Why does a tile floor crack?


We have cracks in our newly installed tile floor, why?

We have discussed within this website, various different floor surfaces and the pros and cons or each. However, this article will summarize the common situations that can result in tile floors, or even stone floors cracking.

It is important to note that any rigid floor material is subject to cracking. The larger the actual individual piece of flooring, the more susceptible to cracking it will be.

Why does this occur?

As in the case of most construction problems, the answers are based on simple practical physical occurrences that most individuals have experienced in their own lives.

Take a piece of a tree limb and bend the limb. In most instances, the wood will allow you to twist and bend it considerably without it actually breaking. The wood characteristics under a bending force, yields to the bending or twisting force without breaking of failing. The material is resilient to the bending force.

Take a thin piece of rock and perform the same twisting and bending exercise. The rock will resist the forces without bending to a much greater extent than the wood, but will not bend without breaking. Once the stress on the rock reaches, what is called the yield point, the rock breaks without bending. The material is not resilient to the bending force.

This same type of scenario is typical for the various materials that can be selected as a floor finish. A wood, resilient tile, cork, or other ” resilient ” material will bend, twist and not yield. A piece of stone, tile, shale, slate, etc that is a rigid material, has characteristics that will not allow itself to be subjected to a bending or twisting force without yielding or breaking.

So why does my tile, stone, or other rigid material flooring crack and break?

If the sub-surface of the floor finish yields, and subjects the finished surface to either a bending or twisting force, the rigid material will crack due to the fact that it’s characteristics will not allow it to yield or bend. If the flooring was a more resilient material, such as wood or vinyl tile, the finish material would bend and twist without yielding, to a certain point.

How can we minimize the cracking and breaking of my rigid floor.

  1. It is important that the sub-base for the floor is rigid and unyielding. In the past, any tile floor would be placed on a ” mud base “, and the application would have been called a ” mud job “. Due to the cost and the need to drop the sub-floor down, to allow the mud base, this technique is rarely used on residential homes. Higher end homes, may still have a ” mud base ” that is placed prior to the application of a hard floor, however, in most cases the application is directly on the plywood sub-floor due to cost and coordination considerations.
  2. If the application is directly on the plywood sub-floor, then the sub-floor needs to be rigid and unmoving. What is the best application for this assembly. It is our recommendation that a tongue and groove 5/8 plywood, ply-score or specialized decking be applied in perpendicular orientation to the floor joists. On the top of this plywood sub floor, should be applied a plugged and sanded 1/2″ piece of plywood, that is butt jointed, and in the opposite orientation as the lower sub-floor. If this application is used, then the sub-floor under the rigid finish flooring material will be strong and non-moving. Both applications should be screwed and glued to further maximize the strength of the entire assembly. This type of construction will almost ensure that there is no cracking of the tile, stone or other rigid flooring finish surface.
  3. It is important that the sub-floor is allowed to dry out, and cure, prior to any application of the finish floor installation. This is important to ensure that there is no shrinkage of the sub floor once the finish tile, stone or other rigid flooring is installed. It is always best to have the climate control established in the home, prior to any finishes, especially flooring. The drying time for framing lumber, plywood, sheathing, should be maximized, to minimize the future shrinkage of all finished building materials.
  4. It is also important in an effort to minimize any cracking or failure of the flooring, to use the proper glues, mortars and grouts. In some instances the need to mix special ad-mixtures to the materials will further minimize any possibilities of cracks or shifting of the flooring. It is best to consult with your local flooring supplier for the recommended add mixtures to be used in your location and environment.

What to do if an existing rigid floor starts to fail, crack or break apart?

Unfortunately, as in most construction issues, it is easier to begin the process correctly, than it is to correct the process after it is completed.

As has already been established, the construction and stabilization of the sub-base, below the finished floor, is an essential element to reduce any cracking and or other failures of a rigid floor material. Therefore, if an existing floor starts to fail, in almost all cases, it is due to the fact that the sub-base is shifting, shrinking or moving.

How can we correct this type of issue?

  1. Start by the removal of all broken floor tiles, stone, slate or other rigid pieces that have cracked or chipped. It is strongly recommended that a minimum, full piece of good flooring be removed around the entire perimeter where the flooring has failed.
  2. Investigate the sub surface, where the flooring had failed. Is the sub-surface wet, deteriorated, heaving, bellying, etc. Are there any obvious flaws, or failures in this portion of the sub-floor?
  3. Remove any compromised pieces of the sub – floor completely, and investigate the structural supports below. Are there any failed floor joists, support posts in that area, etc.? If there is a support post directly below the failed piece of flooring, is this floor post possibly too high or too low. Basically you are searching for any type of physical force, bending motion, etc. that would have placed stress on the area of the floor that has failed.
  4. Based upon your investigation, all compromised sheathing, structural elements, etc. that are found to be compromised or deteriorated, must be removed and replaced. It is always good to correct the issue with a ” belt and suspender ” type correction to minimize any future failures. If the sheathing is deteriorated, replace, glue and screw. If the structural elements are compromised, replace times two. Go overboard, you do not want to re-visit this failure again.
  5. If there is no obvious issue that becomes apparent, from investigation, then the issue could be an overall structural issue that is allowing the sub-floor to flex or move. In this case, the solution is to hire a professional structural engineer that will observe the conditions and recommend a solution to the problem.

There are a few tell tale signs that will normally identify the reasoning for the cracking of a rigid surface that are easily summarized.

  1. Straight linear cracking or grout separation in a constant linear line / If there is a determined straight pattern to the failure of a floor, this will normally be caused by the supporting beam below the crack. This beam could be low, high or moving. A review and alignment of the structure below the crack, will easily determine which structural element is causing this linear breaking.
  2. Random cracking or separation of the grout joints. If the issue with the floor is random, with no pattern, this will normally indicate an overall failure of the sub-floor, the mastic that is securing the floor to the sub-floor, or the mixture of the grout in the joints. If the cracking is random over the entire floor, the removal of the floor, reconstruction of the sub-base is recommended.
  3. The cracking is occurring on a diagonal at a corner. This is a very common type of crack, that is caused by the stresses imposed by the supporting structure at the intersection of the framing. If you consider the loading of the floor on the structure, and the support at a corner, it is obvious that the loading and the support are in two different directions due to the right hand corner of the room or opening. This imposes different stresses on the rigid floor, and can cause a diagonal crack at the hypotenuse of the right triangle formed by the two walls, sides of an opening, etc.
  4. The cracking is more of a chipping of the corners of the tile. This will normally indicate that the tiles are not properly set in the mastic that adheres them to the sub-floor. If the mastic is not evenly spread, not uniform under the tile, or is not covering the entire sub-floor, the rigid tile over the mastic may crack or chip, due to the uneven support of the mastic. Once again, the correction, is a removal of the old floor and the proper installation of a new floor.

This brief summary of why a tile or other rigid floor cracks, is only the tip of the iceberg.

Any significant cracking or breaking should be inspected by a professional floor contractor who will recommend the proper correction of the issue.

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