Sealant Calculator — Cartridges for Window & Door Installation

A standard 310ml cartridge covers approximately 8.5 linear metres with a 6mm x 6mm joint (36mm² cross-section). For a 10mm x 10mm joint, coverage drops to approximately 3.1 metres. Coverage varies with joint profile, technique and waste. Always buy 10-15% extra for waste and tool-up cuts.

For external window frame to wall joints, use a low modulus neutral-cure silicone sealant rated for external use. Internally, acrylic sealant is suitable and can be painted. For glazing bead to glass, use a low modulus silicone. Never use acid-cure silicone near sealed units as it can attack the edge seal.

A frame-to-wall perimeter joint is a movement joint, so the recognised rule for elastic sealants (silicone, MS polymer) is a 2:1 width-to-depth ratio — the sealant depth should be roughly half the joint width, with a minimum depth of about 5-6mm. For example, a 10mm wide joint takes about 5mm of sealant depth. This hourglass bead lets the sealant stretch without over-restraining it and causing premature cohesive failure. A closed-cell backer rod (or bond-breaker tape on shallow joints) is used to set that depth and prevent three-sided adhesion. Use a backer rod on wider joints (roughly 10mm and above). A 6mm x 6mm joint is acceptable on narrow domestic frame gaps where a deeper joint is not practical. See BS 6213 for sealant selection and joint-design guidance.

Silicone sealant typically skins over in 10-20 minutes and achieves handling cure in 24 hours. Full cure takes 3-7 days depending on joint depth, temperature and humidity. At temperatures below 5°C, curing slows significantly. Low modulus silicones generally cure faster than high modulus types.

Modern silicone sealants generally do not require primer on clean, dry surfaces such as uPVC, glass and smooth masonry. However, primer is recommended on porous substrates like rough-cut stone, unpainted timber and some renders. Polysulphide sealants almost always require primer for adhesion. Always check the sealant manufacturer data sheet.