June 2015 Job of the Month:
This Christ Lutheran Church needed a new floor in their youth meeting room. A carpet covered the room's existing concrete floor, and it was stained from spilled drinks and other foods. Finally, they had enough and decided that acid staining concrete might be a great alternative to what they had as it holds up well to these sorts of stains. We were happy to help and decided that acid staining concrete with a brown color stain would be the best renovation for this floor. First, the carpet had to go. We removed it and uncovered the concrete floor underneath. However, that wasn't the end of it; the carpet had been glued onto the concrete layer, and some of the glue remained. This meant that the concrete was covered in thin glue lines.
The contractors who laid down the carpet had used a notched trowel to spread the glue on the concrete surface. A notched trowel is a flat, rectangular blade attached to a handle. This sort of tool can be used to install linoleum as well as a glue down carpet. The contractors push the blade across the surface of the concrete, allowing the notched edges to create thin glue lines as it spreads the glue evenly across the concrete surface. During the process, some of the glue lines will wick into the concrete, while the rest stays on top. Next, the contractors laid the carpet down, adhering it firmly to the concrete. After removing the carpet at the church we found the floor just covered with these visible glue lines from the notched trowel.
Our next step is to clean the surface and remove as much of the glue as possible. Sanding and grinding both helped to remove the glue and whatever trowel marks were above the surface of the concrete leaving hardly any glue above the surface. However, the cleaning process isn't perfect. For one, sanding and grinding can change the appearance of a concrete floor. For another, a glue residue can remain even after cleaning. When acid staining concrete, any glue residue on the surface of the concrete can react with the stain and create a highlighting effect. This effect can look good and create a one-of-a-kind appearance, so it's not necessarily a bad thing; it really depends on the desired outcome.
While we can often remove the glue that is on top of the concrete, it's a harder trick to clean the stuff that wicks below. Sometimes even after extensive cleaning it cannot completely remove the glue lines created by the notched trowel. While these lines look like grooves, they do not have any depth; you wouldn't feel anything even if you ran your finger across them.
Normally our next step of this acid staining concrete project would be to lay down a concrete overlay on top of the floor. This would allow us to avoid any potential problems from residual glue, since the new overlay would effectively bury the glue lines and other blemishes below a new concrete layer. However, the glue lines in the youth room didn't look bad, just different. Most importantly, our clients liked them so instead of covering the existing concrete floor with a decorative concrete overlay, we left it as is and applied a brown acid stain. The glue lines reacted to the stain and created hundreds of lighter and darker brown stripes throughout the youth room's floor. The result of this acid staining concrete project created a floor with an interesting unique finish that looked fantastic.