Tile over a flat roof membrane [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


View Full Version : Tile over a flat roof membrane

03-31-2012, 07:51 AM
I bought a a six year old foreclosed home that had a two story 15x20 balcony with the top one serving as the roof to the second one. The top roof is a railed deck that is very visible from the home's upper floor so it needs to have a finished look and it also serves as a sun deck. The original construction of the top roof had a rubber membrane topped with thinset attached cement backer boards with no-frost porcelain tiles. The slope is minimun and there is a small low spot in one corner that holds water for about an hour after the rain stops. We knew there was problem with the roof because of the ugly mineral leaching off the sides, cracked grout, and loose tiles. I wanted to fix the problem so we started to address the grout and loose tiles but wound up removing the roofing to the rubber membrane. The backer boards were brittle and the thinset underneath them was like compressed powder so the whole roof above the membrane was removed in an hour and a half. The membrane is in good condition and does not leak [ it does have some areas where the thinset did bond to the rubber [about 15%], so it is not totally clean, but mostly smooth. 98% of tiles were removed intact and only had a little thinset on the bottom. I want to retile the roof. What can I do to prevent the same thing from happening? Can I use the old tiles? Is Ditra bonded to the membrane somehow an option? If so, what do I use to bond it with?

My tile contractor wants to pour a mud base over the membrane to enhance the slope and tile over it. I am wondering if that is a good idea since the mud would have problem curing over the membrane and the weight of the mud base possibly compromising the structure. Is he correct to suggest this? He does seem unsure and that bothers me too. The home's builder thinks the structure can hold the weight, but he also thinks that the original install was OK too.

Sponsored Links

Houston Remodeler
03-31-2012, 08:21 AM

Your contractor is on the right track with 'pouring' a new mud deck over the membrane (your primary waterproof layer) What I hope he is referring to is more commonly referred to as a pulling mud, a barely dampened mixture of sand and ceement - no lime. See the library about deck mud.

Over that deck mud would be your secondary waterproofing. You have choices there. Schluter makes an few products, picking one depends on how the water exits your deck. There are also surface membranes from Noble, as well as liquids such as Hydroban,

What can you tell us on how the water exits your deck? Got pictures? We like pictures.

03-31-2012, 08:23 AM
I have done that but only if your in a bind. We did 1"+ of the best Laticrete
we could get our hands on with WWF. Yes, need to check the weight to see how much it will deflect. Our deck was also mostly covered but it has lasted
2 years now in NY

The right way is to use a multi layer system with sub drainage.:tup2:

03-31-2012, 08:50 AM
Welcome, Eric. :)

Do consider that you're dealing with one of the highest liability installations in the residential construction industry. The home's builder thinks the structure can hold the weight, but he also thinks that the original install was OK too.An excellent point. I would not depend upon the builder's testimony, nor that of anyone else about the structural integrity of that deck. I'd want to look in there and see exactly how it's constructed and evaluate it myself, or have that done by a knowledgeable third party. And pay particular attention to the attachment to the house structure and the outside supports.

If you determine the structure is suitable for a ceramic tile installation (joist deflection less than L/360 for the increased loading required by your building code and proper subflooring size and material), you may want to proceed even though your slope is inadequate. I would strongly recommend you repair that defect as well, though.

Adding a properly reinforced mud bed with adequate slope over a drainage material of some kind would be the next step (there is no concern with the mud curing properly over the existing roofing, but the roofing must be protected from the mud by the drainage layer). Then the secondary waterproofing layer, which would also be your tiling substrate.

You'll want to pay special attention to the flashing to the building and proper drainage at the outside edge. You need also to be sure, before you start, that you'll have adequate vertical space between the finished deck surface and any door openings to the deck for flashing and waterproofing.

There is another method of construction that would probably work even better that involves removing the entire surface of the existing deck, sistering the existing joists to provide proper slope (and add strength or/and rigidity if necessary), installing new subflooring, CBU, and a particular sheet membrane from the Noble Company. The membrane, NobleDeck, is warrantied by the manufacturer for single-layer waterproofing of exterior decks over occupied space.

Lot to consider on this project. :shades:

My opinion; worth price charged.