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GRP Materials

NBS specification reference:
H41 Glass fibre reinforced plastics architectural cladding / features / GRP

Conscious of that well used phrase 'garbage in, garbage out', D&D sources its raw materials from leading certified suppliers, such as Scott Bader, Llewellyn Ryland, Colorplas and Euro Resins. The comprehensive range of Crystic products is ideal for architects and designers to build GRP composite constructions and Scott Bader formulate these to meet the demanding regulatory standards of the building industry..

GRP (also known as FRP / glass reinforced plastics / fibreglass) is highly suitable for a wide range of building, construction, exhibition and transportation industry applications - please browse our project or gallery for more information and examples.

Polyester resins can be used with a wide variety of glass fibre reinforcements and core materials to produce complex, moulded shapes of virtually unlimited size.  Polyester composites offer many advantages compared with more traditional building materials: 

  • Lightweight, with an excellent strength to weight ratio, making it easy to assemble on site
  • Excellent weathering and water resistance
  • Requires little maintenance
  • Fire retardant grades available
  • Resins are designed to meet regulatory standards
  • Extremely strong and durable
  • Vandal resistant
  • Structural adhesives such as Crestomer are ideal for many bonding applications.
  • Available clear or in a wide range of colours
  • Gel coats can be pigmented to provide body colour, matched to other parts
  • Polyester resin surfaces can be prepared and over painted to automotive paint finish standards.  
  • Sections and mechanical fixings can be bonded into place

The range of decorative effects possible, such as marble, granite or stone, with Crystic polyester resins is vast. Each has a recommended production method and is supported by our technical experts.

Gel coat/cast resin combinations:

Solid colours - Pearlescent/Metallic/Translucent/Wood/Stone solid surface/Granite

Blended cast resin - Stone/Onyx/Marble

Crystic Stonecast resins are pre-blended with a specified coloured synthetic chip to produce the desired stone solid surface decorative effect.  Crystic Stonecast solid surface resins can be gravity cast into many different solid shapes for interior applications, such as fire surrounds, sinks, spa pools and baths, tiles and panelling.

The most recent development by Scott Bader is Crystic Stonecast 'spray' gel coat, which can be cost effectively sprayed onto a mould or another surface to provide a top-coat stone solid surface decorative effect.   The results are a lightweight material which is tough, durable (with good chemical and water resistance), an excellent surface finish, good colour retention and thus enormous design freedom.

Production Techniques
Given the vast array of projects we undertake we employ a variety of production methods.  In the main these are as follows:

Hand lay-up
Chopped strand mat is the reinforcement most commonly used in contact moulding, though the use of woven roving and various combination materials has grown considerably over the last few years.  Once the gel coat has cured sufficiently, a liberal coat of resin is applied as evenly as possible. The first layer of glass is then pressed firmly into place and consolidated using a brush or roller. Further layers of glass and resin are then applied.

Spray Lay-up
This technique involves the use of a spray gun for the simultaneous deposition of chopped glass and catalysed resin onto the surface of a mould.  A chopper unit attached to the spray gun chops glass roving into specified lengths (usually between 20mm and 50mm), and the chopped strands are then directed towards a stream of catalysed resin and it exits the spray gun.  Resins which are designed for spray application are generally low in viscosity, so they rapidly wet out the chopped strands. This ensures they are more easily atomised into the desired spray pattern. The rapid wet-out achieved by spray deposition allows faster and easier consolidation than would be achieved with hand- lay methods, but thorough rolling of the laminate is still necessary to ensure complete air removal.

Quality Standards
Our company works to H41 standards and its internal quality system based on BS 5750 part 2.  Scott Bader's Environmental Management Programme for the UK gained accreditation to BS EN IS0 14001 in January 2001. This recognises, understands and addresses all significant environmental impacts of the company's activities and products. Through the implementation of ISO 14001, the company has made a clear statement that environmental management is an integral part of the company agenda.


To be read with Preliminaries/General Conditions.


110 GRP
* Manufacturer: Design & Display Structures Ltd
* Drawing reference(s): See drawing issue sheet by D&D
* Panels construction: See D&D drawings
* Finish/Colour:
* U/Value: W/sq m degC
* Fire rating when tested to BS 476:
* Class surface spread of flame.
* Fixing: To manufacturer details.
* Joints: To be advised.
* Accessories/Features/Incorporated components:


Complete the detailed design of the cladding and associated features shown on the drawings to meet the requirements of this specification.

The cladding and associated features must be weather tight under all conditions with full allowance made for deflections and other movements.

* The cladding and associated features must resist all dead and live loads. Wind loads to be calculated in accordance with CP 3: chapter V: Part 2, making due allowance for any internal pressure. The cladding must accommodate without damage all drying shrinkage, creep, deflections and thermal movements.

Make specimens of the proposed panel construction (including core if any) and arrange for specified tests to be carried out by an approved independent testing authority. Submit results demonstrating compliance before commencing manufacture.

* Before undertaking the verification work required by this clause confirm choice of colour with the CA.
* The manufacturer must report to the CA if he considers that use of the proposed pigments and resins is likely to result in an unacceptable change of colour with time.
* Pigments must have a colour fastness to daylight of not less than standard 6 when measured to BS 1006, Section BO1. Submit evidence of compliance.
* If available obtain samples of GRP, made from the proposed pigments and resins, and naturally weathered for not less than 2 years.
* If naturally weathered samples are not available, prepare samples using the proposed pigments, resins and gel coat thickness, and test for 1500 hours in an accelerated weatherometer which subjects the samples to both moisture and ultraviolet light.
* The weathered samples must not show significant change of colour. Obtain approval of colour fastness before commencing manufacture.

* The cladding must be detailed to ensure compliance with requirements for accuracy in manufacture and erection, and to accommodate deviations in the building structure.
* Select types and methods of fixing which will give ample adjustability in three dimensions.
* Liaise with the party responsible for construction of the building structure to ensure co-ordination of dimensions and tolerances.
* Submit details of the proposed system of tolerances and adjustments.

At an agreed stage in the detailed design work make a sample of the proposed construction profile 1000mm in length showing the proposed colour, texture and incorporating a completed section of a joint. Obtain approval of appearance before proceeding.


* Manufacture GRP units carefully to ensure compliance with design and performance requirements, using materials and workmanship appropriate for the purpose.
* All materials must be compatible with each other, and must be stored and used in accordance with the manufacturer's recommendations. Resins must be used as supplied and not adultered: fillers and admixtures may be used only where authorised.
* The standard of finish must be appropriate to the end use and position in the building. Ensure that defects such as wrinkles, spotting, striations, fibre patterning, fish eyes, blisters, crazing, cracking, dry patches and uneven or inconsistent colour do not occur.

Workshops must be warm, dry, clean and well ventilated. Cease manufacture if the temperature falls below 10 degC or if dew point is reached.
430 PATTERNS: Inform CA when each master pattern is complete and not less than 7 days before commencing manufacture of moulds.

Finished dimensions of completed units to be such that the cladding, when erected, complies with clause 630 and all sizes fall within the following permissible deviations:

Overall dimension

Overall dimension
Involved (m)
up to 2 2-33-4.54.5-6
Width & height +0+0+0+0

Straightness of edges deviation from intended line, any variation to be evenly distributed with no sudden bends or irregularities


Squareness: taking the longer of 2 sides at any corner as a base line, the deviation of shorter side from erpendicular,dimension involved is the shorter side.


Twist: deviation of any corner from the plane containing the other 3 corners: dimension involved is the shorter side.


Flatness - deviation under a 1 m straight edge placed anywhere on a flat panel surface: 3 mm

(Measurements taken at 16-18 degC ambient temperature).

* Mix resins thoroughly. All units of one colour to have gel coats from the same colour batch of resin.
* Apply evenly to give an overall nominal thickness of 500 microns.
* Check the wet film thickness(es) of the gel coat(s) of all units in accordance with BS 3900:Part C5, Method 7, four readings per sq m per coat over the external surface area.
* If single gel coating is used, no reading to be less than 400 microns nor more than 600 microns. Average of readings for each unit to be within the range of 450-550 microns.
* If double gel coating is to be used, submit proposals for coat thickness limits based on the resin manufacturer's recommendations, and obtain approval.

Ensure that:
* Each GRP skin contains not less than 900 g/sq m of glass fibre, in not less than two layers.
* Random reinforcement is distributed uniformly, and non random reinforcement is correctly positioned and aligned.
* Each layer of woven fabric reinforcement has a layer of chopped strand mat on both sides.
* The glass is fully wetted out by the resin, with a resin/glass ratio of not less than 2:1 higher as appropriate.
* There is a good overall bond between all gel coats and all layers of laminate.
* The GRP is well consolidated and free from air voids.

Ensure that all core materials, ties, ribs, fixings and accessories are fully bonded to the GRP skin(s) over the full contact surface area.

To be of a suitable type of stainless steel, nonferrous metal or GRP and to be such as to avoid bimetallic corrosion.

* Apply a flow coat to all surfaces of the finished units which are not gel coated.
* Thoroughly seal all cut edges, holes etc., to protect the glass fibre from penetration of moisture.

All units must be adequately cured at not less than 50 degC (higher as necessary) for not less than 8 hours (longer as necessary). Ensure that units are not distorted whilst being cured.

After curing, and at time(s) to be agreed with the CA measure hardness of GRP in accordance with BS 2782:Part 10: Method 1001, one test for each 1sq m of external surface area, not less than 2 tests per unit. Reject any unit in which any Barcol hardness measurement is less than 30 at ambient temperature.

The first unit of each type and size produced is to be thoroughly checked for compliance with the design and specification, and the weight recorded. All subsequent units must then be weighed, and must not deviate from the weight of the first identical unit by more than +/- 10%. Inform CA if any units fails to comply.

* The first unit produced of each of the type(s) listed below is to be inspected by the CA and, if its appearance is approved, clearly marked and kept safely at the shop as a control standard for appearance of subsequently produced units.
1.0m length of cornice.
* Control units to be delivered to site last.

All completed units must be carefully inspected and checked by the manufacturer for match with approved sample(s) or control unit(s) and compliance with specification before despatch to site. Make arrangements with the CA for him to inspect completed units in the shop.

* Keep completed records for each unit including the following information. Unique identification number.Full details of composition.Date of each stage of manufacture.
Dates and results of all tests, checks and inspections.
Dimensions related to specified levels of accuracy.
Specific location in the finished work.
Details of any damage and making good.
Any other pertinent data, eg. If the unit is an approved production control unit.

* Records to be available for inspection on request.

After manufacturing ceases retain moulds and store in a reusable condition to allow manufacturing to recommence if required. The period of such storage is expected to be until practical completion but do not destroy moulds until authorised by CA.


The GRP manufacturer must:
* Provide clear and comprehensive instructions and ensure that they are understood by the site operatives.
* Provide adequate site supervision by a suitably skilled person.

* Prevent mechanical damage and disfigurement. Separate units during transport and storage to prevent chaffing. Pad all slings, ropes, bearers, ladders etc.
* Support units as necessary so they they do not bow, twist or distort.
* Adequately protect units from the weather. Surfaces not having a weathering gel coat must not have prolonged exposure to direct sunlight or water.
* Do not cover units with plastics sheeting or stick adhesive tape on exposed surfaces. * Store fixing and jointing materials indoors.
* Do not deliver to site any units which cannot be erected immediately or unloaded into a suitable well protected storage area.

* Survey the structure, including any fixing inserts, before commencing erection. Report to CA immediately if structure will not allow the required accuracy of erection.
* Set out joint centres for a complete elevation at a time unless otherwise agreed with CA. Erect units using temporary spacers to suit the survey results and ensure generally consistent joint widths.
* The widths of joints must be such as to ensure that the joints perform as intended and are within the recommendations of the joint sealant or baffle manufacturer.
* The finished work must have a satisfactory appearance, being square,regular, true to line, level and plane with a satisfactory fit of all junctions,all to approval.

* Obtain approval of appearance of each elevation before tightening fixings or sealing joints.
* Tighten threaded fastenings to torque figures recommended by the manufacturer. Do not over tighten restraint fixings intended to permit lateral movement.

* Sealant: to CA approval.
* Colour to match GRP Colour.
* Application: As Section Z22.

* Ensure the rear seals are completely airtight.
* Install baffles and flashings securely and accurately to ensure that they function as intended.

Do not repair without approval: such approval will not be given where the units are badly damaged or where the proposed repair will impair appearance or performance. Obtain approval of appearance of all repaired units. Repairs must be:
* Well keyed onto the surrounding GRP using both abrasion and a suitable chemical primer.
* Carried out using the same materials as used in manufacture of the units.
* Adequately cured, using suitable portable heaters for site curing.

Return to site at Practical Completion or when instructed and thoroughly clean down the entire area of the GRP work. Cleaning agents for the purpose must be approved by the GRP manufacturer.

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Design & Display Structures Ltd: GRP Design, Manufacture & Installation
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  Name & Registered Office: Design & Display Structures Ltd, Ground Floor, 1-7 Station Road, Crawley, West Sussex RH10 1HT
  Company reg: 4934691

  Design & Display Structures | GRP Manufacturers, GRP Mouldings, Fibreglass Moulds, Architectural Cladding Systems, London, UK