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Expert Answers
Is Spot-Bonding Tile an Acceptable Installation Method?
QUESTION
My main floor tiles are 19x39” and cover approx. 900 sq. ft. These tiles have been installed using a “spot bond” method which has been confirmed by TTMAC to be an un-acceptable installation method. We discovered this issue when we started to notice that the grout lines were all cracked and then noticed that the edges of the tiles actually flex when stepped on. Some tiles have also started to become dis-bonded and click when stepped on…We are working with our builder to rectify this issue but I have concerns with their proposed method of repair.
First off, the builder is proposing to remove only selected tiles which are currently showing signs of movement. My issue is that if all the tiles were installed via this spot bond method and this is not an approved method of installation, then all tiles should be removed and reinstalled properly. Further, even if a tile is not yet showing signs of movement, because maybe it is in a low traffic area, it will eventually start to move as well. Not to mention it would become dis-bonded just from the vibrations induced by removing surrounding tiles.
Secondly, the builder is proposing to leave the existing scratch coat in place and that new tiles would be installed onto this existing scratch coat. This seems very illogical to me and sounds more like another cost cutting measure. Would the removal of the existing tile not damage the scratch coat such that it would be required to do a complete removal right down to the sub-floor and start with a proper base?
Any feedback you could provide would be very much appreciated.
ANSWER
ANSWERS - it is not acceptable to spot bond tiles on floors. For residential dry area applications, tiles are suppose to have at least 80% thin-set contact with full support at all edges and corners. Tiles in wet areas should have at least 95% thin-set coverage. Areas of the tile that are unsupported are susceptible to damage if subjected to live loads.The tile should not crack or flex, or become debonded. That suggests that the substrate is not stable and may have excessive deflection. To determine if the problem is an isolated condition or systemic, you have to remove and inspect tiles in different areas. If both the problem tiles and tiles without any sign of a problem are found to be deficient then you would likely need to replace all of the tiles.
I assume that when you say scratch coat you are referring to the mortar bed under the tile to which the tile is bonded. If after the tile is removed, if the mortar bed is structurally sound, it can be reused if properly prepared. If the problem resides in the substrate because of excessive deflection, then you have to repair the substrate.
4 thoughts on “Is Spot-Bonding Tile an Acceptable Installation Method?”
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How would you do a level (plumb) installation on a wall if the backing itself is not plumb.
I tried trowel but it’s close to impossible to maintain the big tiles at a level, and not have them trace the imperfections of the wall.
If I use the 254 Laticrete how thick can the layer of thin-set be not to loose effectiveness? That, so I can do a spot installation and thus be able to achieve a plum wall?
The wall needs to be perfectly plumb when finished.
The ANSI A108.02 tile standards state that the wall or floor substrate shall not vary out of plane, or plumb, more than 1/4 inch in 10 feet and no more than 1/16 inch in 12 inches for tiles less than 15 inches long on any side. For tiles that are 15 inches long or more on any side then the substrate shall not vary out of plane, or plumb, more than 1/8 inch in 10 feet and no more than 1/16 inch in 24 inches.
ANSI A118.4 standards state that you cannot use the thin-set mortar adhesive to true or level underlying substrates or the work of others.
So that means you have to use shims to plumb your backer boards and you need to float your walls plumb or you have to use a leveling mortar to plumb your concrete blocks or other concrete surfaces before you try to install the tiles with a thin-set mortar.
The standards say you can’t apply the thin-set thicker than 1/4″ per lift. Laticrete might tell you that you can adjust the wall with their thin-set if you don’t exceed the 1/4″ per lift. Check their data sheet and see what it says.
Yes the walls need to be plumb within the allowable tolerances. And you can adjust the walls during the installation as long as the thin-set isn’t thicker than 1/4″.
Spot bonding leaves excessive voids that diminish the potential bond strength of the tile and allows water to collect in the voids in wet areas or leaves the tile susceptible to damage where the voids are located if they are hit hard enough.
I’m sorry, it’s absolute rubbish. The only way your getting a wall to be absolutely perfect is to level the tiles. Stud walls are extremely hard to plumb as timber tends to twist as it dries out and to get a wall to within 1/16th of an inch over 10 feet, just so you can comb the wall with adhesive, would cost a fortune in labour and can only really be done when dry lining.
There’s absolutely nothing wrong with spot bonding provided one uses a high quality cement based adhesive with good coverage with a good key. I chipped a tile last week and had to replace it. It took most of the plasterboard it was attached to as I smashed it out.
I’ve ripped out hundreds of bathrooms and I can tell you now that most tiles which are combed, have been some of the easiest to remove. You can clearly see from the adhesive pattern that 95% adhesive coverage has no way been achieved, it’s more like 50%, even in the shower area. Still, a 15 year old shower area is still sound, even when it’s just plasterboard with silicone smeared up the wall acting as a tanking. I’ve also seen combed shower areas which have failed.
I work with mainly large tiles 600x600mm – 1200x600mm – 800x800mm and Spot bonding with adequate coverage is perfectly fine and is the only cost effective way of achieving perfection.
Andy
I understand there are tile installers who regularly install tile on floors using a spot bonded method. The spot bonded method makes it easier and faster for the installer to install the tile to minimize tile lippage. They also use less adhesive.
That being said, spot bonding tile on floors is against all industry standards and it isn’t allowed for walls either except when using an epoxy adhesive for certain types of installations. The Tile Counsel of America (TCNA) says it isn’t allowable. ANSI A108 says it isn’t allowable. The Natural Stone Institute (previously the Marble Institute of America) says it isn’t allowed. The ISO international standards says spot bonding isn’t allowed. Manufacturers of tile say it isn’t allowed. The manufacturers of adhesives says it isn’t allowed.
So if you have a problem and you are taken to court you will lose.
The reason why spot bonding is not allowed is for several reasons. First, spot bonding reduces the amount of adhesive contact between the tile and its substrate, so it won’t meet the standards for coverage.
Second, the less adhesive coverage you have the less overall bond strength you have. If there are 50% voids under the tile, then the potential bond strength has been reduced by 50%.
Third, by having excessive voids under the tile by using the spot bonded method, it makes the tile susceptible to damages. Wherever the tile has a void and is not supported, those spots can crack or crush if something heavy is dropped on it or if it is subjected to a heavy concentrated load. This is the biggest problem we see as a result of spot bonding.
Fourth, by spot bonding leaving big voids under the tile it will cause those areas to sound hollow.