How much mud do I need for a shower pan?
A traditional tile shower floor is built on deck mud — also called dry-pack, floor mud, or a mortar bed. It's a stiff, barely-damp blend of sand and Portland cement (no gravel) that you pack down and screed to a smooth slope. Because it's placed by volume, the estimate is simple:
Bags = (floor area × average thickness) ÷ yield per bag, rounded up
The one trick is that a shower bed is sloped, not flat — it falls about 1/4 inch per foot toward the drain so water runs out. So we work from an average thickness rather than a single depth. Pick what you're building above and the calculator sets a typical average; adjust it if your pan is thicker or thinner.
Deck mud coverage by thickness
A 60 lb bag of sand-topping mix yields about 0.5 cubic feet. Here's how far that goes at different bed thicknesses — the thicker the bed, the less area a bag covers.
| Average thickness | Coverage per 60 lb bag | Bags per 10 sq ft |
|---|---|---|
| 1/2″ (feathered pre-slope) | ~12 sq ft | ~1 |
| 1″ (pre-slope) | ~6 sq ft | ~2 |
| 1 1/2″ (top bed) | ~4 sq ft | ~3 |
| 2″ | ~3 sq ft | ~4 |
| 2 1/2″ (full pan) | ~2.4 sq ft | ~5 |
Yields are for bagged sand-topping mix. Mixing your own from loose sand gives similar volume — see below.
Pre-slope vs. top bed — the two layers
A code-correct traditional shower pan is built in two mud layers with a waterproof liner sandwiched between them:
- Pre-slope — the first bed, poured on the subfloor and sloped 1/4″ per foot to the drain. The liner sits on top of it so any water that gets through the tile drains to the weep holes instead of pooling. It averages about 1 inch.
- Top bed — the second bed, packed over the liner and clamping drain, also sloped to the drain. This is what you set tile on. It's a minimum of about 1 inch at the drain and averages around 1 1/2 inches.
Choose Full pan for both layers (the default), Top mortar bed only if you're building a single sloped bed over a topical membrane like Schluter Kerdi or a RedGard-coated base, or Pre-slope only to estimate just that first layer.
Mix your own deck mud (5:1)
Deck mud is cheap to mix yourself: about 5 parts mason's sand to 1 part Portland cement by volume, with just enough water that a squeezed handful holds together without dripping (think damp sandcastle, not soup). The finished, packed volume is roughly equal to the loose sand you start with, so the calculator estimates:
- Sand ≈ the mud volume — about 0.5 cu ft per 50 lb bag of sand.
- Portland cement ≈ one-fifth of that by volume — a 94 lb bag is 1 cubic foot, so a typical shower needs only part of a bag (we show it in pounds).
Bagged sand-topping mix is the same idea pre-blended — handy for small pans; mixing your own is cheaper once you're buying several bags.
Tips for a solid shower pan
- Mix it dry. Deck mud should pack like a snowball and hold a sharp edge — too wet and it won't hold the slope or compact properly.
- Pack, then screed. Tamp the mud firm, then strike it off to your slope with a straightedge. Compaction is why we add a waste allowance — loose mix shrinks as you pack it.
- Protect the weep holes. On a liner pan, keep gravel or pea stone around the weep holes in the clamping drain so the top bed can still drain.
- Don't skip the pre-slope. A flat bed under the liner traps water against it — the pre-slope is what keeps the pan dry and is required by code.
- Let it cure. Give the bed about 24–48 hours before setting tile so it's firm and dry on top.