Man, I hate decks over living space. Seven years after designing one at the insistence of the client, I got a call from the GC (I was the architect) saying the Owner was having severe leaks on this tiled 2nd floor deck patio and wanted him to fix it. (At his own expense, BTW.) He wanted me to take a look and tell him what I thought.
First, he had thought that the deck drains were leaking and had his roofer repair those. (They were indeed leaking, demonstrated through a hose test.) Owner hadn’t ever cleaned them out and they were partly rusted out. Fixed those and the situation improved, but not completely.
He next pulled up a number of the Mexican pavers and exposed the membrane system below. The system had been originally installed by a certified installer of that system. It was supposed to be about 3/16″ thick but had completely worn away in places and was paper-thin in other areas. System was an elastomeric rolled-on membrane followed by fiberglass reinforced, latex modified cementitious top coat.
Turns out the tile, which was supposed to have been thin-set directly on the system (per the manufacturer’s recommendations) was actually set on a thick mortar bed with wire reinforcing. The mortar was directly on top of the waterproofing system, no isolation membrane or anything. (Apparently the tile setter was trying to do a favor by improving the slope of the tapered joists.)
I’m thinking the mortar bed may have caused some sort of chemical reaction because of the alkali content, causing the waterproofing system to deteriorate. However, I’ve never seen anything like this before and am wondering if anyone else has. Have you? TIA–
Richard
Replies
First - IMO, this is a bad design from day one.
Second - though I admit to not being familiar with that membrane, I suspect that it should have been isolated with a drainage plain or at least a slip sheet, based on previous experiences with similar systems.
Third - I sugest contacting the manufacturer opf the roofing membrane system for technical help and advice. If it is an upstanding company, they want to know what kinds of thengs can deeteriorate their product and they may have already run across this situation before.
Fourth - I have learned that the HO who actually does half of what he should to maintain anything is a rare bird and deserves recognition. too bad it's not this one. Anyway, it's a good idea to design systems that are as foolproof as possible. For instance, that is the reason that all the door manufacturers went to composite thresholds instead of oak or veneered woods.
Excellence is its own reward!