Fully factory Finished Joinery; Good Practice Leaflet

It has to be recognised that the long term performance of the timber component and the factory applied coating system, can be very much influenced by a number of design details and manufacturing practices.

This check list below may be useful in terms of enhancing the performance and thereby extending the life of the joinery component and the points made may be used in conjunction with the location, setting of the joinery and design of the building to assess the suitability and expected durability of the chosen coating system.

It is generally accepted within the industry that the standard BS EN 644;2009 should be followed as a minimum requirement when considering the design, build, glazing, coating and installation of fully factory finished timber windows.

Some of the points below recommend factors beyond the minimum requirement as detailed in the aforementioned standard.

·    Consideration should be given to selected laminated or finger jointed sections; this would enable the control of natural defects
·    Where client requirements do not allow the use of selected laminated or finger jointed sections, timber is to be selected in accordance with the standards detailed in BS EN 942: 1996.  With regards to the use of European Redwood, the preferred grading would be J2 which ensures the minimum presence of knots and natural defects.  The minimum acceptable grade being, J30 for frames and sashes and J10 for beading.  Full details can be found in BS 644: 2009.
Please note a coating system should not be expected to provide a guarantee to protect from the effects of resin exudation or discolouration from water soluble extractives.

·    The use of fast grown sapwood should be avoided
·    The moisture content of the timber must at all time during the application and drying of the coating system conforms to the requirements of BS EN 942: 1996 Timber in joinery – General classification of timber quality.  Further details to be found in BS 1186: part 1: 1991
·    Plywood infill panels must be of WBP grade with a surface veneer deemed suitable for exposure to the weathering elements and to confirm to the requirements of Hazard Class 3 – BS 335 Part 2
·    Panels or trims manufactured from Exterior Grade Medium Density Fibre Board must conform to the requirements of BS EN 622 – H2

Within the timber industry it is generally recognised that an extended protruding timber sill section can create serious limitations to the long term performance of the coating system and to the window itself and considerably lower durability expectations can be expected from coatings used on exposed horizontal surfaces.  We do however recognise that at this point in time, and in particular in the South of England, there is a demand for a protruding timber sill section and while our firm recommendation is to avoid the use of sills where possible, should it’s presence be deemed unavoidable, we can offer the following points to ensure the coating reaches the maximum durability possible on this vulnerable area.

The protruding timber sill section should have a maximum protrusion of 75mm from the frame itself, and have an even continual slope away from the bottom of the frame of not less than 15 degrees.  A capillary groove should be included within the design of the underside of the sill, the minimum width and depth of the groove should be 6mm, and should be positioned a minimum of 12mm from the front edge.   The front edge of the sill must be finished with a minimum 3mm rounding and a minimum finished thickness of 25mm
·    All exposed external edges are to be machined to a minimum 3mm radius rounding to all exposed surfaces. Unexposed exterior or interior surfaces should achieve a minimum rounding of 1.5mm radius
·    A minimum slope of 15 degrees must be incorporated within the design to the top of any external glazing upstand or bottom glazing bead
·    The bottom joints of all vertical beads must be designed to ensure that there is no capillary action and moisture uptake

·    Non-ferrous screws, pins, staples , metal stars or wood dowels may be used in the corners to hold the frames securely while the glue sets.  These fixings should be inserted from the inside because they are a potential source of water ingress if exposed on the outside
·    A suitable adhesive of no less than D4 Watt 91 rated (BS EN 204) should be used in full accordance with application temperatures and pressing times detailed in the relevant Technical Data Sheet.

·    The preservative pre-treatment (where applicable) and our factory finished coating system must be applied in strict accordance with the requirements of Akzo Nobel Industrial Coatings Ltd., to achieve an approximate minimum dry film thickness (DFT) of 120 micrometres on all exposed and concealed surfaces including all end grains. Please note the film build should not exceed 150 micrometres total DFT on any surface.
·    Sikkens Kodrin WV 456 End Grain Sealer and Sikkens Kodrin WV 472 ‘V’ Joint Sealer should be applied with all coating systems following base stain/primer application.
·    It is strongly recommended that at least the first coat of base stain or primer be applied by saturation to ensure flow into all areas and achieve good ‘wetting’ of the timber surface.
·    The practice of heavily denibbing a low build base stain/primer should be avoided.
·    All coats should be thoroughly dried before overcoating is attempted. See section on drying conditions below.

·    Choice of colour is significant when determining durability expectations.
·    Colourless/Clear (or ‘near clear’) coatings will require frequent maintenance and are not recommended in anything but the most sheltered situations, when considering long term durability
·    Translucent/ semi transparent coating systems are acceptable in areas of moderate exposure and partly sheltered locations and designs
·    Fully opaque finishes offer the longest durability options, particularly when considering severe or direct exposure conditions, where the above coating systems would require regular maintenance regimes
·    Consideration should be given to the thermal gain potential of dark finishes. This can have a significant effect on timbers prone to resin/gum exudation.

·    A minimum application temperature of 15 degrees (coating, substrate and air temperature) should be achieved at all times
·    See specific application details for coating systems

Exterior quality Joinery Coatings differ greatly from products manufactured for internal surfaces such as doors, frames and skirting, staircases, furniture etc.
Products that have to withstand the elements require a film build capable of flexibility, extensibility and u v resistance; whereas scratch and abrasion resistance is the main property required of internal coatings.

Most exterior quality joinery paints and stains manufactured for application in the factory are now water-borne although solvent borne alkyds are still commonly used as site applied coatings. It is recognised that water-borne acrylic coatings dry quicker than solvent-borne alkyd equivalents but recommended drying times must still be allowed under the specified conditions.
For all water-borne primers and base stains, mid and finishing coats, we specify a four to six hour drying cycle under the following conditions.

Primers , base stains, saturate mid coats and spray applied mid and topcoats
Dip, flow coat or saturate spray all joinery items either assembled or in component form.
Allow to stand for ten minutes in ‘run off’ or ‘flash off’ area; i.e.

·    Ambient temperature        No air movement    High humidity

After ten minutes the coated timber should be moved to a dedicated area e.g.

·    Minimum temperature 20 degrees Centigrade
·    Maximum Relative Humidity 65%
·    Minimum movement of air 0.5 metres per second
·    Minimum air exchange of 15 per hour

It should be noted that the glazing bead system, particularly the bottom horizontal bead, will be subject to high levels of moisture and weathering. A fully coated timber bead system will require more frequent maintenance than other areas of the joinery.
·    The bottom bead should be a vented aluminium bead, fitted tight against the jambs with suitable end caps
·    The bottom joints of all vertical beads must be designed to ensure that there is no capillary action and moisture uptake
·    The use of a full powder coated aluminium bead system is recommended where possible
·    Fracturing of the applied coating system should be avoided during the fixing of glazing beads.  Consideration should be given to secure fixing by clip or invisible pins.  Ensure that a suitable protective capping is applied over the pins and that all faces, particularly end grains are appropriately sealed.

·    All joinery is to be installed and soundly fixed in accordance with the manufacturers instructions, avoiding any damage to the window and its coating system
·    Consideration should be given to the environment and conditions that the recently coated joinery items are subjected to. New build houses may create moisture rich environments, particularly in the winter months, which can have a detrimental effect on joinery items. Newly built houses should be thoroughly dried by heating and ventilation before freshly coated joinery is installed.

·    Care must be taken to avoid any handling/transit/storage damage, we strongly advise the use of protective wrapping on all joinery items/trims; this is to remain undamaged until fixing
·    Freshly coated joinery should be given at least 48 hours further drying time (see drying conditions above) before wrapping for despatch.
·    Consideration should be given to extended drying times before wrapping during winter months or items destined for installation in extreme conditions

·    All components must be stored under cover, preferably inside a ventilated building.  In the event of outside storage, they must be kept clear of the ground on level bearers and protected against dampness and direct sunlight by a tarpaulin or suitable protective cover.  There must be space for air circulation around and between components

·    Ensure all damage during transit or installation is repaired
·    Ensure all surfaces are cleaned and free from installation or building debris
·    The application of Sikkens ‘maintenance milk’ product is strongly recommended after installation and an annual treatment thereafter is advised.
·    Expected durability periods of factory applied coatings will vary and are dependent on the level of weathering the joinery is exposed to, the type of coating used and the design of the joinery and surrounding building.
·    A full maintenance specification is available for all coating systems.

Further useful information and guidance can be found the TRADA booklet “High Performance Wood Windows” by Patrick Hislop BA (Hons Arch) RIBA.  Contact details:  44(0)1494-569600 or

Recommended Coating Systems
A range of factory base stains, primers and durable top coats is available from Akzo Nobel Industrial Coatings Ltd., in various colours and sheen levels.  Compatible brush applied maintenance coating systems and related products are also available from the Sikkens Joinery Team.
Every care is taken to ensure that the information provided in this fact sheet is accurate.  For further information contact a member of the Sikkens Joinery Team. The information is correct at the date of issue, January 2012
  Akzo Nobel Industrial Coatings Ltd.
  Unit 04A,  Mercer Way, Shadsworth Business Park, Blackburn,  Lancs. BB1 2QZ   01254  687950