Single ply and liquid
GRP fibreglass roof: resin, mat, topcoat and catalyst
- where
- waste factor
- waste allowance (%)
- laminating resin (kg)
- area to laminate (m²)
- resin rate (kg/m²)
- chopped strand mat (kg)
- mat weight (g/m²)
- topcoat (kg)
- topcoat rate (kg/m²)
- catalyst (kg)
- catalyst addition (%)
Explain this equation
Takes off the materials for a GRP fibreglass roof: resin, glass mat, topcoat and catalyst. Use it when pricing or ordering a kit.
Each material has a rate per square metre. The resin and topcoat rates are in kg/m², so area times rate gives kilograms. Mat is sold by grams per square metre, so dividing by 1000 converts to kilograms. The waste factor k adds the same percentage to all three. Catalyst is a small percentage of the weight of resin and topcoat it is mixed into.
Quantities scale directly with area; catalyst scales with the resin it cures.
Sense check: 20 m² of 450 g mat at 1.5 kg/m² resin with 10% waste is 33 kg resin, 9.9 kg mat and 8.8 kg topcoat, with about 0.8 kg of catalyst at 2%.
Watch out: catalyst percentage depends on temperature; follow the resin maker's chart. Too much makes it go off before you can wet out the mat.
Estimates the laminating resin, glass mat, topcoat and catalyst for a GRP roof from the area and the system’s published rates.
Enter your values to see the result.
Good to know
Cure It’s standard specification is resin at 1.5 kg/m² with 450 g/m² mat and topcoat at 0.4 kg/m² (600 g mat for heavy foot traffic). Scott Bader Crystic Roof quotes 1.2 kg/m² of resin with 450 g mat and 1.5 kg/m² with 600 g. Catalyst is 1–4% by weight depending on temperature (more when cold, less when hot); Crystic’s chart gives 3% at 13–20 °C and 2% at 21–28 °C. 1% is about 10 ml per kg of resin.
Common mistake
Mixing more resin than can be laid before it gels, or adding extra catalyst to speed it up. Mix small batches and follow the temperature chart.
Limits
Single layer of mat. Mix rates are for the named systems; use the rates for the system you install. Primer, trims and trim adhesive are extra.
Sources
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the roof covering manufacturer’s fixing specification, BS 5534, BS 8000-6, BS 6229, the Lead Sheet Training Academy guidance and Building Regulations. Wind uplift and structural design need a competent designer.