Surface Preparation

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4a :Surface PreparationSpecificationsAugust 2004(i) IndexSP600 Repainting GeneralSP601 Preparation of Old Paintwork in Bad ConditionSP602 Preparation of Old Chalky PaintworkSP603 Preparation of Old Paintwork in Sound ConditionSP604 Preparation of Old Paintwork in Good ConditionSP605 Water RinsingSP606 Solvent CleaningSP607 Hand Tool CleaningSP608 Power Tool CleaningSP609 Abrasive Blast CleaningSP609A Abrasive Blast Cleaning, Class 1SP609B Abrasive Blast Cleaning, Class 2SP609C Abrasive Blast Cleaning, Class 2.5SP609D Abrasive Blast Cleaning, Class 3SP609E Brush Blast CleaningSP610 Flame Cleaning Steel SurfacesSP611 Pickling Steel SurfacesSP612 Preparation of New Wooden SurfacesSP613 Repair of Surface Imperfections in Wooden SurfacesSP614 Removal of Perished Paint by Power SandingSP615 Removal of Perished Paint by Burning OffSP616 Removal of Perished Paint by Chemical StripperSP617 Removal of Mould and MildewSP618 Removal of Moss and LichenSP619 Removal of Chalk, Dirt and DustSP620 Removal of Grease, Dirt and ScumSP621 Removal of Gloss from Paint and EnamelSP622 Removal of Efflorescence from a Set Plaster SurfaceSP623 Treatment of CopperSP624 Treatment of Medium Density FibreboardSP625 Treatment of PlasticsSP626 Acid Etching of Efflorescent Free Concrete SurfacesSP627 Repair of Surface Imperfections in MasonrySP628 Repair of Surface Imperfections in Plaster 2SP629 Preparation for Painting Iron and SteelSP630 Preparation of Aluminium and AlloysSP631 Preparation of Sound Masonry and ConcreteSP632 Preparation of Precoated Galvanised Iron SheetingSP633 Filling of Concrete Blocks Prior to PaintingSP634A Ageing of Concrete for Waterbased PaintsSP634B Ageing of Concrete for Alkali Resistant Solvent Based PaintsSP634C Ageing of Concrete for Alkyd Paints4–2
4a :Surface PreparationSpecificationsAugust 2004SP 600 Repainting General: Ideally paint should break down by gradual erosion of the surfaceleaving a perfectly adhering, etched surface which is ideal for repainting after a simple washdown. Unfortunately this ideal situation does not always occur which necessitates greater surfacepreparation.Breakdown due to loss of Adhesion This is the most serious problem to overcome and caninclude flaking, peeling and blistering. Where any of these breakdowns have occurred, unless specificlocalised reasons for the failure can be identified, it is wise to assume that the weakness could beprevalent over the whole surface.The assessment which has to be made is WHETHER THE EXISTING SYSTEM HAS SUFFICIENTADHESION TO HOLD ON WHEN SUBJECTED TO THE EXTRA STRESS AND WEIGHT OF 2OR 3 MORE COATS OF PAINT. Stresses are, of course, increased if the new system is darker incolour than the existing system.A simple test for adhesion is as follows: Clean an area of suspect coating and apply a strip ofadhesive tape; ensure firm contact by rubbing with a fingernail. Rapidly pull off the tape at 90° tothe surface. Examine the tape for any detached paint. Any poorly adhering paint must be removedby burning, sanding, or solvent strippers. All edges of poorly adhering areas must be featheredand immediately treated with the first coat of the system to prevent “edge curl’ with subsequentweathering.Glossy Surfaces All surfaces, both interior and exterior, should be thoroughly washed down toensure the removal of all surface contaminants before de-glossing.Enamel paints which have aged in the absence of ultra violet light develop an extremely hard,impermeable surface which is difficult to adhere to. In exterior situations this occurs in shelteredsituations such as the underside of weatherboards and under eaves and soffits. In interior situationsthis condition is almost always prevalent, and the surface can be even more difficult to adhereto due to surface contaminants (e.g. soap contamination in bathrooms, grease contaminationin kitchens). In all cases glossy surfaces must be de-glossed by a thorough sanding to removecontaminants and to provide a mechanical key for subsequent coats.Powdery, Hydrolised, or Saponified Paint In some cases paint can breakdown with acomplete loss of film integrity. This normally occurs when paint has been in contact with alkalis andwith water for long periods of time. It is easily recognisable by its ‘cheesy’ nature, and easy removalwith a fingernail. After removal of the source of the problem (e.g. water leaks), the affected paintmust be totally removed by sanding and scraping before recoating.Mould Infested Surfaces Refer Data Sheet. SP 617SP601 Preparation of Old Paintwork in Bad Condition:Procedure: Remove all paint with a paint scraper, wire brush, by burning off or chemical stripperas appropriate. Wash surfaces down with clean water, allow to dry thoroughly. Fill cracks andsurface imperfections in masonry, with mortar or acrylic filler. Gaps resulting from structuralmovement should be filled (Refer SP613). Allow to dry, sand smooth, dust off. Any degradedsubstrate (e.g. dry rotted timber must be cut out prior to painting and replaced). Timber should befilled with acrylic filler or linseed oil putty, priming first. Remove any resin extracts by scraping offand washing with mineral turpentine. Sand any glossy surfaces to provide key.SP602 Preparation of Old Chalky Paintwork:4–3
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