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How to Repair & Paint Exterior Woodwork

When the time comes to redecorate for the first time or refurbish exterior timber window frames and doors, the preparation and repair of the surface is key to ensuring long term durability of the coating and woodwork.

Our guidance and advice are a result of over 30 years cumulative experience of three of the most knowledgeable paint manufacturers of coatings for exterior woodwork. Sikkens, Teknos and Tikkurila.

For more detailed information and assistance with your project
please do not hesitate to call our technical department
on 01793 511 537.

The information applies to new timber as well as previously painted or wood stained timber.

Surface Preparation

Weather conditions

  • Do not attempt surface preparation or apply coatings when there is a risk of rain or frost.
  • In general, solvent-borne coatings should not be applied below 5oC and waterborne coatings should not be applied below 8 oC.
  • If there is any doubt about the quality of the surface or underlying paint film, apply the appropriate products to a small, inconspicuous area, allow this to dry for 24 hours and then inspect the area for appearance and adhesion.

Surface condition

  • Ensure surfaces are in a clean, dry condition, free from dust, dirt, wax, grease and surface moisture.
  • The moisture content of the timber should not exceed 18% for exterior, and 14% for interior use.
  • All coatings should be applied all round to all areas, even those which will be hidden once installed.
  • Where damage has affected the full depth of the coating system, i.e. a deep cut or gouge, the full system requires repair. Abrade the damaged area to remove all unsound coating and feather out to leave a smooth surface.
  • Timber surfaces should not be over-prepared with fine abrasives, as this will reduce the degree of absorption.
  • Wire wool and metallic brushes must not be used.
  • Grey and denatured wood, loose paintwork must be removed and the surface sanded to fresh clean timber.

Failure to provide an adequately prepared surface will result in poor adhesive performance of the coating system.

  • Where applicable and especially on softwood, apply one/two coats of a suitable penetrating wood preserver to saturation, paying particular attention to end grains.
  • Allow adequate drying time between coats and before over coating.

Note: Translucent finishes are not formulated to obscure the grain, therefore filling and stopping should be avoided wherever possible.

  • Use fillers specifically designed for use with timber.
  • General or all-purpose fillers are not suitable, particularly on external areas, often cannot cope with timber movement and work loose.
  • When using translucent coatings, there is little need to filling fascia board joints and butt joints as the change in grain from one section to the other may draw attention to the filler.

Timbers with natural extractives/exudates or exudation from knots or resinous areas

Some hardwoods contain high levels of natural wood extractives or exudates and some softwood can be highly resinous.

Resins are a naturally occurring component of timber and can be found in pockets within the wood or associated with knots. Some timber species are naturally more resinous than others and it is often impossible to detect at the manufacturing stage.

Resin exudation most often occurs on south-facing elevations and on darker colours where the heat of the sun liquefies and mobilises the resins, drawing them to the surface.

Where resin has exuded through the coating

The best remedial treatment is to allow the exuded resin to weather until it dries and oxidises, forming a white crystalline powder. The dried resin can then be removed with a stiff nylon or natural bristle brush. Wipe down with cellulose thinners or methylated spirits (not White Spirit) on a lint-free cloth, frequently changing the face of the cloth. Allow solvent to evaporate fully before overcoating.

Shellac Knotting may be used providing it is compatible with subsequent coatings and timber type. However, the use of knotting cannot guarantee against the discolouring effects of knots, natural timber extractives and/or potential blistering from resin or gum exudation.

The use of Shellac Knotting under translucent systems is not recommended.

Minor areas of coating damage, shakes or open joints

These areas should be locally repaired in line with the relevant recommendations as follows:

First and subsequent redecoration

All areas to be recoated should be washed down with a mild detergent solution and rinsed with clean water to remove dust, insects and other contaminants, which can form a base for algae and fungi growth.

Flaking Paint

Where minor flaking affects small areas of the topcoat surface but the timber substrate is not exposed

  • Abrade the damaged area with a fine grade abrasive paper to remove all unsound coating and feather out to leave a smooth surface.
  • Clean down and wash the abraded area to remove dust, and allow to thoroughly dry.

If the damaged area is widespread, it is recommended that the whole frame is lightly abraded and repaired as described above with the second coat applied to the complete frame.

Moisture penetration

Where moisture has penetrated joints, end grain, mitres or natural movement of the timber has opened shakes:

  • Abrade the damaged area with a fine grade abrasive paper to remove all unsound coating and feather out to leave a smooth surface.
  • Clean down and wash the abraded area to remove dust, and allow to thoroughly dry.
  • Treat bare wood, where appropriate with a surface penetrating preservative primer or priming oil and allow to dry.
  • Seal any open joints with joint sealer applied by mastic gun.
  • Wipe with a damp cloth or spatula to give a smooth joint and allow to dry to a clear finish.
  • Seal any exposed end grain with end grain sealer and allow to thoroughly dry.

Fixing (nail/screw) holes / small defects

Small surface defects
  • Fill small surface defects with a good quality dedicated wood filler.
  • Rub down with a fine grade silicon carbide paper in the direction of the grain.
  • Do not break through the surface of the surrounding coating system.
  • Remove all dust.
Large surface defects
  • Fill surface defects greater than 5mm in depth, including large knots that have been removed, with a good quality two pack wood filler.
  • For optimum performance, fillers should be used on bare timber.
  • Apply masking tape around the defect.
  • Use a filling knife to achieve a smooth, even finish, removing any surplus while still wet.
  • Remove masking tape before the filler has cured.
    Once cured, rub down with a medium grade (P120) abrasive paper to provide a key.
  • Remove all dust.

End grains

  • Exposed and damaged end grains can allow water to enter the timber and cause swelling. Over time this can lead the coating to split and timber to decay.
  • Seal exposed end grains with End Grain Sealer (Sikkens Kodrin WV456 or Teknos Teknoseal 4000).
  • Apply to saturation using a small stiff bristle brush, or small filling knife.
  • Allow to become transparent before overcoating (typically 2 hours).

Personal Protection and Safety Precautions

  • Treatments for the removal of surface coatings (such as sanding, burning off and the use of chemicals) may generate hazardous dust and/or fumes.
  • Work in well ventilated areas.
  • Use suitable personal protective equipment (respiratory, eye and skin), as necessary.
  • Manufacturer’s advice should be followed at all times.

Coverage Rates

When applying coatings, in order to ensure optimum protection and durability, it is essential to achieve the required coverage rate as specified by the product Datasheet.


Following a few simple hints will produce excellent results.


Brush application of waterborne paint requires a different technique from traditional solvent-based coatings, mainly due to its shorter drying time and different flow and levelling characteristics.

Prior to application, thoroughly wet the brush with water, ensuring that the base of the bristles (the heel of the brush) is fully wetted.


The viscosity of the paint will affect the ease of application. Whilst the product can be applied directly from the tin, additional thinning with between 5 and 15% of water will improve the flow and levelling properties of the product, particularly in warmer weather.

For the best results a 3-stage application technique should be developed:

  1. Load the coating generously onto the surface and disperse briskly.
  2. Even out the coating with light diagonal cross strokes … DO NOT OVERBRUSH … the coating will flow and level naturally.
  3. Finish the application with LIGHT brush strokes in the direction of the grain.

Priming and Finishing

  • Spot prime areas of bare timber and allow to dry.
  • Apply the Primer to all surfaces to be painted.
  • Apply the topcoat as per chosen manufacturers datasheet.

Apply and finish each section of the joinery in a systematic method.

This means painting a window or door one component at a time e.g. Top Rail followed by a Stile followed by the Bottom Rail.

Coverage Rates

When applying coatings, in order to ensure optimum protection and durability, it is essential to achieve the required coverage rate as specified by the product Datasheet.

Post Coating Maintenance and Durability

  • Ensure all surfaces are cleaned and free from installation or building debris.
  • Expected durability periods of 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.
  • An annual inspection is recommended to assess joinery and coating condition

A simple annual clean with a Sikkens or Teknos Maintenance Milk or mild detergent and warm water solution is recommended
With proper care and attention, our coatings will give extended life between redecoration cycles.

Best Performance

For best performance, the following should be observed:

  • At least once per year all coatings should be washed with mild detergent and water to remove any surface pollution.
  • All hinge mechanisms and handles should be checked at least biannually for ease of operation and lubricated with light oil suitable for the purpose, as required.
  • Weather seals should be cleaned at least once per year to remove any dust or grime in accordance with the manufacturer’s instructions.
  • Rainwater goods should be cleaned, blockages removed and any leaks repaired.
  • The final overall appearance of the finish is dependent on a number of factors, including colour, absorbency and texture of the timber, as well as the shade and type of coating used.

We therefore strongly recommend that a trial application is undertaken before work is carried out, to confirm its acceptability.

Cleaning of Equipment

Wash out brushes with a mild detergent solution (e.g. washing up liquid) and rinse with clean water.

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