3.Machining and processing HPL
First of all, the basic principles of the general recommendations for working with HPL apply to the processing of special HPL composite elements. Due to specific features of the production of composite elements with mineral substrates and the stress they are subsequently exposed to, the following special processing information has to be noted. This applies in particular to pretreatment of the HPL. In all cases, it is necessary to bond HPL with the same quality and design to both substrate sides (symmetrical structure). It is also advisable to consult the manufacturer of the decorative laminate.
In all cases, it is necessary to bond HPL of the same quality and design on both sides of the substrate (symmetrical structure). It is also advisable to consult the HPL manufacturer.
These substrates must have a cleanly sanded surface (thickness tolerance ±0.3 mm). They must not have any sanding marks or depressions. If it is not possible to manufacture the substrate with the required tolerances, joint- filling adhesives have to be used in order to create an even bond between substrate and HPL as well as a good surface quality. The surfaces of some mineral substrates must be pretreated before bonding, in accordance with the adhesive manufacturer's recommendations. Pretreatment strengthens the surface and prevents the adhesive from penetrating too deeply into the substrate.
Not all mineral boards are suitable for use as substrates for HPL. That is why the supplier should be notified of the intended use in order to obtain a usable product particularly where thickness tolerance and humidity content are concerned. The transverse tensile strength of the mineral substrates should be no less than 0.4 N/ mm². It should also be noted that mineral materials have lower peel strength and lower transverse tensile strength than most wooden substrates, causing possible peeling in the uppermost layer of the substrate as well as tensions in the core.
Table 6: Overview of mineral substrates
| Carrier material | Typical applications |
|---|---|
| Vermiculite boards | Interior construction / ship building |
| Calcium silicate boards | Public buildings / ship building |
| Fibre cement boards | Public buildings / wet rooms |
| Cement-bonded chipboard | Public buildings / wet rooms |
| Plasterboard | Interior work |
| Fibre plasterboard | Interior work / public buildings |
| Compacted mineral wool | Interior work |
Adequate conditioning can prevent dimensional changes from the start. These would otherwise lead to warping of the HPL composite element or to tension cracks after bonding.
Mineral substrates are subject to smaller dimensional changes than wood materials or HPL. They absorb and release moisture faster which means that simultaneous conditioning in the same stack together with HPL is not advisable.
HPL should be conditioned before processing in pairs or conditioned depending on the selected substrate or field of application. The relative humidity during conditioning should correspond to the subsequent climate conditions as closely as possible.
This pretreatment is of great importance for processing mineral substrates as well as for working with wood materials.
Subsequent changes in humidity cause strong tensions between the HPL and the substrate which can cause an increased occurrence of cracks and warping.
Material particles and dust caused by machining have to be removed carefully to avoid scratching the HPL surface.
Due to the increased stress on the tools caused by the mineral substrates, suitable tools must be used for processing.
National environmental and occupational safety conditions for processing mineral materials have to be followed. This also applies to composite elements made of HPL and mineral substrates.
Where the composite elements will later be subjected to dynamic loads through warping or moving, e.g. in ships or vehicles, sufficient room for movement should be provided during installation. This allows e.g. room dividers in ship's cabins to be fixed to floor and ceiling using suitable brackets. Suitable profiles allow sufficient clearance when mounting several plates side by side. The profiles should be interlocking because of the low transverse tensile strength of the mineral substrates. Where interlocking profiles are not possible for design reasons it is possible to work with groove and loose tongue, with the depth of the groove not exceeding half of the thickness of the mineral substrate. If fire regulations require the tongue to be wider, the depth of the groove has to be kept as small as possible in order to prevent the substrate from splitting later on.
If high dynamic loads are expected, the composite elements have to be reinforced at the back side at smaller intervals. Where moisture could act on the edges of the composite elements, these have to be protected with water- proof coatings before installation.
Composite elements made of HPL and mineral substrates are usually used in areas where fire regulations apply. Fixing methods and fixing materials therefore have to comply with these regulations as well. Special attention has to be paid to the connections between the individual elements. This applies to horizontal and vertical connections. Joints can have a crucial influence on fire behaviour. Regulations concerning the selection of joining materials have to be observed.
Where HPL composite elements are used as wall and/or ceiling panels, the area underneath has to be sufficiently dry. Composite elements can be used for partition walls, free-standing in steel frames.
Regardless of the fastening method, the fastening distances should be determined based on the substrate material, the thickness of the HPL composite element and the load to which it is subjected.
For screw fixings, the selected screw types have to be suitable for the respective substrate.
There are many different fixing options for fixing composite elements made of HPL and mineral substrates together and to building components. They can be divided into four categories:
