Joinery design issues

Wooden frame and timber items

ADVICE

Joinery design issues

How long a coating system lasts on timber items is not just determined by the coatings system, but also by the timber used and the design of the joinery.

Optimal protection on timber items

How long a coating system lasts on timber items is not just determined by the coatings system, but also by the timber used and the design of the joinery.

The timber used must be suitably stable and of a sufficiently high enough grade for the item being manufactured. It should preferably be naturally durable or able to accept a suitable treatment to achieve the required level of durability for use as an exterior joinery item.
Wooden window frames

Long term protection

Wood
The timber must be at a suitable moisture content prior to application of coatings and we recommend this is between 12 and 16%.

The timber should be free of microorganisms, such as insects, fungi, blue stain, mould or bacteria and natural defects such as knots and shakes must be removed or repaired to a suitable standard prior to coating. Advice on acceptable timber grades can be found by referring to the latest EN 942 standard.

Recommendations on window construction details that provide the best possible results with the coating system:


End grains should be smoothly planed and protected with 25-0352 Hydrolux End-Grain sealer.




Where v-joints are present these should be sealed with 19-0293 V-joint sealer.

Best choice for your timber items

Fine capillary gaps where moisture can become trapped need to be avoided as these can allow uncontrolled moisture ingress leading to possible coatings issues and potential wood rot.
All edges (arises) should be rounded to a radius of 3 mm as recommended in the British standard. Cill extensions must have a maximum protrusion of 75mm and machined at such an angle that promotes good water shedding.
All glazing should be to a high standard where the glazing sealant or gasket forms a water tight contact with the glass and timber. It should also have a sufficient angle to shed water away from glazing lines. Internally beaded systems are preferable. Where external beading is used it should be constructed from highly stable timber or using wood plastic composite beading material. We recommend that glazing systems should be drained and vented to reduce the risk of condensation.
Joint adhesive must be applied to all parts of the joint and there must be no gap where moisture ingress can occur. Adhesives with good gap filling qualities are highly recommended. These need to be flexible enough to cope with the natural movement characteristics of the timber. Where a fully filled joint is not achievable the adhesive must conform to the minimum D4 specification as described in BS EN 204.
Frencken products
BS 644 details the requirements for window construction. Refer to this for more information.