Dark Marks after Sanding
You may notice dark marks appearing in the surface after sanding.
This guide will help you to diagnose what has caused them & how to resolve it.
Does Sanding Cause Dark Marks in the Microcement?
Sanding the microcement surface with Silicone Carbide sanding discs shouldn’t put dark marks into the surface. These sanding discs are specifically designed to be stronger than cement-based surfaces like microcement, so they should wear down the surface, rather than the other way around.
Check Suitability of Sanding Discs
Check what sanding discs you are using. Aluminium Oxide sanding discs are more suitable for timber, and because the cement is stronger than the discs, the colour of the disc can be rubbed off onto the microcement surface. This should just be a fine dust, that can be wiped away with a dry cloth.
Our high quality Silicone Carbide Sanding Discs have been tried & tested by us & we are confident that they are suitable for use on all our microcement surfaces. Although, if the discs you are using is wearing down too quickly, you may need to move to a coarser grit.
Check for Burnishing
More often than not, it’s not the sanding that has caused the blackening, but the process of sanding has revealed burnishing in the surface.
Is Burnishing a problem?
Not at all, in fact, some installers do this on purpose to achieve more texture, the technique is called burnishing. Burnishing doesn’t effect the performance of the products. But it can look too busy or patchy in lighter colours.
How do I get rid of Burnishing?
To resolve, sand the area flat and apply another top coat, this time not putting too much pressure on the trowel and not going back over it too many times until desired finish is achieved.
You may want to try a plastic trowel or another product like Microne Continuous which will naturally burnish less than Stucco Effect.
You will also find that the surface will be more uniform if you leave the first top coat to dry fully before applying the second top coat.
What if I’ve already sealed the surface?
See our guide to Recoating Microcement after Sealers for full details of what to do if the surface has already been sealed.