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Technical Information Article

​Water damage to kitchen worktops

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Most worktops are constructed from a wood based particleboard substrate (chipboard), typically 28mm or 38mm thickness, and surfaced with a 0.7mm thick decorative facing laminate. A backing laminate of similar type and thickness is sometimes added to ensure panel stability, as well as providing, in the case of kitchen worktops, a barrier against water ingress.

Plastic laminate surfaced worktops have been the fitted kitchen industry’s proverbial workhouse surface for some 40 years or so. Their high durability characteristics, almost limitless surface design options, low maintenance and relatively low cost is testament to their longevity as the most commonly specified kitchen worktop surface option. Whilst the basic make up of this type of worktop has remained essentially the same the subtle changes in surface design and texture, as well varied options for edge profiles, has kept the product lively and fresh within the marketplace.

Early days

In the early days of worktop manufacture decorative surface laminates were relatively thick, often 1mm or greater, and in this form of construction it was important to balance the panel on the reverse face with a non-decorative laminate of similar type and thickness to ensure panel stability. The backing laminate also provided an effective barrier against water ingress.

...and now

Nowadays the majority of plastics laminate surfaced kitchen worktops are constructed from a wood based particleboard substrate (chipboard), typically 28mm or 38mm thickness, and surfaced on the decorative face with a 0.5 mm - 0.8mm thick post forming grade laminate.

The trend toward using thinner laminates, whilst undoubtedly lowering manufacturing costs, was primarily employed to allow the forming of tighter radius bends along the front edges of worktops. The potential for post forming laminate with bends down to 3mm radius became possible, thus allowing the production of ‘squarer edge’ styles of worktop having a continuous surface appearance. However the use of laminates of thickness much less than 0.5mm may prove unsuitable for worktop applications due to lower impact resistance, mainly of concern along front edges. Additionally the masking of the coarse particleboard cores of thick worktops can present a problem when using thin laminate, particularly in the case of high gloss or plain light colourways.

Thinner laminates

Generally the effects of combining thinner laminates and thicker chipboard cores has eliminated the need to fully balance panels and the use of a fully matched backing laminate is now largely omitted by the majority of producers. To some degree the reduced ‘pull’ of thin laminate and the increased bending resistance of the thicker chipboard core has removed the need for a balancing laminate on the back surface of worktops. Most kitchen worktops are now supplied with either a resin impregnated kraft paper or resin coat backing. However it should be recognised that such worktops are effectively unbalanced and that some bow may develop following production. It is therefore particularly important that care is exercised during production to ensure that moisture content levels within the particleboard core and laminates are correct for the intended service environment. Extreme differences here can still result in bowing problems.

Bow

Worktops with bow levels up to 0.5mm over 600mm span should not present major difficulties during installation as this level of curvature can normally be pulled out when fixing down to the base units. Bow levels greater than this can present difficulties when installing and jointing worktops particularly those requiring a ‘mason mitre’ flush surface joint. Cover strip type joints, requiring a flanged plastic or metal fitment, are less problematical. Generally worktop bow problems are rare in respect of replacement kitchens but excessively damp conditions present on building sites have been known to cause difficulties. It is therefore important that worktops are correctly stored on site in dry conditions and retained within their polythene wrappings until required for fitting.

Sealing edges, backs and incisions

The correct sealing of worktop edges is equally important. The exposed short edges of rectangular worktops are normally sealed by adhesive bonded edging strips matching the surface laminate. As the kitchen fitter normally carries out this work the quality of bonding is less easily controlled but should not present major difficulties.

The long back edge of a kitchen worktop is normally factory sealed with either an edging strip or hot rolled wax or resin sealer, which completely fills the open pores in the edge of the chipboard.

Where worktops are supplied without a back edging or seal, or where the sealed edge is cut away as part of the installation procedure, then sealing of the exposed chipboard edge must be reinstated. Sealing can be carried out on site using a silicone, acrylic or similar sealant before fitting to the back wall. This will provide adequate initial protection against, for example recently re-plastered walls, but it is imperative that this is supplemented by additional sealing between tile and worktop.

The use of moisture resistant grades of chipboard can provide improved resistance to degradation caused by water ingress but such boards will not eliminate swelling problems and hence should not be considered an excuse for poor installation practice. Similarly cut outs required for sinks,pipe cut outs and so on should also be sealed to prevent water ingress. Most worktop manufacturers also make provision for a factory applies front edge seal in the form of a hot wax or PUR resin coating applied to the immediate front edge of single post form worktops or at the laminate return edge in the case of double wrap post form worktops. This provides an additional defence against water ingress into the core board.

Jointing

Perhaps the most difficult and vulnerable aspect of worktop installation is that concerning the jointing of runs of worktops.

The cover strip system, popular with DIY’ers is reasonably straightforward and more forgiving of installation errors. Worktops are simply straight cut to length and sealed on the cut edge with silicone sealant or similar. The cover strip is screwed and bonded to one worktop edge and the adjoining worktop fitted into position. Additional sealant underneath the cover strip will ensure a good 'belt and braces' water-resistant joint.

The downside is that the raised appearance of the cover strip is not to everyone’s liking. The ‘mason mitre’ is perhaps visually preferred but this type of joint requires specialist routing jigs and some skill during installation to ensure a waterproof joint. Of primary importance is achieving a perfectly flush surface at the interface between abutting worktops – not always that easy if the worktops have developed some bow. Various worktop jointing sealants are available and these are available colour matched to the worktop, thereby increasing the visual masking of the joint line.

If carried out correctly and ensuring thorough coverage of the raw chipboard edges and sound bolting between worktop sections, such joints will perform satisfactorily over the lifetime of the kitchen. Wherever possible worktop joints are best positioned away from excessively wet areas to minimise the risk of water ingress. Understandably this is not always easily implemented but joints close to sink areas and continually under water or directly under a hot leaky kettle may struggle to perform over the long term.

End use environments and underside damage

The greater use of under worktop appliances, washing machines, dishwashers and tumble dryers has resulted in an increased risk of water damage to the underside of kitchen worktops. The normal kraft or resin seal, applied at the time of manufacture of the worktop, is not always fully effective against water vapour and associated condensation emitted from appliances and some form of additional sealing of the under surface of worktops at the time of installation is advisable. A secondary vapour proof strip or foil bonded to the underside of the worktop, often termed a diffuser, is advisable in areas likely to be subject to such water damage.

An alternative to the above is the use of a special backing paper incorporating a plastic water vapour barrier and applied during worktop manufacture. This will ensure protection over all underside areas of the worktop.

Tiling can cause a problem

The method of tiling the wall behind a worktop is also an important factor affecting the long-term performance of worktops in service use. All too often, tiles are set immediately above the worktop with just tile grout to fill any gaps. This is inadequate and good practice requires a 3-5mm gap between the top of the worktop and the bottom edge of the tiles for filling with a silicone sealant. This thickness of sealant provides an impermeable 'gasket' and ensures a waterproof barrier with enough elasticity and strength to accommodate small movements and deflections at the junction between worktop and tile.

The best profile?

Plastics laminate worktops are available in a wide range of profiles including both single and double post form wrapped front edges. Even square edging strip designs have seen a renaissance – design ways a full circle back to the original early worktops before the advent of post forming laminates. In certain situations, where prolonged or heavy deluges of water over the front edge is likely to be encountered, the specification of a double post from profile can help to minimise water penetration problems. The radiused under edge profile is particularly effective in shedding water from the worktop.

How can I find out more?

E-mail: info@fira.co.uk

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