“ Experience is the hardest teacher… .It gives the test before you learn the lesson

Inspection Day!

Thursday Morning Jobsite Inspection Exterior Tile Wall Failure

Sometimes no matter how hard you work, or how much you emphasize the critical issues, you lose the battle. I normally do not go onto jobsite inspections. It is not part of my scope of work as an Arch Rep., so I brought a company expert with me. We have a Technical Department that is trained and equipped with the proper tools and knowledge to do jobsite inspections. But this project was different. I had been involved since the beginning with the architect, went to a pre-installation meeting(s) with the architect, owner, GC plastering sub, and tile contractor. Our company even supplied materials for a  mock up; unfortunately the best laid plans of mice and men often go awry.

Inspection Day:

We arrived on site on a rainy southern California morning. We did a visual inspection of the exterior tile installation from the ground. Some areas of the installation had no problems. Some areas were showing what the GC called Bulging, or what is referred to in the industry as “tile tenting”… and this is NOT good.

This is where the tile abuts to a hard surface. There were no expansion/soft joints within the tile assembly to accommodate the thermal expansion/contraction taking place. The result was compression of the tile; with nowhere to go but up, the tiles expands and lifts up, then shears away from the substrate itself.

We continue our inspection on the roof top (not a great place to be if you do not like heights). On top of that, we had to climb a ladder to get to the top of the parapet and hang over the edge of the building to examine the tile, holding my phone and taking pictures. We found extreme tile tenting and shearing off the wall, resulting in loose tile in a significant amount of bondloss in this area. We did not do a complete  inspection due to the difficulties of examining an installations that is 6 stories high. Some areas seem to be installed correctly and were still will bonded. This is typical with “tenting”, once relief is gained thru the bond rupture of a few tiles the surrounding tile remain intact.

As with most failing installations, the cause it is not just the result of one item (even though lack of movement joints would be enough to cause this failure.) it is a combination of items. One of the concerns that the architect originally had was to keep the tile veneer installation “lightweight”. It was not structurally designed for a heavy stone or tile. They decided on one of the new thin porcelain tile typically these can weigh less than 3 lbs psf (1.5 to 3 lbs psf) where a tile or natural stone would typically weigh 4 to 6 psf). This thin tile is still relatively new , but it expands and contracts with thermal changes the same as traditional porcelain tile. Another issue with the area that we inspected was the lack of coverage. You should see close to 100% mortar/adhesive coverage, in this case the coverage was much less. The TCNA - Tile Council of North America recommends 95% for mortar coverage between the tile and stone for exterior installations and there should be no voids within 2” of tile corners. All corners and edges of the stone tiles must be fully supported. Back-parging or back buttering, is recommended in all areas. Coating of the back of the tile however does not constitute coverage, which is the area where the mortar makes contact with the tile and the substrate. This is important. It appears that the installers had only back buttered the tile and installed it to the substrate without keying-in the mortar to the substrate by firmly troweling mortar onto the substrate. While they got 100% coverage on the back of the tile there was little mortar transfer to the substrate; making it vulnerable to low shear and tensile strengths.

As more and more tile installations are specified with Large and Heavy tile (LHT), directional troweling becomes crucial to a successful installation of LHT tile and stone. To ensure proper coverage of the bonding surface of LHT, and to provide full support of edges and corners, select a notched trowel sized to facilitate the proper coverage. Key-in the mortar into the substrate with the flat side of the trowel. Comb with notched side of the trowel in one direction. Firmly press tiles into the mortar and move them perpendicularly across the mortar ridges forward and back to flatten the mortar furrows and fill the tile/substrate interface as completely as possible allowing air to escape. Back buttering the tile is highly recommended on vertical installations and most often is the only way to achieve the required proper coverage. Comb the mortar in the same direction as the mortar on the substrate. Once again, the goal is to let trapped air escape and collapse the ridges in the mortar to achieve 95% transfer from the mortar on the substrate to the mortar on the back of the tile or stone. Periodically remove and check a tile to ensure proper coverage is being attained.

Back to the rooftop; looking down from the top you could stick our finger between the tile and the substrate. We could see the waterproofing (RedGard) clearly. It appears that they did not spread mortar onto the substrate. We could see some lines where the back buttered tile was pressed onto the substrate, however not achieving anywhere close to 95% coverage required or any signs of significant “key-in” adhesion to the RedGard. One of the tiles had sheared so much that it had cracked the  adjacent tile it was pushing against (see Photo below). The entire installation was hard grouted between the tile to the metal flashing/drip edge. The flashing drip edge should have been installed over the top of the tile to prevent the water running down the tile and letting the metal expand independently of the tile. There should have been a soft joint between the two dissimilar surfaces.

(above Photo, shot from roof down) Tile sheared off the substrate. Tile cracked due to shear force. Notice the white mortar? This should be close to covering up the RedGard. This is the mortar from the back of the tile bonding to the substrate.

There appeared to be no soft joints in the corners where the tile meets the stucco. As for the building itself, there are signs of movement in the block and cracking inside the ground level parking structure. If this is an issue or normal movement it is hard for me to access.

After a morning rain directly on building which cools the tile, sun comes out and starts to warm the dark tile while the white stucco reflects the heat away from it. This repeated thermal cycling will eventually cause the tiles to crack and loose their bond to the surface without the proper mortar and expansion joints to accommodate the movement.

Recommendations to prevent this type of failure in the future. Specifications:

Single source for all setting materials, waterproofing & antifracture membranes, grouts, sealent and sealers. In this case they are still waiting for the mortar manufacturer to get back to them on testing the mortar over the waterproofing and crack isolation membrane. (this was not a mortar or grout used from the company I work for. On this project, only our waterproofing was used).

Specify a specific mortar. You do not want the tile sub to use the cheapest ANSI A 118.4 or 118.15 for an exterior installation; which is what you may get if you only list standards. Select a specific TCNA installation method (that way all subs are bidding on the same method and materials).

Design/recommend soft joints into the installation per TCNA EJ 171 even if your client does not want to see it. Better to design and get approvals now than have to explain why the tile is falling off the building and being responsible and/or sued for the tile hurting someone.  Listen to the experts. South facing walls and dark tile or stone may need more expansion joints.

Specify 95% coverage for exterior installations and periodically pull a tile off and check coverage. Let the work force know that coverage compliance will be checked and enforced. Proper flashing and drip edges.

Waterproofing membrane and high quality cement mortars and grouts will also help prevent efflorescences. Substrates. The finish is only as good as the substrate it is attached to. It is hard to get the installers of the substrate to get it flat enough for Large Format tile you may have to add an allowance in 093000 for the tile contractor to flatten the substrate so that it will fall into the tolerances and guidelines of 1/8” in 10’ from the required plane, with no more than 1/16” variation in 24” when measured from the high points in the surface.

Best regards, Dale Roberts

CTC, CSI, CCPR, LEED AP