How to avoid unwanted stains or marks when applying microcement

Reasons that cause stains on microcement and solutions to marks. Processes to avoid possible imperfections.

Marking of tile joints

Some points should be considered to avoid marking tile joints:

We should pay attention to the difference in absorption between tiles and joints: the resin contained in the microcement is absorbed differently if no precautions are taken we run the risk of them appearing in the form of a visual spectrum on drying (visual pattern). Moisture in the joints also causes this defect.
The joints are generally hollow, they are not on the same plane as the tile, the retraction of the Microcement once dry creates a relief in the joint area (relief pattern)

This is why with our system we create an insulating and levelling layer. For this reason it is very important that, after filling the joints, it is left to dry for 24 hours before starting the application of the microbase

. marks of the tile joints due to humidity

Trowel marks, highlighting irregularities from the previous coat

We will have to apply the microcement without leaving burrs or reliefs that show the passage of the trowel, sanding these imperfections in each coat. If we apply over a layer with burrs, these reliefs will be copied.

With the steel trowel and excessive pressure, these imperfections cause the effect of "burnt" dark spots that reflect the lack of sanding of the layer below.

Sanding the irregularities

We will have to sand the microcement after each coat to avoid the effect described in the previous section.

We will carry out a soft grinding with a rotary-orbital sander of low revolutions or by means of a sanding glove, and silicon carbide sandpaper.

Approximately 3 hours after application, a change in the tone of the microcement can be seen, becoming lighter, this indicates that the microcement is passable and hard enough to proceed to sanding, the temperature, humidity and ventilation of the room influence this period of time.

We recommend sanding before 12 hours after application so that the coating has not reached an excessive hardness and this step is more complicated.

Excess sanding stains

When sanding the last coat of microcement we must make sure to work smoothly, with one hand we will hold the sander or the sanding glove and with the other we will check with the touch if the sanding is correct. If we work properly we will avoid three types of characteristic stains: circles, contour lines and black marks.

The sander must be of the roto-orbital type to avoid leaving circles. Try to keep it in constant motion without prolonged contact with the same spot. If the sanding were excessive, we would end up seeing the microcement of the previous coat and leaving some level curves" characteristics that would indicate that we have moved on to the lower layer. As soon as the sandpaper wears out we will have to change it, if we do not change it, the sandpaper goes from sanding to polishing leaving black marks on the microcement.

Excessive burnishing on microcement

Touch-ups when the microcement is already starting to dry will leave obvious and unaesthetic marks, the most appropriate thing to do when the finish is not the desired one is to reapply an additional coat.

Excessive trowelling will leave dark marks. This can happen, for example, when material accumulates on floors at the end of the application process, forcing us to pick up the excess microcement and overwork it with the trowel.

If you over-trowel an area, what you are doing is forcing it to dry. This problem is reflected in the whitening of the area. For example: A black wall could have grey stains that are much lighter than the chosen colour.

If the applicator goes over the whole surface too much or presses too hard the surface can become a lighter colour. It is very typical to see a black wall that looks grey.