Microcement Floor Isn’t Strong Enough

The microcement that we recommend for floors is very hard, at around 28-50N/mm2, depending on the spec.  It has a higher compressive strength than most concretes.

To put those figures into some context, this means that 1m2 of the microcement can hold 2.8 – 5 tonnes of weight without deforming.

If your microcement flooring isn’t proving to be as strong as this, then there is most likely a problem with the microcement application or the substrate it was applied to.

The headings below outline the most common reasons for weaknesses in microcement floors:

Recently Laid Microcement

The strength of the microcement increases gradually over time.  If the microcement was laid within the last 28 days, then don’t panic, it is still in the early stages of hardening, which takes time.  Avoid further damage by following the guidelines below:

Aftercare Guide

The microcement will continue to harden over time, and in unfavourable conditions, where heating & ventilation are limited, it will take longer.  So, we would always suggest leaving the floor for at least 3-6 months to naturally strengthen before taking any direct action.

Weak Substrate

Since microcement is a very thin coating that is applied directly to another surface, it is very much dependant on the substrate.  It will only ever be as strong as the surface it is applied to.

Generally, we recommend that surfaces are at least 15N/mm2, but in main living spaces and high traffic areas, it’s advisable to increase the strength of the substrates up to around 25N/mm2, in order to avoid any deformation of the substrate.

Moisture in the Substrate on Application

We recommend that substrates have a moisture content of no more than 5% when the microcement is applied.  If there is excess moisture in the substrate when the microcement is applied, it won’t get the air that it needs to fully cure, this means that it will be weaker than anticipated.

Excess moisture trapped below the surface can also prevent the microcement from curing to it’s full potential, as it also needs air to cure.

On Going Moisture in the Substrate

Leaks or ground water under the surface of the floor can travel through the substrate to the microcement over time.  Which can cause the microcement to weaken, stain or delaminate.

Insufficiently Cured Microcement

If either the microcement base coat or top coat was not sufficiently cured when the subsequent coat was applied, this would prevent the microcement from reaching its full compressive strength potential.  This happens because excess moisture needs to evaporate off the surface as part of the curing process.  If the moisture is trapped under a subsequent coat, the curing process cannot take place.  The microcement, may be soft or chalky as a result.

Microcement Applied Too Thickly

Microcement is intended to be applied very thinly, so that each coat is no thicker than the quartz in the mix.

When applied correctly, there should be no opportunity for compression because the very strong quartz is tightly packed into the surface.

If the microcement was applied too thickly, this will allow for compression which will result in the microcement system not reaching its true compressive strength potential.

Identify the Cause of the Problem

The first step in resolving the issue and strengthening the floor is to establish what has caused the weakness.

In order to conduct a full investigation, you may need to sand back or cut into a discreet section of floor to investigate it fully. You will then need to repair this and will be responsible for doing so.  So always ask permission & proceed with caution, we will not offer any compensation for damage to flooring done during the investigation process.

Review the Substrate

To establish whether there may have been an issue with the strength or moisture content of the substrate, you’ll need to do some investigation into the substrate.  Here are some lines of investigation that you may want to follow:

• What is the substrate? What is the strength of it?  Check the manufacturer’s technical data sheets for this information.
• How long should the substrate take to dry? And how long was it left in this case? This will depend on the depth of the floor, so it’s helpful to know that too.
• Is there anywhere that the substrate is exposed, so you could do a test, with a moisture meter. This will help you to establish whether there is any moisture in it now.
• Depending on the time that has passed, if there is moisture in the subfloor now, it is likely to be an on-going problem, in which case, the source of it will need to be identified & repaired. Look for leaks or ground water.
• If you have underfloor heating, was it turned on before the microcement was applied or after? Turning the underfloor heating on after the microcement was applied, may force moisture through the surface up to the microcement.

Review the Microcement

• With the moisture meter, check the moisture content of each layer to establish whether any of the layers have a moisture content higher than 5%.
• Also check for any obvious signs of weakness in each layer of the build-up: sub floor, base coat & top coat.
• And check the depth of each layer in the system. You should be able to see 4 distinct microcement coats, the 2 base coats should be no thicker than 0.8mm each & the top coats not thicker than 0.4mm each.

Strengthening the Substrate

If the substrate is weak or has a high moisture content, you will need to establish the extent of the problem and make a call on how to repair or strengthen it before moving forward.

Speak to your builder or flooring contractor to establish the best way to strengthen the substrate or plumber regarding water leaks.

Strengthening the Microcement

If you have identified a weakness in the microcement, there are 2 possible solutions that you could try:

Option 1: Polyshield

Apply a coat of Polyshield over the surface.  Polyshield is our strongest sealer, which cures to give a thick protective coat over the floor.  It’s not guaranteed to solve the problem, but is the least intrusive way to increase the strength of the microcement at this stage.

The floor would need to be clean and dry before the Polyshield is applied.

Click below for more information on the application process:

Polyshield Application Guide

Option 2: Sand Back & Recoat

If you have identified a weakness in one of the coats of microcement, it’s best to sand back to the coat, so that you can remove it & reapply the microcement system from there up.

So, if the weakness is in the top coat, sand back through the sealer & top coat, until you have a nice solid base to reapply the top coat & sealer to.

Give the floor plenty of time to dry out, before reapplying the coats.  You may also want to consider upgrading to a stronger system than you had previously to be sure that it will be sufficient for your needs going forward.

This guide explains more about the process of recoating:

Recoating Microcement Surfaces