CSLB C-54 Ceramic and Mosaic Tile (Trade Exam) — All Questions

Which is one of the three jobs thin-set mortar does in a tile assembly?

• a.Levels an uneven slab
• b.Supports the tile✓
• c.Waterproofs the substrate
• d.Colors the grout joint

Mortar bonds to the substrate, supports the tile and bonds to the tile back. It is not a leveling or waterproofing material.CTEF, troweling

What happens during the slaking step of mixing mortar?

• a.The mix rests✓
• b.Latex is poured on top
• c.Extra water is added
• d.It is mixed at high speed

Mixing has three phases: initial mix, slaking (the materials rest) and remixing. Adding water during slaking changes the mix the maker designed.CTEF, mixing

An installer mixes thin-set at high drill speed. What problem does industry guidance warn about?

• a.Better flow into the notches
• b.Air whipped in, weakening it✓
• c.No effect on strength
• d.Faster curing and better bond

Speeds above about 300 rpm can whip or entrain air, making the mortar light and weak. Faster mixing does not improve bond.CTEF, mixing

What minimum mortar thickness must remain between tile and backing after the tile is beaten in?

• a.3/32 inch✓
• b.1/4 inch
• c.1/2 inch
• d.1/32 inch

The ANSI method requires sufficient mortar for a minimum of 3/32 inch after embedding. 1/4 inch is the typical maximum for thin-set.ANSI A108.5 via CTEF

For 8 × 48 inch planks, which way should the trowel ridges run?

• a.In circles
• b.Diagonally
• c.Parallel to the 48-inch side
• d.Parallel to the 8-inch side✓

Ridges run in the same direction as the short side so trapped air has the shortest path to escape.CTEF, troweling

What minimum coverage applies to porcelain tile on an exterior wall?

• a.85 percent
• b.80 percent
• c.70 percent
• d.95 percent✓

ANSI A108.5 raises the 80 percent minimum to 95 percent on exterior and shower installations.ANSI A108.5 via CTEF

Under the TCNA Handbook's stone rule, where may no voids occur under natural stone tile?

• a.Within 6 inches of the edges
• b.Only at the center
• c.Anywhere under dry-area tile
• d.Within 2 inches of corners✓

Stone requires 95 percent coverage with no void over 2 square inches and none within 2 inches of the corners.TCNA Handbook via CTEF

For which tile does industry guidance recommend back buttering?

• a.Glass tile✓
• b.Small unglazed mosaics on a dry floor
• c.Tile set in organic adhesive
• d.Any 4 × 4 wall tile

Back buttering is recommended for large format tile, glass tile, natural stone and exterior tile. It adds bond, not coverage.CTEF, troweling

Why does industry guidance advise against a V-notch trowel for setting floor tile?

• a.It leaves too much mortar
• b.Too little support✓
• c.It scratches porcelain
• d.It is only for epoxy

The narrow point of V-notch mortar does not provide the coverage needed to support the tile. The tempting belief that it leaves excess mortar is backward.CTEF, troweling

A 6 × 24 plank will be set in running bond. Without a manufacturer's other limit, what is the maximum offset?

• a.10 percent
• b.33 percent✓
• c.66 percent
• d.50 percent

ANSI A108.02 limits offsets to 33 percent where the offset side exceeds 15 inches, unless the manufacturer specifies otherwise. 50 percent amplifies warpage.ANSI A108.02-4.3.8.2 via CTEF

A porcelain floor has 1/16 inch grout joints. What is the allowable lippage?

• a.1/16 inch
• b.3/16 inch
• c.1/8 inch
• d.1/32 inch✓

For joints from 1/16 to under 1/4 inch, allowable lippage is 1/32 inch; 1/16 inch applies to joints 1/4 inch and wider.ANSI A108.02 via CTEF

What is the absolute minimum grout joint width under ANSI A108.02?

• a.1/8 inch
• b.1/32 inch
• c.No minimum
• d.1/16 inch✓

In no circumstances shall the grout joint be less than 1/16 inch, and it must also be at least three times the tile's size variation.ANSI A108.02-4.3.8 via CTEF

A 20 × 20 inch rectified tile is being set. What average minimum grout joint does ANSI require?

• a.1/16 inch
• b.1/4 inch
• c.1/8 inch✓
• d.3/16 inch

Tiles with any side over 15 inches need an average minimum of 1/8 inch if rectified and 3/16 inch if calibrated.ANSI A108.02-4.3.8.1 via CTEF

What tool is used to pack 100 percent solids epoxy grout into the joints?

• a.Hard rubber float✓
• b.A caulk gun
• c.A margin trowel
• d.A soft sponge

A118.3 epoxy grout is installed with sufficient pressure using a hard rubber float. A soft sponge or float pulls grout out of joints.ANSI A118.3 via CTEF

When should cleanup begin on a portland cement grout?

• a.Immediately, while wet
• b.After it sets up✓
• c.After 7 days of curing
• d.Only after acid washing

Cement grout must set up so moisture can hydrate out before cleaning; washing too early pulls grout from the joints.CTEF, low grout joints

A white tile floor is grouted in a contrasting dark gray. What does the NTCA Reference Manual say about the result?

• a.It emphasizes variations✓
• b.It hides size variations
• c.It makes lippage disappear
• d.It has no visual effect

A contrasting grout emphasizes the joint and any variation in tile size and position; a matching grout de-emphasizes them.NTCA Reference Manual via CTEF

A slab has a 1/2 inch expansion joint under a new tile floor. How wide must the tile's movement joint be?

• a.No joint is needed
• b.At least 1/2 inch✓
• c.At least 1/4 inch
• d.Grout-joint width only

Joints through tile over structural joints must never be narrower than the structural joint.TCNA Handbook via CTEF

Under the VA specification, what space is left at the lip of a tub where backer board meets it?

• a.No space; butt it tight
• b.1/16 inch for thin-set
• c.1 inch for grout
• d.1/4 inch for sealant✓

The VA specification leaves a 1/4 inch space for sealant at lips of tubs, sinks and plumbing receptors.VA 09 30 13

What is the purpose of a foam backer rod in a sealant joint?

• a.Hold grout in place
• b.Waterproof the substrate
• c.Fill the joint instead of sealant
• d.Set depth; stop three-sided bond✓

Backing forms a joint enclosed on three sides at the specified depth, and sealant must bond only to two opposing surfaces.VA 07 92 00

A sealant joint is 1/4 inch wide. How deep should the sealant be under the VA specification?

• a.1/2 inch
• b.1/8 inch
• c.1/4 inch✓
• d.1 inch

At widths up to 1/4 inch, sealant depth equals width. Half-depth applies only to wider joints.VA 07 92 00

Why do acrylic latex caulks fail in tile movement joints, according to industry guidance?

• a.They stain the grout
• b.They are too flexible
• c.They cure too slowly
• d.They harden and shrink✓

Acrylic and siliconized latex caulks dry hard, shrink and fall out when the structure moves. Silicone, urethane and polysulfide are suitable.ANSI A108.01 via CTEF

White powder appears on grout lines over a slab-on-grade after a wet winter. What does it indicate?

• a.Grout that was mixed too dry
• b.Water carrying up minerals✓
• c.A sealer that is curing
• d.Normal cement dust

Efflorescence requires water to carry minerals to the surface, evaporate and leave salts. The water source must be found.CTEF, efflorescence

Under the VA stone specification, how is a damaged stone repaired?

• a.Per the stone producer✓
• b.With any color-matched epoxy
• c.By sanding it flat
• d.By sealing over the damage

Stone is repaired using methods recommended by the stone producer, and replacement stone must not show evidence of replacement.VA 09 63 40

A heated tile floor fails where a toilet was bolted down after tiling. What is the likely cause?

• a.Grout that is too thick
• b.A fastener hit the cable✓
• c.A thermostat set too low
• d.Tile that is too dense

Screws and fasteners from later trades, such as toilet bolts and door stops, are a common cause of heating cable failures.CTEF, radiant heating

A new tile floor over concrete floods 20 days after installation. What does industry guidance recommend?

• a.Ask the mortar maker✓
• b.Tear out all tile at once
• c.Seal the grout immediately
• d.Ignore it; tile is waterproof

For installations within 28 days of flooding, contact the setting materials manufacturer for an opinion on how to proceed.CTEF, flooded installations

Which shower size fails the California minimum listed in city handouts for the 2025 codes?

• a.30 × 60 inches
• b.36 × 36 inches
• c.30 × 30 inches✓
• d.32 × 32 inches

A compartment needs at least 1,024 in² and a 30-inch circle; 30 × 30 is only 900 in². A 30 × 60 receptor is exempt.CPC shower size per city handouts (2025 codes)

What minimum drain and trap size do city handouts list for a shower?

• a.2 inches✓
• b.3 inches
• c.1-1/4 inches
• d.1-1/2 inches

Showers require a minimum 2-inch drain and trap; tub-to-shower conversions increase smaller waste outlets to 2 inches.CPC per city handouts (2025 codes)

A tiled niche shelf in a shower is set dead level. What does the ANSI standard require?

• a.Slope it away from the drain
• b.Seal it instead of sloping
• c.Level is correct for shelves
• d.Slope it toward the drain✓

All horizontal ledges and rims shall slope so fluid flows toward the drain, and TCNA details extend this to seats, sills and curbs.ANSI A108.01-3.6.4 via CTEF

Why does the TCNA Handbook require a pre-slope under the pan liner of a clamping-ring drain shower?

• a.To thicken the tile bed
• b.To hold the liner flat
• c.To feed the weep holes✓
• d.To replace the mortar bed

The sloped fill under the liner lets water that passes the tile reach the drain's weep holes; without it, trapped water eventually smells.TCNA Handbook via CTEF

What slope do industry sources give for a steam shower bench?

• a.1/4 inch per 12 inches to the drain✓
• b.2 inches per foot
• c.Level
• d.1 inch per foot away from the drain

Benches and horizontal surfaces in a steam shower slope 1/4 inch per 12 inches to the drain; 2 inches per foot is the ceiling slope.TCNA SR613 via CTEF

How thick is the mortar bed placed on top of a shower pan liner under ANSI A108.01A?

• a.Thicker at the drain
• b.Tapered from 3 inches to zero
• c.A uniform 1-1/2 inches✓
• d.1/4 inch

The mortar bed over the membrane is the same thickness at the walls and at the drain, 1-1/2 inches; the pre-slope below provides the pitch.ANSI A108.01A via CTEF

In one California city's curbless-shower guideline, where must the top of the drain inlet sit?

• a.At least 1/2 inch above the floor
• b.Level with the threshold
• c.2 inches below the threshold top✓
• d.Anywhere, if sloped

The guideline requires the drain inlet top to be a minimum of 2 inches below the top of the finished threshold, so the receptor holds water.City of Mill Valley curbless shower guideline

A homeowner reports a musty odor from a shower that does not leak. What does industry guidance link this to?

• a.Epoxy grout
• b.Glass tile
• c.Too much grout sealer
• d.No pre-slope✓

Without a pre-slope, trapped and stagnant water on the liner eventually emits an offensive odor even if nothing leaks.CTEF, slope to drain