ACT Mortar (Mud) Floors

Which TCNA Handbook method describes an unbonded (floating) mortar bed over a concrete substrate for interior floor tile without a topical waterproof membrane?

• AF112
• BF121
• CF122
• DF125

Which TCNA method adds a waterproof membrane to the unbonded mortar bed assembly over a concrete substrate?

• AF112
• BF121
• CF125A
• DB415

What is the primary purpose of a cleavage membrane in an unbonded mortar bed assembly?

• AWaterproof the substrate against vapor drive
• BAllow the mortar bed to float independently of substrate movement
• CIncrease compressive strength of the mortar bed
• DProvide a vapor retarder for radiant heat

Which material is most commonly specified as a cleavage membrane in a TCNA F112 unbonded mortar bed?

• A4-mil polyethylene sheet
• BSelf-adhered SBS membrane
• CSilicone waterproof coating
• DCementitious crack-isolation membrane

Which reinforcement is specified within an unbonded mortar bed per TCNA F112?

• A#3 rebar at 12 in on center
• B2 in x 2 in 16-gauge welded wire fabric or equivalent
• CCarbon fiber strands at 6 in spacing
• DPolypropylene fibers blended into the mortar

Which TCNA Handbook method places thinset over a waterproof or anti-fracture membrane on a concrete slab — not a floated mortar bed?

• AF112
• BF121
• CF122
• DF121A

Which TCNA method is used where crack suppression must be provided only over existing in-plane cracks, not the entire floor area?

• AF125
• BF125A
• CF122
• DF121

On an F112 unbonded mortar bed, where is the 2x2 wire reinforcement placed within the bed cross-section?

• ADirectly on the cleavage membrane, before mortar placement
• BNear mid-depth of the bed, raised off the cleavage membrane
• COn top of the finished bed before tile is set
• DIt is not used in F112

Which of the following best describes "unbonded" in the context of TCNA F112?

• ATile is not bonded to the mortar bed
• BThe mortar bed is not adhered to the substrate
• CGrout is not bonded to the tile edges
• DThe tile is set without a bond coat

When is TCNA F121 (unbonded bed with waterproof membrane) preferred over F112?

• AHeated radiant floor outdoors
• BWhere moisture from above (wet areas) must be contained or substrate may transmit moisture
• CWhenever large-format tile is used
• DNever — F112 and F121 are interchangeable

Which of the following is NOT a valid substitution for a 4-mil polyethylene cleavage membrane?

• A15-lb roofing felt
• BTwo layers of red rosin paper
• CSelf-adhered sheet waterproof membrane (used as the cleavage layer)
• DAsphalt-saturated felt that meets ASTM D226

In TCNA F125 vs F125A, what is the main difference?

• AF125 uses thinset, F125A uses mortar bed
• BF125 applies the crack-suppression membrane only over existing cracks; F125A covers the e…
• CF125 is interior only; F125A is exterior
• DThere is no difference

Which statement about reinforcement in unbonded mortar beds is correct?

• AReinforcement is optional and rarely used in interior dry areas
• B2x2 16-gauge WWF or galvanized expanded metal lath is required by TCNA
• CReinforcement is replaced by latex admix in modern systems
• DReinforcement should bond directly to the slab through the cleavage membrane

What is the role of the bond coat ("mortar slick") on top of the floated mortar bed?

• AIt seals weep holes in two-stage drains
• BIt increases compressive strength of the mortar bed
• CIt is a thin layer of neat cement paste or latex-cement slurry that bonds the tile to the…
• DIt is a waterproof membrane

Which TCNA method should be specified for a commercial kitchen interior floor where slab moisture is high but the slab is structurally sound?

• AF112
• BF121
• CF125
• DF122

An ACT field-test inspector confirms that a candidate placed the cleavage membrane and reinforcement correctly. Which step typically follows immediately?

• AApply tile with thinset on top of the dry wire fabric
• BMix and place deck mud, then screed to slope and finish-trowel
• CCure the wire fabric for 24 hours before mortar placement
• DPour a self-leveling underlayment over the wire fabric

What is the ANSI A108.1A standard mix ratio for a Portland-cement deck-mud mortar bed?

• A1 part cement to 3 parts sand
• B1 part cement to 4 parts sand
• C1 part cement to 5 parts sand
• D1 part cement to 7 parts sand

Which sand is preferred for deck mud?

• AFine masonry sand (graded for mortar)
• BSharp concrete sand (also called torpedo sand)
• CBeach sand washed with potable water
• DManufactured silica flour

How is the correct water content of deck mud judged in the field?

• APourable consistency, like pancake batter
• BSlump test of 4 in (100 mm)
• CCompressed handful holds together with no visible free water
• DDry powder that flows like sand

ANSI A108.1B (latex-modified mortar bed) requires the admixture to comply with which ANSI specification?

• AA118.1 (dry-set cement mortar)
• BA118.4 (latex-Portland cement mortar)
• CA136.1 (organic adhesive)
• DA118.10 (load-bearing waterproof membrane)

What is the primary benefit of latex-modifying a mortar bed instead of using a plain Portland-cement-and-sand mix?

• AHigher compressive strength only
• BImproved flexural strength, freeze-thaw durability, and reduced water absorption
• CQuicker initial set, in under 10 minutes
• DEliminates the need for reinforcement

An installer adds too much water to a deck-mud batch. Which symptom is most likely to result?

• AThe bed will compact harder than specified
• BExcessive shrinkage cracking and weak surface
• CFaster cure with no negative effects
• DIncreased flexural strength

What ASTM standard is referenced for the Portland cement used in deck mud?

• AASTM C150 — Standard Specification for Portland Cement
• BASTM C926 — Application of Portland Cement Plaster
• CASTM C920 — Elastomeric Joint Sealants
• DASTM D1970 — Self-Adhering Polymer-Modified Bituminous Underlayment

Which ASTM standard typically governs the sand used in deck mud?

• AASTM C144 — Aggregate for Masonry Mortar
• BASTM C33 — Concrete Aggregates (fine aggregate)
• CASTM D2487 — Soil Classification
• DASTM C150 — Portland Cement

When using a richer 1:4 cement-to-sand mix instead of 1:5, what is the most common drawback?

• ALower bond strength
• BGreater shrinkage and increased risk of cracking
• CInability to support tile loads
• DFailure to meet ANSI requirements

What is the function of a small "bull" or trial batch when mixing deck mud on site?

• ATo verify the slump for the engineer
• BTo dial in water content and confirm hand-squeeze consistency before mixing the full load
• CTo pre-coat the cleavage membrane
• DTo calibrate the screed bar

Why is masonry sand sometimes considered less ideal than concrete sand for a floor mortar bed?

• AMasonry sand is too coarse and will not compact
• BMasonry sand is finer and more rounded, giving less interlock and more shrinkage
• CMasonry sand contains harmful lime
• DMasonry sand cannot be used with Type I cement

Which addition is acceptable in a latex-modified mortar bed when ambient temperature drops below 50 °F (10 °C)?

• ACalcium chloride accelerator at 2% by weight of cement
• BUse the manufacturer's cold-weather latex admix and protect the work above 50 °F during c…
• CAdd hot water above 140 °F to the mix
• DReduce the cement content by 25%

If a contractor adds too little water to a deck-mud batch, the most likely defect is:

• AThe mix becomes too sticky to spread
• BInsufficient cement hydration, producing a weak, friable surface
• CExcessive shrinkage cracking
• DGlossy, hard-troweled finish

Which mix is most appropriate for a heavy commercial floor expected to experience light vehicle traffic?

• APlain 1:5 cement-to-sand deck mud
• BLatex-modified mortar bed conforming to ANSI A108.1B / A118.4
• CSelf-leveling cementitious underlayment
• D1:7 cement-to-sand mix to reduce shrinkage

What is the typical lap dimension at the seams of the polyethylene cleavage membrane?

• A1/2 in lap, no need to tape
• B2 in side lap, with sheets shingled in the direction of slope
• C4 in side lap, taped at joints
• DButt-jointed with no overlap

How should the cleavage membrane be turned up at the perimeter walls?

• ACut flush with the substrate — no turn up
• BTurn the membrane up the perimeter walls to at least the height of the finished mortar be…
• CTurn the membrane down into the wall cavity behind the base
• DTape the membrane to the wall with duct tape

Which substrate-preparation step is required before placing a cleavage membrane on a concrete slab?

• AApply a bonding primer to the slab
• BRemove loose debris and standing water; verify substrate is structurally sound and reason…
• CAcid-etch the slab to expose aggregate
• DApply a vapor barrier paint

Which thickness of polyethylene is most commonly specified for the cleavage membrane?

• A0.5-mil
• B2-mil
• C4-mil
• D10-mil

When using galvanized expanded metal lath as the bed reinforcement, what is the most important reason for choosing the galvanized version over painted lath?

• AGalvanized lath is cheaper
• BGalvanized lath resists corrosion within the moist alkaline mortar bed
• CGalvanized lath bonds chemically to Portland cement
• DGalvanized lath is easier to cut

Which is the correct WWF specification for a typical floated mortar bed?

• A6x6 W1.4xW1.4 welded wire reinforcement
• B2x2 16-gauge welded wire fabric
• CChicken wire (1 in hexagonal poultry netting)
• DDiamond mesh stucco lath only

Two adjacent sheets of WWF reinforcement should be:

• AButted edge to edge with no overlap
• BLapped at least one full mesh square (~2 in) and tied
• CSpaced 6 in apart for thermal expansion
• DWelded continuously at every wire intersection

Perimeter expansion in a floated mortar bed is most commonly created by:

• ALeaving a gap between the bed and walls, isolated by the turned-up cleavage membrane
• BPouring mortar tight against the walls and grouting later
• CSetting tile flush to the wall surface without a sealant joint
• DAdding rebar dowels into the wall studs

On a wood-frame subfloor that will receive a floated mortar bed, what is the typical assembly?

• AMortar bed directly on plywood, no membrane
• BCleavage membrane plus 2x2 WWF on the plywood, then the mortar bed
• CSelf-leveling underlayment, then thinset, then tile
• DTile direct on plywood with mastic

Concrete substrate flatness for a tile installation using tile smaller than 15 in must be:

• A1/4 in in 10 ft (6 mm in 3 m)
• B1/2 in in 10 ft
• C1 in in 10 ft
• DNo flatness requirement

Concrete substrate flatness for large-format tile (any one side over 15 in) must be:

• A1/8 in in 10 ft and 1/16 in in 2 ft
• B1/4 in in 10 ft and 1/16 in in 2 ft
• C1/2 in in 10 ft and 1/8 in in 2 ft
• DNo tighter requirement than for small tile

Why is concrete substrate often unable to meet 1/8 in in 10 ft flatness without a mortar bed?

• AConcrete shrinks during curing and slabs frequently curl at joints and edges
• BConcrete is too smooth
• CConcrete is too porous to support tile
• DConcrete cannot accept thinset

When a cleavage membrane is installed over a substrate with a small protrusion, the correct action is to:

• ACut the membrane around the protrusion and bond mortar to it
• BGrind or remove the protrusion before installing the membrane
• CAdd more wire over the protrusion
• DIncrease the mortar bed thickness at that point only

Which is NOT typically part of substrate preparation under TCNA F112?

• ASweep slab clean and remove debris
• BVerify slab is structurally sound and dry to the touch
• CAcid-etch and prime the slab
• DInstall 4-mil poly cleavage membrane

Wire fabric for an unbonded mortar bed should be placed:

• AFlat on the cleavage membrane and forgotten
• BAbout halfway through the bed thickness, sometimes lifted into position after a screeded…
• CJust below the surface so it can be troweled flat
• DOn top of the finished surface for tile to set into

When a floor drain is present in the substrate, the cleavage membrane should:

• ACover the drain so the bed isolates from it
• BBe cut close to the drain body, leaving the drain accessible for proper sealing/clamping…
• CBe tucked into the drain throat
• DBe omitted within 12 in of any drain

What is the minimum unbonded mortar bed thickness for an interior floor per TCNA F112/F121?

• A3/4 in
• B1 in
• C1-1/4 in
• D2 in