How much deck mud do I need for a shower pan?

A standard 3×5 ft shower pan with a 1-inch pre-slope plus a 1¼-inch final mud bed needs about 2.5 cubic feet of dry-pack mortar — 4 bags of 80 lb sand-topping mix. For each 1 ft² of pan area, plan on 0.17 ft³ per inch of mud thickness. Deck mud (also called "dry pack" or "floor mud") is a stiff cement-and-sand mortar used to build the sloped base under a tile shower floor — NOT the same as drywall mud. The shower pan typically gets two layers: a "pre-slope" (sloped toward the drain, ¼ inch per foot) under the waterproof membrane, and a "final mud bed" on top to receive the tile. Both use the same dry-pack mix. Use Quikrete Sand/Topping Mix or a 4:1 mix of mason sand to Portland cement.

What is the difference between deck mud and thinset?

Deck mud is a stiff sand/cement mortar used to BUILD the sloped substrate under a shower or tile floor — it goes under the membrane and tile. Thinset is a thin, polymer-modified mortar used to ADHERE tile to the substrate. You use both in a typical shower install: deck mud for the slope, thinset for the tile bond.

Can I use regular concrete mix instead of sand/topping?

No — regular concrete has gravel/aggregate that prevents the proper packing density needed for a slope. Use only sand/topping mix (Portland cement + sand, no aggregate) or premixed dry-pack mortar (Quikrete Sand/Topping, Mapei 4-to-1, etc.).

How much water do I add to the mix?

Very little — about ½ to 2/3 the water you would use for regular mortar. The mix should hold its shape when squeezed in your hand without crumbling AND without dripping water. This is the "dry pack" consistency. Too wet and the slope sags; too dry and it does not bond.

How thick should a shower mud bed be?

Pre-slope (under the waterproof membrane): ½ inch at the drain, increasing to 1-1¼ inches at the perimeter (¼" per foot of slope). Final mud bed (on top of the membrane, holds the tile): 1¼ to 1½ inches consistent thickness across the pan, sloped to match.

How long does deck mud need to cure?

Walk on it gently after 24 hours. Tile installation: wait 48-72 hours for the pre-slope before installing the membrane. After the final mud bed, wait 24 hours minimum before setting tile with thinset. Full strength at 28 days like all Portland-based mortars.

Deck Mud Calculator: Shower Pan Mortar by Sq Ft

Dry-pack mortar needed for a sloped shower pan (pre-slope + final bed)
Shower pan size	Total mud volume	Bags of 80 lb sand-topping
2½ × 2½ ft (corner)	0.85 ft³	2 bags
3 × 3 ft	1.20 ft³	2 bags
3 × 4 ft	1.60 ft³	3 bags
3 × 5 ft (standard)	2.50 ft³	4 bags
4 × 4 ft	2.13 ft³	4 bags
4 × 5 ft	2.67 ft³	5 bags
5 × 5 ft (large)	3.33 ft³	6 bags

Dry-pack mortar needed for a sloped shower pan (pre-slope + final bed)

Shower pan size

Total mud volume

Bags of 80 lb sand-topping

2½ × 2½ ft (corner)

0.85 ft³

2 bags

3 × 3 ft

1.20 ft³

2 bags

3 × 4 ft

1.60 ft³

3 bags

3 × 5 ft (standard)

2.50 ft³

4 bags

4 × 4 ft

2.13 ft³

4 bags

4 × 5 ft

2.67 ft³

5 bags

5 × 5 ft (large)

3.33 ft³

6 bags

How to calculate it yourself

Dry-pack volume (ft³) = pan area × average mud thickness in feet. Pre-slope thickness averages ½–1 inch (¼" per foot of run from the drain). Final mud bed averages 1¼–1½ inches. Total avg thickness = 1¾–2½ inches across the whole pan. One 80 lb bag of sand-topping mix yields 0.6 ft³.

Common scenarios

Standard 3×5 ft shower pan (most common)

Pre-slope: 0.85 ft³ + final bed: 1.65 ft³ = 2.5 ft³ total = 4 bags of 80 lb sand-topping ($24-36 in materials). Mix small batches; dry pack is workable for only 30-45 minutes once mixed.

Curbless / zero-entry shower (4×5 ft)

2.67 ft³ total = 5 bags. Curbless designs need extra attention to slope (closer to ⅜" per foot toward the linear drain) — order one extra bag for grading adjustments.

Steam shower with bench (5×5 ft + bench mortar)

Floor: 6 bags. Bench top mud bed: 1-2 extra bags depending on bench size. Plus thinset on top to set the tile. Total dry-pack budget: $50-65.

About this calculation

Written and maintained by the BuildMaterialCalc editorial team. The math is derived from published codes and manufacturer specs — see our methodology page for the full source list and review process.

Last reviewed: 9 May 2026. We update cost references quarterly using the Bureau of Labor Statistics Producer Price Index plus regional supplier spot-checks.

References used on this page:

Every result is an estimate. Real-world projects vary with sub-grade conditions, ambient humidity, supplier spec sheets, and local code amendments. For structural, code, or safety-critical applications, confirm with a licensed professional. See our full disclaimer for details.

Deck Mud Calculator: Shower Pan & Tile Underlayment Mortar

At a glance

How to calculate it yourself

Common scenarios

Standard 3×5 ft shower pan (most common)

Curbless / zero-entry shower (4×5 ft)

Steam shower with bench (5×5 ft + bench mortar)

Frequently asked

Related calculators

Drywall Calculator

Insulation Calculator

Paint Calculator

Deck Calculator

Concrete Calculator

Roof Pitch Calculator

About this calculation

At a glance

How to calculate it yourself

Common scenarios

Standard 3×5 ft shower pan (most common)

Curbless / zero-entry shower (4×5 ft)

Steam shower with bench (5×5 ft + bench mortar)

Frequently asked

Related questions

Related calculators

Drywall Calculator

Insulation Calculator

Paint Calculator

Deck Calculator

Concrete Calculator

Roof Pitch Calculator

About this calculation