You guessed it, floor prep! No matter what type of flooring product you install you just can’t seem to get away from floor prep. This is certainly not a new subject and creates a sore spot with installers nearly every time it comes up. If all we had to do was install floors, or walls, most of the time we would make good money. As soon as we walk on a job we already have a real good idea of how things are going to turn out based on the level of preparation the substrate will require. I think few would argue that by far excessive floor prep has to be the number one money loser on every job. Does it always have to be that way? Well, I suggest that it doesn’t have to be unless you let it. Reasonable floor preparation should always be expected. The question becomes what is reasonable. Because there are so many substrates to deal with, for the purposes of this article we will confine ourselves to concrete and see if we can define what is reasonable. The same methodology would follow suit for other substrates.
So just who is responsible for floor tolerances? All substrate trades have their own trade organizations similar in function to the Tile Council of North America’s Installation Handbook (www.tileusa.com) for the tile trade. These organizations form balanced committees representing their respective trade for the purpose of establishing basic guidelines and in some cases procedures. For concrete, that organization is the America Concrete Institute (www.concrete.org) which publishes extensive recommendations for all concrete including slab construction. I can now only wish I had awareness of this organization and their documents in my prior contracting life. Understand the substrate trades performance levels and recommendations can go a long way to preventing problems before they occur. All recommendations and tolerances for concrete floors to receive any type of floor finish can be found in Guide for Concrete Floor and Slab Construction, ACI 302.1R-4. This is the document used in all architectural specifications. There is another document that all soft flooring installers, workrooms, and contractors should have, ACI 302 2R-06 Guide for Concrete Slabs that Receive Moisture Sensitive Flooring Materials. This is a 42 page document that provides an in-depth look at floor moisture problems, why they occur, and how to prevent them.
If you are going to have a discussion about who is responsible for what, you need to understand what the other party is responsible for. The tile industry recommendations of a ¼” in 10’ with no more than a 1/16” variation in 12” comes from these documents. When specified, it is a floor slab performance requirement. If large unit tile is specified, closer tolerances many also be specified on commercial projects and specified or requested in residential projects. However, because it is specified does not necessarily mean that it will be at that flatness level when you arrive to install the flooring. The flatness measurements for compliance are taken before final cure and do not include control joint areas. Rapid water loss at control joints often results in peaking at the control joints. This may all sound too in-depth for an installer or retailer, maybe so. But, if I would have known and understood slab construction when I was contracting like I do now, I would have saved thousands and thousands of dollars, certainly enough to pay for 4 years of college. If that sounds like you, then maybe it is worth purchasing a copy of these documents.
The first thing any installer needs to know about concrete is if a curing compound was used?” If you read the concrete industry documents they specifically state that curing compounds should not be used in areas to receive ceramic tile. Historically, many contactors chose to use a curing compound and grind it off at a later date in the areas to receive ceramic tile. It seems that step has all but disappeared as a concrete contractor’s customary practice. On commercial work, if you have knowledge of the concrete specifications and they reference ACI documents, you can have the concrete contractor remove the curing compound, if the project has been properly specified. Unfortunately if you are in a residential or remodeling setting and no specification was used, it still needs to be removed. This can often be a great challenge as in many cases, specialized equipment is required. All concrete requires damp curing to avoid curling while it dries. The easiest, cheapest, and most common practice is to use a liquid curing compound. These work by restricting the amount of moisture leaving the slab. Unfortunately, they also restrict water from going in the slab. Water is what carries the cement and/or polymers used in thinset mortars into the slab. If water does not penetrate the slab, the cement will lay on the surface producing little if any bond. The same can be said for many other types of adhesives or latex/polymer modified products. Most manufacturers recommend the coating be removed regardless of adhesive used. This is where things get both complicated and time consuming. Curing compounds are also made from various polymers. There are chemicals that will remove curing compounds but unfortunately, they do not discriminate between old and new polymers and may wick back out of the slab causing bond loss of the newly applied thinset or adhesives. It is very difficult to completely extract the adhesive or coating removal product from concrete. Some may erroneously recommend an acid wash of the floor. Acids do not remove curing compounds, they eat cement. They can not expose the cement under a curing compound. At best, they will eat a minor amount of cement in areas were the curing compound has been abraded off the surface. Acids are not recommended for this purpose by any cement company, organization, or the tile industry. That leaves us with only mechanical means.
There are many options for removal of curing compounds. None are simple or cheap, hence the reason it would be in your best interest to understand whose responsibility it would be prior to bidding or accepting a job. The easiest indication noting the presence of curing compound is known as the water drop test. A few drops of water are placed on a slab. Their absorption by the slab within several minutes is a good indication that no curing compound is present. If there is some minor delay, perhaps all that is required is a scoffing of the surface with some sandpaper. A very simple and common practice is to use swing arm or buffer type machine with some 4 ½ -12 paper. A heavy coating of curing compound may require weight be placed on a swing arm machine to encourage removal. Not all machines are designed to accept weights. Rigging a machine not so designed can result in both personal and property injury. Sanding concrete may also expose anyone in the area to free silica, a natural component in cement all products. Prolonged exposure to silica dust may cause respiratory damage known as silicosis. Some equipment can be fitted with dust collection devices to avoid breathing or exposing others to excessive cement dust. There are many options for this type of equipment available in many price ranges for both hand-held and larger grinding devices. They range in size from a Dremel Tool to a Road Profiler. Yes, we did have a Road Profile machine on a rather large job, 40,000 feet in a half a day. It was a little outside the box thinking, but very impressive and only .20 a foot! For exceptionally stubborn coatings, adhesive residue, and paint, there is nothing better than a shot blaster. These machines typically shoot steel balls at high speed and are self contained units vacuuming as they go. They leave a perfectly clean and slightly abraded surface, perfect for bonding ceramic tile. This equipment is highly specialized and very expensive. Unless the shop is very large, this type of work is often subcontracted to firms who specialize in surface preparation.
After all this, it is still not time to install floors. Now the flatness of the slab should be checked to see if any remedial measures are needed. With any tile larger than an 8x8 the standard tolerance of ¼” in 10’ simply does not work. In cases where variation above that recommended flatness level is marginal, it may be possible to install 12x12 if the grout joint is wide enough. Tile larger 12x12 is typically going to require either additional floor preparation above the standard ¼’ in 10’ or use of a larger notched trowel and a suitable medium bed mortar. Standard thinset, those not designated a medium bed mortar, typical have a maximum total thickness not to exceed 3/8”. Installing standard thinset in a thicker layer may result in weak bond strength and excessive shrinkage. Few want to take the time to flatten the surface prior to installation and convince themselves they will flatten as they go. This may prove short sighted and more expensive that taking the time to correct the surface conditions. We studied this issue extensively with numerous variations and almost always found it was cheaper and faster to repair the deficiencies prior to installation as opposed to during the process. Tighter grout joints also call for flatter slabs. Large tile does not conform to the surface. A wider grout joint will allow for some slab variation, a small grout joint on large tile requires a very flat floor. These are called super flat and are very expensive to place, therefore seldom specified or requested. Knowing this, an additional charge would always be warranted and appropriate when either is desired. When flatting a floor it is also important to properly access the most economical means of doing so. It may be just a few areas to fill with a cement underlayment, a matter of grinding down some high spots, or in some cases use of self leveling cement products.
Having spent many years in the real world of installation, I understand the challenge and frustration of floor preparation. You get caught between the shop or retailer and client or customer. One wants to sell it, the other who pays the bills wants it installed perfect, neither wants to pay to fix a floor not suitable for the product being installed or grout joint width selected. The answer varies with each individual situation but if you think it through and know the responsibility of others, you can turn floor preparation into income opportunity, and that is why we work.