Photo 1a


Photo 1b
As strange as it may sound, cracks in concrete subfloors are a very common condition, and even more unusual is who gets blamed for them. The following are two job sites (new construction at the time) where the customer's complaint was the same: the VCT tile is cracking, and it must be either bad tile or improper installation, right? Right.

Photo 2a
Photos 1a-3a are of one installation that is 15 years old above-grade. Reportedly the cracks started to show five years after, but no complaint was filed. So, no repairs were done because matching tile was not available and a tripping hazard had not yet occurred, causing concern to the building owner.

Photo 2b
Photos 1b-3b are of a five-year-old new construction on-grade where the cracks reportedly started within months of the installation. Both have what appear to be very similar conditions, but are they? Is this installation related? Is this manufacturing related? Or could it be site related?

You Make the Call!



Photo 3a
Location of the cracks, the number of cracks and how they telegraph themselves on the surface of the floor covering is what we should be looking at. In Photos 1a-3a, they appear somewhat straight, but not as straight as those found in Photos 1b-3b. Is the tile pushed upward or is there a depression or divot to the tile? Surely if there are gaps in the tile or the tile has separated from itself, then there is movement so dynamic that tile adhesive and patching compound could not restrain it.



Photo 3b
There are three basic types of joints used in concrete slab-on-ground construction. 1.) Control joints are grooved, formed or sawed into floors so that cracking will occur in these joints rather than in a random manner. 2.) Isolation joints are also called expansion joints. They permit both horizontal and vertical differential movement at adjoining parts of a structure. 3.) Construction joints occur where concrete work is concluded for the day; they separate areas of concrete placed at different times.

Photo 4a
They usually align with and function as control or isolation joints.

There are two basic causes of cracks in concrete. One is stress due to applied loads and; the other is stress due to drying shrinkage or temperature changes in restrained conditions.

Photo 4b
Drying shrinkage is an inherent, unavoidable property of concrete; therefore, properly positioned reinforcing steel (re-bar) is used to reduce crack widths, or joints are used to predetermine and control the location of cracks.

Now look at Photo 4a. Do you see what I see? That’s right; the crack in the floor runs up the block wall! This is a site-related condition that is due to major movement in the slab; usually these cracks are not straight, and are very random. They are not foreseen or engineered by the architect. This, of course, is not installation related, and the general contractor and his concrete people should look at this condition. What about Photos 3b and 4b? Do you see how the crack forks around the steel (vertical) support? This is a great example of an isolation joint that has done its job. Can the installer be held responsible for this? This too is a site-related condition; no patch and adhesive combination will keep this from happening. Now look at Photo 5b; this will give you some indication as to the amount of movement at this crack. The repair will be to ramp the patch up to the higher edge and feather it out to the lower field.

This is a type of repair, involving labor and material costs, which the building owner will have to pay for. It is no secret that the floorcovering industry and the concrete industry at times seem to be miles apart on several schools of thought. But, we must understand who knows best about their particular area of expertise and listen and learn from them. It is customary in our industry to use a fortified Portland cement patching compound to level out subfloor irregularities in concrete when a resilient floorcovering is to be installed.

Photo 5b
Many times the manufacturer of the patching compound is called out to inspect a so-called failure of their product. They look for proper product usage, and may take samples of the patch installed to ensure that primers and ratios of water and/or additives were used as directed. It is very important that their particular instructions be read and understood, as they may vary from job site to job site and manufacturer to manufacturer. The information used in this article was referenced from "Design & Control of Concrete Mixtures." If you would like to read it, go to the library or check it out on online.