Gilles' Outlet

June 2, 2007

Repairing a titled porch

Filed under: House Remodelling — Gilles @ 6:31 pm

A tiled porch is repaired after a few tiles fell by themselves during a moderate rain storm.


Skill Level: 2 (Basic)

Time Taken: About 2 Hours

During a moderate rain storm, several tiles fell off a porch. We inspect the tiling job for loose tiles, prepare surfaces for repair, mix some modified thin-set, apply and comb it. Tiles are installed and grout lines are filled.

Left: the affected section of the porch. I know tiles were laid less than 6 months before they fell. Well installed tiles last for years, even outside.

Combs in mortar are clearly visible. This means that the back of the tile did not come in contact (or very little) with the mortar. This is clearly the signature of a hack job done by a clueless homeowner.

Right: I started the repair by inspecting all other tiles. To see if a tile was not set properly, pros hit it gently with their index or the back of a plastic putty knife. If this produces a hollow sound, the tile has not been set properly.

I found about 7 improperly installed tiles, some had already started to separate from their substrate. I tried to pry them loose with a putty knife but none gave way.

I would normally use a flat piece of metal to force tiles off but I had only time to repair the existing damage. In the future, more repairs will likely be needed in this area.

Left: I inspected the back of the failed tiles. There were no trace of any mortar. This told me that the tiles were not pressed down in the mortar or there was not enough mortar applied.

The small areas where the mortar actually touched tiles were breaking, almost like sand. This indicates that the mortar used was not designed for exterior use. Rain washed the mortar away, leaving the sand behind.

It is difficult to see but most tiles still had the store’s price tag sticker attached to it (left, under my wrist). This prevents adhesion so it needs to be removed.

Right: using a flat tipped cold chisel and a masonry hammer, I removed all pieces of loose mortar. I also removed all high spots to ensure there would be enough room for the new mortar.

Left: as I was removing loose mortar, the chisel caught under an adjacent tile and pried it loose. I got lucky not to break it. The tile’s back came off clean, like all others. I cleaned the old mortar under the newly removed tile.


Right: I used a masonry brush to clean the area. For the mortar to adhere well, surfaces must be perfeclty clean, dry and free of dust. This step is critical.

Left: a 25lbs bag of VERSABOND Fortified Thin-Set Mortar which can be purchased at most home centers. It is polymer modified and approved for interior and exterior use.

Non modified thin-set will cure hard and will be prone to cracks if the substrate moves. Polymer modified thin-set will cure flexible which dramatically reduces future cracks.

Right: I pourred about 1/4 of the bag in an empty 5 gallons bucket. The tool in the bucket is a mixing paddle. It is attached to a corded drill and makes mixing thin-set an easy and quick task.

NOTE: When pourring thin-set, it is important to be in a well ventillated area and to wear respiratory protection. This product contains Portland cement, which is bad for lungs.

I added about 3/4 quart of water (as indicated on the bag), turned on the drill on low speed and mixed the thinset for a few minutes. It is essentially like making custard with a beater.

Left: the mixed batch. Instructions said to let it set for about 10 minutes so I cleaned the paddle and prepared the tools I’ll use when laying tiles.


Right: after about 10 minutes, I gave the thin-set a gentle mix as specified by the instructions. When mixed right, it has the consistency of a paste.

Left: I used the flat side of a square notched trowel to apply the thinset.

When applying mortar, it is important to use the right notched trowel. For this thin-set, the manufacturer calls for a 1/4” x 1/4” x 1/4” notched trowel. It means that notches are squares 1/4” deep and 1/4” wide.

Right: the bead of thin-set before combing. I made sure there was enough mortar for tiles to come in contact with it almost everywhere. In this case, it took a more mortar than usual because the substrate was so uneven to begin with.

Notice that the bead is relatively flat.

Left: using the notched side of the trowel, I notched the bead of thin-set.

Notches help thin-set to spread evenly and to adhere to the back of tiles.



Right: I laid the first tile in position, carefully aligning it with the previous tile in the row. I also tried to leave a small gap between the tiles so the repair would blend in.

Left: I gently moved the tile left and right, back and forth about 1/4” to ensure an even distribution of mortar under it.

Right: I laid a scrap of 2×4 over the tile and genty tapped the tile down with a hammer. This pushed the title down into the mortar. I repeated the operation over the whole surface of the tile.

Now, these two steps were not done when the porch was originally tiled and this is why it failed less than 6 months after.

I laid the remaining tiles following the same technique. It took only a few minutes to lay the tiles.

Once all tiles were laid, I applied a thin bead of thin-set to fill in the gaps between tiles (called grout lines). Now you should (unlike me) wear rubber gloves: touching thin-set with bare hands can damage your skin and is not recomended.  

Using a wet sponge, I removed all thin-set traces on tiles but not on grout lines. Essentially, the technique here is the same as if I was applying grout, only I am using thin-set instead of grout.

Now, this is wrong. Thin-set should not be put in between tiles. This is a place reserved for tile grout. I did it this way because the whole porch was done like this and I wanted the repair to visually blend in.

Whoever did this job could not be bothered with waiting for the thinset to dry and then filling gaps with grout.

The two vertical slates had a tendency to fall down so I wedged two pieces of scrap 2×4 to maintain them in place, down in the mortar.

I let the thin-set dry overnight. On the next morning, I removed the supports and finished clean up the area.

Tools Used:

  • Masonry Hammer
  • Cold Chisel
  • Masonry Brush
  • Notched Trowel
  • Corded Drill & 4” Mixing Paddle
  • Spunge

Materials Used:

  • Polymer Modified Thin-Set (exterior) – about 6lbs 


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