Maintaining Value of Gelcoat


Cleaning, care, polishing: terms that we already know from caring for our cars. But what about gelcoat? That' s what we'll show you in this article. Even more knowledge is available for download in our White Paper.


Reading time: 8:00 min.

How do I care for a gelcoat?

The car is new, the black paint shines elegantly, every droplet of water is a little annoying. You quickly take out the soft cloth to polish away the annoying drops. But when winter arrives, the new car is dirty in no time. Proper cleaning and care is essential for maintaining its value. But that is nothing new. Non-aggressive cleaners, sponges, or cleaning cloths made of soft and non-abrasive material and the correct polish, — these are the essentials when cleaning car paintwork. But how does our approach to cleaning change if suddenly, we are no longer cleaning paintwork, but the outer wall of the mobile home? And the surface of the outer wall is not painted, but made of glass fibre-reinforced plastic with a gelcoat layer?

What exactly is a gelcoat?

A gelcoat is a protective layer for the glass fibre-reinforced plastic laminate — similar to the paint on a car body. It ensures a smooth surface and can be coloured as desired. The smooth surface is not only easy to clean, it is also chemically resistant and can withstand the use of industrial cleaners. The gelcoat also ensures that the laminate underneath is protected from UV radiation and the effects of weathering.
Due to their chemical similarity, gelcoat and laminate resin are very well-connected, but functionalized differently: A stable bond with the glass fibres is important for the laminate resin and the above-mentioned protective functions for the gelcoat resin.

A gelcoat can therefore be described as a sealing of the underlying material. This seal protects the material from scratches, weathering and chemical influences, but should also withstand knocks and bumps without damage. The gelcoat also makes the surface particularly smooth. And it has an almost imperceptible roughness — which primarily influences the cleanability of the surface. For maintaining value, it is therefore important for the gelcoat to be able to withstand all external influences. To ensure this, there are various application-related tests that recreate the loads under comparable laboratory conditions. Proper and regular cleaning and care is just as important for maintaining value.

What does a gelcoat have to withstand during its life cycle?

If we stay with the example of mobile homes: A caravan like this does not just stand on a beautiful campsite and offer sleeping accommodation. Holidaymakers who decide to travel in a mobile home often travel hundreds of kilometres. Entire countries are crossed, coasts are traversed, shorelines are explored in the USA. And what does a mobile home holiday like this look like in the USA? Correct: Pure sun, heat, dry areas, vegetation that doesn't always appear lush, green and soft. The caravan must withstand all this. In tight situations when manoeuvring on the campsite, branches might brush against the roof or side wall of the vehicle. To ensure that they do not leave unsightly scratches on the surface, the gelcoat must be sufficiently hard.

How is a gelcoat tested for resistance to scratches?

To find out how resistant a gelcoat is to scratches, the hardness of the gelcoat is determined with a special test, the Barcol hardness test.

Barcol hardness tester on GRP | insights by LAMILUX
Barcol hardness tester on GRP

The process is primarily designed for measuring the hardness of glass fibre-reinforced plastics (GRP), thermosets and hard thermoplastic materials. There are special Barcol hardness testers for the determination of Barcol hardness — in the form of mobile hand-held testers or benchtop tests. During the test, a hardened steel cone insert integrated in the test device is pressed into the surface to be tested by a spring system. The indentation depth is determined directly via a measuring line. The hardness is displayed on a scale of 0 to 100. The value 0 corresponds to the maximum indentation, i.e., a very low hardness. While the scale value 100 corresponds to a very high hardness and thus practically no indentation. The valid standards for this test procedure are DIN EN 59 and ASTM D 2583 (American Society for Testing Mat).

How are the effects of weathering on a gelcoat tested?

If the travellers are driving along the coast of the USA in their mobile home, the gelcoat must withstand a wide range of weather conditions. Starting with the high UV radiation from the sun, for example, the gelcoat must not fade. LAMILUX tests the resistance of the gelcoat with artificial weathering tests to ensure this. For example, resistance to weathering testing involves exposing material samples to rapid weathering for hundreds of hours in a simulated environment. To achieve this, LAMILUX conducts the so-called Xeno test in accordance with DIN EN ISO 4892-2. The test method has already proven itself in the automotive industry.
LAMILUX also analyses the long-term light-fastness and colour-fastness of a material using the so-called SUN test. Material samples are irradiated with extreme UV light for hundreds of hours and the colour deviations and material changes are measured at specified intervals.
But it is not just the sun and its UV radiation that presents challenges to a gelcoat during its life cycle. It must also withstand hail.

Ball drop test on sandwich panels | insights by LAMILUX
Ball drop test on sandwich panels

Nobody likes to see unsightly dents after a heavy hail shower — regardless of whether they affect their car or the rented motorhome. Here, a roof made of glass fibre-reinforced plastic offers enormous advantages due to its impact resistance. For this purpose, the impact test is regarded as a particularly meaningful test method, since it very effectively maps the stresses on the material through a ball drop test. LAMILUX considers that the gelcoat can withstand these tests without damage.
In addition to all these test methods under controlled laboratory conditions, LAMILUX Composites also tests its gelcoat under real outdoor weathering. Not only at the Rehau production site in Germany, but also worldwide: including in Arizona.

How do I care for a gelcoat correctly?

LAMILUX uses in-depth, application-related tests to develop a gelcoat that is ready for the rough stresses during its application — but the right cleaning and care also plays an important role in maintaining its value, to maintain the high-gloss appearance of the gelcoat. More detailed information can be found in our White Paper.

Outdoor exposure GRP sheets | insights by LAMILUX
Outdoor exposure of GRP material samples
Scratch Polish GRP | insights by LAMILUX
Polishing out a scratch on GRP

In general, no aggressive cleaners should be used. Neutral cleaners, for example, are better. Scouring agents abrasive cleaning agents such as scouring sponges or steel wool are not suitable for cleaning a gelcoat. This can damage the surface. As with car washing, it is best to clean with warm, hand-warm water and then rinse the cleaned surface with enough cold water to completely remove the cleaner. 
And if scratches do appear in the gelcoat? Smaller scratches can be polished out with a little skill, in the same way as they can be removed from car paintwork. In this way, the gelcoat can shine again like it did on the first day. To ensure the proper and safe care of the gelcoat, we have put together a White Paper for you as a free download.