It gives a distinct and attractive 3-dimensional appearance, whether internal or external. The Textured Finish is achieved with the application of an acrylic texture basecoat, in addition to the normal painting system of Sealer, Undercoat and Topcoat (refer to Table 6A). It is commonly used for masonry and cementitious surfaces, and can be applied either by rollers or the spray method, rendering various design patterns, i.e. mountainous, head-cut, or some special designs on the surface.

Performance of the paint system is affected by one or more of the following factors:

• Substrate on to which it is applied;
• Surface preparation;
• Types of paint (types and quality of materials used and its formulation;
• The paint system used;
• Application methods and conditions during application;
• Overcoating interval;
• Degree of curing of coating and conditions under which the process is taking place.

Hence, the basic principles or criteria when selecting the paint system can be listed as follows:

• Type of substrate to be painted;
• Surface preparation and its condition prior to painting;
• Environmental conditions to which the painted surface is exposed;
• Expected durability of the substrate to be painted and that of the system;
• Conditions of painting, i.e. new painting or repainting;
• Economy (budget).

Cement-plastered and concrete surfaces are by far the most common substrates encountered. Very often undesirable appearance begins to mar the painted surfaces, such as fading and discolouration, peeling, stains and unsightly algae growth. Factors from the substrate contributing to these problems are high moisture content and alkalinity, porosity and profile of the substrate.

Bricks as an exposed finish surface are often used perhaps as a contrast to the common concrete surfaces or to eliminate the need for painting. Nonetheless, there have been numerous situations where leakages have occurred through cracks in the mortar joints or the bricks itself. Often, whitish stains are also observed presumably from lime brought out by the drying moisture. Treating the surface with water-repellent silicon can alleviate this problem.

It is common to find layers of wood and paint flaking off timber surfaces after sometime. The reason lies with the substrate undergoing much dimensional changes especially when subjected to weathering. Layers of fibre in the wood will dry and pick up moisture from the air continuously. Dimensional variation depending on the density of the layers will result in adhesion loss of the top layer and with it the paint film. The following are some recommendations to minimise the problems:

a. Select the suitable type of wood for various building application;
b. Painting should be done before wood surface shows signs of deterioration;
c. Use paints with excellent penetrative properties to improve adhesion and durability. Solvent-based paints are preferred, e.g. Aluminium Wood Primer, 1 & 2-pack Polyurethane, Alkyd Enamel, Amino Alkyd (acid-cured) & Epoxy;
d. Check moisture content of the wood. It should not exceed the recommended limit of 20%. Alternately, use wood that has been left for drying in a well-ventilated room for at least a month.

With the natural tendency of metals to corrode, there is always the task of protection against moisture, salts, acids and air. Even the presence of impurity of other metals within the steel can contribute to rust. Problems encountered are:
a. Rust – always found on mild steel; is an unstable matter to paint on. It can cause paint to destabilise and cause further corrosion beneath the paint due to electrolytic action.
b. Oil – applied for protection after processing of the metal, will affect adhesion. Treatment is therefore necessary to remove the oil.
c. Dirt – foreign matter in the form of salts, dust or other forms of chemicals.

Several methods can be used to counter the above-mentioned problems. The appropriate method will depend on the level of protection required and the paint system selected. Understanding the environment in which the substrate is put into service is also crucial to the type of surface preparation selected.

Non-ferrous metals such as galvanised steel, aluminium and alloys do not normally required painting. Painting is necessary when the appearance or colour is found unappealing. However, in the case of galvanised metals, painting is a good practice as it enhances protection against corrosion. Application of an Etching Primer is highly recommended on non-ferrous metals. This primer contains mild acid that reacts with the metal to form a stable base for subsequent coats. It is common to find severe peeling on non-ferrous metals where an Etching Primer has not been applied. The peeling is a result of the paint resin reacting chemically with the metal (saponified) leading to loss of adhesion. Although Zinc-based Primers can last longer than others, its resin content still give rise to adhesion problems. This is further aggravated by the smoothness of the metal surface.

Many pipes and ducting have been replaced by PVC and UPVC (Unplasticised PVC) in buildings. Treatment such as mechanical sanding and selection of high-flexibility paints and use of PVC conditioners is recommended. Examples of flexible paints are 2-pack Polyurethanes, Alkyd Enamels and Acrylic Emulsions.

No matter how superior the paint used may be, full beneficial effects of the paint film are unattainable without adequate and appropriate surface preparation. There are several methods used in surface preparation and each of these will be specific to the type of surface to be prepared. All preparation works must bring the substrate towards three essential conditions, viz. clean, dry and stable. Inadequate preparation of the surface will result in the failure of any paint system used. The following describe the different types of surface preparation.

This is used to remove unstable matter from the substrate and is usually done on external surfaces. Manual scraping will follow where necessary.

This is done either manually with sandpaper or mechanically with a power brush to remove old paint or stubborn matter. It is much faster than scraping but it creates dust and sometimes surface defects.

It involves chipping, scraping and wire brushing. It is reasonably efficient but unsuitable for removing mill scale from new steelwork.

This involves the removal of mill scale by passing an oxy-acetylene flame over the steel surface. It is not suitable for sections less than 6mm in thickness. Wire brushing and application of primer must be done immediately after flame cleaning while the steel is still warm.

This is the blasting of mineral, polymer or metal abrasive onto steel surface by air pressure or centrifugal action (spinning) on to the surface. The aim is to achieve a coarse, rust-free surface suitable for painting. After blasting, abrasive residues and other debris from the surface should be removed by brushing or air-blasting. Priming should follow quickly to avoid deterioration of the cleaned surface through rust.

This is a highly specialised technique used under factory controlled conditions. It employs the use of high frequency magnetic waves passing through degreasing batch which cause the foreign matter to vibrate off.

Paints removers which contain strong penetrating material, alkaline and chlorinated hydrocarbon compounds, are used to break the adhesive bonds of the paint film. After application, it should be left for about 5 minutes before removing the paint film with a scraper.

This is the quickest and most economical method of removing paint from wood surface but is less effective on metals and other heat-conducting substrates. It should not be used on plasters and cement-rendered surfaces due to the risk of cracking and disintegration.

It involves the immersion of steelwork in hot solutions of hydrochloric, sulphuric or phosphoric acids. Inhibitors are added to prevent attack on the metal while the oxide layer is being dissolved. The treated materials must be neutralised, rinsed and dried after immersion and treated with inhibitor to prevent rust during drying.

The removal of oil and grease is most effectively done by immersion in a bath of boiling solvents such as trichloroethylene (thinner) under factory conditions. Large quantities of oil and grease can be removed by wiping with a cloth soaked in a suitable solvent. To reduce problem of residue, liquid detergents can be added to solvents and applied. A little brushing will help the solution to dissolve oil and grease which can be shortly flushed away with clean water.

Patching should be done with fillers which contain a resin/binder system. Cement with additives is also acceptable. However, gypsum-based fillers should not be used as they tend to be soluble when in contact with water.

Moisture, especially in concrete and wood, must be controlled to prevent occurrence of paint defects such as Discolouration, Blistering or Peeling. The moisture level of concrete and wood should not exceed 16% and 20% respectively. This is done by allowing the surface to dry thoroughly before painting.

These surfaces include cement-based, brick, stone works and plasters. Moisture is a major cause of paint defects on masonry surfaces. Moisture-related defects are Blistering, Discolouration and Efflorescence.

As moisture is one of the major causes of paint defects, wood surfaces that are to be painted should have a moisture content of not more than 20%. Beyond 25%, blistering of the paint film can occur. Wood should be thoroughly dried before being painted. Moisture Meter (Protimeter) should be used to indicate the moisture content. If such a device is not available, then the wood should preferably be left and stored under well-ventilated and dry conditions for several weeks before it is painted. It is imperative also to note that before any painting on wood, unsound and aged wood fibre should be removed including any rotten wood.

For New Paintwork
The wood surface should be cleaned, smooth and free from surface defects by patching with wood filler or putty. Unstable splinter and foreign matter should be removed by sanding followed by a wipe-off with a tack cloth before the first coat of paint is applied.

For Repainting
Internal: Defective paintwork should be stripped off with a solvent-type paint remover. Alkaline strippers should not be used as they can cause damage to the wood surface by retaining residues which are detrimental to subsequent coats.
External: The wood surface should be cleaned to remove dirt, grime, chalk, etc. Where there is cracking, flaking or defective adhesion, the entire surface should be removed by solvent-stripping or burning off.

Priming
A coat of appropriate primer should be made on all surfaces of joinery. Primed surfaces should not be exposed to weather for long periods. An undercoat should be applied not later than 4 weeks after the surface has been primed.

When iron and steel surfaces are exposed under atmospheric conditions, rust will form very quickly. Corrosion can, however, be prevented by:
a. Keeping the steel surface thoroughly clean;
b. Applying a primer with anti-corrosive pigment;
c. Ensuring the paint film is not less than 125 microns (5 mils) in thickness.

For New Paintwork
Structural steelwork has a layer of mill scale on its surface. This should be removed and the methods used will require the surface to be free from oil and grease. After the surface has been cleaned, the first coat of primer should be applied to prevent corrosion from taking place. The methods of scale removal include degreasing, manual cleaning, pickling, flame-cleaning and blast-cleaning. The method selected is constrained by budget or practical reasons. After preparing the metal surface, all forms of abrasive residue and debris must be removed from the surface before painting commences. Priming should be done quickly to prevent rusting.

For Repainting
Existing painted steel surfaces can develop rust, accumulate surface oil/dirt or unstable paint film. Depending on the extent of unstable paint, this can be removed by chipping, sanding or scraping. Alkaline strippers can also be used but the chemical should be removed by washing thoroughly. Blasting is very effective in removing old paints. Patches of oil and grease can be easily removed by washing down with a solvent or detergent solution. Rusty areas should be isolated and removed by grinding or sanding. Spot prime to prevent corrosion. Chemical rust remover and rust converter can help overcome the problem of reaching difficult spots. For good condition paintwork without corrosion, the surface should be washed and allowed to dry thoroughly before painting.

Priming
A corrosion-inhibiting primer should be applied immediately after the mill scale and other contaminants have been removed. As primers are not intended to withstand the weather, an undercoat should be applied to exposed surfaces within 4 weeks.

Non-ferrous surfaces include Aluminium, Aluminium Alloys, Magnesium Alloys, Zinc and Galvanised Surfaces, Cadmium, Copper, Brass, Bronze and Lead. Painting of such surfaces is only for decorative purposes requiring a thin paint film.

For New Paintwork
In most cases, the surfaces can be adequately prepared by removing oil and grease using the appropriate methods discussed earlier. In addition, Etching Primer should be used as a pre-treatment to provide a surface with good adhesion without chemical reaction to subsequent coats.

For Repainting
If unstable paint film is found, etch priming of the surface is usually not required. Instead, blasting with high pressure water jet will remove the paint film easily. For stubborn paints, sanding lightly with fine sandpaper should be sufficient. Chemical remover such as Methylene Chloride can be used to strip off the paint film. Care should be taken to avoid chemical reaction with metal by rinsing thoroughly with clean water as soon as possible. Mild detergent should be used to remove residue, if necessary. Oil and grease can be removed by the normal degreasing method. Rust on oxidised non-ferrous metals can be sanded away. In the case of galvanised metals, the white rust (Zinc Oxide) need not be removed if found stable.

The environmental conditions in which the painted surface is exposed to, have direct and significant influences and effects on the paintwork and the selection of a paint system. Identifying the environment and its harmful effects on the paintwork will enable the correct paint system to be used and this will mean considerable savings in terms of upkeep. Listed below are the different types of environment categorised in order of their ‘corrosive’ nature (Table 1) and the performance of the different paints in these environments (Table 2).

In the selection of a paint system, the emphasis will inevitably be on its performance. The Easy reference Charts illustrate the different types of paint systems possible on different substrates namely Masonry, Wood and Metal surfaces. The Charts aid the specifier in deciding the most appropriate paint system for the desired purpose.

The following are Explanatory notes on the use of the Easy Reference Charts (Table 3A, 3B and 3C).