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Understanding Fibreglass

Ship Fibreglass consists of two main ingredients:

(1) Glass Reinforcement - very fine glass threads.
(2) Resin combined with hardener which sets and holds the glass threads in place.

General Comments: When the hardener is added to the Fibreglass Resin in accordance with the directions, a chemical reaction takes place and after a comparatively short period of time, (the pot life) sends the resin into a gel stage and then hardens it to a tough plastic material. The fibreglass mat is used as a reinforcing agent for the resin. This combination, after hardening is complete, will give a strong resistant material, in many repair jobs, will be stronger than the original article.

Here are a few points to remember:
(a) Always ensure that the surface on to which you intend to apply the material is clean, dry and free from loose rust, dust or grease.
(b) Similarly, tools and other equipment must be in a clean condition. This particularly applies to the brush which you use for applying the resin & hardener mixture. Clean brushes in Acetone and dry well before use. Do not use Mineral Turps, Kerosene, Petrol or Water.
(c) Make sure that whilst preparing the mixture do not unintentionally contaminate the resin or the hardener with the opposite component as they will be spoilt for future use.
(d) Proper impregnation of the fibreglass mat with the resin & hardener mixture is most important to the success of the finished job. Apply the resin & hardener mixture to the fibreglass mat with a full brush and work well into the fibres. Air bubbles should be worked out through the fibreglass mat using the flat edge of a knife or steel fibreglass roller.

The Glass Reinforcement: When the glass reinforcement is properly impregnated with the resin & hardener mixture it changes from white in colour to almost clear. There are many different forms of glass fibres and each has its own particular application. A high quality fibre has been specially treated so that the resin can really stick to it; in an interior fibre, the bonding is much weaker. The fibres are made into:

(1) Mat: These are batches of fibres about 50mm long laid criss-cross and lightly held together with a binder. These are used for boat building, roofing sheets, mouldings, repairs etc. and are available in 225 grams, 300 grams, 450 grams and 600 grams weight per square metre.

(2) Woven Rovings: These are long batches of glass fibres woven together in much the same manner as chaff bags. This gives high strength in a certain direction, and can be used where a rough finish does not matter.

(3) Glass Cloth: There are many varieties of cloths, the main difference between cloths and woven rovings is that the fibres are spun and twisted like wool. This spinning gives much greater strength, easier saturation and allows the cloth to cover easily over all sorts of shapes without crinkling.

Resin: In appearance, resin is somewhat like thin honey, and usually has a pink or blue trace of colour which indicates that hardener is required. If kept cool (Lower than 15.5oC) resin will stay liquid for some months. The first sign of an expired shelf life is evident when it becomes like jelly. At this stage, it is not useable. Colour may be added to the resin by the addition of special pigment pastes, usually 10% on weight of resin. The glass should always be saturated with clear resin first. Colour is normally only added in the 2 final coats.

Setting the Resin: Resin is made ďglass hardĒ in a short time (Less than 1 hour) by the addition of a catalyst (Hardener). When mixed to the resin, the chemical action takes place, generating heat and so causing the resin to become solid. The hardener is generally supplied in a clear liquid form and extra precautions are required in handling this product. If more hardener is added, the resin will set much quicker so that varying setting times can be obtained.

For normal use 1 1⁄2 % of hardener to resin will set in approximately 1 hour at 23oC. The table below shows the amount of Hardener in mls to use for an given amount of resin.

Amount of Resin Catalyst @ 1% Catalyst @ 1.5% Catalyst @ 2%
250 ml 2.5 mills 3.8 mills 5 mills
500 ml 5 mills 7.6 mills 10 mills
1 Litre 10 mills 15 mills 20 mills

Naturally a higher temperature of the day gives quicker setting and therefore a thicker coating of resin will set quicker than when spread out thinly.

Saturation: Once the hardener has been added to the resin, it is important to use it quickly, this means saturating the glass as soon as possible. Therefore, as much work as feasible should be done before mixing resin & hardener together. Cloth or mat should be cut roughly to shape with mixing containers, brushes and rollers ready to hand. If mat is being used it sometimes helps to wet it out thoroughly with resin on a piece of paper and the wet side put on to the work, as this helps saturation. Let the resin soak into the glass for 2 or 3 minutes. This can save a lot of brush work. Large areas are quickly covered by using a paint roller but usually this can be only used once unless repeatedly washed and dried in cleaning solvent. This can be expensive.

Hardener: Recommended Hardener (M.E.K.P in D.M.P.) level is between 1% and 2 1⁄2%.
Remember: The lower the temperature the longer the resin & hardener will take to set. The higher the temperature the resin & hardener will be faster to set. Hardener should be fresh and must be evenly mixed into the resin. Accurate measurement of hardener to resin is essential. Do not rely on counting drops.

Mixing Resin: The ideal temperature in which to apply the resin is approximately 23oC, any temperature hotter than this will cause the resin to set more rapidly, and likewise if too cold the setting will be slower.
If the air temperature is below 10oC then artificial heating may be introduced to simulate a strictly controlled environment.
It is advisable to mix the resin in 1 litre lots, particularly if the day is warm. Should too much be mixed at one time, it may set hard in the container before it can be applied. Do not return mixed resin and hardener to the original cans.
If the temperature is over 28oC it is not recommended to proceed with the project at hand.

Important Do's and Dont's:

Do check the shelf life of the resin. If stored in a cool place the shelf life of the resin is approx 6 - 9 months.
Do periodically clean paint brushes and tools in solvent (Acetone) during application.
Do note that once the resin & hardener has set Acetone will not dissolve it.
Do store the resin in a cool place and always make sure it is sealed properly.

Donít forget to add hardener before using resin.
Donít make the mistake of mixing too much resin at one time.
Donít allow the resin or the hardener to remain in contact with the skin for long periods.
Donít guess the amount of hardener to use. Measure it accurately. Use a syringe, graduated dropper or similar.