What causes cracked or loose grout?
There are several things that can cause cracked grout and we would be guessing as to the cause. It could be that a field inspection is needed to determine why your grout is cracking.
Typically, the most common causes are as follows:
- Excessive deflection in the substrate. This movement can cause the grout to crack, and if sufficiently severe, can cause tile to crack.
- Grout that is insufficiently packed into the joint. This most often occurs with wall tile. If insufficient force is used while grouting wall tile, it is easy to “bridge” the joint where the grout does not penetrate to the back of the joint. This is especially true if sanded grout is used in joints narrower than 1/8″. The sand grains can easily bridge a narrow joint – in this case the grout may be only on the surface and have little strength.
- Grout made with an excessive amount of water or polymer additive. The liquid that goes into the grout ultimately must evaporate (except for that consumed by cement hydration). This evaporation can cause pinholing in the grout and a weak grout structure.
- Grout packed after cement hydration started. All cement based materials have a pot life. Iif water is added to the mix after the grout begins curing in the bucket, the grout will be sufficiently plastic to pack but will not cure into a hard homogeneous block – rather it will be crumbly and weak.
Does your installer have any idea as to the cause? The least likely cause would be defective grout. Some other possible things to look for:
- Spacing of joists
- Type and size of floor joists
- Span of floor joists
- Direction of the plywood sheets and placement of gaps
- Were there gaps between the sheets of plywood?
- Type of adhesive and coverage of that adhesive
In some cases even the type of tile can affect this (high or low water absorption tile bodies can vary the methods and materials needed).
Therefore, you can see this can be difficult to assess without an on-site inspection. Usually minimum requirements are 16″ o.c. (on center) joists (2X10 or better depending on span), 3/4-inch subfloor with 1/2″ underlayment (or backerboards made for tile). The plywood sheets should be run with the long side perpendicular to the joists (both layers). The top sheet should be installed so that the joints don’t fall over the lower layer gaps nor above the joists. The adhesive needs to coverage at least 80% in the dry areas. The grout should be very dry and well packed into the joints. The joints should not be flooded with water when they are being cleaned.
Joints cannot be “grouted over” successfully. At least 2/3 by depth of the old grout needs to be removed when replacing or repairing grout.
Generally, grout fails because of movement of the substrate or improper mixing and installation of grout. A ¾”-subfloor with 3/8″-underlayment may not fail but it is marginal and could cause problems. Stapling the two layers together could be problematical. The best method is to screw and glue the two sheets together. The underlayment should be plywood designed for that purpose too – not just any plywood will do.
Our subsidiary consulting company, TCA-Team, LLC is available for site consultations and failure analysis on a fee basis should you desire an investigation.
Why is my grout and tile cracking?
There are many things that can cause excessive deflection in your subfloor (and consequent cracking in the tile) or you may have a perfectly sound subfloor but not have prepared the floor properly for tile.
Here are a few of the most common questions:
- Is the subfloor plywood over joists 16″ on center? If not, has the installation system been designed to work with the actual type of subfloor present?
- What is the span of the joists? Are they suitably sized for the span to achieve the L/360 deflection standard under the expected live and dead load? Are there any cracked, rotted, or termite damaged joists?
- Was the subfloor screwed to the joists? Is there any possibility of movement between the subfloor and the joists themselves?
- Does the thinset used match the conditions present (was a polymer additive used and if so was it appropriate for the subfloor?)
- Was the thinset coverage satisfactory? What was the notch size of the trowel used?
- Were expansion joints used in the installation to allow for normal movement?
- Are any dimensionally unstable or questionable materials also in the tile/subfloor/joist sandwich? How about cushion vinyl, luaun, water-soluble patching compounds or mortar materials.
Were all layers present installed according to the applicable ANSI standards?