Why is my Tiled Balcony Leaking and How Can I fix it?


I have a 500 sq. ft. balcony with terracotta tiles that for whatever reason were not sealed. Water has intruded into cracks that have formed over a three year period, some as wide as 1/16”, but most are small micro cracks in the grout as well as the tile itself. The result has been rain water intrusion into the sub-structure of the wooden balcony support system, which I am afraid that over an extended period of time will cause damage that may call for structural repair. The balcony structure consists of 2 x 12 wood joists @ 12" o.c., covered by 3/4" ply-wood sub-floor. A peel and stick moisture barrier is properly installed over the sub-floor and and the adjacent vertical walls from the balcony edges. Three inches of fiber mesh concrete was poured over the peel and stick to form the floor. The terracotta tiles were installed over the concrete using the proper thin set and grout. Leaks have appeared in areas near the bottom of the joists at their connections to the ridge boards going along the front, vertical surface of the balcony. The intrusion is in the tile cracks. Can this be stopped with a sealant, or do I need to remove the entire tile floor, grout included, put in a membrane on top of the concrete, and re-tile. The concrete is only 2500 psi fiber mesh. I am afraid of damaging it if I remove tile with a demo hammer. I would have to chisel out each tile and then use a diamond embedded circular grinder plate to grind down the thin set. Please Help!


ANSWER - When there is a problem it normally is not due to one deficiency, but due to multiple compounding deficiencies.

You state that the peel and stick moisture barrier was properly installed.  If if were properly installed it would not be leaking.  If in fact it was installed properly, then something structural would have had to happen to cause a breach in the waterproof membrane to allow it to leak.  Or perhaps after it was installed and before it was tiled over, something happen that caused damage to the membrane?

Bottom line, is if there is a leak, then the membrane isn't working for one reason or the other.

Cracks in the grout joint won't cause a leak in the underlying membrane.  Cementitious grout is porous so water does go through it whether it has what sounds like shrinkage cracks, or stress cracks due to not having adequate movement joints installed.

Sealers over tiles do not make them waterproof.  Even if the tile had been sealed it would not have prevented the leak.

You should have movement joints in the installation to mitigate stress caused by the tile expanding when wet or when it heats up, and contracting when it cools and drys.  A movement joint is a grout joint with a polyethylene closed-cell backer rod with an ASTM C920 sealant (100% silicone or urethane). There should be a movement joint at the perimeter of the installation at all transitions, and every 8' to 12' in all directions.

You should have drains on the balcony.  Either a drain within the balcony or having it drain off the side of the balcony that has a drip edge flashing so it doesn't stain the side of the building.  Not only should the surface of the tile be sloped to the respective drains at the rate of 1/4" per foot, but the surface of the underlying peel and stick membrane should be sloped to a drain weep system at the rate of 1/4" per foot.  If there is not adequate drainage at the waterproofing surface then in effect you are creating a reservoir of water that can't escape.

The only way to properly fix it is to remove the tile assembly to find the problem and fix the problem. Otherwise you are only treating the symptom and not the problem.

Some repair options that will not fix the problem, does not meet industry standards, and may or may not solve the problem are:

1.  You can remove the tile from the 3" fiber reinforced concrete.  If you do it carefully and if it is structurally sound, you can remove the tile so you can re-use the concrete base.  You might have to patch some divots from the removal process.  Prep the concrete and the apply a liquid applied waterproof membrane meeting ANSI A118.10 over the concrete and up the walls.   Then install your tile over it.

2.  Remove all grout from the tile installation and fill them all with backer rod and an ASTM C920 sealant.  Make sure the perimeter joint is done too.  Tool the joint to a concave shape so it doesn't get dirty from walking on it.  Depending on how porous your Terra Cotta tile is, water may still be able to pass through it.  In theory, if you use this type of sealant in all of the joints, it makes the joints watertight, it gives you movement joints in all joints to mitigate potential movement stresses, and it gives you some additional bonding strength between the tiles.



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