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How Do I Work With Fibreglass?

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#1 Frost Auto

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Posted 02 February 2017 - 07:26 AM

How Do I Work with Fibreglass?


Getting started…

The essential ingredients for working with fibreglass are easily understood for DIY use.
The bottom line
If you can use wallpaper paste, a paintbrush and scissors, then creating GRP repairs, moulds and components is well within your grasp. Bought in bulk, all materials become much cheaper over the length of a project, so don’t underestimate how much you’ll need to complete a job.
Top Tips
Only ever mix as much as you can realistically use in 15-20 minutes. Always wear gloves, goggles and a face mask to protect from fumes and fibres.
Work in a well-ventilated room, preferably outdoors if possible. Lloyds (shipping) approved resins are a good indicator of quality.
Skill: Confident DIYer
Time: Varies
Cost: Dictated by surface area


You’ll be needing…
- A suitable, well-ventilated working environment. Not your front room!
- Safety awareness.
- Brushes, scissors, re-usable polythene plastic buckets.
- A trial run beforehand to see how well the materials combine with each other.
Parts Specialist
All the items featured on this page are available from Frost Restoration. Prices vary according to sizes of materials. More details at: www.frost.co.uk.





Fibreglass science made easy. What it is and how it works…

Since its adoption as a material by boat builders in the late 1940s/early 1950s, fibreglass (GRP) has been the choice of many vehicle manufacturers. GRP’s versatility lends itself to low-volume production and enables design changes to be made relatively easily compared to the new tooling associated with pressed metal bodied cars. In this respect, the material is created by the user, unlike metals, which are merely shaped by the user.
More out of unfounded fear and lack of knowledge, GRP bodied cars are given a wide berth by some enthusiasts. But those in the know relish a classic that’ll never suffer the ravages of rust to its bodywork. GRP classics benefit from a regular cleaning and waxing regime.
GRP – glass reinforced plastic – is commonly referred to as fibreglass. Fibreglass is a registered trade name, and like the Hoover/vacuum cleaner scenario, it’s passed into common acceptance.
The clue’s in the name – glass fibres are reinforced for strength using polyester (plastic) resin. The resin protects the fibres from moisture, making them rigid and incredibly strong as a result. GRP is a thermosetting plastic it becomes irreversibly solid by chemical reaction using a catalyst (hardener) and heat. An accelerator is also required to reduce the curing time but this is usually pre-mixed nowadays with the resin before you buy.
Versatile and strong, with the potential to be lighter than steel, GRP has created many classics.


To expel air from resin
Vital for flat areas especially. Expels air, creates strength and saves resin.
Allows removal of items from moulds
To prevent resin from permanently adhering to a surface, such as in mould making, a barrier between the resin and the mould is required: Wax polish – good quality carnauba wax polish is ideal for this. Usually applied as four or five coats to a mould.
PVA (polyvinyl alcohol) – coloured versions enable you to see where it’s been applied. Not ideal for vertical surfaces because it drains off easily. Best if used in conjunction with wax.
Various types
General Purpose – Popular resin type for most GRP work. Usually comes pre-accelerated.
High Duty/Marine – superior quality with water resistance.  Also includes a thixotropic (anti-sag) agent to allow its use on vertical sections. Useful for in-situ repairs. More expensive than general purpose resin. Other types exist but these are sufficient for the vast majority of classic car work.
Tough outer skin protecting fibre laminate
The gel coat is comprised of special resins that are designed to give a tough, resilient outer skin, which then protects the strengthening resin and fibre layers beneath. Any of you who’ve been keeping up with Jerry’s Project Elan will know all about gel coats!
Vital safety protection
Avoiding skin and eye contact with GRP-creating materials is essential.
A dust mask capable of filtering airborne fibres from high-speed sanding of GRP is a must. Equally, gloves must be worn. Longer, gauntlet-type, resin-resistant gloves are great for mixing but can be awkward when applying matting and resin. Disposable latex gloves are easier to use and should be discarded once they prevent you from working easily.
Various types for specific purposes
Loose, mat, roving and tissue are a few of the choices available. Once combined with resin, the fibres mould easily to contours, assuming a given shape with ease and with great strength. Large, sharp scissors are best for ease of cutting when wearing gloves.
Accurate mixing
Catalysts must only be added in correct proportions for chemical hardening of the GRP. A syringe is cheap, easy to use and helps to reduce premature or non-hardening of resins.




Various types
Softer brushes are used to apply PVA and gel coats. Stiffer brushes, including stipling ones, are best for resin and matting use. A good tip is to cut down older, past-their-best brushes to create your own stipling brushes if necessary. Match the size of the area being worked to the brush size needed. Use acetone to keep brushes clean and resin-free.
Vital for curing (hardening)
Ambient temperature is an important factor when using resin. Work to a 15-20 minute curing time. To achieve this in hot weather, one per cent per 500g of resin is best. Two or even three per cent is preferred in colder weather. Gloves must be worn.
More useful GRP advice


- Coloured pigments can be added to resins, such as in gel coats.
- Using dark over light and vice versa enables you to see where resin has been previously applied.
- Acetone is your best bet for utensil rinsing and removal of spilt resins and catalysts.
- Jack Wiley’s handbook, Fibreglass Repair & Construction, is a well spent if you intend to have a go yourself. Frost also sell Basic Fibreglass Techniques DVD
(Words Gary Stretton, Photos Matt Richardson, November 2007 issue, Classics Monthly, p74-75)  660.jpg



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