Dark Marks in the Surface
This happens when the surface has been trowelled a lot of times with a lot of pressure on the trowel. As the steel of the trowel is rubbed over the surface, it causes the surface to blacken in areas. The areas that blacken more tend to be raised slightly more than the rest of the surface.
Are dark marks 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 dark marks?
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.