Parge Coat Calculator
Enter your wall length, height, and coat thickness to get bag count, coverage, weight, and a cost estimate for parging a foundation or block wall.
Measure only the area actually being parged, such as the exposed foundation reveal.
Two coats roughly doubles the material needed for the same wall.
10% covers spillage and hawk loss. Use 15% for rough or heavily pitted block.
Mortar mix typically runs $12–$18 per 80 lb bag at home centers.
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Parge Coat Calculator
Short answer: multiply wall length by height (in feet) to get area, multiply by coat thickness in feet to get cubic feet, add waste, then divide by bag yield. A 30 ft by 4 ft wall at 1/4 inch thick needs about 2.75 cubic feet with waste, or roughly 4 bags of 80 lb mortar mix.
Formula
Parge coat volume follows the same logic as any thin coating: area times thickness, then converted to bags using each bag’s actual yield.
| Bag size | Yield | Source |
|---|---|---|
| 80 lb mortar mix | 0.83 ft³ | Manufacturer yield data |
| 60 lb mortar mix | 0.62 ft³ | Scaled from 80 lb yield by weight |
Worked example
Wall: 30 ft long, 4 ft exposed foundation height, 1/4 in thick, 1 coat, 10% waste.
- Area: 30 × 4 × 1 = 120 ft²
- Cubic feet: 120 × (0.25 ÷ 12) = 2.5 ft³
- Add 10% waste: 2.5 × 1.10 = 2.75 ft³
- 80 lb bags: 2.75 ÷ 0.83 = 3.31 → 4 bags
- 60 lb bags: 2.75 ÷ 0.62 = 4.44 → 5 bags
Assumptions this calculator makes
- Bag yields are based on manufacturer-published data for standard mortar mix, not a specialty acrylic-modified or polymer parging product.
- Wall surface is reasonably flat. Heavily pitted or spalled block needs extra material beyond the waste allowance.
- Two coats roughly doubles material by multiplying area, which assumes both coats are applied at the same thickness entered above.
- Cost estimate covers material only, not labor, lath, bonding agent, or waterproofing additives.
Common mistakes
- Parging over loose, cracked, or delaminating old coating instead of chipping it off first.
- Applying mortar to a dry, dusty wall without pre-wetting it, which pulls moisture out of the mix too fast and weakens the bond.
- Skipping a bonding agent on smooth or painted surfaces where mortar has nothing to grip.
- Troweling too thick in one pass instead of building up in coats, which causes sagging and cracking as it dries.
- Working in direct sun or high heat, which flash-dries the coat before it can cure properly.
- Not curing the finished coat with light misting for the first day or two in hot weather.
FAQ
How many bags of mortar do I need to parge a foundation wall?
A 30 ft by 4 ft foundation wall at 1/4 inch thick needs about 2.75 cubic feet of mortar with waste included, which works out to roughly 4 bags of 80 lb mortar mix or 5 bags of 60 lb mortar mix.
How thick should a parge coat be?
Most parge coats run 1/8 to 1/4 inch thick. A quarter inch is the common default for smoothing exposed concrete block on a foundation. Go thicker, up to 3/8 inch, only when filling significant surface irregularities or applying a second coat.
Can I parge over old parging or a painted wall?
Sound, well-bonded old parging can usually be recoated after cleaning and dampening it. Loose, cracked, or delaminating parging needs to be chipped off first. Painted or sealed surfaces need the coating removed or a bonding agent applied, since mortar will not adhere reliably to paint.
Does a parge coat need two coats?
A single coat is usually enough for smoothing sound concrete block. Two coats, a scratch coat followed by a finish coat, are common on rougher or more porous substrates and roughly double the material needed.
How much does parging cost per square foot?
Materials alone typically run a few dollars per square foot in mortar mix and bonding agent. Professionally installed parging, including labor, commonly runs $6 to $15 per square foot depending on region, substrate condition, and finish.