Mortar Beds: thickness and bond [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile

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saiello
08-19-2008, 02:11 PM
Hello Tile Forum!

Newbie here. Just discovered this resource today. Fantastic clearing house for practical advice. I've been in architecture and construction since 1991 and have designed, cut, and thinset up to 3/8" floor and wall tile remodeling my home in the past. But i have no direct experience designing or installing mortar beds on any of my past projects. I'm detailing the floor assemblies now.

I’ve reviewed both the TCNA Handbook and Dimension Stone Design Manual, done some web research, and consulted Architectural Graphic Standards. None of which gave me a satisfactory answer. So, I figured I'd post for forum input on good installation practices.

This is a new construction hotel located on a deserted island in the Carribean, so it will be subject to wet and hurricane conditions and the labor may or may not be well-skilled even though imported to the site. My questions are:

• Mortar bed maximum thickness – What is the practical upper limit? the TCNA says that anything greater than the recommended 2” maximum thickness should be detailed by architect (!). We have an exterior balcony condition where the structural slab slopes ¼”/foot and the finish stone tile slopes 1/8”/foot, so the mortar bed would thicken as it gets closer to the balcony edge. The interior and exterior finish floors are flush, requiring the mortar bed to be 1-1/2” at the thin side at the door and 3” at the thick side at the balcony edge. I have other options to reduce the thickness at the edge but wanted to get some real world input on mortar bed limits before pursuing them.

• Bonded versus Un-bonded mortar beds – Is there a rule of thumb used to choose between the two depending on slab thickness? The structural slabs are 5” slab-on-grade, and 10” & 12” elevated slabs. The tiles are 18 x 18 x 3/8” thick travertine (mfr recommended ¾” medium mortar bed) and 26 x 26 x ¾” thick limestone (mfr recommended 1-1/4” to 2” thick mortar bed).

Any guidance provided by the forum is greatly appreciated!

Thanks!
Steven

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cx
08-19-2008, 03:15 PM
Welcome, Steven. If you go to the UserCP, find Edit Signature, and add that first name there it will appear in each post for for folks to use. :)

Sounds like this is gonna be more of a project thread than a technical discussion, but we'll start with it here and see where it goes.

First thing we need to know is whether this deck is over occupied space.

I don't think it's a good idea to reduce the deck surface to less than 1/4" per foot of slope on an exterior installation. If that's in the specs, I think I'd wanna discuss that with the designer. If you're the designer I'd wanna know how's come you did that.

The general requirement for decks over occupied space is to waterproof the subfloor, install some sort of drainage plane, the required deck mud (usually minimum 1 1/4" reinforced layer (F111-07)), a second waterproofing layer that is suitable for a direct tile installation (A118.10) and your tile.

The Noble Company (http://www.noblecompany.com/Products/SheetMembranes/tabid/58/Default.aspx#products) makes the only membrane indicated for single-layer waterproofing of such decks. You might wanna have a look at that.

You'll require all the necessary flashings to the structure and at the drainage edges.The interior and exterior finish floors are flush,That's pretty scary to me, specially in an area with a large average percipitation rate. I'd want a drop below the doorways of at least an inch and a half with appropriate flashing under them.Bonded versus Un-bonded mortar beds – Is there a rule of thumb used to choose between the two depending on slab thickness?Don't know how a fella'd use a bonded mud bed if he's using the double waterproofing system. With the Noble membrane I suppose you could do that.and 10” & 12” elevated slabs.That the actual elevated slab thickness? How large are these balcony areas?

My opinion; worth price charged.

saiello
08-19-2008, 04:23 PM
Thanks CX.

Yes, the balcony decks do occur over occupied space below. For consistency, we are using the same assembly over unoccupied space.

The designer in my firm is concerned about tilting balcony furniture (example: water level in glass looking off-kliter on a tilting table top) from the 1/4"/foot structural deck, and would prefer a gentler slope for the 1/8"/foot finish surface with the difference to be made up in the mortar bed.

The exterior deck assembly is currently detailed as: WP bondcoat + WP layer (Noble Deck looks like a great suggestion!); bondcoat + 1/2" drainage composite (Miradrain); bondcoat + reinforced mortar bed (thickness varies from 1-1/2 to 3"); 1/8" thinset bondcoat + 3/8" travertine stone tile. In certain exterior locations, the tile is 3/4" limestone. Is 3" thick OK for a mortar bed?

I had not considered a second WP layer above the mortar bed and below the tile. Will have to think a little more about that. Manufacturer suggestions if a 2 layer system?

Currently, there is a 3/4" minimum step-up in the structural slab from the exterior to the interior for the WP layer to wrap up and over the step and thus flashing below the CMU wall assembly. Part of my detail design exercise is to determine the exact step height necessary to get the floor assemblies aligned for ADA accessibility requirements, which limit us to a maximum 1/2" difference in finish floor height at thresholds.

The exterior assemblies will be unbonded because of the WP & drainage composite. However, the interior tile assemblies can be either bonded or unbonded. Not sure if there is an advantage to one or the other depending on slab thickness, which is an actual 10" and 12" for the elevated portions (entire building footprint is about 30,000 sf per floor). The balconies vary in size but average about 12' deep (thus the 1.5" drop in the structural slab at the balcony edge) by about 16' wide.

Thanks for your feedback, and looking forward to more!

cx
08-19-2008, 06:06 PM
The designer in my firm is concerned about tilting balcony furniture (example: water level in glass looking off-kliter on a tilting table top) from the 1/4"/foot structural deck, and would prefer a gentler slope for the 1/8"/foot finish surface with the difference to be made up in the mortar bed. Quarter-inch per foot's only a two percent slope, Steve (but you knew that). :)

Even on a really wide glass, say four inches, that's not but eight-tenths of an inch outa level. Even a six-inch soup bowl ain't gonna show even an eighth of an inch.

Think I'd rather have the water drain off my deck. Your get grouted tile on a one-percent slope, you can easily have standing water in the grout joints, even. It's also the industry standard here, if that's of any concern to y'all.

At any rate, it would be a consideration for me.The exterior deck assembly is currently detailed as: WP bondcoat + WP layer (Noble Deck looks like a great suggestion!); bondcoat + 1/2" drainage composite (Miradrain); bondcoat + reinforced mortar bed (thickness varies from 1-1/2 to 3"); 1/8" thinset bondcoat + 3/8" travertine stone tile. In certain exterior locations, the tile is 3/4" limestone. Is 3" thick OK for a mortar bed?
Too many bond coats in there, methinks. And the NobleDeck would be essentially wasted in that application.

If you're only gonna use a single waterproofing membrane, it would go on top of the mud bed and you would not bother with the waterproofing layer over the slab nor the drainage membrane/material.

Take a look at the Schluter Products (http://www.schluter.com/142.aspx) for the double waterproofing system for balconies over occupied space.

If you elect to use the Noble single waterproofing method, I'd very strongly suggest you contact the Noble company before you go any farther in your planning. They can give you very good, specific advice on how to detail those balconies. One very easy way to get started is just to send a PM to our resident Noble rep, Eric (e3) (http://www.johnbridge.com/vbulletin/member.php?u=1793). He'll be more than happy to help you get off on the right foot.

I'd sure recommend you also contact Schluter and talk with a rep about using their system, also. 800-472-4588.

Either one will also be able to give you sound advice about waterproofing that transition from interior to exterior where it needs to remain at the same floor height. That's a substantial consideration to my thinking.

My opinion; worth price charged.

bbcamp
09-03-2008, 04:42 AM
Eric, if you can get the concrete slab clean enough (yes, scrape the Redgard off), you can bond deck mud to it with a slurry of thinset or portland cement and achieve the required slope. After that, follow either Noble's or Schluters recommendations for balconies over occupied spaces