p r e p a r a t o r y w o r k 17 4. Pr e pa r a to r y W o r k 4.1 PLANNING Quality control starts with good planning and management. An Inspection and Test Plan, ITP (refer to Appendix D) which lists down the project’s inspection and testing requirements should be prepared to detail the checks required to achieve good workmanship. The plan should cover the responsibilities of each party, inspection methods, requirement references and frequency of inspections. Checklists for the in-process and final inspection on painting works should also be prepared (as in Appendix E and F). Pri or to sta rting any painting work, it i s importa nt for the parties involved to plan and agree on the compatible paint system as per project specification, surface preparation method, sequence of work, drying out time and method of access. In ge nera l, the s che dule of painting w orks s houl d be planned in relation to the work of other trades, so as to ensure that the surfaces to be painted are prepared on time and that the subsequent construction works will not da ma g e t he pa int work. T heapplicator should con fir m on t he t y peand num b e r of coa ts , loca tion of appl ica tion, surface prepa rat ion method and application method are in accordance with project specification. For verification of the paint colour, uniformity and compatibility of the paint system, it is a good practice to have a mock-up unit for the approval of the architect or owner before the commencement of the actual works. 4.2 SURFA CE PREPA RA TION Good surfac e pre para tion is c ritica l for the pa int sy st e m to function effectively. As the performance of the paint system depends largely on its adhesion with the substrate, and paint adheres best to surfaces that are clea n and sound, i t is e ss e ntial to e sta blish the re quired standard and level of surface preparation works. The receiving surfaces should be dry, and free from foreign and unstable matters such as dust, dirt, rust, spatter, salt, grease, oil, loose paint film and so forth before proce e ding with the painting work. Works by other trades that might affect the painting shoul d be sa ti sfa ctoril y complete d. The appli ca tor should inform the designer of any change in the nature or condition of the receiving surfaces, which may necessitate modification of the specifications. Refer to Table 4.1 to Table 4.4 for more details on surface preparation for various types of surfaces. Ta ble 4.1 Preparat ion of Concret e/ Cem ent Plas ter Surface s Condit ion Tools/Metho d s Remarks Uncoate d S ur f a ce Coa t e d S ur f ace Moisture – Ch ec kin g wit h mois t ur e me t e r – T o ensuremois t ure content not e xce eding 6% (or refer to manufacturer’s recommendation) – Allo w dr y ing a ft er plastering for minimum of 21 days (in compliance with CP22) – T o ensure mois tu re content not e xce eding 6% (or refer to manufacturer’s recommendation) – T o c he c k for s our ce ofdampness Surface Contaminants such as construction soot, algae, loose paint- film (for coated surface only) etc – High pr e ssure water jetting – T o r emove for e ign and unstable matters such as construction soot, concrete / ce ment splashes, cement salts etc – T o re mo v e loose particle s and existing paint with flaking, dirt or chalking e tc
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– Manual cleaning by chipping,scrapping or wire brushing
– To remove foreign and unstable matters such asconstruction soot, algae, concrete/cement splashes,cement salts, loose paint film etc
SurfaceImperfections
(i) rough, open-textured orcoarse-grainedsurfaces
– Sanding/grinding/skim coatingfollowed by rinsing with cleanwater and wiping dry
– Brushing or sweeping – To remove foreign and unstable matters such asconstruction soot, algae, concrete/cement splashes,cement salts, loose paint film etc
– Fungicidal wash – To kill fungal/algae spores and rootsSurface Treatment
Microbiologicalgrowth, e.g. algaeor fungi growth
– To reduce roughness
– To improve adhesion to substrate/existing coating
– To remove foreign and unstable matters such asconstruction soot, algae, concrete/cement splashes,cement salts etc
(ii) hairline cracks,nail & screwholes, open
joints, cracks andsimilar localcavities, deep andshallowdepressions
– Patching – Use fillers that contain a resin/binder system e.g. acrylicbased putty or cement with additives
– Water sensitive types e.g. gypsum-based fillers arenot recommended as they may dissolve in water
– Prime surface before patching if oil-based fillers are used
– Patch in two stages if cavities are deep
– If applied immediately beneath finishing coats, shrinkageand variations in gloss, sheen or colour may occur
Table 4.4 Preparation of Non-Ferrous Metal Surfaces
(include aluminium, aluminium alloys, magnesium alloys, zinc and treated steel such as galvanised surfaces, anodised aluminium etc)
Condition Tools/Methods Remarks
Uncoated Surface Coated Surface
Surface
Contaminants(i) oil, grease
– Wiping with cloth dampenedwith solvent
– To remove grease and oil
– Mechanical washing down withsolvent or detergent solution
– To remove grease and oil
– Degreasing – To remove grease and oil
(ii) loose paint-film, dirt, rustetc
– High-pressure water jettingfollowed by sanding
– To remove foreign and unstable matters such as loosepaint film, abrasive residue etc
– Stripping by paint removers NA – Rinse thoroughly withclean water after strippingto avoid chemicalreaction with metal. Milddetergent should be usedto remove residue
– Sanding – To remove foreign andunstable matters such asloose paint film, abrasiveresidue etc
– White rust need not beremoved if found stable
Surface Treatment – Coating the exposed surface withan etching primer.
– To ensure good adhesion – To ensure good adhesion
– Spot prime exposedsurfaces immediatelyafter cleaning
4.3 PAINT PREPARATION
Proper paint preparation is important in delivering
quality work. Refer to Table 4.5 for details on
preparation of paint.
In mixing of paint, the following factors should be
considered:
• mix ratio;
• type of thinner used;
• induction time;
• pot life; and
• ageing time
Mixing should be carried out in compliance with the
specifications and manufacturer’s recommendation.
No unauthorized thinning or adulteration should becarried out and no addition of driers is permitted.
Where additions are authorized, the correct proportions
should be strictly observed.
There should be sufficient stirring until uniformity of
the paint is achieved. The pigment in paints is heavier
than the vehicle and tends to settle at the bottom of
the container. Failure to stir the paint properly is a
common cause of unsatisfactory results. It is, hence,