Guides
Plaster and skim coat consumption
Choose per-mm or per-coat consumption, measure thickness and turn planned mass into whole bags.
Mortar consumption is meaningful only with units, thickness and the product-data basis. Select the right plaster or skim mode and distinguish theoretical mass from purchased bags.
Key points
- kg/m² and kg/(m²·mm) require different operations.
- Thickness comes from measurement and the product's permitted range.
- Bag mass does not define the volume of the hardened layer.
In this guide
Prepare your inputs
- Net area with explicit deductions.
- Current exact-product sheet and consumption units.
- Thickness measurements, calculation mode and bag mass.
1. Identify the consumption basis
For kg/(m²·mm), multiply area, thickness in mm and consumption. For kg/m² at a specified finished thickness, multiply only area and consumption when planning that thickness. Do not add another thickness multiplier.
Select per-coat or per-mm data in the skim tool according to the sheet. Two coats need not have equal thickness. With per-mm data use actual total thickness; with per-coat data use the coat count within the manufacturer's stated conditions.
Source: [1] Knauf — MP 75 product and technical documents · [2] Knauf — Rotband Flächenspachtel
2. Measure substrate and thickness
Record several measurements across the surface and check local irregularities. One measurement can miss deep hollows. Separate substantial repairs from a uniform finishing coat when they require different material.
Check minimum and maximum thickness, preparation and time between coats in the instructions. The calculator does not assess adhesion or moisture and cannot approve thickness. This model's thickness unit is mm: enter 2 for 2 mm, not 0.002.
Source: [1] Knauf — MP 75 product and technical documents · [2] Knauf — Rotband Flächenspachtel
3. Convert mass to bags
Apply the chosen allowance to theoretical mass, divide by bag mass and round upward. Retain the difference between planned and purchased mass.
Combine demand before purchasing for rooms using the same product. Keep different mortars separate. Check shelf life, storage conditions and the available package variant.
Bags = ceil(area × thickness in mm × consumption × (1 + allowance / 100) / kg per bag)
Skim with per-millimetre data
Hypothetical inputs: 20 m², 2 mm, 1.2 kg/(m²·mm), 5% allowance and 20 kg bags. This rate is not a product recommendation.
| Stage | Result |
|---|---|
| Net: 20 × 2 × 1.2 | 48 kg |
| Planned: 48 × 1.05 | 50.4 kg |
| Bags: ceil(50.4 / 20) | 3 |
| Purchased mass | 60 kg |
| Surplus over plan | 9.6 kg |
Three bags cover numerical demand. Two provide only 40 kg, less than even net demand.
Use the other mode for kg/m² at finished thickness; this example does not justify an additional multiplier.
Try this example in the calculatorCommon mistakes
| Mistake | How to avoid it |
|---|---|
| Multiplying a rate for 10 mm by 10 again. | Check whether it describes finished thickness or one mm. |
| Entering metres in an mm field. | Enter 2 for 2 mm. |
| Replacing dry-product consumption with density. | Use product consumption; density is a different quantity. |
Check before using the result
- Mode matches sheet units.
- Thickness is measured and permitted.
- Allowance occurs once and bags are whole.
Method limits
- Theoretical demand does not inspect the substrate or application losses.
- The model does not specify preparation, drying or layer compatibility.
Questions and answers
What if consumption is a range?
Calculate both endpoints and record why they differ. Do not automatically choose the minimum for an unassessed substrate.
Are two 1 mm coats equivalent to 2 mm?
For quantity, yes, with the same product and per-mm data. Application feasibility and intervals still come from the instructions.
Sources and verification scope
- Knauf — MP 75 product and technical documents
Example of separate product sheet, system sheet, declaration and safety sheet. Check the consumption basis and exact pack on your selected product.
Access checked: - Knauf — Rotband Flächenspachtel
A product example with consumption expressed per square metre per millimetre. The illustrative rates in this guide are not this product's specification.
Access checked: