Obviously the smoother the surface the less build up of paint required:
Synthetic paint consists of the following to make the paint medium:
The early natural types of pigment were earth pigments, umbers, yellow ochre or sienna.
Lead was once used as the main ingredient in paint, nowadays it is more likely to be found in glazes or ceramics, although lead paint can still be purchased for use on listed buildings.
The pigment solid is suspended in a fluid vehicle that does not dissolve. Oil based paint and varnish dry slowly by oxidation when exposed to oxygen which is when the oil and oxygen combine leading to a hard dry skin.
Modern resin based synthetics: Alkyd for example dry by a process called polymerisation which is a chemical reaction where molecules join together forming one component as the resin and the simultaneous evaporation of solvents (usually turpentine) take place.
It is worth noting that to obtain optimum performance from any paint material (if possible) the paint should be applied at room temperature 68°-72° Fahrenheit 21°-23° Celsius, This temperature not only ensures correct drying and application time it also allows moisture to evaporate completely.
Two finely applied thin coats are much better than one heavily applied thick coat that may give a rough brushy appearance.
The term primer has become a much misused name to describe a primer coating, Primer is a primary or foundation coat offering the first layer of protection prior to building up subsequent paint layers.
There are several synthetic primers suitable for steel as follows:
Primers are generally porous because they lack oil which is what provides the protection from the environment, Synthetic primer should be painted over as soon as possible preferably within a fortnight otherwise it will become too hard and will not allow itself to become part of the paint system.
Aluminium which is described as an oily metal in terms of painting requires etch priming to provide a suitable key to promote paint adhesion.
Aluminium (or Birmabright used on Land Rover) is classed as a reactive metal and like iron it reacts with oxygen causing surface corrosion. Aluminium left in its bare metal state corrodes producing aluminium oxide which is a form of corrosion that will completely cover the surface and yet to some degree protects it from further corrosion. This white aluminium oxide powder formed on bare aluminium can be scraped off, which will lead to further corrosion because the oxide is naturally weak having little or no strength. This process is called anodising.
However anodising aluminium, by an electro chemical process for example, physically alters the metal surface and produces a really tough dense layer of oxide offering maximum protection to bare aluminium.
Sealers or barrier coats are designed to isolate paint substrate reactions from volatile solvents. An example would be if you wanted to spray cellulose over a synthetic base you simply apply a sealer coat first so that when cellulose is applied over the sealer coat because it has isolated the synthetic substrate, so the strong volatile nitro-cellulose thinners will not be able to attack or soften the synthetic substrate.
Iron ore in its natural state does not rust. The rusting process only starts after being wrought when the ore is converted into iron or steel, which is then susceptible to rusting caused by moisture. When the metal is exposed to moisture the rust or ferrous coating, which forms on bare metal as a reddish coating, must be treated immediately to prolong the conversion. Halting or at least slowing down the conversion process is achieved by applying a primer coat initially then subsequent coats of various paints in a bid to improve long term protection from the elements.
However if the surface has become deeply pitted in rust the best way to deal with it is to have the area sandblasted and then use one of the many phosphoric rust converters on the market, which will neutralise rust and keep the metal free from ferrous oxide for a considerable amount of time.
Severely rusted areas that compromise the overall strength of a panel should be cut out and a new section welded in situ. This procedure may be beyond the scope of the average DIY person who is perhaps intent only on providing a vehicle with a repaint without wishing to perform more than just cosmetic paint repairs.
To provide a good base on wood (after rubbing down the surface ready for paint and before any paint is applied) the surface should be wiped over with a solution of boiled linseed oil, goldsize and turpentine or white spirit. The solution should be rubbed well into the grain, impregnating the wood fibres, or until it becomes dispersed and when dry it will prevent the wood grain from raising when further coats are applied on top.
The traditional way of filling the grain of wood was with a knifing filler or brushing filler. Modern methods use a premixed or powdered decorators type filler for wood obtainable at hardware or paint outlets.
Polyester filler should be used on metal but it is a harder filler.
When rubbing with a rag or single piece of wet-or-dry your hand must rub in a sideways direction. Rubbing in a forward or backwards direction produces unwanted finger-marks that will show as furrows.
When the rubbing down is finished it should be washed off with clean water and thoroughly dried with a chamois leather and allowed ample time for the moisture to evaporate completely. It is recommended to leave areas that have been wet flatted overnight to thoroughly dry otherwise moisture may cause blistering or peeling to subsequent coats. Initially it is quite practical to rinse bare metal with hot water because this will heat the metal and increase moisture evaporation.
Waterproof rubbing down paper called wet-or-dry is ideal for rubbing as opposed to the old traditional method of pumice stone or cuttlefish bone and it comes in many different grades for almost every surface.
During the rubbing process, copious amounts of water must be used to keep the area clean from rubbing slush which, if left to build up, will result in scratching to the surface. The rubbing slush should not be allowed to dry on the surface-it must always be washed off and leathered dry as it contains salts or alkaline. The dried flatting water or sludge can be difficult to remove and may scratch the surface whilst attempting to wash or rub it off.
A propriety panel-wipe or pre-wipe is a very rapid-drying degreasing solvent that should be used to clean and inspect flatted areas just prior to paint, removing any contamination (including fingerprints) that can cause adhesion problems.
To obtain the finest quality work it may be necessary to apply filler to certain areas: usually low spots or deep scratches.
Do not confuse the term rubbing down with polishing.
The task of rubbing down requires a moderate amount of skill or the surface may become damaged by rubbing too hard or choosing the wrong grade of wet-or-dry paper. Older paint surfaces are generally harder to rub down and will need extra care when choosing the correct grade of rubbing paper in order to rub down properly.
Cuttlefish bone, pumice stone and pumice powder were the traditional rubbing mediums used on synthetic based paint or varnish before wet-or-dry paper was invented. Cuttlefish bone in particular was less likely to damage a paint surface because of its natural soft composition but it requires preparation before use.
Rottenstone is derived from decaying limestone (hence the name) and was used initially to polish wood finishes. However it can also be used to polish synthetic finishes providing the paint film has thoroughly dried or cured. Oil lubricants (linseed oil or tung oil, also known as China oil, for example) can be used with rottenstone on a piece of cotton wool or felt pad.
Various grades of wet-or-dry grit are available ranging from very coarse to very fine. Low numbers represent coarse grit, high numbers represent fine grit.
Production paper however must be used dry and its purpose is mainly for use on filler or very rough paint areas that require machine rubbing.
The number corresponds to the grade of grit per inch so a typical 180 grade would produce far more visible scratches per inch than an 800 grit.
Rubbing down with any grit produces scratches than can be measured by the number or type of grade used. The finest grade of paper produces tiny fine scratches, unseen by the naked eye, whereas coarse papers will produce deep wide scratches easily seen with the naked eye.
When a particularly old painted or varnish surface is peeling, blistering, cracked or simply just perished it has to be removed completely whether on wood or a metal surface.
Paint consisting of linseed oil visibly ages usually after five years when the substrate becomes chalky. Modern paints now tend to use alkyds and acrylic resins as opposed to traditional linseed oil.
Application of undercoats and colours:
The application is probably the most important quality because the material has to spread evenly and hold up without forming runs or sags.
Do not stir varnish or paint too vigorously or bubbles will form that can be transferred to the object being painted and ruin the finish by creating air bubbles that may not flow out properly.
Brush-marks are the most likely cause in spoiling a finish and should be kept to a minimum. This can be achieved by using only finely ground pigments thinned with turpentine to a suitable consistency before being applied. Camel hair is the softest type of bristle and can be best used in the application of heavy pigmented undercoat to reduce brush-marks.
If an undercoat is found to set too fast to allow laying off then it should be layed off as you go without any further laying off in a criss-cross way. Once a finish starts to pull or drag on the brush it is unlikely to flow out properly and should be left to set.
Certain colours actually increase brush-marks as they dry and this may be due to thinning with white spirit. This ploughed field effect is more noticeable at the point where the bristle has touched the surface, leaving the paint film somewhat thinner at the low furrows than at the higher ridges. The remedy is to use a slower drying turpentine instead.
Quick setting paints should be applied in vertical strokes or strips, with each full stroke performed in a wavy fashion to blend into the previous stroke, without horizontally crossing and keeping the edge wet in a steady downward direction.
Some colours tend to float, greens and blues in particular. This is when a pigment raises to the surface during application, changing the colour slightly, which usually shows as darker streaks and can sometimes be seen as each brush-stroke is drawn across the surface. A substrate suffering from pigment floatation will look similar to a zebra crossing only the stripes will be coloured.
Floating can usually be cured by extending the open time, for example by adding a little turpentine or raw linseed oil, allowing the material to spread thinner and more evenly and thereby reducing flotation.
The finished gloss surface should be completely free from seediness. Seediness is when a coloured film has dried after solvent evaporation leaving behind a sandy finish which is actually caused by a coarse pigment. Coarse pigments are associated with cheaper paints where the pigment has not been ground finely enough.
Most colours can be wet flatted, this may be required on certain colours when a varnishing coat is necessary to provide optimum durability (although this usually applies to reds and greens).
It may be necessary to apply more than one coat of colour (especially if a good wet flatting is required prior to varnish) to ensure a solid all over colour. It is quite common in the trade to wet flat a colour and then apply varnish over the top.
The theory behind the painting process is to build up a series of paint layers which become hard yet still remain flexible.
The finishing coat, either gloss or varnish, should be the most flexible to sustain the influence of what the environment can thrust upon it.
Runs or Sags:
These are caused by too much paint material being applied. Temperature can also affect drying times which can lead to runs or sags because the paint is allowed to stay wet too long and will start to slip off the surface.
Sinkages usually occur after a few months have elapsed and may be due to the whole paint system failing as a result of continued shrinking,
Blistering or peeling:
This is usually caused by trapped moisture which when heated by sunlight will expand and burst through the substrate in the form of blisters.
Do not brush the floor prior to painting final gloss or varnish as dust will be introduced into the atmosphere which will settle on paintwork and spoil the finish.
Varnish should be applied with a Namel-Var brush designed specifically for applying varnish and the task of varnishing should be carried out on a warm, dry, still day with no wind.
The Hamilton traditional oval shape Namel-Var brush is ideal for use on concave and convex surfaces. Extra long seamless steel ferrule consisting of an extra thick head of 100% selected pure black China bristles which gives maximum pick-up and is perfectly suited for woodstains and varnish.
Polyurethane varnish in normal conditions dries in about eight hours or less and is not always suitable for quality brush work. In my opinion polyurethane is more suited to varnishing floorboards or less quality work.
A good quality coach varnish should have a low viscosity, full body, flow out freely and be hard enough to flat down in about sixteen hours.
Paint or varnish can be successfully strained through a piece of nylon stocking into a purpose-made paint kettle. The stocking can be cut into lengths of approximately six inches with a knot tied at one end then turned inside out so the knot is in the inside as you pull the cut piece of nylon right over the paint kettle.
Long oils have a longer open window than short oils and this applies to both paint and varnish. The longer the open time the greater chance of a good flow out and the easier it will be to remove bristles or flies, and if picking out straight away with the edge of your brush the painted area will still flow out.
Oil provides elasticity and life to a paint but must be strengthened by gum resin or rosin. There are various grades of gum resins ranging from soft to hard.
During the paint manufacturing process it is generally noted that resins which melt at low temperatures are used in cheaper, lower quality varnishes. Resins melting at higher temperatures, that take longer, are the type used in top quality expensive varnish ideally suited as a finishing vehicle or carriage varnish.
Poor quality varnish will appear sandy or have a dusty finish when dry This is caused by metallic stearate sediment on the bottom of the varnish were the material has not been processed thoroughly.
It is advisable not to shake the contents of varnish because this not only mixes unwanted sediment (if present) back into the varnish but also introduces air bubbles.
It may be an advantage to apply paint or varnish to a test panel first to see how it performs before attempting to varnish a large area. The simple test panel however must be in the same state of preparation as the intended panel work to ensure a comparable working surface with regard to porosity, suction, etc. It should also be painted at the same temperature.
Polishing with rottenstone or pumice:
Use moderate pressure when rubbing with the felt pad in straight strokes, checking frequently as you go to avoid rub through. Continue rubbing until you obtain the level of gloss required: this can range between matt, semi-gloss and full-gloss depending on the amount of rubbing or the grade of powder used.
When painting or varnishing the amount of dust floating about in the working atmosphere is not always noticeable but note should be made that sunlight can pick out minute particles and these particles will inevitably fall onto paintwork, spoiling the finish.
The condition of the surface to be painted will play an important part in how the finish will look: the porosity, type of undercoat used, roughness of surface, even the colour can affect the overall finish.
Too much drier can spoil the paint or varnish. It is strongly recommended to only apply the correct percentage of drier when adding to paint material. An overdose of driers can undermine adhesion and damage the finish.
Terebene is a concentrated liquid form of drier where the principal components manganese or cobalt are dissolved in linseed oil and thinned with turpentine, which can be added to oil paint or varnish.
Turpentine is a commonly known dilutent for synthetic oil based paint but should also be noted for its other lesser-known properties.
Adding copious amounts of turpentine in an attempt to ease out thick paint only increases the drying time, it does NOT reduce it.
However turpentine substitutes and white spirits will shorten the drying process, not necessarily increase it, and although white spirit can be used to thin primers or undercoats it should not be used to thin gloss enamels or varnish as it will disintegrate the resins.
It is false economy to buy a cheap brush-especially when you have spent a considerable amount of time on preparation only to have it spoilt by the poor performance of a brush. It is always best to purchase the most expensive brush, leaving you safe in the knowledge that this is one factor you do not have to worry about with regards to performance.
A Namel-Var brush contains soft pliable bristles perfect for spreading the lighter varnishes across panel work.
Enamel or gloss brushes contain hog or china hair which has a stronger bristle for spreading the harder to spread gloss across the surface.
A paint brush is by far the most important item in producing a finish and its quality will reflect this.
Stand the brush upright on its bristles and push down firmly at the tip of the handle using the palm of your hand (thus bending the bristles at almost 45 degree angle) then release the pressure and the brush should immediately spring back into position with considerable force from the bristles.
Usually paint brushes are cleaned in turpentine or white spirit if oil-based and warm water if emulsion. Either way they should also be washed out in soap and water allowed to dry thoroughly.
A brush should be stored in its original wrapper which keeps the bristles clean and helps retain the shape of the brush. The brush can also be stored in a plastic bag or container to prevent moths from laying eggs so that their grubs will not eat the bristle.
Oil paint can be quite difficult to remove as it dries because it is not resoluble and sometimes it has to be scraped off the bristles. Hardened paint can often be left in the stock: this is one reason why a brush should not be wiped over the edge of a paint kettle because it forces paint into the stock making it difficult to remove if left to harden.
A brush should only be charged with paint material by dipping in the paint and dabbing the brush on the inside of a paint kettle keeping the paint material at the tip of the brush rather than the stock or ferrule.
Oil paint and varnish, although not resoluble in their own solvent (which is turpentine) can be dissolved in solvent brush cleaners, but I prefer to use my own solution of cellulose thinners and turpentine mixed at 75% turpentine, 25% cellulose. This mixed solution is still powerful enough to dissolve hard oil paint but will not damage delicate bristle. The turpentine or white spirit will neutralise some of the powerful strength of cellulose thinners that can make the bristles go floppy or even rot if left standing in neat cellulose for too long.
Mineral naphtha is better than cellulose but it may be harder to source because cellulose is more readily available.
Primers and undercoats are usually very heavy in pigment and difficult to spread. They therefore require a firm brush that can push the paint evenly across a panel. Varnish on the other hand, being a lighter substance, only requires a soft brush to spread the substance evenly (like a Namel-Var varnish brush).
Gloss and varnish finishes form a continuous solid film when dry but are liable to skin dry, which means the outer exposed surface has dried but the surface underneath remains soft. Skin drying prevents oxygen from reaching the inner layer and is usually caused by an overdose of driers-this is more likely to occur on long oils which contain a higher percentage of oil.
Colours can alter on their own even if kept in dark places and when a colour is varnished it might tint a little towards yellow.
White pigment increases opacity and helps resist UV radiation.
Cellulose is a completely different material from the conventional air-drying synthetic oil-base materials.
Cellulose or nitro-cellulose dries by evaporation of a spirit solvent, not by the oxidation process (as do synthetic oil-based paint and varnishes).
Because cellulose dries very rapidly it should be applied by spray gun to obtain the best result. A decent brush application is not possible except on very small limited areas.
The spraying process is classed as semi-skilled although preparation requires real skill.
As with any proposed paint application, preparation is absolutely vital and must be thorough. There must be no trace of any foreign body on the surface, such as dust or grease. Metal in particular should not be over- handled-even your fingerprints can cause adhesion problems. This is more apparent with cellulose paint systems than oil paint or varnishes.
Paint has been used for thousands of years and has been recognised for the following three purposes: Decoration, preservation and sanitation.
Decoration goes back as far as the stone age with evidence of cave painting.
Preservation was particularly important during the early 17th century for protecting wooden carriage work and architecture.
Sanitation was more of priority in hospitals where painted surfaces can easily be cleaned with a simple wash down but exposed wooden areas for example would harbour dirt and germs etc.
White lead powder (lead carbonate) was once the main ingredient in paint manufacture and paint originally contained more than 75% white lead.
Flatting down can often expose inner paint layers or bare metal, particularly if the paint area has been repaired or simply through removing rust. These areas will require extra attention prior to repainting by flatting or feathering back. This process is necessary to make good a repaired area by feathering down the surrounding area so that the hollow of a repair will be blended in to the thickness of the paint edge.
This is simply a way to flat down an area with wet-or-dry abrasive paper. Water lubricates the paper and eliminates dust.
Rust is a prime concern on panels whether it be surface or ingrained. Sand blasting is an ideal method of removing light or deep pitted rust because the small particles of sand will get deep down into the rusted area, almost completely removing the rust, leaving a clean dull area ready for treatment with a proprietary brand of phosphorus rust treatment and then primer etc.
This is a method of applying a contrasting colour to the substrate very lightly to use as a guide when flatting, very useful for showing low spots or other paint defects that may require further rectification or stopping.
If you do not have access to spray equipment or aerosols there is another, perhaps preferable method of applying a guide coat called Dry Guide Coat, made by 3M. This is a cartridge that contains a powder which you simply wipe over the substrate with the supplied applicator pad.
Bleed through is a term describing a saturation in which the colour underneath can still be seen, even through the substrate has been painted over, For example, red painted over in white would reveal a pinkish colour underneath-even after several applications the colour can still bleed through. The preventative measure is to isolate the red or yellow colour first by applying a barrier or sealing coat before applying the colour white.
Bare metal can often hold contaminants even when it appears clean. Such contaminants can undermine the adhesion or durability of the paint which is why OEM panels go through a matriculate six stage cleansing process to prevent corrosion. The main ingredient is phosphoric acid which removes all traces of oil, grease, fingerprints, residues and rust. Phosphoric acid also etches into the bare metal providing maximum adhesion for subsequent paint layers.
The paint process on OEM panels is called electro phoretic and in most cases this finish should be left intact unless it has been damaged.
Primary, Secondary and Tertiary colours:
Primary ColoursTheoretically there are only three colours : Red, Yellow and Blue, all other colours are made from these three.
Two primary colours mixed together will produce a secondary colour: Orange, Green and Purple.
Primary colours cannot be created by mixing other colours.
Secondary coloursProduced by mixing two primary colours. The secondary colour is halfway between the two primaries. Mixing Red with Yellow will produce Orange, Mixing Yellow with Blue will produce Green and mixing Red with Blue will produce Purple.
Tertiary coloursColours produced by mixing a primary colour with one of its secondary colours. Mixing Red with Orange produces a Red Orange. Mixing Blue with Green produces a Blue Green. Mixing Yellow with Orange produces a Yellow Orange.
A greater variety of colours can be achieved by varying quantities of the primary colours, for example;
To make a clean bright orange the red must lean towards yellow and the yellow must lean towards red. If the red contains blue or the yellow contains blue the resulting orange will be dull because a small portion of the blue primary colour has been added which reduces the purity and brightness of the secondary colour being produced.
It has been said that black and white are the negative and positive of colour.
Back to TOP