Fibreglass Roofing

Fibreglass Flat Roofing

A properly laid glass fibre (GRP) roof will last for at least 30 years with no measurable deterioration. The roof must be laid onto a dry deck in dry conditions at a temperature not below 5°C. The resins and top coats should be suitably for use in roofing. This guide relates only to the application of the GRP laminate and top coat. The deck should be of 18 mm exterior plywood or Sterling Board and be well fixed to the underlying joists. Typically two men can strip, re-deck, laminate and top coat a roof of about 20 square metres in one day. Always try to plan starting the roof when a settled period of weather is forecast. The deck may be a new deck, or may be formed over an existing roof. You should ensure that the new deck is laid to adequate falls in order to allow good drainage, so that there is no standing water on the roof after completion.

Materials:
Once the new deck has been formed you will need the following.

Resin: allow 1.5Kg/m2 for 450g glass or 2 Kg/m2 for 600g glass.

Top coat: allow 0.5Kg/m2. 

Glass: Emulsion bound chopped strand mat (CSM). The minimum should be a single layer of 450gm or for a heavier laminate a single layer of 600gm mat.

Acetone, which is the solvent for the resin. 

Catalyst (hardener) along with a Safety Dispenser. 

Brushes, Consolidation Rollers and Application Rollers. 

You will need to form the edge detail with various preformed edge Trims.

Application:
When you have prepared the new deck, the work is carried out in the following sequence.

1: Trimming: Fitting the edge trims.

2: Bandaging: Reinforcing the board joints.

3: Laminating: Applying the GRP membrane.

4: Top Coating: Applying the final top coat.

Trimming:
The trims are supplied in 3m lengths and should be fitted as shown by nailing the bonding edge to the deck. The facia, drip and upstand trims should be bonded to an underlying slate batten (as shown) in order to support the edge. 

The A200 - Drip facia trim can be offset in order to ensure that the drip stands over the gutter. Preformed corners may be used, or if preferred, mitres can be cut into the trim to form the corner then sealed on site with a patch of glass fibre.

The choice of trims is as follows:

A200 - Drip facia, used wherever the roof drains into a gutter.

B230 or B260 - Used along any free standing edge wherever no drainage is required.

C100 or C100MT - Used in place of lead wall flashing, usually used with fillet trims.

D240, D270 - Fillet trims used wherever a roof meets an abutting wall.

E280 - Expansion joint used only on roofs over 100m2.

F300 - Flat flashing used mainly as a slate flashing where a pitched roof meets a GRP flat roof.

For Complete Trims Information

Bandaging:
All the board joints and all the trims must be "bandaged "to the roof to ensure that no stress cracking can occur at the joints. This is done by applying a 3" wide glass bandage to each joint and to all the trim edges. These bandages must be well consolidated. 

The procedure for bandaging is the same, on a smaller scale as that used for the main laminate. A small amount of resin, usually about 1 kilo is decanted into a small bucket and mixed with catalyst. (See catalyst addition chart for a guide to the correct amount of catalyst). The resin is the applied to the board edges and to the trim edges with either a 3" brush or small roller. The pre-cut bandage is then rolled out over the resin and a further amount of resin is then applied to the glass bandage, which is allowed to wet out before consolidating with a small consolidation roller. All the detail work may also be completed at this stage, drain outfalls, channels, pipes and roof fittings can all be sealed with GRP You will find that a brush is more useful to form complex shapes and to consolidate the glass than a roller for these details.

Laminating: 
The main laminate may be applied before or after the bandage has cured. The laminating must be planned depending on the air temperature. Long runs may be attempted in cooler conditions while short runs must be used in hotter conditions. Remember that the resin will always cure faster in hotter conditions and an allowance must be made for this when deciding how much glass to lay in one mix. (The Glass : Resin ratio should be 1:2.5). Before the laminate is applied the glass must be pre-cut to the desired length., shorter lengths in hotter conditions. The laminate need not be laid to falls, i.e. it does not matter in which direction the joints are lapped. Clear all unnecessary items off the roof and mix sufficient resin and catalyst to complete the first "run". Wet out the first area to be done and roll out the glass. Apply the remainder of the resin to the glass, allow to wet out for a few minutes, then consolidate the glass with the consolidation roller ensuring that no dry patches of glass remain and that no air is trapped in the laminate. 

Continue with the next "run" of glass overlapping the first by 5Omm. Do not step on the wet glass and resin. Continue this until the roof has been completely covered and the laminate has been well consolidated.

Top Coating:
The laminated roof must be top coated as soon as possible - Try not to leave the laminate overnight. Test the laminate for cure by using slight finger pressure. The laminate is about half cured when it is impossible to move the glass fibres within the resin matrix. At this point it will withstand light foot traffic so that you may stand on the laminate to complete the top coating. Mix up sufficient top coat to complete the roof with the same amount of catalyst used on the main laminate. Decant a small amount to finish the edges and all details work with a small paint brush and apply the rest to the main roof area with a clean 7" lambswool roller. 

Ensure that the top coat is even and not more than half a mm thick. If the top coat is applied too generously, there is a danger that it will crack. The roof is then complete and will take several days to fully cure. It will not deteriorate and maybe cleaned occasionally with soap and warm water. DO NOT USE BLEACH or any strong alkali on the roof. The roof will withstand foot traffic and may have planters or tiles or other decorative finishes applied to it with no detrimental effects. The edge trims may be painted if required.

*These times may vary according to mix type and catalyst activity used.

Catalyst additions:

1) Never use less than 1% even in summer. Just mix less at a time.

2) Never use more than 4% - the cure time will not reduce with more catalyst beyond 4%.

3) Never underestimate the effect of temperature. Resins will not cure at or below freezing and will always cure much faster in direct sunlight.

4) Remarks - when Top Coating late in the day - add more catalyst to allow for the lack of sunlight.

5) You can buy catalysts of different strengths, to partially compensate for winter and summer conditions.

6) Remember any catalysed resin left in the bucket will exotherm. Heat is generated as it cures and it should be left well away from other stored materials. Water may be poured over the resin layer in order to suppress heat gain.

Troubleshooting:
You may encounter some problems when laying the roof or after its completion. If these instructions have not been followed.

1) Delamination of the laminate from the boards: Moisture in the deck when laminating.

2) Flaking and Cracking of the top coat: Top coating onto a wet laminate or applying the top coat too thickly.

3) Resin cures too fast: Conditions are too hot to lay resin or addition of too much catalyst.

4) Top coat cures too fast: See No.3.

5) Resin cures too slowly or not at all: No catalyst addition or temperature too low. The cure will stop and temperature drops to freezing.

6) Patch or Streaky cure of resin or top coat: Insufficient catalyst and inadequate mixing.

7) Resin does not cure and appears milky white: Water contamination.

8) Excessive fibre pattern: Too little resin and insufficient consolidation.

For Complete Trims Information

Rough Price Guide (Including standard delivery)

Prices include delivery but do not include timber & equipment VAT must be added. Trim costs are approx. £3.10 per running metre.

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