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| COMMON
PAINTING PROBLEMS
Outlined on the following few pages are a number of the more common painting problems that are encountered by painters and decorators in the industry. The information given has been structured to give a description of the defect, the common causes and the most effective remedy. Including Bittiness
Bleaching Bleeding Blistering Bittiness is the description given to a paint film which shows signs of small particles of dust, grit or skin below the surface. This problem is caused by applying paint to dust-aden areas, using dirty equipment, or mixing the skin of a partly used can of paint into the liquid. The only remedy for this defect is to allow the paint film to harden sufficiently to rub down and then re-coat. Bleaching A 'whitening'
or change in colour of the paint film. Bleaching is caused by the
action of acid fumes or alkali upon pigments in the paint film,
and usually occurs where the paint and colour selected is incompatible The
only effective treatment for this problem is repainting with a more Bleeding Bleeding
is the term used to describe the discolouration of a paint film Bituminous surfaces and creosote based wood stains frequently cause discolouration by bleeding into solvent based paints which are applied direct. Wallpaper colours can also bleed into water based paints, and many of the older type ceiling boards bleed if activated by water leaks. The only effective remedy for this problem is the proper sealing of the surface - water soluble stains should be sealed with a solvent based paint, and solvent based stains with an aluminium priming paint. Blistering Blistering refers to the defect when portions of a paint film become detached from the surface or previous coats of paint and form raised blisters. Blistering is caused by small pockets of air, gases or liquids which become entrapped beneath the paint film, and often occur when vapour pressure builds up as the result of moisture in the surface being subjected to heat (such as exposure to the sun). Blisters on painted wood may also result from resin being exuded from knots and resinous areas during hot weather. The best way to remove blistered paint is by burning off the coating, especially where moisture Is a factor, as immediate evaporation will result in quicker drying out in-depth. After burning, the areas must be sanded smooth and re-primed. Blooming / Cratering Blooming appears as a milky or misty film which is particularly visible on deeper colours of gloss paints. Whilst it may be difficult to determine the exact cause of blooming, atmospheric changes during a critical stage of drying are often a factor. To overcome this problem, the "bloom" should be washed with a detergent solution and then leathered off dry. If blooming occurs again later in the life of tile paint, due to atmospheric pollution, this procedure should again be followed.
Brushmarking is visible mainly in high gloss finishes. Although the marking is usually in the undercoat or primer, it may not be seen until tile gloss finish has been applied, when it is too late for an easy remedy. Brushmarks can be minimised by careful application of undercoats and primers. With solvent based paints, should the material have thickened up due to solvent loss, slight thinning will help minimise brushmarking. With water based paints, brushmarking can be the result of overbrushing or inadequate thinning, particularly on highly absorbent surfaces. The only effective remedy for unacceptable brushmarking is to rub down the surface and repaint. Chalking Chalking refers to the powdery residues which form on a paint finish when the surface begins to erode from exposure to the weather. Unless this occurs prematurely, chalking is not usually considered to be a defect. Fine
residues of chalking can usually be removed by wiping the surface
with a damp cloth, revealing a sound paint surface of good appearance.
Heavy residues, due to ineffective In the event of bad chalking, the surface should be brushed down thoroughly with a stiff fibre brush to remove all powdering particles, and then primed with one coat of Bonding Liquid to seal the surface. Cissing Cissing occurs when a fresh coat of paint fails to form a continuous film, exposing the surface or previous paint coatings in places. This occurs most frequently when water based paints are applied over solvent based paints which are contaminated in some way or contain water rejecting components such as wax, grease, or silicones. Special care should always be taken to remove hand grease from the vicinity of handles and switches, as well as floor polish or wax residues from bottom edges of doors, skirtings, etc.
Condensation Condensation occurs when warm moist air comes into contact with a cooler surface, forming moisture deposits. Adequate ventilation will usually correct the situation, however in view of varying conditions there is no standard approach to this problem. In the presence of slight condensation a good quality water based coating will usually be unaffected. However, should the degree of condensation be such that existing water based paints are showing unsightly stains or flaking, then application of a solvent based system is advisable. Because solvent based systems are relatively impervious to moisture, any moisture condensation on the paint film will not be absorbed into the surface - whilst the condensation problem is uncured, a surface has been provided which can resist damage as it is easily wiped dry and maintained in sound condition. Corrosion Metal corrosion costs the country many millions of rands every year. Most forms of iron and steel tend to revert to their oxides by gradual combination with oxygen and moisture to form rust. Iron and steel are subject to corrosion from the moment of manufacture; blue millscale forms on steel during the manufacturing process as a result of the iron being subjected to very high Rust and millscale must be removed from steel before painting if adequate protection is to be achieved. Non-ferrous metals such as galvanised iron, aluminium and aluminium alloys, although much less prone to corrosion than iron and steel, also react with atmospheric contaminants. Deterioration is in the form of an oxide deposit on the surface which can normally be removed with fine abrasive paper.
Crocodiling
is the term used to describe the more extreme forms of cracking.
This defect is caused mainly by hard drying paint being applied
over a soft and elastic paint film. Efflorescence Efflorescence is the term used to describe the white crystalline substances which often form on plaster, brickwork and other building surfaces. They result from the evaporation of water from the soluble salt solutions which are carried to the surface during the drying out of the structure. These white deposits should be removed by brushing off as they become visible, and the process repeated at regular intervals until their formation on the surface ceases. Painting should not be carried out until this stage has been reached. Efflorescence can also occur on old surfaces should the structure become wet, and in these cases the only remedy is to locate the point of water penetration and effect a cure. The damaged area must then be allowed to dry out thoroughly before repainting can be safely carried out. Efflorescence may also result in blisters or nodules in the paint film without any visible salts. efflorescent salts may also become attached to the back of a paint film, causing no visible disruption but weakening adhesion. Flaking / Peeling Flaking or peeling is the result of the splitting and subsequent lifting of paint coat or system, due to loss of adhesion. This may be due to one of the following causes: - moisture penetration into wood, causing movement which cannot be tolerated by the paint system. - paint
being applied to a chalking or powdering surface where adhesion
is poor
- paints of a porous nature being subjected to severe and frequent wetting and drying out the resultant expansion and contraction of the paint film eventually weakens adhesion and results in flaking/peeling Flaking or peeling paint and adjacent areas of suspected weakly adhering paint should be completely removed. When repainting, care must be taken in providing a clean, dry surface and the correct sealers and primers must be used. Grinning-Through Grinning-through refers to the underlying surface coating showing through the finishing coat. This defect is caused by over-thinning or over-brushing the top coat, attempting too great a colour change in one application (e.g. white to black) or using an undercoat of the incorrect colour. The most effective treatment is to rub down the surface when hard and apply an additional finishing coat. Lifting / Picking-up The lifting or picking-up of a previous coating during application of a new coat, producing a wrinkled finish. The principal cause of this problem is applying the top coat before the previous coat has fully dried, or applying a paint containing powerful solvents over a coating which is not resistant to the solvents. The remedy is to completely strip the applied paint and when re-coating, to ensure that complete drying has taken place and that compatible coatings are used. Loss of Gloss (Sleepiness / Matting) The early loss or deterioration of gloss is usually caused by either adverse weather conditions quickly following application (particularly during fog or cold mist when moisture condenses on the paint) by application of the paint over a porous undercoat or through use of the incorrect thinner. The only effective remedy for this problem is to rub down the surface and re-coat.
Mould, fungus, algae, moss and lichen growths which appear on a number of surfaces are referred to as organic growth. This growth is promoted by dampness, poor ventilation and condensation, and multiplies and feeds on the organic matter in paints, papers, pastes and surface deposits. The only remedy for-this defect is complete removal of the growth by scraping and brushing, followed by sterilisation of the infected areas with Bio-Fungicide. Pinholing Pinholing
is the term used to describe the formation of minute holes in a
newly applied paint Should
the pinholes affect only the top coat the surface should be rubbed
down and re-coated, however. if other coatings have also been penetrated,
these must be stripped and the paint Retarded Drying Retarded
drying of paint is often caused by one of the following factors: _ the addition of unsuitable thinners to the paint - applying paint over a previous coat which is not fully dry painting under adverse conditions when moisture may condense on the surface. Drying problems are considerably reduced when paint is applied to clean, dry surfaces under favourable weather conditions. Whilst each product data sheet in this manual states drying times of the various paint types, it should always be remembered that drying times do vary with temperature and relative humidity.
This problem is defined as an uneven paint film which flows down the vertical surface, along which wrinkling normally follows. The major cause is over-application of the paint or lazy brushwork with insufficient effort to properly spread the paint. The remedy for this problem is to allow the paint to dry thoroughly (remembering that the thick sags will take longer than normal), rub down to a level surface and re-coat. Saponification Saponification refers to the reaction between the oils in oleo-resinous paints and alkali in cement based building materials. In mild cases this will cause the paint to become sticky and discoloured, whereas in serious cases the paint may become completely dissolved in a soap-like substance. This problem is caused by applying oil based paints to new surfaces containing alkali, or surfaces which are likely to be splashed by alkali solutions. The only treatment is to completely remove the faulty paint film, thoroughly wash down and apply a coat of Alkali Resistant Sealer before applying oleo-resinous paints. Alternatively, an alkali resistant finish coat can be used - e.g. emulsion paints, chlorinated rubber or epoxy based paints. Sheariness / Flashing Sheariness refers to the variation of sheen or gloss on a surface. This is often the result of over-brushing, failure to join up quickly enough to a partially dry area of paint, or applying paint to a previous coating which has not dried sufficiently hard. A sheary result can also occur when paint is applied to an unevenly porous surface, and in this Instance, the surface should be primed with a thin sealing coat of the finishing material. Sinking-in Sinking in refers to the loss of gloss or sheen due to the medium from a finishing coat of paint being absorbed into a porous surface. To counter this problem, a thin sealing coat of the finishing material should be applied prior to the finishing coat.
Wrinkling of a paint coating is caused by the paint having been applied too thickly. The surface of the paint dries to form a skin while the under surface area remains in a soft, semi-dry state for a considerable time. This results in movement within the paint film and the resultant stresses cause the top skin to wrinkle. Depending on the depth of the wrinkling, rubbing down when the paint film is hard enough may be sufficient before re-coating, otherwise complete removal will be necessary.
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