Preparing Surfaces for Microcement
Microcement is incredibly strong, durable and hard wearing, but because it’s applied in very thin coats, it relies heavily on the surface that it’s applied to for support.
Here we have summarised all the types of surface (AKA substrate) that are commonly used alongside microcement. We have outlined the best ways to prepare each surface so that it will stand the best chance of performing well alongside the microcement.
Golden Rules:
• Surfaces should be completely smooth – as if you were going to paint onto them.
• Surfaces should be well consolidated, so that any chance of movement is eliminated.
Additional Important Rules:
• Never Microcement directly onto natural timber or across cold joints/expansion joints.
• Surfaces should be free from oil stains, dirt, dust and excessive laitance.
• There must be no risk of water getting to the microcement during the install process.
• Surfaces must be damp-proofed and edges siliconed so that no water can get to the Microcement from underneath at anytime.
• Allow 3-4mm as the finished depth.
For External Surfaces Only
- MicroRock can only be installed on a substrate with a minimum compressive strength of 25N/mm2 and a Tensile Strength of 1.5N/mm2.
- MicroRock is waterproof both above and below, so as long as substrate is less that 10% moisture, it can be applied.
You can microcement onto both painted, plastered and plaster boarded walls. Because plaster is completely flat, it is a lot easier to microcement onto. Plasterboard will need some additional prep.
Painted Walls
Sand the paint with 120 grit sand paper to remove any loose paint and give it a key.
Plasterboards
Ideally use tapered edge plasterboards. Ensure the boards are well glued and screwed in place. Tape the joins and flush with a compatible filling and finishing compound or MicroDur Base. IMPORTANT: Leave until dry, minimum 24 hours. If it isn’t completely dry, the lines may ghost through the microcement and be visible in the finish.
These are often used in wet rooms on floors and walls. Brands include: KNAUF AQUA-PANELS® / NO MORE PLY® / HARDIE® BACKER BOARDS
Well Consolidated
Make sure the boards are well glued and screwed in place to eliminate any chance of movement. If you are fitting the boards yourself, use a suitable adhesive between the joins, leave to dry overnight and razor scrape/sand the excess off once set. Make sure silicone is not left on the surface to be microcemented. Refer to cement board manufacturer for best adhesive products to use. Countersink screw holes.
Completely Flat
Boards must be flush with one another, ridges will highlight in the microcement. There must be no voids, even around the bottom edge. Microcement can’t be used to level surfaces/fill voids – it must only be applied as thinly as the grain. The surface must be completely flat. As with all surfaces, microcement will follow the contours of the substrate it is going onto.
Fill the Joins and Screw holes with MicroDur Base or Suitable Repair Mortar so that they are flush with the boards.
IMPORTANT: Leave until dry, minimum 24 hours. If the MicroDur Base/Mortar isn’t completely dry, the lines & holes may ghost through the microcement and be visible in the finish. Once the MicroDur Base/Mortar is dry, use wide, self adhesive skrim tape to bridge the joins in the corners. be visible in the finish.
Cement Faced with Foam Core. Brands include: WEDI BOARDS® / JACKOBOARDS® / PROWARM® BOARDS / STS® TILES BACKER BOARD
These are not recommended for use with Microcement. They rely on the rigidity of tiles to complete the system, which means they aren’t rigid enough themselves to microcement directly on to. They are also, often held in place with large washers that make the surface uneven.
If they are already installed then you will need to complete the following extra prep to be able to Microcement onto them.
Boards must be firmly glued and screwed in place, and flush with one another, ridges will highlight in the microcement. There must be no voids, even around the bottom edge. Microcement can’t be used to level surfaces/fill large voids. The surface must be completely flat. As with all surfaces, microcement will follow the contours of the substrate it is going onto.
Counter sink washers and fill joins & screw holes with MicroDur Base so that they are flush with the boards. You may find it easier to purchase some thick base and use that instead.
IMPORTANT: Leave until dry, minimum 24 hours. If the MicroDur Base isn’t completely dry, the lines & holes may ghost through the microcement and be visible in the finish.
The following prep & conditions apply to preparing tiles for microcement:
Well Consolidated and Flat
Make sure tiles aren’t drummy or loose. Take out any which are & relay them. The surface must be completely flat.
As with all surfaces, microcement will follow the contours of the substrate it is going onto. If a lot of the tiles are loose or uneven, it may be better to remove them. If they are fixed firmly in place but uneven, you could consider self levelling over them to flatten off – follow manufacturer’s recommendations for applying the leveller over tiles.
Clean Tiles & Give them a Key
The tiles must be clean and free from dirt, dust and grease. Grout lines must also be clean and free from moisture. Ideally, run an abrasive sander over the surface to ensure the primer achieves good adhesion with the surface.
There are 2 different options for filling the grout lines:
Option 1: Fill the Grout Lines with MicroDur Base
This is the more basic process. Choose this option for vertical surfaces.
Fill the grout lines with MicroDur Base so that they are flush with the tiles.
IMPORTANT: Leave until dry, minimum 24 hours. If the MicroDur Base isn’t completely dry, the grout lines may ghost through the microcement and be visible in the finish. Once the MicroDur Base is dry, cut mesh and lay it over the whole area, not overlapped, flip the mesh so it curls towards the surface and apply Primer TAC over it with a medium pile roller. The Primer TAC will hold the mesh in place. Primer TAC will keep it’s TAC so for floors, you will need spiked shoes to walk on it.
Option 2: Fill the Grout Lines with Epoxy, Mesh & Sand Blind
This is the more advanced process. It can only be done on horizontal surfaces e.g. floors. The best way to minimise the chance of movement transferring through to the surface is to apply Epoxy, Mesh & Sand Blind over the entire floor.
The epoxy will also fill the grout lines to make the floor flat. Many installers choose to use it on all floors as it ensures the floor dries at a uniform rate, helps to prevents stains in the substrate ghosting through to the microcement and strengthens the base. Use a trowel to apply an even coat of Epoxy over the sub-floor and mesh. You’ll need to ensure you have completely filled the grout lines in the sub-floor and also completely covered the mesh.
Whilst the Epoxy is still wet, spread the quartz sand across the surface. You can scatter it by hand, starting at the entrance to the room and walking on the sand into the room. Or by walking on the Epoxy with spiked shoes. The following day, sand any high spots and hoover up all the loose sand.
Epoxy, mesh & sand are contained within the Floor Strengthening Kit available to buy from relentlessmicrocement.com.
You will need to prime the surface with Primer 100, you can apply a neat coat directly onto the sand. The Primer is applied with a medium pile roller.
Because microcement needs a completely flat surface, it’s best not to use angle beads on corners. The microcement is very strong as well so there isn’t the same risk of it failing on the edges like plaster.
If angle beads are already installed, then you will need to make sure they’re well screwed in place and use a compatible filling and finishing compound or MicroDur Base to flush out the angle bead and leave to dry for 24 hours.
There must be no voids between adjacent walls or the wall & floor. If you are fitting the boards yourself, use an adhesive sealant along the bottom edge of the boards and squash the boards down to the tray/floor. Don’t smear silicone on the surface, instead, let it ooze out and razor scrape off the excess once it is dry. Use wide, self-adhesive skrim tape to bridge the internal corner.
All boards must be well glued and screwed in place. so that any chance of movement has been eliminated.
Boarded floors are more susceptible to movement than any other sub floor. So the prep needs to be done carefully and we highly recommend using epoxy, mesh and sand blind – included in high performance kits & floor strengthening kit.
Well Consolidated
Make sure the boards are well glued and screwed in place to eliminate any chance of movement. Boards must be recommended as “floor grade” by the manufacturers. If you are fitting the boards yourself, use tongue & groove boards, with a suitable adhesive between the joins, leave to dry overnight and razor scrape/sand the excess off once set. Make sure silicone is not left on the surface to be microcemented. Products that you can use include: adhesive sealant or polyurethane wood glue. Countersink screw holes.
Completely Flat
Boards must be flush with one another, ridges will highlight in the microcement. Microcement can’t be used to level surfaces – it must be applied as thinly as the grain. The surface must be completely flat. As with all surfaces, microcement will follow the contours of the substrate it is going onto.
You have 2 options for achieving a flat surface:
Option 1: Filling the joins and screw holes with MicroDur Base or Wood Filler
This is the basic process – it relies on there being no movement at all in the sub-floor.
Fill the joins and screw holes with MicroDur Base or Wood Filler so that they are flush with the boards.
IMPORTANT: Leave until dry, minimum 24 hours. If the MicroDur Base/Wood Filler isn’t completely dry, the lines & holes may ghost through the microcement and be visible in the finish. Once the MicroDur Base/Wood Filler is dry, cut mesh and lay it over the whole area, not overlapped, flip the mesh so it curls towards the floor and apply neat Primer 100 over it with a medium pile roller. The Primer 100 will hold the mesh in place.
Option 2: Filling the Joins & Screw holes with Epoxy, Mesh & Sand Blind
This is the more advanced process, which we highly recommend for boarded floors where there is more chance of movement when compared to solid surfaces. These products are included in high performance kits & floor strengthening kit.
It can only be done on horizontal surfaces e.g. floors. Reduce the chance of movement transferring through to the surface by applying Epoxy, Mesh & Sand Blind over the entire floor. The epoxy will also fill the joins and screw holes to level off the floor. Use a trowel to apply an even coat of Epoxy over the sub-floor and mesh. You’ll need to ensure you have completely filled the joins and screw holes in the sub-floor and also completely covered the mesh, so that it has good adhesion with the floor.
Whilst the Epoxy is still wet, spread the quartz sand across the surface. You can scatter it by hand, starting at the entrance to the room and walking on the sand into the room. Or by walking on the Epoxy with spiked shoes. The following day, sand any high spots and hoover up all the loose sand.
Epoxy, mesh & sand are contained within the Floor Strengthening Kit available to buy from relentlessmicrocement.com.
You will need to prime the surface with Primer 100, you can apply a neat coat directly onto the sand. The Primer is applied with a medium pile roller.
NATURAL TIMBER FLOOR BOARDS will need to be over boarded with a timber composite like OSB/Plywood or Cement Board.
Before microcement is applied to concrete, screeds or self leveller, the following actions must have taken place:
Cured to less than 5% Moisture Content
If there is still moisture in the substrate, the microcement could blister or de-laminate as moisture is trapped under the surface. Floors that aren’t fully cured are also more likely to crack as they do so whilst curing. The moisture content can be tested with a moisture meter or by checking with the manufacture of the screed. The drying time will depend on the depth of floor & the type of product used. Be aware that Anhydrite screeds can take a lot longer to cure than sand and cement.
Special Prep for Anhydrite Screeds
Remove laintance by grinding back the surface until there is no more loose dust. Vacuum dust away, apply Epoxy, Mesh & Sand Blind. It’s not essential that you include mesh with the Epoxy, but it is advisable since that is the strongest option.
Put Underfloor Heating through a Full Cycle
Once cured, take underfloor heating up to max temperature & back down to off @ small intervals – as per screed manufacturers recommendations, no more than 5°C per day. The initial thermal expansion & contraction may force out cracks which must be repaired.
Repair Cracks under 3mm Wide
Use a 5” grinder to open up the crack (take care not to cut into any underfloor heating), hoover out any dust then mix Epoxy with Epoxy Hardener (Ratio 5:2) and pour into the
crack. Leave to cure fully, this will take for at least 12 hours. It may need topping up depending on how deep the crack is.
Repair Cracks over 3mm Wide
Use a 5” grinder to open up the crack and grind approx 100mm “stitches” horizontally across the length of the crack around 40mm apart (take care not to cut into any underfloor heating), hoover out any dust then insert steel helical stitching bars into the stitches. Mix Epoxy with Epoxy Hardener (Ratio 5:2) and pour into the crack. Leave to cure fully this will take for at least 12 hours. It may need topping up depending on how deep the crack is.
Epoxy, Mesh & Sand Blind
Where crack repairs have taken place, the best way to reduce the chance of cracks transferring through to the surface is to apply Epoxy, Mesh & Sand Blind over the entire floor. Many professional installers choose to use it on all floors as it ensures the floor dries at a uniform rate, helps to prevents stains in the substrate ghosting through to the microcement and strengthens the base. Use a trowel to apply an even coat of Epoxy over the sub-floor and mesh. You’ll need to ensure you have completely filled any voids in the sub-floor and also completely covered the mesh.
Whilst the Epoxy is still wet, spread the quartz sand across the surface. You can scatter it by hand, starting at the entrance to the room and walking on the sand into the room. Or by walking on the Epoxy with spiked shoes. The following day, sand any high spots and hoover up all the loose sand.
Epoxy, mesh & sand are contained within the Floor Strengthening Kit available to buy from relentlessmicrocement.com.
Priming the Surface
Whether you have applied Epoxy & Sand or you are going straight onto the screed, you will need to prime the surface with Primer 100. If you are going directly onto concrete, screeds & self leveller, apply 1 x Primer 100 diluted with 50% water, leave to dry and then apply a neat coat of Primer 100 with Fibreglass Mesh. For Epoxy & Sand you can apply a neat coat directly onto the sand. The Primer is applied with a roller and dries in about 1 hour. You must apply the 1st base coat within 12 hours.
Never Microcement over Cold Joints/Expansion Joints
Microcement doesn’t need expansion joints itself but where they are in the sub floor, they must be carried through to the surface. Use 4mm dural expansion joint beads – these need to be screwed into the floor and epoxied over.
MicroRock Base is used externally, to ensure ground water won’t affect the microcement system. It is a very strong epoxy based products so has some special requirements:
Strength of Substrate
MicroRock can only be installed on a substrate with a minimum compressive strength of 25N/mm2 (aka MPa) and a Tensile strength of 1.5N/mm2 (aka MPa)
Completely Flat
Surfaces must be completely flat before microcement is applied. It will follow the contours of the substrate and can’t be used to fill large voids. Blocks and bricks will need to be rendered before microcement is applied or over-boarded.
Generally, the following surfaces meet this critera, but please check with the manufaturer to be sure: CONCRETE, SCREEDS, SELF LEVELLER & CONCRETE RENDER INC. SWIMMING POOLS
Cured to less then 10% moisture content
If there is still moisture in the substrate, the microcement could blister or de-laminate as moisture is trapped under the surface. Floors that aren’t fully cured are also more likely to crack as they do so whilst curing. The moisture content can be tested with a moisture meter or by checking with the manufacture of the screed. The drying time will depend on the depth & the type of product used.
Repair cracks under 3mm wide
Use a 5” grinder to open up the crack (take care not to cut into any underfloor heating), hoover out any dust then mix Epoxy with Epoxy Hardener (Ratio 5:2) and pour into the crack. Leave to cure fully this will take for at least 12 hours. It may need topping up depending on how deep the crack is.
Repair cracks over 3mm wide
Use a 5” grinder to open up the crack and grind approx 100mm “stitches” horizontally across the length of the crack around 40mm apart (take care not to cut into any underfloor heating), hoover out any dust then insert steel helical stitching bars into the stitches. Mix Epoxy with Epoxy Hardener (Ratio 5:2) and pour into the crack. Leave to cure fully this will take for at least 12 hours. It may need topping up depending on how deep the crack is.
Do not Prime the Surface
It is best to go directly onto the surface with MicroRock Base, no primer or mesh. However if there are a lot of cracks &/or joins in the substrate. It may be appropriate to use epoxy, mesh & sand blind.
Epoxy, Mesh & Sand Blind
This is the more advanced priming process, which we highly recommend for floors with joins, cracks or grout lines where there is more chance of movement when compared to solid surfaces.
The products required to Epoxy, Mesh & Sand Blind are included in the Floor Strengthening Kit from Relentless Microcement.
This is the ideal system for wet rooms and shower trays, the panels and trays are completely waterproof and rigid. And the solvent weld bonds the tongue and groove edges of the panels together very well. The solvent weld can also be used to flush joins between panels & cures within 1 hour.
Refer to Aqua4ma Installation Guide for full details of how to install.
Well Consolidated & Completely Flat
Make sure the boards are well glued and screwed in place to eliminate any chance of movement. Use Kudos Aqua4ma Solvent Weld to join the boards. Countersink screw holes and use the Solvent Weld to flush joins and screw holes so that the surface is completely flat.
Boards must be flush with one another, ridges will highlight in the microcement. There must be no voids, even around the bottom edge. Microcement can’t be used to level surfaces/fill large voids. The surface must be completely flat. As with all surfaces, microcement will follow the contours of the substrate it is going onto.
Shower Trays for vinyl floors are rigid shower trays which allow for 3-4mm of product to finished floor height, making them good for use with microcement. Brands include: MARMOX SHOWERSTONE® / PURUS® / ON THE LEVEL®
Well Consolidated & Completely Flat
Make sure the tray is well glued and screwed in place to eliminate any chance of movement. Countersink screw holes.
Around the Waste
Do a dry run with the waste so that you can see how it comes together, and check the levels, bearing in mind the microcement will only add 3-4mm to the surface of the tray. Ideally, you will have a clearly defined edge to work up to with your microcement – so no water can get underneath it. If not, you may need use MicroDur Base to flush it out &/or silicone the edge so that no water can get behind the microcement.
Around the Tray
If you are microcementing the floor outside of the shower tray, the tray must be flush with the boards, ridges will highlight in the microcement. There must be no voids. Microcement can’t be used to level surfaces/fill large voids. The surface must be completely flat. As with all surfaces, microcement will follow the contours of the substrate it is going onto.
Internal Corners (Between Wall & Floor/Tray)
There must be no voids between the wall & floor. If you are fitting the boards yourself, use an adhesive sealant along the bottom edge of the boards and squash the boards down to the tray/floor. Don’t smear silicone on the surface, instead, let it ooze out and razor scrape off the excess once it is dry. Use wide, self adhesive skrim tape to bridge the internal corner.
You have 2 options for achieving a flat surface & bridging the join between the tray and the other boards on the floor:
Option 1: Fill the Joins and Screw holes with MicroDur Base/Suitable Repair Mortar/Filler
This is the basic process – it relies on there being no movement at all in the sub-floor. This is the correct process for walls. Fill the joins and screw holes so that they are flush with the boards. IMPORTANT: Leave until dry, minimum 24 hours. If it isn’t completely dry, the lines & holes may ghost through the microcement and be visible in the finish. Once the MicroDur Base/Mortar/Filler is dry you can prime & mesh. For non-absorbent surfaces apply Primer TAC & for absorbent surfaces use Primer 100. Cut fibreglass mesh and lay it over the whole area, not overlapped, flip the mesh so it curls towards the floor and apply the primer over it with a medium pile roller. The primer will hold the mesh in place.
Option 2: Fill the Joins and Screw holes with Epoxy, Mesh & Sand Blind
This is the more advanced process, which we highly recommend for joins in floors where there is more chance of movement when compared to solid surfaces.
It can only be done on horizontal surfaces e.g. floors. Reduce the chance of movement transferring through to the surface by applying Epoxy, Mesh & Sand Blind over the entire floor. The epoxy will also fill the joins and screw holes to level off the floor. Use a trowel to apply an even coat of Epoxy over the sub-floor and mesh. You’ll need to ensure you have completely filled the joins and screw holes in the sub-floor and also completely covered the mesh, so that it has good adhesion with the floor.
Whilst the Epoxy is still wet, spread the quartz sand across the surface. You can scatter it by hand, starting at the entrance to the room and walking on the sand into the room. Or by walking on the Epoxy with spiked shoes. The following day, sand any high spots and hoover up all the loose sand.
You will need to prime the surface with Primer 100, you can apply a neat coat directly onto the sand. The Primer is applied with a medium pile roller.
First 14 Days
Like all cementitious products, microcement takes 28 days to full harden. It’s at it’s softest for the first 14 days after laying. During this time it should only be subjected to light use and light foot traffic.
Any heavy work is not recommended, but if it does take place then we recommend covering the floor with a breathable material or only cover down whilst working & lift the protection off for the majority of the time. The surface needs to dry out and harden. If airflow is restricted, it will stain & not cure correctly.
Fixing to Microcement Surfaces
Microcement can be drilled and screwed into using bits that are suitable for the substrate. Any holes or cuts will need protecting from moisture penetration by either putting silicone into screw holes or by surrounding fixtures & fitting entirely with silicone. Care must also be taken not to scratch the sealers whilst installing fixtures & fittings.
No Dragging or Dropping
Dragging heavy objects over the surface, or dropping them onto the surface is not recommended, as damage could occur. Lift furniture rather than dragging it, and use lids or felt pads to protect flooring from pressure points or abbrasive surfaces.
Microcement is strong, but due to its limited thickness, it will deform in the event of a strong blow if the support beneath deforms. Generally, abrasion and impact resistance is comparable with hard wood.
Stain Resistance
Chemical resistance depends on the sealer used to protect the product. Our sealers are among the best in the industry for both hardness & strength.
Products containing Dyes & acidic or alkaline products like tumeric, vinegar, lemon juice or bleach, may leave slight marks on microcement if left on the surface for prolonged time. If cleaning is done quickly, they shouldn’t stain.
If water stains appear within the 1st 4 weeks of use, let the stain dry out & reseal immediately. Stains will become permanent if not treated quickly.
Prolongued Exposure to Water
If water is trapped against the surface for a prolonged length of time it may stain & potentially cause the microcement to blister. It is not advisable to leave wet towels, plant pots, wet shampoo bottles etc. in direct, prolongued contact with the microcement.
Cleaning
Microcement surfaces can be cleaned with any pH neutral cleaning products.
Do not clean microcement surfaces with aggressive or descaling products, such as those which contain chlorine, bleach and ammonia as they can damage the sealers.
Aftercare
Use Cemher Floor Protect every 2 -3 months to protect you microcement and to help build up the sealers.