The main objective of a paint is to create a film once applied to a surface. There a number of reasons for doing needing this:
- Protection – paint will protect the surface below from weathering and ensure that it lasts longer
- Decoration – If a surface is drab or ugly, then we will use paint to make it more attractive or colourful
- Other uses – paints can be used to seal and make a surface more hygienic or they can be used for identification
Varnish is used for the same reasons as paints are, however it is generally used on wood, although it can be used on other materials if needed. Varnishes are transparent, although slightly coloured, so the texture and appearance of the wood will show through.
Unlike paints, stains (and to a lesser degree varnishes) are designed to penetrate the surface being coloured. As stains do not form a film on the surface they offer no protection and therefore are only used for decorative purposes.
For more information see our project that explains all about Varnishes and Stains.
Paints and What are They Made of?
Once the paint has been applied the film then has to do three things:
- Disguise the surface below
- It has to stay glued to the surface
- It must protect the surface below
This is achieved through the three main ingredients – The pigment, the binder and the carrier. Many paints will also have other additives too. We will look at these more closely here:
Pigment for Paints
The pigment provides the colour effects and hiding ability to the film. Traditionally these were minerals and earth minerals or derived from plants or other organic materials. For example the purple used in roman times was made from the mucus of a snail.
Since the industrial revolution, metal compounds, salts and synthetic pigments have been used, the most notorious is White Lead (lead carbonate), which has now been banned.
There has now been a resurgence in the use of natural pigments again as these are thought to provide a deeper and richer colour. You can see a range of suppliers of paints using natural pigments on our project about eco-friendly paints.
The pigment is added to the other ingredients of the paint, which hold it so that you can get an even coverage when you apply the paint.
The pigment is generally held in suspension, rather than solution, which means that it can “drop out” if the paint is left to stand too long. This is why you should thoroughly mix your paint immediately before use.
Binder in Paint
This has the job of binding all the particles together to form a continuous film when the paint dries and it also bonds the two surfaces together.
In more traditional paints, this used to be a natural substance such as glue size or linseed oil, depending on the paint type, but in today’s more modern paints this is usually synthetic resins such as alkyd, acrylic, vinyl or polyurethane.
As well as “sticking” the pigment to the surface that is being painted, the binder also will provide a layer of protection to the surface. It actually forms the hard film that provides the protection. It is often too thick or viscous to be applied to the surface and therefore needs to be thinned.
Carrier or Thinners
Also called the Solvent, this ingredient makes the paint flow very smoothly as it is applied to the surface being painted. As the paint dries this substance evaporates. This can be water or a solvent, depending on the type of binder that it is thinning.
The binder and the carrier together are sometimes called the Vehicle, as they are the “vehicle” that carries the pigment to the surface in an even and uniform coverage.
Most paints that you use for decorating and home improvement will be ready made and mixed. This means that there is no need to add a thinner to water them down before applying the paint – you just need to mix it thoroughly.
The exception to this is if you have to use a mist coat when painting a very porous surface which will suck the carrier straight out of the paint. This is most commonly needed when painting new plaster.
Additives for Paints
These are a wide variety of compounds and substances that can be added to the other three components of the paint to improve its various properties. While the other three components must be present, additives do not have to be used, although it is very uncommon for them not to be.
They do a huge range of things, for example, they make the paint easier to pour, quicker or slower drying, harder or water, rust and mildew-proof.
They can improve properties for withstanding UV (sun) light or adhesion to materials such as metal. And this is only a few of the properties that additives improve!
The main domestic paint types have different Vehicles (binders and carriers – see above). There are two basic types:
These are water based paints, where the carrier is water. When the water evaporates the paint dries.
The water-based paint types have the pigment and binder suspended in water as very tiny droplets. This tends to be a milk like, emulsion and is aptly named “Emulsion” (In the USA this is usually referred to as Latex paint, we understand). As the water begins to evaporate the droplets coalesce and form the film of the paint.
Modern emulsion paints have acrylic or vinyl resins added to them to make them perform better that traditional emulsion paints. This increase the sheen and hardness of the paint, making them more hardwearing.
Emulsion paints are generally used for internal decoration, such as for walls and ceilings, however there are specialist emulsions for wood and other materials now too.
These are paints where the binder is some type of oil. The carrier is then a solvent of some kind.
The solvent-based alkyd paints have the binder and pigment dissolved in a petroleum based solvent. These types of paint tend to take a lot longer to dry than the water-based paints (In the USA these are known simply as oil, or oil-based paints).
A characteristic of this paint type is the “painty” smell as it’s drying. Many people find this rather unpleasant.
With the great awareness at the moment concerning the growing health risks associated with the inhalation of solvents, these paint types are becoming rather unpopular.
Thixotropic, also known as non-drip, contains a range of additives to increase its performance. In this case the additives go towards allowing the user to load more paint onto a brush and a thicker paint film can be applied.
One coat of this type can often be sufficient.
Names Used to Describe Types of Paint
Over and above the two main types of paint, there are a number of common names that you will see on the tin in the merchants.
These names describe the level of gloss that the paint will have, ranging from Gloss to Matt. Here are some of the most commonly used paint descriptions:
- Gloss: Traditionally these would have always been oil based paints. They are the most hardwearing type and will need an undercoat. They are sometimes called “Liquid Gloss”. Polyurethane Gloss is an oil based gloss made using polyurethane, which makes an incredibly hardwearing finish
- Satinwood: This is slightly less glossy and therefore slightly less hardwearing that a full gloss paint
- Eggshell: This is not a gloss paint nor matt either, but somewhere in between. It is typically used for internal finishing in areas such as architrave and skirting
- Matt: This is a competently un-shiny finish which is ideal for walls and ceilings as there will be no reflection
The paints used for interior decoration are generally Vinyl Emulsion paints now. These are used for covering walls and ceilings and they have a range of finishes of their own:
- Silk: These have the highest sheen to them and are the most durable. They are typically used in areas with a higher than normal moisture content, such as a bathroom or kitchen, often with mildew suppressing additives
- Satin: These are less durable and have less sheen than the silk paints. These should be used on walls that might need to be washed down periodically
- Matt: This is completely non glossy and as a result will be a little less durable than the other versions. A matt paint does not reflect the light which is preferred on most walls, and it also hides any imperfections in the surface of the wall, as these are easier to see on a reflective surface
The application of one coat in most cases is never enough and a paint system must be applied to ensure that there are plenty of coats. The nature of the system often depends on the paint being applied and the surface being covered.
The first coat will be a sealer and will be used where necessary to seal the surface.
The second coat will be a primer, which will provide a good key for the paint film to adhere to.
The third coat will be an undercoat, which builds up the film to form a flexible, non-absorbent base of uniform colour, often very close to the fourth and final coat, the top coat, which provides the colour and actual finish.
You will often see dedicated primers and undercoats being sold either separately or as a combined primer and undercoat.
Using a single coat of combined primer and undercoat is never going to be as good as using separate ones, but often it is simply not needed. If you understand how the separate parts work, you will see why:
- Primer: As the name suggests, this paint is used to prime the surface that is going to be painted so that the paint will adhere to it. They stop the paint being absorbed by the material being painted. Primers are specific to the type of material; wood, metal, plaster, etc. It is possible to get an all purpose primer that will prime lots of different types of material. Check that it is suitable for what you want to paint as all purpose does not mean every type of material
- Undercoat: This is a coat painted under the finishing coat(s). They are generally used with oil paints, or if an existing surface is being repainted especially if it is a different colour. They provide a base colour so that the underlying colour will not show through the finished surface making it blotchy. It will be the same colour, or very near to the colour of the finishing or top coat
There are a range of specialist paints that are used around the home. Here are the most commonly used:
- Radiator Paint: These are for painting radiators and central heating pipe work, which get hot so you need a very durable paint which will not crack or discolour
- Fire Retardant Paints: These reduce the rate that fire will spread and should be used to protect structural elements (such as beams) to slow the rate of deterioration in case of fire, or to slow fire through your home, such as on doors. They are also known and Intumescent Paints
- Anti-condensation Paint: Specifically for bathrooms and kitchens where you are likely to have greater amounts of condensation, they are designed to maintain a slightly higher surface temperature so hopefully reducing the levels of condensation. Most will have a mould and mildew suppressant in them too. There are also paints that suppress mould growth (anti-mould paints), and paints that stop the stains from coming through when there has been a leak, although there is a clever trick to stopping these water stains reappearing which we explain in our project here
- Eco-Friendly Paints: These aren’t necessarily specialist paints, but concern for our health and the environment has driven an interest in these. Also as our understanding of how to make these paints improves, their performance is now as good as synthetic paints, and perhaps better particularly when it comes to the depth and richness of colour a natural pigment can achieve
- Masonry and Tiles Paints: Masonry paints will adhere to stone, brick and masonry much better than a normal paint. Step and Tile paints will be much more hard wearing. See our range of masonry and tile paints here
- Metal Paints: These are paints that are designed for use on metals. Metal offers a particularly smooth surface so it is important to ensure that the paint that you choose will adhere to it, hence using a specialist metal paint. Often with metal you will have rust, particularly when the iron is outdoors. In this instance you will need to consider using a specialist rust prevention paint. These can even be used to build up the pits created from rust damage as well as offering protection from more rust damage. There are a lot of different rust protection paints for use in different situations; see here for more details
There paints for almost every task and substrate being painted. It is worth researching which paint you should use for the job that you are doing.
Hopefully now, with a little understanding about the different types of paint available, you can choose the right paint for your next project more easily.
All project content written and produced by Mike Edwards