Roof Waterproofing Chemical Calculator

Roof waterproofing chemical quantity per square foot calculator — litres and drums for your roof. Use the free Roof Waterproofing Chemical Calculator below — enter your values and get instant results, right in your browser. Litres = roof area (sq ft) × coats ÷ coverage per litre (40 bitumen, 50 acrylic, 35 cementitious). Drums = litres ÷ 20.

How to use the Roof Waterproofing Chemical Calculator

A leaking roof ruins ceilings, paint and furniture, and waterproofing chemicals are too expensive to buy by guesswork. This roof waterproofing chemical quantity per square foot calculator uses the real coverage rates: bitumen coatings cover about 40 sq ft per litre per coat, acrylics about 50, and cementitious coatings about 35. Enter your roof area and the coats your applicator recommends, and you get the litres — and the 20-litre drums — to buy before the monsoon arrives.

  1. Measure the roof area in square feet and enter it.
  2. Select the number of coats (2 minimum, 3 for old leaking roofs).
  3. Select the chemical type your applicator will use.
  4. Click Calculate to see litres and 20-litre drums required.

Formula

Litres = roof area (sq ft) × coats ÷ coverage per litre (40 bitumen, 50 acrylic, 35 cementitious). Drums = litres ÷ 20.

Worked example

Waterproofing a 1,000 sq ft roof with 2 coats of bitumen coating: 1,000 × 2 ÷ 40 = 50 litres. That is exactly 2.5 drums of 20 litres — buy 3 drums to be safe on a rough old surface.

Frequently asked questions

Two coats minimum; three coats on old roofs with cracks or previous leakage.

Bitumen or acrylic coatings suit concrete roofs; cementitious coatings work best on terraces that will be tiled over.

No — apply on a dry surface with at least 48 hours of dry weather ahead for proper curing.

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