Wonderglass GC

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Australia’s most experienced and largest manufacturer of fibreglass roofing introduced “Wonderglas GC” gel coated sheeting to Australia in 1994, adapting the process originally developed by BP chemicals in the United States, to expressly combat Australia’s very harsh environment.

Strength And Flexibility

Over the life of the sheet “Wonderglas GC” retains it’s strength and flexibility, it does not lose it’s tensile strength or become brittle as happens with film surface coated and polycarbonate materials. Generally speaking, film coated fibreglass reinforced polyester sheeting has a history of failure under Australian conditions. While it has been a means of delivering natural light, the short comings of erosion, combined with loss of light transmission, discolouration and water penetration, have called for a decided improvement. Wonderglas GC, with a UV resistant Gel Coat of 100 microns in thickness, replacing surface film of just 20 microns, has provided this improvement.

Since then Wonderglas GC has been proven in many thousands of installations throughout Australia and New Zealand, and in many Asian regions. Zammit Roofing’s policy of continual product improvement, as new technology and materials are available, ensures product leadership. The highly UV resistant resins used in the manufacture of Wonderglas GC provide the ultimate in protection – ahead of even the latest surface film technology. The 100 micron thick gel coat is integral with the sheet (chemically cross bonded), and no delamination is possible. The gel coated sheet surface becomes an almost impenetrable barrier that reduces surface erosion and loss of light transmission to negligible proportions. The proven performance of Wonderglas GC remains unsurpassed and puts this Australian made product at the cutting edge of world resin technology.

Chemical Resistance

In addition to exceptional performance, even under adverse conditions, Wonderglas GC has a very high resistance to a range of common chemicals. So much so, that entire industrial plants are clad with gel coated woven mat reinforced fibreglass (“Webglas GC” also an Zammit Roofing product) to eliminate corrosion.

Special Purpose Variations

The benefits of Zammit Roofing’s “Cool-lite” Heat Reduction sheeting, or “SR76” Fire Retardant sheeting can be incorporated into Wonderglas GC. Many installations utilise these options, sometimes combining them.

Available Profiles

All current profiles (see link below) such as Corrugated, Trimdek, Speed-dek, etc. plus most superseded profiles are available.


Australian made Wonderglas GC premium grade glass reinforced polyester sheeting is manufactured in strict accordance with AS/NZS 4256.3:1994. Standards Licence No.986.

Zammit Roofing is a quality Endorsed Company complying with AS/NZS ISO 9001:1994, Licence QEC 4787.

Hail Resistance

Zammit Roofing warrant series 2400 (and upwards) Wonderglas GC premium grade gel coated industrial fibreglass sheeting against damage from hailstones up to 20mm in diameter accompanied by winds up to 100 km/hr for 10 years.

Superior Features of Wonderglas GC

Light transmission is maintained. Loss of light transmission after 10 years is just 10% compared to a loss of 30% for standard 20 micron surface film protected fibreglass sheeting. Wonderglas GC has a highly UV resistant gel coat of 100 microns.

Very high resistance to yellowing and discolouration. Over 10 years changes are negligible and are covered by warranty. Only minor changes may occur in later years.

Surface erosion (fibre show) is eliminated. It is covered by warranty for 25 years.

Low surface erosion. This also improves weathering properties. The 100 micron gel coated surface provides an impenetrable barrier and the sheet is warranted against water penetration for 25 years. Inbuilt UV protection eliminates 99% of harmful UV rays.

Durability and Cost Effectiveness

Fibreglass sheeting has progressively overcome UV attack with the development of UV Stable Resins, and has retarded weathering by the application of surface films. However, surface films, are just 20 microns thick, and only prolong weathering and do not defeat it. The newer surface films have no history in actual use, and must rely on “Weathermeter” testing to predict likely deterioration over a long period of years.

The introduction of Wonderglas GC in 1994 has proven to be a very significant advance in fibreglass sheeting. Wonderglas GC has a highly UV resistant gel coat 100 microns thick chemically cross bonded to the UV resistant base resin. The gel coat is 5 times the thickness of surface film, it is integral with the sheet and cannot delaminate. Premium grade Wonderglas GC permanently withstands weathering, retards fading, maintains excellent light transmission and has a higher resistance to a range of common chemicals than standard fibreglass sheeting. Actual usage has proved that gel coated Wonderglas GC is eminently suitable for long term industrial and commercial use.

In determining the cost effectiveness of Wonderglas GC over a term of 25 years, or the life of the building, consideration must be given to the benefits. These include lower maintenance or replacement costs, the continuing benefit of excellent natural lighting with only minor deterioration over the products lifetime. Also, lack of brittleness and high resistance to hailstones over many years. Finally, the sound weatherproofing of the building and its better appearance long after other materials have failed.

It is estimated that commonly used surface film protected fibreglass sheeting can actually cost up to 300% more based on replacement of product at useful life intervals, at present day cost per square meter. Testing undertaken by CRC (an independant government body) in Report No. CRC-P-TR-030 came to the conclusions that: “Gel coat was the most resistant coating. A correctly formulated gel coat being more effective than the use of weather resistant thermoplastic surface films.”

Wonderglas GC has also been tested at Allunga QLD, through the Allunga Exposure Laboratory. Allunga is an independent laboratory that specialises in natural weather testing, and is well known in Australia and overseas. All methods of testing are performed to strict Australian Standards. The Altrac system (in which the sample tracks the sun), is generally accepted to have a 5:1 weathering value. The Wonderglas GC result was a light loss of 22% over a period equivalent to 20 years exposure. The test product still displays a very smooth, glossy surface with no fibreshow at all.

The Wonderglas GC technology was developed in the United States through BP Chemicals, and has been in the American market for in excess of 25 years and widely used throughout Australia since 1994.

Spanning Capacity

Industrial Standard and Premium Grades
Series 2400 3050 3660 4270 4880
Corrugated 1200mm 1500mm 1700mm
5 Rib 1500mm 1700mm 2000mm 2300mm
Spandek 1600mm 2000mm 2300mm 2600mm 2800mm
Kilplok 406 1400mm 1700mm 2000mm 2300mm 2600mm
Kliplok 700 1400mm 1700mm 2000mm 2300mm 2600mm
Speed-dek 1400mm 1700mm 2000mm 2300mm 2600mm
LT7 1700mm 2100mm 2400mm 2600mm 2800mm

The above spans are recommended for wind loads up to 1 kPa. For information regarding recommended spans in high wind and cyclonic regions please contact your local Zammit Roofing office.

Sheeting Grades

Series Weight (Kg/m2)
2400 2.4
3050 3.05
3660 3.66
4270 4.27
4880 4.88

Important: Heavier grades give the specifier the option to use Zammit Roofing sheeting in cyclonic zones, or match the span of the nominated steel roofing material (see ‘Spanning Capacity’ above).

Light and Heat Transmission

Grade 2400g
Light % Heat %
Ice Clear 74 68
Opal (white) 72 64

For Light and Heat transmission of Series 4270, 4880, please contact your local Zammit Roofing office. Other colours can be produced to order for viable quantities.

Expansion Data

Materials Expansion Comparison. 0° to 40° Temperature Variation. Sheet Length 12 metres
Fibreglass Polycarbonate Steel Aluminium
Thermal Expansion 14.4mm 32.4mm 5.8mm 11.5mm
Thermal Co-efficient 3.0 x 10-5 cm/cm°C 6.75 x 10-5 cm/cm°C 1.2 x 10-5 cm/cm°C 2.4 x 10-5 cm/cm°C

Physical Properties

Tensile Strength 80 Mpa
Impact Strength 8 Joules
Shear Strength 90 Mpa
Modulus of Elasticity 5500 Mpa
Compressive Strength 135 Mpa
Flexural Strength 150 Mpa
Specific Gravity 1.45
Thermal Expansion 3.0 x 10-5 cm/°C
Water Absorption .2% in 24hrs./26°C
Thermal Conductivity 0.158 watt/m°C
Curved Roof Radius 2400g/m2 “Corrugated” and “5-Rib”
Minimum Radius 4.0 Metres
Recommended Service Temperature Range -20° to +96°C


The following installation procedures are recommended by the product manufacturers — Zammit Roofing Australia Pty Ltd.

These recommendations closely follow the Australian Standard: Design and installation of Sheet Roof and Wall Cladding, Part 3: Plastic. AS 1562.3-2006

Where wire safety mesh is incorporated under the fibreglass sheeting and over a purlin, a protective purlin strip must be installed to prevent fracturing. Zammit Roofing manufacture a 65 mm wide self adhesive fibreglass strip which, when viewed from below is not visible.

In roofing applications, fixings shall be fitted through the crest of any profile. Oversize screw holes from 10 mm up to 15 mm must be drilled at all points of fixing. Only 32 mm ‘Weatherlok’ seals should be used. These seals are large enough to cover the oversize hole and are sufficiently flexible to contour to any corrugation (or rib) when medium pressure is applied. Medium pressure means that the ‘Weatherlok’ seal is contoured to the shape of the corrugation (or rib), but rib or corrugation must retain its shape without any sign of buckling.

Contractors must make sure that the fixing is located in the centre of the oversize hole, or the benefit of the larger hole is lost. To ensure accuracy, Zammit Roofing recommends the following:

  1. Fasten fibreglass sheeting in the same manner as metal.
  2. When Job is completed, remove fasteners on fibreglass section.
  3. Using the existing screw hole as a guide, drill an oversize hole, swap neoprene washer (used in step 1) with ‘Weatherlok’ seal and reinstall the fastener.

Zammit Roofing design and recommend the fibreglass sheets to be installed on top of metal roofing on both sides. The sheet rib can still go over and under when fibreglass sheets are installed side by side.

Where fibreglass sheets are end lapped including those with dissimilar materials, two lines of Lapseal Tape or a flexible sealant shall be placed across the full width of sheet. Each strip is placed approximately 150 mm apart with one line located 25 mm from the end of the fibreglass sheet. Zammit Roofing recommends the use of 25 mm Lapseal Tape as silicone sealants can harden and cure due to exposure to daylight. The over-lapping sheets then become locked together as one sheet, effectively stopping movement between the sheets, and possibly causing buckling. With decking profiles install Lapseal Tape in the tray only or use a flexible sealant.

Fibreglass sheeting is not easily reshaped after manufacture, and will require special weather seals to be provided at all flashing and capping points. Typically, a foam closure strip matching the profile of the fibreglass sheet should be bonded to the pans or valleys with a flexible weatherproof sealant. Ideally it should be fitted at least 100 mm behind the turn down of the flashing.

Zammit Roofing fibreglass sheeting (with the exception of Webglas GC) is a non-trafficable material. Sheets should be handled with care to avoid damage to the surface coating which is either Melinex film or Gel Coat according to the grade. Guarantees will not apply to sheeting that has been damaged in handling, or mechanical damage due to foot traffic.

Furthermore, unless the above instructions are strictly adhered to, Zammit Roofing Australia Pty Ltd cannot accept any responsibility for consequent leakage problems, caused by sheets buckling or “ocean waving”.