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This article is written without prejudice. The views expressed are solely those of the author.
The term 'Composite Door' is used to cover a wide range of products with very different properties. Both in performance and looks.
One major variation amongst different composite doors is the material used to manufacture the outer skins. These are the visible faces of the door from both sides and are normally a few millimetres thick. The common variations are steel, uPVC and fibreglass. There are a number of companies using each material.
STEEL SKINS
Because of the nature of steel and the thickness of the skin, many steel faced composite doors are highly suceptable to denting from knocks. They are generally manufactured with a smooth surface as oppose to having a grained effect like uPVC and fibreglass. As a result, these dents are quite apparent and difficult to repair effectively. Steel composite doors are usually manufactured with an unfinished surface and require painting.
UPVC SKINS
uPVC skins are commonly made by taking a flat sheet of uPVC and moulding (forming) it to the shape required including the mouldings and grain. This process has the benefit of being able to use a coloured sheet of uPVC, so allowing for a finished surface. The disadvantage to this process is that it is difficult to achieve a fine grain definition and often results in a 'wide' grain. The other issue which may arise is cracking in the corners of the mouldings. This is because the uPVC sheet is 'drawn out' in the corners of the mouldings resulting in a thinner and weaker area compared to the rest of the skin.
Under variations of heat and cold, uPVC skins (especially darker colours) will expand and contract enough to put strain on the bond between the skin and the core. Under these stresses, the skin may 'delaminate' or crack in the corners.
FIBREGLASS SKINS
Fibreglass skins are made using fibreglass and resin. The skin is moulding from resin which starts in a liquid form and chemically sets during the manufacturing process. This allows for a much finer grain definition. This process also means that, once set the skin is very dimensionally stable under variations of heat and cold. This drastically reduces any stress on the bond between the skin and the core. Because there is only a nominal expansion and contraction, there is very little stress throughout the skin. This also means that darker colours, which reach higher temperatures do not cause problems.
This begs the question of why steel and uPVC skins are used to manufacture composite doors. The answer is simple. They offer a more economical solution which may be required in some areas of the market (eg. new house builders).
This article is meant to educate people wanting to find out more about the choices offered to them. It is the hope of the author that the information in this article will better arm the reader in their decision.
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