How to use Fibreglass Roofing Kits

MATERIALS
Fibreglass (GRP) Roofing Kits are supplied with the following materials

1. Fibreglass Matt
2. Polyester Resin
3. Grey Topcoat
4. Catalyst / Hardener
5. Tools

OVERVIEW
Flat Roofs are generally constructed with fibreglass or Bitumen Based substrate. Fibreglass cannot be laid on Roofing
felt or asphalt. If you are repairing an old felt roof, the felt must be removed prior to starting. When the timber has
been exposed check for traces of rot and repair if necessary.

When repairing a GRP roof, clean off the damaged area and sand the GRP surface to ensure the new layer of GRP will
adhere. Sand at least 150mm past the damaged area.

It is important to plan your work before you start. If you are working on a large area, leave a dry section for access on
and off the roof, finish this area last.

WORKING AREA
Laminating should be done at warm temperatures ideally around 20ºC, as this ensures the resin will cure correctly.
A resin will not cure adequately below 15ºC, and at temperatures above 30ºC, it will cure too quickly.

MIXING CATALYST
All resins/topcoats require the addition of a catalyst (hardener) to initiate the curing process. Use a dispenser to add
20ml of catalyst per kilo of resin. Stir thoroughly. The hardening process begins immediately, so only add a catalyst to a
working quantity.

Once catalysed the resin gradually cures, taking on a jelly-like consistency in about 10-20 minutes before becoming
hard in about 30-40 minutes at room temperature (about 20ºC). The curing process generates heat within the resin.

Too much catalyst or large volumes of the resin increases this heat, so a thick laminate or a large casting should preferably
be built up in stages. Over-catalysing the resin can cause the resin to overheat and sometimes cause a fire.

The thorough mixing of catalysts into resins and topcoats is very important. Also, the correct quantities should be used for
the best results. Dispensers are advised for accuracy. 1% catalyst is considered a slow mix, 2% is ideal, and 3% is a fast mix.

The higher the temperature the faster the cure. As a general guide, 2% addition at 20ºC gives 15-20 minutes of pot life.

APPLYING THE LAMINATE
Mix a maximum of 2kg of resin at a time, enough for 2m² of fibreglass mat.

Paint on a coat of catalyzed resin to the surface and then lay on the first section of fibreglass, apply more
resin to “wet out” (saturate) the fibreglass. Then apply the next layer, which should overlap the previous
layer by approximately 75mm and again apply more resin. Stagger the joints so that they do not overlap.

Once the fibreglass has been ‘wetted out’ it is necessary to consolidate the fibreglass and this is done using a
metal roller. The roller when used removes any trapped air, this appears in a laminate as a white blister, and
care must be taken to ensure that this is done.

The best method is applying wet-on-wet, if you do leave laminate for more than 24 hours make sure you
sand the surface to assist adhesion.

When the layer of 450g matting and resin has cured, sand down any rough or sharp protrusions and check
for dry mats or gaps, and ensure any defects are removed or repaired.

A second layer can be applied to give a more durable surface. This layer is not supplied as standard in the
kits.

TOP COATING
The top coat is designed to achieve a fire-retardant roof covering to BS476 Part 3. Topcoat is also known as painting
resin. Topcoat forms a very hard-wearing surface. When fully cured it can be sanded with wet & dry paper.

Once the resin has cured, check for any dry patches (lack of resin) within the laminate, if you are satisfied with your work, sand
lightly prior to applying the topcoat finish.

CATALYST / HARDENER
Catalyst is added and stirred to activate the topcoat. Add catalyst at the rate of 2%-3% but never less than 1.5%. Mix
enough topcoat for no more than 2m2 to 3m2 to avoid wasting material. The top coat can be painted on.

COVERAGE
Approx. 600g of topcoat is required per m2 of the surface area.

CURING
When activated with a catalyst at 2% in temperatures of 20ºC pot life is approx. 20 minutes. Higher temperatures and
higher catalyst additions will reduce pot life. 

Note: Please familiarise yourself with the Material Safety Data Sheets before starting. Personal protection should be worn at
all times, safety goggles, gloves, apron and overalls.