Why is my exterior tile deck leaking?


Hi I purchased a problem and have been looking for a solution. My deck/balcony located on 4th floor leaked into 3d floor unit and 2d floor unit.

I re-did the whole deck determined to solve this issue once and for all because building owner just kept on trying to patch. Long story it is leaking again after 6 months.

Tore deck part to trusses replaced rotted trusses and put down 3/4 ply and 1/2 inch chip board applied fiberglass on top of those lipped the fiber glass into a stainless steel drain with weep holes. Filled in the mud floor let dry grouted and tiled on top. 6 months later leaking into units.

Cut a 1' by 1' around drains. The chip board and ply underneath is completely saturated with water. Contractor is telling me it will dry out eventually and no need to tear whole deck apart to put in new "dry" wood. He suggests re-fiberglassing around the drains. Note I have 3 drains an the fiberglass failed on all 3.

Our guess is water got into the mud floor saturated it and clogged the weep holes and then over time the fiberglass separated from the drain and water got through to the wood and the rest is history. I am concerned that this will happen again if I have 3 fiberglass failures on 3 drains in 6 months.

I am being told that the fiberglass guy did not add a certain chemical to the fiberglass to allow it to adhere to stainless steel. Now that I see this all apart it makes sense to me to a waffled vapor barrier under the tile this would have kept the mud floor from getting wet. The contractor said it does not matter if the mud floor is wet the fiberglass is supposed to work.

I am working with the contractor and he is agreeing to repair everything for free but I am concerned about the soundness of the repair and the fact that water is getting into the mud floor and testing my last line of defense..THanks for your thoughts


ANSWER - Exterior decks are one of the most common failures in building construction because they are normally constructed incorrectly.

When there is a failure it is normally due to compounding deficiencies rather than only one thing being wrong.

Fiberglass coatings are not normally used for waterproofing at least in the tile industry.   The waterproofing layer must be sloped to a drain away from the building at a 1/4" per foot.  Over occupied space there should be a primary roofing membrane first and then a secondary waterproof membrane over the mortar bed.

An exterior deck has to be constructed like a shower pan.  Pre-slope the subfloor towards the outside of the house to a drain or to weep holes to allow it do drain if water gets to that point.  The waterproofing must transition up the sides of  the building exterior walls at least 3 inches above the tile surface.

The waterproofing can be a asphalt hot mop or it can be a sheet waterproof membrane recommended as a primary roofing membrane.  It should tie into the sub-drain at the weep holes and there should be a weep hole protector over it.

Then a wire reinforced mortar bed should be applied in a dry-pack consistency at least 1.25" thick.  It's surface should have the same 1/4" per foot slope to drains.

A secondary liquid applied waterproof membrane meeting ANSI A118.10  should be applied over the cured mortar bed and transition up the wall at least 3 inches above the tile surface.  Use an ASTM C920 silicone sealant around all drains and other transitions.

The tile can be adhered to the membrane with a modified dry-set cement mortar (thin-set) meeting ANSI A118.4 or better.  Use an ASTM C920 silicone sealant around all drains and other transitions, and within the field of tile every 8 to 12 feet.


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