QUESTION
I am working on a project where there are requirements that I am not comfortable assuming. Below is the information given to me by the GC as we finalize our takeoff and put together our proposal. What is the best way for me to finish a floor at 4” or 5”? I typically self-level, but not to this depth, particularly for an exterior installation where sloping is required.
I am also not familiar with the compatibility with the Soprema 2-ply SBS waterproofing system. Would that be installed by a waterproofing company or by us?
The sealants, expansion joints, and pressure cleaning are understood. If all components must be polymer-modified based, does that eliminate my ability to dry pack unbonded mortar followed by a thinset installation? Would I be adding latex to unmodified mortar? I am still learning the intricacies of mortar-set exterior pavers compared to interior installations.
Requirements specified by the architect:
- All components of setting materials (mud bed, thinset, etc) are to be polymer-modified based
- Total floor assembly at the lobby/ground level, including the tile: 4”
- Total floor assembly at the level 14 pool deck, including the tile: 5”
- Must include all exterior expansion joints, including sealant, per TCNA standards
- Includes sealant at any horizontal tile/paver intersection with vertical surfaces (i.e., planter walls, building walls, etc.)
- Setting material must be compatible with Soprema 2-ply SBS waterproofing system
ANSWER
A few important technical items need to be clarified before this can be properly priced or constructed.
First, per the TCNA Handbook, methods that include a mortar bed clearly state under Requirements: “Mortar beds in excess of 2 inches thick shall be detailed by an architect.”
A 4” to 5” total floor assembly strongly suggests a mortar bed exceeding 2”. That thickness is not something to field-design. It requires an architectural detail showing reinforcement, cleavage membrane (if applicable), slope, and interface with the waterproofing system.
Second, if the roof deck is waterproofed with a Soprema 2-ply SBS membrane and a mortar bed is being installed over it, the drainage strategy must be clearly defined.
A key question to address is: How is water that migrates through the tile assembly going to drain once it reaches the top of the SBS membrane?
Exterior mortar-bed systems over roofing membranes typically require a drainage layer or drainage mat above the membrane to allow water to migrate to drains. A mortar bed placed directly on a roofing membrane without a drainage plane can trap moisture, leading to saturation, efflorescence, freeze-thaw stress (if applicable), and long-term failure.
This must be detailed by the design professional. It cannot be assumed.
Regarding Soprema compatibility:
- The exact SBS product must be identified.
- Written confirmation from Soprema is required stating that a mortar bed can be installed over their membrane.
- Trade responsibility (roofing vs. tile contractor) must be defined.
Regarding the “all components polymer-modified” requirement:
- Thinset mortars can comply with ANSI A118.4 or A118.15.
- Traditional dry-pack mortar beds per ANSI A108.1A are not typically polymer modified.
If the specification intends for the mortar bed itself to be polymer-modified, that requires written clarification and manufacturer direction.
Bottom line, this assembly needs:
- The specific TCNA method reference
- Architectural detailing for mortar beds exceeding 2”
- A clearly-defined drainage strategy above the SBS membrane
- Soprema’s written compatibility approval
- Clarification of polymer-modified requirements
- Defined scope between roofing and tile trades
An elevated exterior pool deck over a roofing membrane is a high-risk assembly. It should not be constructed based on interpretation.
