Preparing the surface by sanding it.

Preparing the surface by sanding it.

I was recently contracted to grind and seal the concrete floor of a lobby and the 2 flights of steps leading off from it. The building was old and there was a lot of glue on the floor and especially the staircase from previously installed carpeting. The glue was old and hard and the only way to remove it was with a hand-held diamond grinding disc.

The job was pretty straightforward. We grinded the surface layer of the concrete stairs, but had to angle the grinder a little to get the glue off as the surface was not completely flat. The staircase had taken some abuse over the years with different contractors fitting varying types of flooring over the stairs.

We had to apply the first coat of sealant at night using a floodlight as the building was under renovation and there were workers in and out during the day. The hand-grinding had removed the surface layer of cement and had polished up the stones in the concrete, and the effect was stunning. The sealer brought out all the detail in the concrete and we were very pleased with the outcome.

The following morning we went back to inspect the job and were horrified to discover that due to the positioning of the building, the morning light shone brightly on the flight of stairs leading up from the lobby, and the stairs looked terrible. The bright light enhanced all the tool marks from the grinder on the steps, especially the ones that were at eye level, showing up every single imperfection.

The only way to fix it was to spend an enormous amount of time smoothing off the surface and reapplying the sealer with a matting agent added to reduce the glare. Obviously we had not budgeted for this extra work and expense, but the lesson was priceless.