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One of the hardest details with a GRP flat roof is the external corners. When we fit any of the roof edge trims that meet at an external right angle the outer corner has to be reinforced we can buy a preformed external angle for either a drip trim or a water check detail. These can be mechanically fixed into place then the joints will have to be bandaged and resin applied.
Behind the trim fit a bonding mastic or nail the underside of the trim edge to the previously placed counter batten. If a preformed external corner is not available, then one will have to be formed. Where a water check corner meets a drip trim corner, cut a piece of mat or CSM (450g) , the thicker the matting the more visible the bandage corner will be, slightly set the water check corner back by 5mm from the drip trim corner, this allows for the build-up of resin/ CSM matting.
Cut the CSM approximately 300mm Square. Lay the square near the edge then with a ‘wet board’ (used so that any excess resin does not affect the finish of the rood) apply a ‘wet out’ with catalysed resin on both sides, using a soft roller.
Peel away from the deck and drape the wetted mat into position to the corner drip trim/ water check edge, make sure that the bottom edge is level with the trim bottoms. Fold around the corner and turn the mat over onto the other sides of the trim and create a ‘75mm turn around’, turn the over sail onto the deck and with the roller, smooth out any creases, work the matting and form it not the contours of the trim. Then with a small ribbed or consolidation roller work out any air or creases and fold are worked out.
To ‘disguise’ the application of corner bandage, a strip of 100mm staple tissue can be laid on the bandage to smooth the course texture of the glass fibre. The application can easily be formed using the residue of base coat resin and work the corner until the bandage in place disappears and creates a union finish. Once the resin has dried, apply 60 grit sandpaper and start to smooth off the finish (a mechanical handheld sander can be used).
Once the surface is touch smooth, brush down the area and use a Stanley knife to cut away any hanging CSM strands. If the detail has been left longer then 24 hours then a ‘acetone’ clean will have to be applied. When all the dust and debris are removed apply a generous coat of UV protection topcoat to the area avoiding any drips running down. Once the UV coat has dried you are left with a unified smooth looking corner detail that sets the roof edge finish off.
To learn more about GRP Roofing, please click on the link below: