Finding Faults in Paintwork: Terms Used In Painting
Paint finishes are often marred by faults in technique, poor surfaces, inadequate or incorrect preparation. Recognising the likely flaws in painting, described in this article’s glossary of faults, will help you to achieve better results. It is also essential to choose the right paint for the work in hand.
A lid should be replaced firmly on a paint tin, or a skin may form. Use the foot or a block of wood to exert an even pressure to shut the tin. Avoid distorting the lid, or air may enter and skin will form. All paint should be kept airtight, to prevent skinning.
Bristles should always be cleaned thoroughly. If you have been using an oil-based paint, white spirit or a proprietary brush cleaner will be satisfactory. Paraffin can be used, but take care to see that the bristles are completely paraffin-free, since this, left in the bristles, could slow down the drying time of future paintwork.
If you are merely stopping work overnight, the brushes may be stood in white spirit. A word of warning-do not let the brush rest on the bristle tips. Sediment will collect at the bottom of the kettle and clog the bristles.
Terms used in painting
Cutting in is the technique of painting up to an adjoining surface. This is done where walls of different colours meet, at the edges of cupboards or round window frames and doors. To achieve a straight edge, use a 25mm brush in which the bristles are worn at an angle, or a special, angled ‘cutting-in’ brush. Charge the brush with paint but do not overload it. Remove excess paint by touching the bristles lightly against the side of the container.
Draw the brush down in one continuous movement, steadying the heel of the hand against the clear surface. Masking tape can be used to prevent paint from spreading on to an adjacent surface, but remove it before the paint has dried.
Apply paint in one direction with carefully controlled strokes, lifting the brush gently at the end of the stroke. You should not need to recharge the brush during this, though sometimes a little extra paint on the brush may aid the laying off. Laying off helps to avoid brush marks, to achieve an even flow, and to eliminate runs or curtaining on the surface.
The wet edge is the furthest edge of the area being painted. When the next section is painted, the two edges are merged together, without dragging, to avoid a demarcation line. Quick-drying paints restrict the amount of paint that can be applied at one time. If the paint is fast drying, do not work to a wet edge. Apply the first coat in one direction; the next in the other direction. Work across the grain for the first coat, and with the grain for the second.
Small pimples on the surface caused by dust or particles of paint skin in the finish coat. Rub down with fine glass-paper and apply a further coat of fresh paint.
The premature fading of new paint caused by fumes which attack ultramarine. The cure is to remove the source of the fumes or change the colour. Alkali salts, merging through new plaster, also cause bleaching. Use an alkali-resistant paint to allow the plaster to ‘breathe’.
This occurs when a sub-layer of paint bleeds through the surface, causing staining of the top-coat. This may be caused by the reaction of the constituents of old paint with new, if, for example, oil-based paint is applied over a bituminous paint. To treat, rub down, apply a layer of stop-tar knotting, followed by a coat of aluminium primer, then repaint. Another cause is where inks used in a wallpaper design bleed through a covering paint. Strip the wallpaper to the plaster and repaint.
Small ‘blisters’ on the paint surface are caused by moisture which prevents adhesion between old and new paint layers.
This may be caused by painting on a moist surface, or in moist conditions, and can be remedied by scraping off the blistering and repainting in dry circumstances.
It is also caused by seepage of water along the grain of the wood from other areas. Remedy by sealing the weak spots. If caused by water seepage from poorly primed woodwork, adjacent to brickwork, seal the gaps between wall and frame with a mastic.
Blistering on new timber, painted for the first time, is treated by stripping the paint surface, glasspapering smooth and allowing the timber to dry out thoroughly before repainting.
Blistering may also be caused by resinous knots. Apply a patent knotting or cut out the knots, prime the holes, fill with hard-stopping, rub down, prime and repaint.
This is a whitish haze on the paint, or, more often, varnished surface, caused by a damp atmosphere or draught during drying. The remedy is to rub down with glasspaper and repaint in dry conditions. Blooming, after drying, is caused by a damp atmosphere. Rub down with a chamois leather. If this does not help, rub down with a mixture of raw linseed oil and vinegar.
Brush marks, which show in the form of ribs in the finished paint, may be caused by brushing out after the paint has started to dry or show through from an inadequately prepared undercoat. In both cases, rub down the surface and apply a new finish coat.
This is a white, powdery film on the surface, which powders as the paint film wears away, leaving the dry pigment. It can be rubbed down with a damp cloth and repainted. Chalking may also be caused by the porosity of the surface. Brush down, wash clean and apply an undercoating, adding a little linseed oil.
The formation of fine hair cracks or fissures in the paint surface. There are four causes:
• Where a hard-drying paint has been used on a wet or oily undercoat;
• Through painting over a sized surface;
• As a result of using quick-drying cellulose paint over an oil-based undercoat;
• Where a hard-drying paint was applied over a bituminous paint.
Minor blemishes can be cured by gently rubbing down the surface and repainting. Badly affected surfaces should be stripped to the bare wood, re-prepared and repainted.
This is an unstable surface condition, caused by alkaline salts affecting the paint surface. It can be remedied by using an alkali-resistant primer and paint. Use a porous paint, unless the surface is completely dry. It is also caused by too much linseed oil in the undercoat. The remedy is to strip the coats and repaint.
This generally occurs on varnished surfaces in the form of circular patches, drawn away from paint surfaces. It is caused by painting over a waxy surface; or painting an oldthat has not been roughened. In both cases, clean the surfaces with white spirit, and use abrasive paper to flatten the surface before repainting.
This is caused by alkaline salts, in the plaster or walls, reaching the surface and producing a white crystalline deposit. The remedy is to give the surface adequate time to dry out and then to apply an alkali-resistant primer and porous paint. Non-permeable decoration should be left until the wall has dried out.
A fatty-edge occurs where two paint coats, painted at different times, meet at an angled edge. The ridges must be rubbed down before repainting the whole surface.
Flaking is where paint falls away from the surface. It is often caused where there is dirt or moisture in the undercoat, size on the surface or where old paint has been inadequately removed. This may be remedied by stripping off the coat, cleaning and repainting in dry conditions.
Another cause is efflorescence. Strip down, allow to dry and apply an alkali-resistant primer and paint. Apply a porous paint unless the surface is completely dry.
Paint fatigue, where paint is used in rooms subject to high condensation, may also cause flaking. The paint film expands and contracts, and may be remedied by re-moving old paint and repainting with a porous paint.
Corrosion on metal surfaces, and rust breaking through the paint film, is another cause. To remedy, strip down the paint, apply a rust inhibitor, prime with a metal primer and repaint.
This occurs when stored paint turns to jelly. Tt is caused by frost or the addition of an unsuitable thinning agent. Paint affected in this way is useless and should be thrown away.
This is when the undercoat shows through the finish coat. It is caused by an undercoat of an unsuitable colour being used or by changing from a contrast colour too quickly-from a dark to a light colour. The remedy is either to strip off the paint, rub down and apply the correct coloured undercoat and top coat, or rub down and apply further finishing coats.
A condition where a new coat of paint pulls away from the surface. It is caused when the top coat has been applied to a still-wet undercoat, or where the solvent in the new coat affects the base coat.
It is possible to rub down the surface, touch in the parts that have lifted and apply a fresh finish coat.
These are gaps in the finishing coat, usually as a result of poor workmanship or through working in a poor light. The only remedy is to rub down and repaint the finish coat.
Mildew-mould-fungicide growths These occur in damp, humid areas. If mould appears on the surface, rub down the affected parts with a solution of one part of bleach to three parts of water, wash off and allow to dry before repainting. Repaint with fungicidal-resistant paint. Treat the underlying cause of the growth.
This describes a wrinkled appearance of a sprayed paint surface, caused by incorrect thinning of paint or paint applied at the wrong pressure. Treatment is to rub down and respray.
Pinholes are tiny holes in the paint surface and are caused by imprisoned air bubbles which expand with heat and then burst. This should be treated by rubbing down and recoating the entire surface. Where a quick-drying paint has been applied to a porous surface, the surface should be roughened and a sealer applied, followed by an undercoat and a finishing coat.
It may also be caused by oil or moisture in the air line of a spray gun. The paint coat should be removed and the surface resprayed.
Sags, runs or curtains
These are lines of paint or drips on a painted surface. There are four causes:
• A paint coat applied too thickly;
• Insufficient brushing out;
• A wet-edge left too long and starting to set before the next area is painted and the wet-edge picked up;
• Paint bristles catching on an irregularity and leaving a paint deposit.
In all cases the surface should be rubbed down until it is smooth and a finish coat applied.
A condition where the paint surface goes spongy. It is caused by the oil in the paint mixing with the alkaline salts present in the surface to produce a soapy solution. Treat by stripping down the paint coats and applying an alkali-resisting primer and then repaint.
Sheeriness occurs when gloss appears uneven, or there are glossy patches in a flat or eggshell finish. Five causes are:
• A surface with porous patches which has been painted over;
• Use of an unsuitable thinner which may cause uneven drying;
• Failure to keep the wet-edge when painting;
• Paint insufficiently stirred;
• Mixing resin and oil-based paints that do not ‘marry’.
The remedy is to roughen the surface and apply a fresh finishing coat.
Skin forms over paint when it is trapped in the can. Remove the skin-never attempt to stir it in-and reseal the lid of the tin tightly. A layer of white spirit can be floated over some paints to prevent skinning but care must be taken to see that the spirit does not mix with the paint.
Wrinkling occurs if the paint dries too quickly. It happens where paint coat is applied too thickly; when the sun is hot or where old putty is painted.
Treat by removing all paint, rub down the bare surface, then prime, undercoat, and apply a finish coat.
Paint may dry slowly for several reasons:
• Painting over an undercoat that is not completely dry or using an unsuitable thinner. The coat must be stripped and repainted;
• Painting in cold or damp conditions. Allow the paint to dry, then rub down if necessary and apply a finish coat;
• Paint applied over a dirty or greasy surface. The surface must be stripped and cleaned thoroughly before repainting.
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12. June 2012 by admin
Categories: Decorating, Painting | Tags: Bristle, Brush, Gloss, Oil paint, paint, sandpaper, Varnish, White spirit | Comments Off on Finding Faults in Paintwork: Terms Used In Painting