This is an extract from the Sikkens web site on propper timber restoration techniques.
It is very involved and can mean the difference between a great result or making your investment look worse.
If your painter is quoting on restoring your timber decks make sure their scope of works details the preperation process that applies to your decks or exterior timber work.
Resource provided by; http://www.tenaru.com.au/
SPECIFICATION FOR RECOAT OF EXISTING SIKKENS SYSTEM
1. All surfaces to be coated must be dry, free of dirt, grease, wax. dust or any contaminates. Wash down with mild detergent and water and rinse well.
2. Areas of discolouration, peeling or flaking must be sanded off (always along the grain) to a sound substrate. Check adhesion of old coating on random sections of the board – ie cut a small X through the paint film with a razor blade. Place a piece of cellotape over the cut and press down firmly – then quickly pull the tape off. If the tape pulls the coating away, the substrate is unsound and further preparation will be necessary (by sanding and / or complete removal of the coating to bare wood) to obtain proper adhesion of new paint layers. The edges of the paint film around bare wood areas should be ‘feathered’ to a smooth surface with sandpaper.
3. Due to the transparency of these coatings, it is not always possible to “spot prime” bare wood areas – as a patchy appearance may result. Instead, the ‘old’ paint film may require sanding / stripping back for the full length of the board / section to a natural break. To remove Supernatural (a waterborne acrylic type product) use a stripper such as ‘Citristrip’ made by The Flood Company. Where the Supernatural finish is in reasonable or good condition, rub down with a Scotchbrite multi flex abrasive sheet, grade S-ULF to ‘flatten’ the coating prior to applying refresher coat(s) of Supernatural.
4. Mould affected surfaces must be treated before repainting, otherwise mould will continue to grow underneath the new paint film. Thoroughly wash down the surface with a solution of one cup household bleach (sodium hypochlorite type) and five cups of water, using a soft brush or sponge. Leave on surface for 10 to 20 minutes, then rinse off. Repeat if necessary. When dry, treat with a proprietary anti-mould solution. Allow to thoroughly dry before commencing recoat.
5. Weathered / grey and dirty discoloured surfaces may be cleaned, and the wood restored to its natural appearance, by washing the surface with a mixture of 100 grams Oxalic Acid to 1 litre of warm water*. Leave on the surface for approximately 30 minutes before washing off with clean water. Allow to dry thoroughly before commencing recoat.
*Alternatively, use a proprietary brand wood cleaner – eg Dekswood by The Flood Company.
6. Spot prime bare areas with previously applied base coat (refer to note 3 above). Allow a minimum of 24 hours drying time. Do not apply Cetol HLS over other Sikkens products.
7. Apply the two final coats of Cetol HLS, Supernatural, Cetol Filter 7 Plus, Cetol Deck, Cetol Deck Plus or Cetol TGL Gloss plus – whichever system was previously used. Allow a minimum of 24 hours drying time between coats. If applying to ROUGH SAWN wood Supernatural can be diluted with up to 5% water. Do not apply any coatings if rain is likely to occur within the following 24 hours or in the late afternoon / evening when a sharp drop in temperature (or dewfall) could be expected. This can adversely affect a not yet dried coat.
8. Do not apply coatings to a hot or wet / damp surface.
9. Always work along the board to a natural break. By going down the board in sections, lap marks may be noticeable in the final result.
10. To clean down rough sawn timber, use a copper wire brush not steel.
11. Do not thin Cetol HLS, Cetol Filter 7 Plus, Cetol Deck or Cetol Deck Plus and do not add tinters. Cetol HLS, Cetol Filter 7 Plus, Cetol TGL Gloss plus, Cetol Deck and Cetol Deck Plus brushes wash out in mineral turps. Supernatural brushes wash out in water then mineral turps or with a 50 / 50 mix of mineral turps and methylated spirits.
12. Where a three coat system of Cetol Filter 7 Plus has previously been used (on rough sawn or hardwood) spot prime* with Cetol Filter 7 Plus before finishing with further coats of Cetol Filter 7 Plus. Due to the high film build of Cetol Filter 7 Plus, it is not recommended to overcoat with Supernatural. (*refer to note 3).
13. Remember, to achieve a good result it is necessary to ensure that the surface is clean, dry and sound before painting.