From the Technical Expert: Questionable Substrates for Ceramic Tile and Dimensional Stone
It appears that many times the acceptance of an unsuitable or questionable substrate is the result of the following:
1. Lack of knowledge
2. Lack of experience
3. Pressures upon the installer either due to time constraints or cost considerations
4. Poor estimating and pricing
Therein lies the hope that no complaints arise prior to warranty period. Many of the substrates that can present a failure problem may be utilized if properly prepared, i.e. using good floor prep, and standard of care. Many of the substrates within a questionable category can be used providing the setting product manufacturer has a product they can provide as a suitable bonding material for that particular substrate. It is important that you communicate your concerns to all parities well before starting an installation. Look for warranties!
The following is a short list of substrates and conditions that without proper preparation may present installation problems.
1. Contamination by the tile and carpet adhesives
3. Excessive deflection
4. Concrete curing compounds
5. Vinyl,br> 6. Post-tensioned concrete
7. Epoxy coatings
8. Cracked concrete
9. Light weight, Portland cement, concrete
10. Gypsum underlayments
A few suggestions:
1. Contamination by the tile and carpet adhesives. In the case where asphalt cut back or asphalt emulsion is on the slab it, pays to scrape at least 80 percent of the adhesive off the slab. Then find a manufacturer that allows their setting products to be use in this condition.
2. The problem with asphalt tile adhesives is that they are moisture/alkali susceptible. If moisture vapor transmission occurs the combination of moisture and alkali can cause a breakdown in the asphalt with loss of bond resulting and/or staining of the tile or stone.
3. Excessive deflection: The limits of deflection for ceramic tile is L/360 and L/720 for marble. The ceramic tile L/360 requirement is tested using ASTM C627 guidelines. What does L/360 mean? L refers to length of the span in inches. This figure is divided then by 360. If you have a 12-foot span (144 inches) divided by 360 = 0.4 inches which is maximum allowable deflection. If the substrate is in question use an accepted industry anti-fracture membrane.
4. Concrete curing compounds: Portland cement mortar will not bond tenaciously to curing compounds. Some curing compounds are supposed to self destruct via wear or ultra violet (solar) rays. You can't take this for granted. Put a few drops of water around your field area. If they disappear shortly you may proceed. If the water "beads" up the curing compound need to be removed by some form of abrasion.
5. Post-tensioned concrete: What is a post-tensioned slab? Concrete slabs containing steel tendons stressed by jacks after the concrete has been placed. Stressing usually occurs when the concrete reaches 75 percent of its 28-day strength. Usually 4 to 7 days after placement. Interesting note; 50 percent of all residential post-tensioned are built in Texas, about 25 percent in California, with the remaining 25 percent throughout the USA. With concentrations in Nevada, Louisiana, Arizona, Florida, Georgia and Colorado. In Texas these slabs are generally cast directly onto the vapor retarder, while in California these slabs are cast on a thin sand base placed on the vapor retarder. The Tile Council of North America (TCNA) recommends methods F111 for slabs subject to deflection or movement. F113 provided that all requirements are met. Industry associations recommend an anti-fracture membrane.
6. Cracked concrete: Most concrete text books curves indicate that about 1/2 the total shrinkage will occur in the first 60 days. Some structural engineers recommend the use of a membrane under hard surface flooring since, shrinkage cracks may continue early on.
7. Gypsum concrete underlayment: This has become a very high growth substrate due to its weight, sound effectiveness, fire resistant characteristics, and ease of installing floor heat.
The Ceramic Tile Institute of America recommends use of membranes meeting ASTM standard A118.10 and also the use of a latex primer to the underlayments surface to prevent direct contact between gypsum concrete and wet Portland cement mortar. However, the latex primer chosen must have small polymer particles so that the latex primer may penetrate the underlayment. Not all latex primers are made with small particles polymers.
For installing ceramic tile or stone care must be taken. In most cases I would recommend an anti-facture, "slip sheet" type of membrane meeting ASTM 118.10 standards. ANSI, American National Standards, does not recognize gypsum concrete as a suitable substrate. A Tile Council of North America (TCNA) detail is being balloted and may appear in the next publication.
Now, unsuitable or unacceptable substrates: Most are unacceptable due to susceptibility to moisture; these materials include masonite, scribing felt, building paper, felt paper OSB, paneling particle board and Lauan board. Others are unsuitable due to their lack of bonding ability; this includes products such as pressure treated plywood, fire resistant plywood, paint and oil contaminated floors and curing compounds.
Remember: It only takes one call to your suppliers of bonding material, all with 800 numbers, or either to the Tile Council of America or National Tile Contractors of America or Ceramic Tile Institute of America to discuss the steps you need to take to have a trouble-free installation. There is always enough time to do this, especially compared to the time spent on a complaint or failure.