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How to Fit a GRP Roofing System

To install a GRP Roofing System, you will need the following tool items:

• Stanley Knife

• Sweeping Brushes

• Sandpaper (60 grit)

• Claw Hammer

• Mastic Gun

• Circular Saw

• Grinder

• Roll Polythene,

• 3-inch Roller

• 7-inch Roller

• 1 Paddle Roller

• 6-inch Paddle Roller

• Catalyst Dispenser

• Laminating Brushes

• 14l Mixing Bucket

• Thermometer

Once we have our hand tools, we can install the roof, if the roof build up is just OSB build up we would ideally use 2440x570x18mm OSB 3 t+g boards, laid at 90’ to the joints. The label or writing side of the board facing upwards, this is so that the joists are flooded with resin, at all wall junctions an expansion gap is required, in case the wall is damp and this will transfer damp into the board over a period of time, this would cause the board to expand and crack the fibreglass roof.

All boards are to be screwed with all screw heads counter sunk. If board is laid onto insulation the boards need to be fixed with screws and also glue to stop any ‘thermal expansion’; counter battens for air flow will need to be introduced, otherwise a high heat build up in the timber deck which will cause it to ‘move’ under expansion pressures, through a greater range of movement then which would normally be experienced.

This can lead to “stress relieving” in the timber deck that which is manifested as ‘cracking sound and will often trigger a chain reaction of stress relief cracking across the roof.

All drip trims are fitted and are fixed to counter battens this is not only for fixing properties but also for bonding and to stop wind uplift. All trims are nailed back bonded and corners reinforced, trim joints lapped or connected with a soaker then a resin/ 75mm bandage/ resin is applied to trim edge details and trim joints.

Should OSB board be installed without t+g then every board joint will need to be reinforced with 75mm bandage. Wall trims are applied, and a separating flashing detail is added the flashing is placed into the chase line and this comes with or without a moisture trap.

Mastic is then applied to the joint and any oversailing mastic is smoothed off and tooled in for a continuous bead. With the roof ready to be waterproofed we need a 1m² wide roll of chop stranded matting, the board needs to be clean and dry the roll is rolled out set and rolled backwards, then the resin is applied to the deck and the CSM rolled out with 50-75mm side/ head laps, then another generous coat of resin ( with added catalyst) is applied and with a ‘ribbed roller’ we start to break down the CSM we consolidate the CSM with transparent the resin will dry in about 20mins depending on temperatures and catalyst added.

We repeat this same process until the whole roof is covered with the ‘feathered’ edge on the overlap side. Once the resin has cured, we can start to prepare the surfaces by sanding down any rough areas a further layer of resin can be applied if any ‘pin holing’from resin starvation.

Once the roof has been sanded with the (40-60 Grit) sandpaper we sweep or wash down with (acetone) if the deck has been left for more than 24 hours. Then mix the paint UV coating with a small roller. Once the details have been covered mix a more generous amount and paint the field area with a large roller (if a small roller is used this will show on the finish) and apply a generous coat making sure that this is not added too thick as the topcoat is not a waterproof layer and can crack as stated too thickly.

Once cured we can add a mineral or non-slip finish for balcony or walkway area’s (600g matting will be applied to the walkway) these are broadcasted over the wet UV coating, allowed to cure, then either left or top coated to give a continuous uniform look.

If you would like any more information about fitting a GRP roofing system, please get in touch with Guaranteed GRP or call us now on 0208 702 8063 one of our GRP specialists will be happy to help.

To learn more about GRP Roofing, please click on the link below: