TAPE MARKS ON CONCRETE FLOORS

Source:www.stonediamondtool.com Date:2022/4/18 Read:136

Question:

I have a question about an integrally colored concrete floor that a subcontractor poured for me. The pigment was added to the concrete at the ready-mix plant, and the contractor added no additional water to the concrete at the jobsite or while finishing the slab. About two months after the floor was installed, we had the interior of the house painted, and the painting contractor covered the concrete floor with sheets of paper, using painter's tape to hold them in place. When he pulled up the tape a week later, after he finished his painting, it took off the top surface of the concrete down to sand and stone. What caused the surface to come off with the tape, and can anything be done to fix the floor? The tape marks are about an inch wide.

Answer:

The reason the tape pulled the surface up is because of plasticizer migration. Plasticizers are polymers that make glue, plastic and rubber flexible. In the case of tape, plasticizers are used to allow the glue to migrate into anything porous, like concrete. Most often I see situations where the tape pulls up the concrete sealer and stain, but every so often it can pull up the concrete surface as well. When painter's tape pulls off concrete, it's typically because the concrete mix contained too much water or the concrete was overfinished. Concrete strength is directly related to the water content when placed and finished. The more water you have, the weaker the concrete surface. Since the water was added at the ready-mix plant under controlled conditions, it's more likely that your concrete was overfinished. If concrete is worked too much with a trowel, too much water and cement paste are brought to the surface, producing a weak top layer that is often soft and dusty. Try performing a cross-hatch test to see how the surface holds. This test is often used to test sealers for adhesion to concrete, but it will also work on the concrete surface itself.

To treat concrete with a weak or soft surface, apply a concrete densifier or hardener. These types of sealers contain sodium or lithium salts that chemically reinforce the concrete surface and further solidify the crystalline network that makes up the "glue" in concrete. In the areas where the tape removed the surface paste, you can apply a microtopping  or a patch material colored to match the existing finish.