Dry-pack mortar for shower pans & mortar beds — bags of sand, Portland cement & liner
For a standard 36×36 inch shower pan with a 2-inch average mud bed depth, you need approximately 1.5 cubic feet of dry-pack mortar — about 3 bags of 50-lb sand and 1 bag of 47-lb Portland cement. Our deck mud calculator gives you the exact quantities for any floor size, including waste factor, liner measurements, and estimated costs.
Deck mud — also called dry-pack mortar, floor mud, or sand mix — is a stiff mixture of coarse sand and Portland cement used to create a sloped, stable base for tile in shower pans, bathroom floors, and mortar beds. Unlike premixed thinset or mortar mix bags, deck mud is mixed on-site and packed by hand to create the precise slope needed to drain water properly.
The standard recipe is 4 parts coarse sand to 1 part Portland cement by volume. Some tile setters prefer a 5:1 mix for lightly trafficked floors; others use 3:1 for extra strength in commercial applications. All three ratios are supported in this calculator.
The TCNA (Tile Council of North America) Handbook specifies a minimum mud bed thickness of 3/4 inch at the drain, but most professional tile setters use 1.25 to 1.5 inches at the drain and build up to 2.5 to 3 inches at the walls. The required slope is 1/4 inch per foot toward the drain. For a 3-foot wide shower, that means a 3/4-inch rise from drain to wall — achievable with a 1.25" average mud bed.
For planning purposes, use 1.75 to 2 inches as your average depth — this covers the slope and gives you enough material to work with.
The formula is straightforward:
Example: A 3×4 ft floor with 2-inch average depth = 3 × 4 × (2/12) = 2 cubic feet. With 15% waste = 2.3 cubic feet. That requires approximately 5 bags of 50-lb sand (184 lbs) and 1 bag of 47-lb Portland cement (46 lbs).
Yes, for a wet shower floor. A CPE (chlorinated polyethylene) or PVC liner, minimum 40 mil thickness, goes directly under the mud bed on top of the subfloor. The liner must extend at least 6 inches up each wall and be folded neatly at the corners — no cuts. The liner creates the waterproof envelope; the mud bed sits on top of it.
To calculate liner size, add 12 square feet to your floor area to account for the wall upturns. A 36×36 inch floor needs: (3 × 3) + 12 = 21 sq ft of liner, which rounds up to a standard 3×8 ft sheet (24 sq ft).
Use coarse, washed sand — also sold as concrete sand or sharp sand at hardware stores. Avoid fine masonry sand or play sand; they have too many fines and will crack when the mud dries. Do not use bagged "all-purpose sand" unless it specifies coarse or concrete grade.
The mix should feel like damp beach sand when properly combined: it holds its shape when squeezed into a ball but does not drip water. If it slumps immediately, it's too wet. If it falls apart and feels powdery, it needs a small amount of water.
The most frequent error is using a premixed mortar bag (thinset or mortar mix) instead of separate sand and Portland cement. Premixed bags contain additives that prevent the proper compaction deck mud requires. Always buy the two ingredients separately.
The second most common mistake is not verifying the slope before the mud cures. Use a level and a straight edge to check that water will flow toward the drain from every direction. Once the mud is packed and begins to set (within 1-2 hours), adjustments become very difficult.