Preparing for laminating
Avoid spillages by masking off the roof properly, a fine spray is caused when using the consolidator roller and 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 has cured, there is no easy way of removing it from car paintwork without also
removing the paint.
Mixing the resin
GRP 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 (the hardner which resin requires for it to cure) 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 that 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 (though you should allow for 1.5kg for every 1m2 allowing for wasteage and difficult details.)
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 remaining 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.
For catalyst amount use our online catalyst calculator
Catalyst addition
There are a number of important rules of to follow when deciding how much catalyst to add:
- Never use less than 1% or more than 4% catalyst.
- Never underestimate the effect of temperature. Resins will not cure at or below freezing and will always cure much quicker in direct sunlight.
- When topcoating late in the day, add more catalyst to allow for the lack of sunlight.
- In Winter use fast catalyst, in Summer use standard catalyst, in very hot conditions use LPT (Long Process Time) catalyst.
- Remember: Any catalysed resin left in the bucket will exotherm. Heat is generated as the resin cures, so it should be kept well away from other stored materials. Water can be poured over the resin to suppress the heat gain.
- Always mix the catalyst into the resin thoroughly before using the resin (a couple of minutes for a 10 litre bucket.) Failure to do this can result in 'streaking' on the laminate, where streaks of uncured resin will remain visible and ultimately lead to a failure in the laminate.
Laying the 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. 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. Cut 200mm squares of mat for each corner and 200mm strips of bandage for each trim joint.
Corners
For corners, lay a 200mm square piece of mat on the roof deck and ‘wet out’ on both sides with well mixed, catalysed resin (see catalyst addition chart) using a 2½” polyester roller.
Place the mat on to the face of the corner trim 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, using the same technique as the corners. 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 the main 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.