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Composite Doors in PVCu, GRP and aluminium
Composite doors have existed for decades, with insulating glass sealed units installed in aluminium profiles and then fitted into timber sub-frames before being fixed to the reveals of house walls. The word composite simply means two or more constituent materials within the same product and composite doors are just that. The three types of composite doors dealt with here are: –
Aluminium Composite Doors
Early in the second half of the twentieth century, extruded aluminium windows and doors were introduced to the United Kingdom, some say from Canada, some from Scandinavia. Either way it was a start of a revolution in door design for the UK which had predominantly hardwood or softwood frames to choose from prior to this. It soon became apparent that aluminium windows and doors performed more efficiently if they were fitted into a timber sub-frame – and the composite window and door was born.
Today aluminium windows and doors in timber sub-frames are still offered to the domestic market but they have mostly been overtaken by PVCu windows and doors in popularity. The excellent durability and strength of aluminium frames for windows and doors means that they are more popular in the commercial market and are used widely for shop fronts and offices. The ease, with which aluminium can be painted practically any colour, also makes them entirely suitable for companies wanting their fenestration branded in company colours.
Aluminium windows and doors are still available for domestic properties but are more expensive than PVCu windows and doors due to the method of manufacture, longer installation time and low manufacturing quantities. Advancements have been made however, and modern aluminium windows and doors tend to have thermal breaks so that the inner surface is not as cold as the outer surface. They also tend to be powder coated to various different colours, rather than remaining the plain aluminium colour.
Specialist manufacturers have also come up with variations on the above theme with some offering windows and doors which include virtually maintenance-free aluminium on the outside and timber for appearance on the inside.
PVCu Composite Doors
Ever since the first white PVCu door was manufactured and installed, companies have strived to make a PVCu door look like a timber one and composite doors were seen as the answer. To achieve this, woodgrain effect foils were produced which attempted to replicate the appearance of various types of timber. These foils are bonded onto the surface of the PVCu extrusions prior to fabrication, either onto both sides of the frame or just on the outside. The early versions of woodgrain effect composite doors attempted to provide the appearance of mahogany, with little success but not being UV stable, they tended to discolour and fade over time. Woodgrain foils with UV filters were produced to prevent discolouration but the poor interpretation of mahogany remained.
With further advancements in technology of composite doors, more realistic woodgrain foils were produced and now versions of rosewood, oak and other species of timber began to appear. They also had a definite grained feel to the surface, rather than being flat surfaces. Nevertheless, although these new foils were realistic interpretations of the various types of timber, manufacturing processes of PVCu doors ensured that they couldn’t have the appearance of genuine hardwood. The main reason for this is that when PVCu windows and doors are manufactured, the frames have diagonal welds in the corners and at the intersection of transoms and mullions.
Although little could be done about the manufacturing process of PVCu door fabrication to improve the situation, manufacturing companies acknowledged that sometimes real hardwood windows and doors were painted a solid colour rather than stained to bring out the grain. This led to foiled profiles for PVCu windows and doors in traditional colours such as cream, pale green, grey and black – all with a grained feel to the frames.
One point which we have a particularly unfavourable view on is the appearance of moulded woodgrain effect panels which are fitted into woodgrain PVCu doors. In real timber the grain would ‘travel through’ a carved panel in a straight line, just as the tree would have grown. The wooden panel highlights any change in direction of the grain because the timber panel is solid. With moulded PVCu woodgrain effect panels the foil, which is bonded to the surface of a plain PVCu panel, follows the contours of the shaped surface. This looks entirely false and due to the manufacturing process, cannot replicate timber.
GRP Composite Doors
In recent times, when people refer to composite doors they generally mean GRP composite doors rather than aluminium or PVCu. GRP composite doors are manufactured from thermoset GRP (glass reinforced polyester compression moulded under heat) to give a highly defined panel design with the appearance of timber. The GRP skin on GRP composite doors is bonded to door stiles and rails composed of a water-resistant polymer and filled with an insulating core of CFC-free polyurethane which provides excellent heat and sound insulation. As a result, GRP composite doors should not expand or contract.
GRP composite doors also have a laminated timber frame (separate lengths of timber, glued together with the grain at 90º to each other), in order to avoid twisting and warping. GRP composite doors tend to be fitted with mortice locks rather than the shoot bolt systems seen on PVCu double glazed doors. Regarding woodgrain effect PVCu door panels, because the GRP skins of composite doors are pressed under heat using steel moulds the opportunity exists to create a more realistic grained effect which does not simply follow the contours of the surface.
Typically, between 15 and 25 door styles are available, with 1,000’s of glazing combinations from composite doors with a completely solid door, clear or obscure glazing, leaded or Georgian designs, or stained or bevelled glass. Some manufacturers also offer optional enclosed mini-blinds inside the sealed units of half glazed composite doors to provide excellent light control, privacy and reduced Ultra Violet light.
Other options include GRP composite doors which split in half horizontally to act as a barn door or stable door and low thresholds to allow easier disabled access.
A typical range of coloured composite doors, with a selection of obscure, stained and bevelled glass