Home Installation Guide Traning manual Stage 3 - Laminating the roof

Stage 3 - Laminating the roof


Roofing resin

Roofing resin is supplied in tins of 20kg (approximately 18.5 litres.) The mixing buckets are graduated in litres which will allow easy calculation of the amount of catalyst needed depending on the ambient temperature. To remove the lid from the tin a 4-6 inch nail is required to bend back the lugs.

It is very important to stir the resin before use, ensuring the styrene wax that has settled at the bottom of the tin gets thoroughly mixed in. Prepare enough tins of resin to complete the day’s laminating at this stage, as mistakes such as using unmixed resin are difficult to rectify later. The resin to CSM ratio is 1.35kg of resin for every m² of glass.

It is good practice to mix a small quantity resin (1 or 2 litres) to start with to laminate the corners and bandage the trims. This will give the best indication of the curing time of the resin and confirm if the correct amount of catalyst has been added to the mix. Ideally, it is best to aim for a curing time of between 20 to 30 minutes. Once all the detail work has been laminated the resin can be mixed for the main body of the roof.

Techniques: If a laminate of GRP requires a perfect finish, i.e. it is somewhere likely to be frequently overlooked such as a balcony, join lines between CSM rolls can be avoided by feathering the CSM. This is achieved by roughly ripping a small strip off the cut end of the CSM. When this is laid on top of another feathered roll, the join will be seamless.

Chopped strand mat

Before the chopped strand mat is laid out, the deck must be clean and dry and all the trims fixed in place. The mat has a cut edge and a feathered edge. Always overlap the feathered edge on top of the cut edge.

The mat is usually best laid parallel to the drip trim. Start by rolling the mat out, overlapping the trim by at least 50mm but not over the edge of the trim. Leave the ends long at this stage. Roll out each 1m wide strip.

Overlapping each time by at least 50mm right across the roof. The ends can be cut off with a Stanley knife into the corner of the trim to leave a straight and neat edge.

Overlap (never less than 50mm) or cut short pieces of mat and overlap them along the roof.

Decide on the best place to finish laminating the roof from. Roll the mat up to the furthest point from the ladder. Leave the rolls on the roof where they have been laid out to avoid any mix up if there is a deviation in size or angle from one length of mat to another.

Corners and joints

Cut 200mm squares of mat for each corner and 200mm strips of bandage for each trim joint.

Note: Avoid spillages by masking off the roof properly, a fine spray is caused when usingthe consolidator roller, wind can carry this a considerable distance. It is important to ensure that this is considered before the resin is used on the roof. When resin hascured, there is no easy way of removing it from car paintwork without also removingthe paint (see spillages in the troubleshooting section).


Corners bandaging

Lay a 200mm square piece of mat on the roof deck and ‘wet out’ on both sides with resin (see catalyst addition chart) using a 2½” polyester roller. Place the mat on to the face of the adjoining trims with the bottom edge on the radius of the trim.

Fold around the corner and fold over the top of the trim down on to the deck. It will be easier to dress and feather if the mat is cut vertically from the top corner of the trim upwards. Using the 2½” roller, 2” paint brush and small consolidating roller, feather the corners in to place. Any joint in the trims should be bandaged using the same mix of resin, in a similar fashion to the corners (Figure 1).

Corners bandagingFigure 1


If any boards are not completely engaged these joins should be bandaged, even a small gap may cause resin to leak through the boards which will lead to porosity in the laminate.

If any nails holding the trims are not going to be covered with laminate on the deck or corners they should be laminated with a small piece of mat.
The deck of the roof can be laminated before the corners and bandages have cured.


Laying the main laminate


Unroll 1m of previously cut mat along the lowest part of the roof and align so it can be unrolled across the roof without running off-line. Carefully roll the mat back.

Laying the main laminate

Figure 2.

To get a ratio of 3:1 one-third resin should be applied on the board and two thirds resin on the mat dip the 7” polyester roller into the bucket of catalysed base resin. Lift the roller out of the bucket and without letting the excess run off, drop 3 rollers full onto the board and coat 1 square metre. This will ensure that there is a ratio of one-third resin on the board.

Laying the main laminate 2

Figure 3.

Unroll the mat on to the resin coated board. In strips of 7” (1 roller width) wet out the mat by dropping 1 roller full in the middle of each 7” run, push the roller away to the end of the 1 metre run, then pull back over the full 1 metre (figure 4).

Laying the main laminate 3

Figure 4.

Continue across the 1m² (approximately 6 runs) and then roll the roller over the whole area again to ensure good even coverage.
Wet out the next 1m² of board in the same way, remembering to use one third of the resin on the board and two thirds of resin on the mat. Roll out the mat over the next 1m² of wet out board and continue to roll out the resin as previously described.

Note: Never attempt to lay a roof in wet weather or when wet weather is forecast.

If it starts to rain while you are laying a roof, the roof must be covered and must not get wet, always keep a large visqueensheet on site to cover the roof. The visqueen will not bond to the curing laminate.

If rain is forecast while laying boards, the boards can be temporarily sealed with a coating of catalysed resin. Always ensurethat as much of the roof is covered as possible, ensure that edges, or areas of possible water ingress are covered.

If decking has become damp, do not attempt to lay laminate on top.

Always ensure that the surface you are laying onto is completely dry and free from debris before you start. A wet surface can leadto delamination.


Let the resin soak into the mat to break down the emulsion binder for 2 to 3 minutes. Using the paddle roller and applying a little pressure, roll back and forth along the 2 edges and the end of the wetted out mat, feathering them in as you go. Now roll the paddle roller over the whole of the wet out mat, ensuring the paddle roller makes at least 2 passes over the whole area. In colder weather the resin will be thicker and will take a little longer to wet out. When a laminate is correctly wetted out it should be transparent, there should be no white or opaque areas. Take care near the edge of the roof and in windy conditions as a fine spray will be emitted from the roller.

Make regular close inspections of the laminate as it is consolidated, checking for ‘pin holes’ and areas short of resin. Pinholes in the laminate will lead to porosity and water penetration.

On all overlaps of the mat, pay extra attention to the ‘feathering in’ as this will improve the overall appearance of the finished roof.

Preparation for topcoating

Taking care and paying attention at this stage will produce a roof of superb appearance. Using a sanding pad with a 40 grit sand paper, lightly sand the corners and trim bandages. Sand off any unsightly fibres, taking care not to sand too heavily on the corner itself as this may lead to holes appearing. Cut any excess cured mat protruding beyond the trim with a sharp Stanley knife.

Seal any abutments with walls using a clear silicone sealant. Fit any C100 simulated lead flashing before top coating and seal off with a clear silicone sealant.

Techniques: A number of different finishes can be achieved using slate granules. they can either be sprinkled over the top of curing topcoat for the appearance of mineral felt. Alternatively, a fine sprinkling of granules can be rolled into the topcoated roof for a coloured non-slip finish.

Non-slip-finish-mixed-with-topcoat Non-slip-finish-greent

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