations and underfloor heating should have completed a full cycle in advance of installation.

Cold Joints & Expansion Joints

Wherever 2 separate subfloors meet, whether they have been laid at different times or have intentional expansion joints in them, movement is most likely to occur along the join. Whilst we take every care to fill and mesh the joints, if there is movement in the subfloors, this may cause the microcement to crack.

In order to prevent cracks in the microcement caused by cold joints, concrete & screed subfloors should be poured in one complete pour wherever possible. Or we can insert a bead or threshold to separate the 2 surfaces and microcement up to the bead on either side.

Level Surfaces

Floors must be level to within 5mm tolerance maximum.  Floors that are not level will need to be levelled off with a self-leveller. Please leave 4mm to finished floor height for microcement.

Microcement can be laid onto a wide range of surfaces, including concrete, screeds, cement board, ceramic, plasterboard, ply board, chip board & mdf.  It cannot be applied directly onto timber which is at risk of warping.  And it cannot be applied over voids between adjoining surfaces.

Timber floor boards will need to be covered with a suitable cement board. These should be butted up against one another with silicone squeezed between the joints leaving excess to dry so that it can be cut cleanly off.

The boards should be glued and screwed in place to create a stable base for the microcement.

Less than 5% Moisture Content

All surfaces will need to have less than 5% moisture content when we come to install.  We can test the moisture content on arrival, but please work to the manufacturer’s recommended lead times for freshly laid surfaces.  If surfaces are not dry when we arrive on site, extra costs and/or delays to the build will be incurred.

Access & Floor Prep

The area will need to be completely clear, with no access to other trades for the time it takes the installer to complete the work (usually 6 days).  We would prefer that skirting boards & kick boards are removed/left off prior to work commencing.

Until sealed, the microcement will be very porous so any water spilt on the surface will stain. Anyone who spills water on the surface must take responsibility for the cost of repairs.

Curing Times

The microcement will not be fully cured until 4 weeks after it has been laid.  Please take care not to scratch, cut, drop or drag items on the floor during this time.  The cost of repairing any damage caused will need to be paid by those responsible.

Once cured, microcement is strong, anti-slip and has a good resistance to stains.  You can treat it as you would a hard wood floor.

Underfloor Heating

Underfloor heating must have completed a full cycle prior to microcement being applied. This will force cracks to appear in advance, reducing the liklihood of them appearing post-installation.

Please ensure underfloor heating is turned off 48 hours before work is due to start & keep it off for the duration of the work.

After applying the microcement, at least 48 hours should pass before the heating is gradually turned on (+5°C each day).

Maintain the water entering the circuits at 25°C throughout 2 or 3 days. Then gradually increase the water temperature to 45°C and keep it on for several days.

Always change the temperature gradually, both at the beginning and at the end of the heating period.

Ensure the heating is turned on within 4 weeks of us laying the floor.

Make sure that the relative air humidity in the rooms is not too low.

Always avoid an accumulation of heat caused by rugs and carpets, or the lack of space between the furniture and the floor.

Showers & Wet Rooms

Prior to microcementing, shower areas and wet room floors must be covered in fit for purpose cement board or aqua board shower trays & flooring.  These should be fitted as per the manufacturer’s recommendations.

Water resistant plaster boards should be fixed to walls and siliconed at the joint with the floors or shower tray. We ask that the walls are plastered to ensure the surface is level. Tanking tape & paste should be used to seal the join between walls and floors.

Any Questions?

Please feel free to get in touch. 07487 247 388 | info@relentlessinteriors.com