Sandbed Shower Pan Calculator — Dry Pack 4:1 Mud Bed

4:1 mud bed mix — also called dry pack mortar for shower pans — is 4 volumes of clean masonry sand mixed with 1 volume of Portland cement. The ratio is by volume, not weight, because sand compacts differently than cement powder. Portland cement comes in 94 lb bags that are 1 cubic foot volume, which makes measuring simple: one Portland bag plus four equal-volume buckets of sand = 5 cubic feet of 4:1 mix. The mix is damp, not wet — it should hold a ball when squeezed and crack when you poke it, not slump like concrete or run through your fingers like dry sand.

Yes. Sakrete Sand Mix, Quikrete Sand Topping Mix, and Mapei 4-to-1 Mud Bed Mix are all premixed 4:1 sand-to-cement ratios. They come in 60–80 lb bags with the Portland and sand pre-blended. The only thing you add is water. Bagged 4:1 costs about 2× mixing your own raw Portland + sand, but it eliminates measuring errors and the dust cleanup of mixing dry powder on-site. For professional shower pan work, bagged 4:1 is the standard because consistency matters — a 4.5:1 mistake makes the pan weaker than expected.

Yes. Portland cement is the hydraulic binder that makes the sand harden when wet. Without it you just have wet sand that never sets. Use Type I or Type II Portland — both work for shower pans. Type III is faster-setting for cold weather but unnecessary in normal conditions. White Portland is optional if you want a lighter-colored pan, but it costs more and the tile floor hides it anyway. One 94 lb bag of gray Portland makes exactly 1 cubic foot of cement component, which is the basis of the 4:1 volume calculation.

Minimum 3/4 in at the drain, stepping up to 1-1/2 to 2 in at the curb. The thickness is the vertical distance from the top of the pan membrane to the top of the sloped mortar bed. Thinner than 3/4 in and the pan flexes under foot traffic, stressing the tile above. Thicker than 2 in and you should add a wire mesh reinforcement stapled to the subfloor to prevent the thick bed from sagging. The slope must be exactly 1/4 in per foot of run to keep water moving to the drain without pooling.

Dry pack (4:1 mix, damp consistency, compacted in lifts) is what every tile contractor uses for shower pans. Wet pack adds extra water so the mix pours, which sounds convenient but is wrong for shower pans — it settles unevenly as it cures, which means the slope disappears in the middle of the pan and water pools there. Wet pack is used for poured concrete or mortar beds where slump is acceptable. Dry pack for shower pans must be damp, compacted with a tamping tool or 2 × 4 scrap board, and worked in 2–4 in lifts so each layer compacts fully before the next goes down.

The curb top should sit 1/2 to 3/4 in above the highest point of the pan mud bed. This ensures water hitting the pan runs toward the drain instead of over the curb. The finished curb top — with tile — typically ends up 2–3 in above the pan floor. Build the curb from 4:1 dry pack too, packing it in 1–2 in lifts and tamping each layer. Do not use bricks behind the curb only — they need dry pack packed around them to hold the curb rigid.

Yes, and it goes on top of the subfloor (not the mud bed), folded up the walls 8–12 in, and secured at the curb. The mud bed goes ON TOP of the liner. Code requires a PVC or CPE liner with a collar around the drain clamping ring. A proper liner with dry pack on top and tile on the dry pack is the layered system that prevents water from migrating into the subfloor or walls. Skip the liner and you will get mold behind walls or rot in the subfloor — that repair costs 10× the liner install.