GRP Roofing Kit Guide: What You Actually Need

The laminate: resin, matting, topcoat

Roofing resin is a pre-accelerated polyester resin — you add catalyst and it cures. It's the structural glue of the roof, consumed at about 1.5 kg/m² with 600g mat. It comes in 20 kg tubs at around £102.

Chopped strand matting (CSM) is the reinforcement. 600g/m² is the standard flat-roof weight; 450g suits sheds and light-duty roofs. Powder-bound mat drapes and wets out well for roofing. We sell it per kilo (around £7.80/kg for 600g) so you don't pay for half an unused roll.

Topcoat is the pigmented, waxed finish coat that seals the laminate and gives the roof its colour and UV resistance. The wax rises to the surface and lets it cure tack-free — which is why you never use topcoat as a laminating resin, and never leave a laminate without topcoat for more than a few days. Applied at about 0.72 kg/m²; 20 kg tubs from around £108.

Catalyst and consumables

MEKP catalyst (hardener) triggers the cure. It's dosed by weight — 1–4% of your resin and topcoat depending on air temperature — and sold in 5 kg (around £50.40) or 25 kg packs. It's a corrosive, oxidising liquid: gloves and eye protection are not optional, and it ships as hazardous goods.

Acetone keeps your rollers, brushes and hands' worth of tools alive between mixes — without it you'll bin a roller with every batch. Allow about 0.1 L per m²; it comes in 5 L (around £33) or 25 L.

Jointing bandage — a 75 mm strip of matting or woven tape — reinforces every board joint, trim edge and upstand corner before the main laminate goes on. Skipping the bandage is one of the most common causes of cracking along board lines a winter later. Add trim adhesive (roughly one cartridge per 6 m of perimeter) to bed the trims down.

Trims: the perimeter system

Every edge of the roof needs a GRP trim profile, all sold in 3 m lengths at around £13–16: A200 drip trims where water discharges into a gutter, B230 raised edge trims on verges to keep water on the roof, D260 wall fillets where the roof meets brickwork (topped with a C100 simulated-lead cover flashing), and F300 flat flashing where the roof runs onto a slope or joins an existing felt area.

External and internal corner mouldings (the C-series) finish the junctions where two trims meet — mitring trims without them is possible but rarely watertight first time. Count your corners off a sketch of the roof.

Our trims guide covers each profile in detail. The short version: walk the perimeter, name what each edge does with water, and the trim choice makes itself.

Tools and sundries

The minimum tool kit: a paddle (washer) roller for consolidating the laminate and chasing out air, lambswool rollers for applying resin and topcoat, brushes for detail work, mixing buckets, a catalyst dispenser or measuring cup, and scissors or a knife for the mat. Budget a few extra roller sleeves — they don't survive a skipped acetone rinse.

PPE: nitrile gloves, safety glasses (catalyst splash is an eye injury, full stop), and a respirator if you're sensitive to styrene or working somewhere enclosed. Barrier cream saves your forearms.

For the deck itself: 18 mm OSB3 tongue-and-groove is the standard substrate for a new GRP roof, screwed (not nailed) at 200 mm centres. GRP goes on dry, sound board — never straight over old felt.

Essential, Protect or Premier?

Essential is a 450g laminate system — right for sheds, garden offices and outbuildings where budget matters and foot traffic is rare. It uses about 20% less resin than a 600g system.

Protect is the 600g system and the one most people should buy: the standard domestic flat-roof spec for garages, extensions and porches, with the durability to take occasional foot traffic and a 25–30 year service life when laid properly.

Premier is the 600g laminate finished with fire-retardant CrysticROOF topcoat, with optional anti-slip. Choose it for balconies and terraces, roofs near boundaries where fire performance matters, or anywhere people will regularly walk.

Frequently asked questions