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Example Data Table
| Scenario | Area (m²) | Coats | Thickness/coat (mm) | Efficiency (%) | Wastage (%) | Total mass (kg) |
|---|---|---|---|---|---|---|
| Garden path waterproofing | 12.000 | 2 | 2.0 | 95 | 5 | 54.73 |
| Pond edging sealing | 8.500 | 3 | 1.5 | 92 | 6 | 45.17 |
| Planter box lining | 4.200 | 2 | 1.0 | 96 | 4 | 9.46 |
Formula Used
1) Area: If using length and width, A = L × W.
2) Total thickness: t = (thickness per coat × coats) / 1000 to convert mm to meters.
3) Volume: V = A × t.
4) Theoretical mass: m₀ = V × ρ, where ρ is density.
5) Efficiency adjustment: m₁ = m₀ × (100 / efficiency%).
6) Wastage allowance: m = m₁ × (1 + wastage%/100).
How to Use This Calculator
- Select how you will provide the coated area.
- Enter thickness per coat and the number of coats.
- Pick a grade or set density for your product.
- Set efficiency lower for rough, porous surfaces.
- Add a wastage percentage for safe purchasing.
- Enter package size and optional price per kg.
- Press Calculate to view totals and export files.
Selecting the right coating rate
Bitumen in gardens is often used to waterproof planter boxes, seal masonry edging, and protect timber near damp soil. Start with a realistic coverage rate for the substrate. Smooth concrete usually needs less material than rough blockwork or weathered wood. If a product datasheet lists m² per litre per coat, use that value and treat thickness as a check rather than a guess. Always confirm compatibility with soil contact, plants, and drainage details before coating during installation.
Converting thickness and coats into volume
The calculator converts millimetres to metres and multiplies area by coats to get wet-film volume. Example: 20 m² at 1.5 mm for two coats equals 0.06 m³ of film. With density, volume converts to mass, which aligns with how most products are sold. Using density also helps compare emulsions, cutbacks, and hot-applied grades on the same basis.
Allowing for losses and surface absorption
Theoretical numbers must be adjusted for absorption and practical losses. Corners, joints, screw heads, and porous faces increase usage, and material is lost in mixing, transfer, and tool loading. Efficiency models how much of the mixed product reaches the surface, while wastage covers unavoidable over-application and leftover in containers. Increase allowances for textured stone, old timber, or intricate planters.
Packaging, storage, and on-site handling
Once total kilograms are known, packaging becomes a planning step. Smaller packs reduce leftovers but increase handling time. Larger packs are faster for big areas but need careful storage and resealing to avoid skinning. The pack-count output rounds up so you do not run short mid-coat. Optional pricing estimates material cost for budgeting and comparing alternatives.
Quality checks for garden waterproofing work
Good results depend on preparation and verification. Measure area carefully, confirm coats, and select thickness that meets the moisture barrier goal. Apply evenly, respect drying times, and pay extra attention at overlaps and penetrations. After curing, inspect for pinholes and thin spots. Record actual usage and update your allowances for future garden projects.
FAQs
What units should I enter for area and thickness?
Enter area in square metres. Enter thickness in millimetres per coat. The calculator converts thickness to metres internally and multiplies by coats to estimate total wet-film volume and mass.
How do I choose density if I don’t know it?
Use the product datasheet value when possible. If unavailable, keep the default and treat results as an estimate. Different formulations can vary, so confirm density for accurate kilograms and pack counts.
Should I increase wastage for porous surfaces?
Yes. Porous timber, rough masonry, and old concrete absorb more and cause higher tool losses. Increase wastage and/or reduce efficiency until your estimate matches past jobs or a small site trial.
Does this work for bitumen emulsion and hot-applied bitumen?
Yes, if you enter an appropriate density and thickness. The math is volume-based, so it applies to most coating types. Always follow the manufacturer’s application temperature and curing guidance.
Why does the pack count round up?
Bitumen is typically applied in complete coats. Rounding up prevents shortages that can leave thin spots or incomplete coverage. Extra material also covers touch-ups at corners, seams, and penetrations.
Can I estimate cost with this calculator?
Yes. Enter a price per kilogram to get an approximate material cost. Labour, primers, tools, and surface preparation are not included, so use the cost output as a budgeting baseline.