Deck Mud Calculator

How to Use This Calculator

Enter the length and width of the area in feet, then the average thickness of the mud bed in inches. For a shower pre-slope, the bed is thin at the drain and thicker at the walls, so use the average, which is usually around 1.5 inches. The calculator returns the total deck mud in cubic feet with 10% waste added, then breaks it into bags of sand and Portland cement for a traditional 5-to-1 mix, plus a bag count if you would rather buy ready-blended sand and topping mix. Toggle between shower pan presets to fill common sizes fast.

How to Calculate Deck Mud

Deck mud, also called floor mud or dry-pack mortar, is a stiff mix of sand and Portland cement in a 5-to-1 ratio by volume. The finished bed volume is essentially the sand volume, because the cement and water fill the gaps between the sand grains.

First find the volume: length in feet times width in feet times thickness in inches divided by 12 gives cubic feet. Add 10% for waste and screeding losses. For a 3 by 3 shower pan at 1.5 inches: 3 × 3 × (1.5 ÷ 12) = 1.13 cubic feet, times 1.10 is about 1.24 cubic feet.

That 1.24 cubic feet needs roughly 1.24 cubic feet of sand and one fifth of that in cement. At 0.5 cubic feet per 50 lb sand bag and 1 cubic foot per 94 lb Portland bag, that is 3 bags of sand and 1 bag of cement.

Deck Mud Tips

Mix deck mud on the dry side. Proper dry-pack holds its shape when you squeeze a handful and should barely stick together, not flow like concrete. Too much water makes a weak bed that crumbles and will not pack under a float.

Work the pre-slope before the top bed. A shower floor is built in two layers over the liner: a sloped base under the liner and a top mud bed above it, each sloped a quarter inch per foot toward the drain. Screed to your slope with a straightedge, then pack the edges firm.

Mix only what you can place in about 30 to 40 minutes. Deck mud stiffens as the cement hydrates, and mud that has started to set will not pack or bond properly. For larger floors, batch it. Let each bed cure a day before tiling.

What to Buy

For a mix-your-own bed, buy washed masonry or all-purpose sand in 50 lb bags and one bag of Portland cement (Type I/II) per five bags of sand. This gives you full control over the dry-pack consistency that tile pros prefer. For small showers, a single 94 lb bag of Portland covers several beds.

If you would rather skip the measuring, ready-blended sand and topping mix in 80 lb bags is pre-proportioned and just needs water, though it runs a little wetter than classic dry-pack. Add a latex or acrylic mortar admix in place of some of the water for a stronger, more water-resistant bed in wet areas.

Frequently Asked Questions