Ask the Experts

QUESTION

We had an issue recently with a White Thassos mosaic where the individual pieces on the sheet had inconsistencies in spacing on the mesh, with a few pieces exceeding a 2mm joint. The factory specification was made to a 1.5mm joint, but I’m told from our vendor that various factors (handling,

Thassos White Marble Mosaic

shipping, etc) can cause shifting to occur over time.

Can you confirm if there’s an industry standard tolerance for deviation on these types of mosaics? I’m sure the Marble Institute of America has something to this effect, but I don’t have access to their documentation to verify.

ANSWER

I am able to provide the specification for ceramic mosaic tile from ANSI A137.1.  Table 6 of ANSI A137.1 states the specifications for mosaic ceramic tile, including mounting/crooked tiles and for mounting/wide & narrow joints.  Those specifications are:

  • Mounting/Crooked Tiles:  Individual joint range <30% of the average joint width of the sheet.
  • Mounting/Wide & Narrow Joints:  Average joint widths for each tile must be within +/- 25% of the average joint width of the sheet.

ANSI A137.1 section 6.2.2.1.11 describes this a bit more:

The tile shall be uniformly mounted and in patterns specified.  Joints between tile shall be in accordance with manufacturer’s specifications.  For all mounted mosaics, the range of an individual grout joint shall be no more than 30% of the average joint width for the sheet.  For sheets containing mosaics of the same color, the individual average joint widths shall also be within +/- 25% of the average joint width for the sheet.  Sheets shall be accepted or rejected (for grout joint variations) based on the number of grout joints in the sheet.

As you stated, the manufacturer specification for the tile in this installation was for a nominal joint width of 1.5mm.  Some of the joints exceed 2mm.

When we apply the tolerance of <30% of the average joint width of the sheet for the mounting of Crooked Tiles, the acceptable narrowest part of the joint adjacent to a crooked tile would be 1.05mm.

When we apply the tolerance of +/- 25% for Wide & Narrow Joints the acceptable range becomes 1.125mm to 1.875mm.  2mm would be outside the range of tolerance.

Section 9.5 of ANSI A137.1 describes the laboratory testing method for variations in mounted mosaic ceramic tiles.  That is where we learn how many tiles and grout joints are to be examined and how many variations are acceptable based on the size of the individual tiles on the sheet and overall size of the sheet.  I am not certain if the specifications for stone mosaics are similar, but I am able to refer to the following.

In the Marble Institute of America’s “Q&A Manual (Expert Answers to Technical Questions About Working with Natural Stone)” the following is stated with regard for a reasonable tolerance for joint width:

“Tolerance is normally correct at a variation from true (specification) of 1/4 of the specified joint width. With a joint width of 3/32”, a tolerance of ± 1/32” is reasonable. A 3/32” joint is correct at 1/16” wide and at 1/8” wide. The joints should “eye up” straight and true. Be careful though, if the joint is specified at between X and Y.” *

To paraphrase the first sentence of the MIA’s statement, “a variation tolerance of 1/4 of the specified joint width” may be equivalent to +/- 25% for ceramic mosaics.

I have seen many instances where inadequate adhesive has been applied to the mesh allowing individual tiles to become loose or shift.  I have seen instances where the adhesive has dried out and allowed the individual tiles to become loose and shift on the sheet.  Many of these adhesives are water based; when they become damp they re-emulsify and lose their bond.  I personally have received a shipment of tile that had become damp at some point during the fabricating, mounting, packaging, shipping, storage and delivery process to such a degree that the mesh adhesive had lost most of its bond to the back of the tiles and the tiles themselves were mildewed.  I rejected that entire shipment.

When installing any type of mesh- mount mosaic, an installer should inspect each sheet for broken, loose or very inconsistently spaced tiles.  These should be cut off the mesh and individually placed or replaced.  Depending on the size of the installation, I always expect to repair at least several throughout the installation.

Some types of mesh used for mounting are less rigid than others.  Some mesh material used has thinner strands or larger spaces in the mesh fabric that make it flimsier.  This makes it more difficult for the installer to achieve consistent spacing when setting individual sheets and throughout the installation.

I hope this helps.  For more specific guidance, perhaps the Marble Institute of America would be willing to comment on your question. — Mark Heinlein, NTCA Technical Trainer / Presenter

* Quoted from Marble Institute of America “Q&A Manual (Expert Answers to Technical Questions About Working with Natural Stone)”  www.stonesofnorthamerica.com/technical/Expert_Answers_to_Technical_Questions_about_Working_with_Natural_Stone.pdf

Ask the Experts – March 2017

QUESTION

I have a school cafeteria with marble thresholds, all of which are broken. Is there something more stable that I can use to replace them? There are several:  3′, 4′ and up to 8’ lengths. Thanks.

ANSWER

While marble is among the softer natural stones, if the substrate is sound with no deflection and if the marble is properly bedded, it should hold up well.

As an alternative, I would suggest contacting a stone fabrication shop.  They often have remnant pieces of harder stone, Corian, or composite materials that they can mill to your specifications for length and width.  They can also put beveled or bullnose edges on them for you.  I have found that 2cm thick material works well for this sort of thing.

TCNA Handbook Method TR611-16 is your reference for more information and a schematic detail for proper installation of a threshold.

Any material you install will still require proper preparation of the substrate and proper bedding with appropriate mortar. —Mark Heinlein – CTI #1112 NTCA Technical Trainer / Presenter

QUESTION

Any chance you’ve seen discoloration on grout that’s brownish red? I have a few theories, but I honestly, never seen anything quite as grungy as the discoloration on this client’s shower.  

ANSWER

Sometimes mold that appears on grout is superficial and resides only on the surface of the installation. Most shampoos and soaps contain organic matter, some more than others .When you have organic materials temperatures and moisture, you have a great environment for mold to grow. Proper and regular cleaning of showers removes those materials. When used and not cleaned regularly you can end up with a “grungy” situation. Always use a neutral PH cleaners approved for cleaning the stone or tile in your shower. And always test them in an inconspicuous area to make sure you will have no adverse reactions. Double check for mold or wet areas outside the shower as well to ensure there are no leaks. If water has escaped the shower assembly and has reached the wood substructure this can also provide the organic matter needed for mold to grow. – Robb Roderick, NTCA Technical Trainer/Presenter

Ask the Experts – February 2017

QUESTION

I’m a homeowner in Berkeley, Calif. On my recently completed bath renovation, we’ve found that the shower curb collects water and it takes a long time to dry even with ventilation. I’m trying to determine if this condition meets industry standards or if it would legitimately be considered a defect. Someone online recommended NTCA may be able to provide help.

ANSWER

Thank you for contacting The National Tile Contractors Association. The TCNA Handbook’s wet area guidelines state that horizontal surfaces must be sloped to direct water to the drain. The slope recommended is no less than 1/4” per foot.

I couldn’t tell a whole lot from the picture you sent, but it appears there is metal endstop trimming out your curb. If that endstop edge is above the edge of the tile, it can sometimes act as a dam on curbs that are sloped. Many shower systems incorporate surface waterproofing that lays right under the tile and can be easily damaged by removing tile. I would suggest tiling over the existing curb tile using a chair rail or some type of specialty trim to maintain the integrity of the waterproofing below the surface. Guidelines for tiling over the existing tile are found in the renovation section of the TCNA Handbook in section TR711. Scarification or primers are sometimes needed. And always make sure to use the correct adhesive for tiling over tile in a wet area.

– Robb Roderick, NTCA trainer/presenter

QUESTION, part 2

Thank you very much for the prompt and helpful response! Much appreciate the advice to tile over rather than break tile and risk waterproofing damage.

You are right – there is a stainless steel edge on the curb; it seems to be proud and acting as a dam.

Regarding the tile-over repair – a question. The manufacturer says the 24” x 24” tile we are using is slightly bowed for water runoff. I suspect the current ponding is related to this. Can this type of tile be cut for successful use on a curb like this, and if so are there standards for how to do this correctly so the repair is successful?

ANSWER, part 2

The tile you have selected appears to be pretty typical as far as inherent warpage. A byproduct of the firing process in tile manufacturing is that tiles become bowed or warped. This normally manifests itself with the center of tile being the high point and the edges being the low points. There are ANSI standards for what is and is not allowable for warpage. Considering you purchased the material from a reputable manufacturer, I’m sure it would follow in the acceptable guidelines for warpage, since this company has a great track record of offering quality tile.

As far as doing the repair within standards, the requirements are for the existing installation to be sound, well bonded, and without cracks. All soap scum, wax, or coatings must be removed from the surface prior to installation. You may want to scarify or prime the surface of the tile prior to the installation to increase bond strength. Always select a mortar that is approved for tile-over-tile installations. Incorporate your 1/4” per foot minimum slope in the new assembly. Most curbs are 6” so this would equate to a minimum of 1/8” drop.

– Robb Roderick, NTCA trainer/presenter

Ask the Experts – January 2017

QUESTION

Attached are pictures of an exterior grout leaching problem we are having on concrete, waterproofed with a membrane with a latex-modified thinset mortar and sanded grout with additive. Latex leaching (or efflorescence?) came through the grout not long after installation.
We removed all the grout three weeks ago and covered with plastic as you can see. It never got wet for those three weeks and we had fans on the tile. Yet when a penknife was pulled through the joints, the material was still a little damp and the latex is still coming through.
We feel it is in the mortar we used. A manufacturer rep is supposed to look at it. The manufacturer said for us to use unsanded grout with an additive. I do not feel like that will work at all – the latex is leaching through, even with no grout in the joints.
We felt like an epoxy grout would be the answer to fix this. What is your professional opinion on this?

ANSWER

My suspicion is that this is latex migration coming from the mortar.
This does not necessarily mean it is a problem with the mortar itself. I suspect the latex in the mortar may not have been allowed to fully coalesce and may continue to be an issue. Have you lifted a tile to examine the coverage and condition of the bond coat?
It is good that you have asked the manufacturer for a review. They will be able to assist you in determining whether this is efflorescence or latex migration, and its source. If the residue is powdery and salty it is efflorescence. If it is hard and more difficult to remove it is likely latex migration.
It is important to solve the problem then select the grout. Trying to lock in the migration with epoxy grout is not necessarily a cure for the issue. The source of the efflorescence or latex migration must be determined then remedied to ensure a long term successful solution.
If epoxy is eventually selected as a grout, ensure it is rated for UV exposure on an exterior installation.
– Mark Heinlein
CTI #1112,
NTCA Technical Trainer/Presenter

Ask the Experts – December 2016

SponsoredbyLaticreteQUESTION

We have a contractor who used two different tiles. He bought the 4” x 4” tile elsewhere but after installation it appears to have changed color. The tile he bought from another source at the bottom, stayed looking like it did prior to installation. What could have caused this?

ANSWER

glazed-wall-tile-ateThe color of some tiles can change with grouting, for example this can occur with soft, natural stones and unglazed, honed or polished through-body ceramic/porcelain or quarry tiles (and/or if grout release wasn’t used).

It appears the tiles shown in this installation are glazed ceramic. You stated the two sizes of tile were procured from two different distributors. It is possible that even if the tiles are from the same manufacturer they may have been manufactured on different dates or in different lots. That being the case, the glaze may have a slight variation between the two. The glaze also appears to be different on the bullnose tile.

If spare, uninstalled 4” x 4” and 3” x 6” tiles from this job, new from their cartons, are placed side by side, I suspect you may notice the difference in color between them. Have you checked to see if the two tiles are from the same manufacturer and what their date of manufacture and manufacturer lot numbers are? This information should be available on the end flaps of the tile cartons. If the manufacturer, date of manufacture or lot numbers differ, there may well have been a difference in glaze color out of the box that wasn’t noticed until the tiles were installed and grouted

It is important to verify that all of this information aligns between all cartons of tile before beginning the installation.

Mark Heinlein – CTI #1112, NTCA Technical Trainer/Presenter

QUESTION

I need to know what the TCNA standard for slope in a commercial kitchen is.

ANSWER

The minimum slope for floor drains is 1/4” as specified by ANSI A108.01 2.2, which directs compliance with ANSI A112.21. The Universal Plumbing Code also specifies minimum slope of 1/4” per 12”.

The mortar bed is to be of a uniform thickness. ANSI A108.01 2.6.1.4 and 2.6.1.5 include a chart and discussion of minimum and maximum mortar bed thicknesses based on the service rating of the floor. For a commercial kitchen rated as Extra Heavy/Heavy, the bed thickness is 2-1/2” minimum to 3-1/2” maximum. Appropriate size and gauge galvanized welded wire mesh (i.e. 2” x 2” 16 gauge) must be suspended as reinforcing wire in the mortar bed. If the mortar bed will be in excess of 3-1/2” thick, heavier reinforcing, larger aggregate, richer mix and greater compaction may be required and must be detailed by the specifier.

To keep the mortar bed from becoming too thick or the slopes to a drain too long, multiple drain locations should be planned based on the layout of the kitchen.

Mark Heinlein – CTI #1112, NTCA Technical Trainer/Presenter

Ask the Experts – November 2016

SponsoredbyLaticreteOne of the benefits NTCA offers is its technical staff, and seasoned know-how that can be tapped to address problems and questions. Here’s an example of the profusion of information from the NTCA technical staff for the questions of one Hawaiian homeowner. – Lesley Goddin

QUESTION:

I am a homeowner in Hawaii looking at installing a large-format porcelain tile floor (planks are ~9” x ~47”). I have two questions.

My first question is what is the NTCA convention for pricing that tile install? Is the convention for an install price per square foot based on the actual footprint of the rooms (actual tile on floor when job is done) or does it also apply to the tile waste?

As an example:

– Lets say I have a simple 25’ x 40’ room: 1,000 sq. ft., once the tile is installed.

– Lets say I plan on 10% waste. So I purchase 1,100 sq. ft. of tile

Would your convention for the installers bid price be X dollars per sq. ft. based on the 1,000 sq. ft. or based on the 1,100 sq. ft.?

My second question is what sort of waste percent should I expect for that large-format 9” x 47” tile?

Thank you for your time and feedback.

plank-tile-ateANSWERS

We have three technical trainers on staff, and they are all coming off of extensive travel dates for training programs, so I am taking a shot here on this question, and they will likely provide additional or a slightly varied response.

In my experience on this subject, the labor bid for the job generally covers the 1,000 actual square footage of the room in the bid. However, if you have a 10% waste factor for materials, you would be charged for the 1,100 sq. ft. of material. My customers usually ordered about 3-5% in a straight-cut square pattern and 7-10% with a pattern design, like what you are describing below. This depended on room size and how it is laid out. I will see if they chime in with a different response but this has been my experience in the past.

Bart Bettiga, 

NTCA executive director

Bart has provided you correct information. I would add that with a plank tile such as your 9” x 47,” I may consider estimating upwards toward 12% depending on the pattern, obstacles, squareness of the room(s), etc. This is especially critical for special-order material to ensure it is all from the same manufacturing lot. Any remaining tile should be retained as “attic stock.”

There is not a standard pricing convention for labor. A contractor may base the labor rate on square footage, hourly or daily rates. A qualified contractor using Certified Tile Installers will be very familiar with the intricacies of installing large-format tile. Large tile is not necessarily faster or easier or less expensive to install. Additional substrate preparation is almost always required to ensure a quality installation based on tile industry standards.

The NTCA does have member contractors in Hawaii. Please search for them on our web site at: http://www.tile-assn.com/search/custom.asp?id=2759

To locate a Certified Tile Installer please search the Ceramic Tile Education Foundation at: https://www.ceramictilefoundation.org/find-certified-tile-installers

I hope this helps.

Mark Heinlein – CTI #1112, NTCA trainer/presenter

In my area, most installers are paid for the amount of material they use rather than the square footage that they cover. They do have to handle, cut, and dispose of that tile and usually will include it in their invoice.

As far as percentage waste to figure, two things should be considered: the layout of the area and the pattern to be installed. One single square room usually requires very little waste, while an installation with many corridor and rooms would require more.  Also a straight-lay pattern requires very little waste, while a herringbone pattern or an installation on a 45-degree would require much more. I figure somewhere between 5 and 15% waste considering all the factors just mentioned.

On a commercial project, the spec book often times calls for 5% attic stock to be left on site at completion. If that’s the case you would also want to add that on to your estimated waste amounts.

Robb Roderick, NTCA trainer/presenter

Ask the Experts – October 2016

QUESTION

I have a project in Park Ridge, Ill., which requires replacing the ceramic tile on the floor. Originally the owner decided to install a 12” x 24” tile, but due to sloping issues, such tile cannot be installed. Therefore the owner switched to a smaller tile, a 3” x 3” mosaic. Would the labor to install either size tiles be the same? If not, which one costs more? Please advise. Thank you!

ANSWER

Installing mosaic tile typically requires additional time for the cutting, straightening and handling of many individual tiles and grout joints even if, or sometimes because, they are mesh-mounted.

Installing large format tile such as 12” x 24” on a substrate that does not meet minimal acceptable flatness requirements of 1/8” in 10’ can require additional labor and materials for such activities as grinding and flattening the substrate with appropriate patch or self-leveling underlayment and their primers. Large-format tile (any tile with one side longer than 15”) will also require setting material designed for large-and-heavy tile. Due to any inherent warpage, this may require the use of a larger gauged trowel to assure required minimum bond coat coverage, which may result in the need for additional mortar.

I hope this helps.

Mark Heinlein,
NTCA Technical Presenter
mark@tile-assn.com

QUESTION

Our rectified porcelain wall tile is three years old. We need to re-grout or caulk these thin grout lines. Which is better: silicone caulking or unsanded grout? For both I would use the caulking gun. Thank you!

ANSWER

Grouting is a complex and integral component of any tile installation. Grouting requires a degree of knowledge and experience with materials, environmental conditions, tile types, tools and techniques. Qualified professional tile contractors possess these traits.

I do not recommend using caulk in the joints between the tiles.

When removing the existing grout, take care not to chip the edges and corners of the tiles. You will want to ensure that you end up with a joint that is at least two-thirds the depth of the tile. Sharp utility knife blades, high quality grout rakes and oscillating tools with carbide grout removal blades are some of the tools you may want to consider using. It often requires a combination of all these tools to do the job.

ate-1Depending on the width of the joints you will want to select a grout that will adequately fill the joints. If using a portland cement-based grout:

  • Use unsanded grout for joints 1/8” wide and less.
  • Use sanded grout for joints 1/8” and wider.

Many manufacturers now make an acrylic, siliconized-acrylic or urethane based “single-component” or “ready-to-use” grout that may be acceptable for all ranges of grout joints. This information will be listed on the grout packaging. Whether the wall is in a dry or wet area, such as a shower, may make a difference for your grout selection.

You will want to grout the joints using an appropriate type of grout float making several passes at 45-degree angles to the joints to ensure you pack the joints full of grout. Then hold the float at a 90-degree angle to scrape the excess grout off the face of the tiles and across the joints, again at a 45-degree angle to the joints to avoid dragging any grout out of the joints. Based on the type of grout you are using, allow it to set up per the manufacturer’s instructions before forming the joints with an appropriate sponge. Then, based on the manufacturer’s instructions, clean the tile with single passes of a lightly damp sponge, once again at 45-degree angles to the tile. Change your grout cleaning water frequently. Again – read and closely follow the grout manufacturer’s instructions for the type of grout you have selected.

I do strongly recommend using a 100% silicone sealant (caulk) in the perimeter joints and any changes in plane (such as where your wall meets the floor and ceiling and where it meets an adjoining wall). Many grout manufacturers make 100% silicone sealant that color matches their grouts. Be sure to use a sealant (caulk) and grout from the same manufacturer.

Depending on the size of the wall, you will want to consider the need for expansion joints (soft joints) within the tile field.

ate-2I suggest you consider hiring a qualified tile contractor to perform this work. In addition to performing the work, a qualified contractor will be able to analyze the existing installation and help you determine the best materials for the job, saving you the hassle of trying to become an expert on your own. You may do a zip code search on either the NTCA or CTEF websites located at these links.

http://www.tile-assn.com/search/custom.asp?id=2759

https://www.ceramictilefoundation.org/find-certified-tile-installers

I hope this helps.

Mark Heinlein,
NTCA Technical Trainer/Presenter
mark@tile-assn.com

Ask the Experts – September 2016

SponsoredbyLaticreteQUESTION
When installing floor tiles, should you tile to the walls or leave a small space for movement and flexibility?

exp-01ANSWER
In answer to your question about whether to leave a space where a floor meets a wall – Yes! A gap of approximately 1/4” should be left at all changes in plane (for instance where a floor meets a wall) around the perimeter of the installation. This gap should be present in the underlayment and tile. If no trim will be installed to cover the gap, a “soft joint” can be made with appropriate sealant, or certain trim profiles can be installed to accommodate movement and expansion. This gap should also be left where tile abuts cabinetry, pipes or other permanent fixtures. Any other change in plane such as where a wall meets another wall must also have a soft joint installed to allow for movement and expansion. Also, expansion joints must be properly placed and installed in the tile field depending on the location and size of the installation. Additionally, control joints and saw cut joints in concrete must be honored through the surface of the tile to avoid future cracks in the finished installation. These specifications and the many, many other details related to a successful tile installation can be handled by your qualified contractor and certified labor.

– Mark Heinlein,
NTCA technical trainer/presenter

QUESTION
I have a job we are installing a wet bed on top of concrete and I would like to install an uncoupling membrane on top of the wet bed for crack prevention. My question is, will an uncoupling membrane help to prevent cracks in the concrete from penetrating through to the tile?

ANSWER
There are many products and some installation methods that can help mitigate in-plane cracks from telegraphing to the tile surface.

Manufacturers of uncoupling membranes are best at describing the performance characteristics they warrant their individual products for. If you share with me your geographic location and contact information I can request a technical representative from that company get in direct contact with you, or your preferred uncoupling membrane distributor should be able to put you in touch with a technical representative from the company.

Since it sounds like you are installing a mortar bed, perhaps installing a cleavage membrane to create an unbonded mortar bed system may be an additional solution for you to consider. Details for this type of installation can be found in the Method F111 in the TCNA Handbook for Ceramic, Glass and Stone Tile Installation.

– Mark Heinlein,
NTCA technical trainer/presenter

Ask the Experts – August 2016

SponsoredbyLaticreteThe following conversation took place between a contractor and NTCA technical trainer/presenter Mark Heinlein.

QUESTION

I would like some feedback on a recurring issue with a shower pan that was installed about a year ago (see attached pictures). The curbless shower pan is staying damp and not drying out even after days with electric heat set at 85 degrees.

The installation procedure used was as follows:

  • Prepan liner
  • Membrane over prepan
  • Mud sloped to drain
  • Liquid-applied waterproofing over pan and up inside and outside walls
  • Heated floor (skimcoated)
  • Liquid-applied waterproofing over that

I am looking for a way to rectify this issue and to prevent it from occurring in the future with light colored stone.

exp-01

ANSWER

I have reviewed the photos you sent and read the description of your installation and have a couple of questions.

Did you install a pre-slope and liner with a clamping ring drain?  Or did you use a bonding flange-type drain, or a divot method?

Are the fixed glass panels mounted with fasteners (i.e. screws) to the floor/pan?

Please let me know.

I suspect that water may have pooled in low spots beneath the tiles that has caused the minerals in the soft marble to stain.

– Mark Heinlein,
NTCA technical trainer/presenter

QUESTION

Yes, there was a pre-slope drain with a clamping ring drain.  Workers installing the shower door said they drilled only through the tile for the shower door. There is really no area for water to pool due to the mosaic tile being installed with a small notched trowel.

If they penetrated through our waterproofing and mud bed, do you think that could have created the issue by the shower door?

ANSWER

Yes. Very likely the screws were longer than the thickness of the tile. If the liquid-applied waterproofing applied to the surface of mud bed / heat mat installation was penetrated, water can seep into the screw holes and wick into the bond coat and up into the stones. By what I can see in the photos, it appears this is the area where the staining has occurred.

Required mortar-bond coat coverage in a wet area, especially for natural stone, is 95% minimum. It is even more critical to have full-coverage bonding of soft stone on a shower floor. Were you able to get full coverage with a small notched trowel? There may be voids in the bond coat that are filing with water and staining the tile from beneath.

I also have some concerns about encapsulating the mud bed and heat system with a liner at the bottom and one or two layers of liquid applied membrane on top. How is the topical liquid membrane making a waterproof connection to the clamping ring drain?

Please take a look at TCNA Handbook Methods B421-15 and 422-15 for details regarding bonded waterproofing membranes on a sloped mortar bed shower receptor.

If you find there is no water entering through the screw holes, and if you have a good connection of the liquid waterproofing to the clamping ring drain, and if you have full-mortar bond coat coverage under the tile, this may be an example of when water stains soft stone tiles in shower pans in many types of installations. This phenomenon is currently being researched by an NTCA Technical Sub-Committee.

– Mark Heinlein,
NTCA technical trainer/presenter

Ask the Experts – July 2016

SponsoredbyLaticreteQUESTION

I am trying to find out if tile can be installed over tile. I have a ranch house in Florida built in the late ’70s with an original slab floor and terrazzo. Ten or so years ago the then-owner installed 12” x 12” tiles over the terrazzo. We want a new tile floor but do not want to remove the current tile. I know it’s “all about that base,” and our current tile floors are solid as a ROCK, level, not a single hollow or loose spot anywhere. As a matter of fact, it is almost impossible to get this tile off! No contractor will lay tile over tile, but I have read many, many articles online – from contractors – that say it can be done. What do you say? Thank you!!!

ANSWER

Thank you for contacting the National Tile Contractors Association.

Cementitious terrazzo is really just a type of mortar bed that has been ground very smooth. The only problem with going over it is the terrazzo is usually highly finished or waxed, with multiple layers. This finish must be completely removed and the terrazzo re-ground to open up its pores before tile installation. When properly prepared with the right materials, it becomes an excellent substrate for a new tile surface.

A qualified tile contractor is the best person to determine whether your existing tile installation is well bonded to the terrazzo.

expert-01

Twin City Tile Co. Ltd., of Kitchener, Ontario, was responsible for restoring the Registry Office of the Waterloo Region, which was constructed in 1938 and designated as a Heritage Landmark by the Historical Society. This included the original terrazzo floors, many of which consisted of nine cement colors and eight different colors of terrazzo chips of various sizes, with intricate geometric patterns and three different thicknesses of zinc and solid brass strips. Although you wouldn’t want to tile over a terrazzo floor of this quality and beauty, terrazzo CAN be an excellent substrate for tile, given the proper preparation by a qualified tile contractor.

Tile-over-tile is a method in the Tile Council of North America’s TCNA Handbook for Ceramic, Glass and Stone Tile Installation, providing the bottom layer of tile is well bonded and properly prepared to accept the bonding materials for the new layer of tile. This can be done by scarifying or grinding the surface of the existing tile and/or by applying an appropriate primer that will allow the new setting material to achieve a proper bond. Grinding the surface of existing tile can create a lot of dust and may release potentially hazardous particles into the air from the materials used in the glaze. It is best to have this work performed by a certified, experienced professional installer. Such an installer will also be familiar with the primers and setting materials that will work best for this type of installation.

A well-experienced, qualified, certified tile installer/contractor will know and understand the methods detailed in the TCNA Handbook and will be able to examine your existing installation and determine the best approach for the new tile. Look for a contractor who is a CTEF Certified Tile Installer and a member of the National Tile Contractors Association. I have included links below to help you find one near you. A contractor who is a member of the NTCA has a direct connection to us for any technical advice and support if needed.

If this is an above-ground construction or on a wood frame subfloor, consideration must be made to support the weight of the new tile installation. A qualified tile contractor can assist with this, but an additional contractor or engineering assessment may be required. Floor-height transitions to other areas must also be considered. The contractor you eventually hire should discuss this with you.

To locate an NTCA member contractor: http://www.tile-assn.com/search/custom.asp?id=2759

To locate a Certified Tile Installer: https://www.ceramictilefoundation.org/find-certified-tile-installers

I hope this helps!

Mark Heinlein
NTCA Technical Trainer/Presenter

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