Understanding the difference between a stain and a varnish means knowing when to use one or the other to achieve the finish you are looking for.
Here we explain the characteristics and differences of each material so that you can see when and why to use them.
We will also show you how to properly apply stain or varnish with a spray gun.
Stain or varnish: how to choose?
Both types of paint are fluid and are generally intended for woodworking.
However, they have their own distinct specificities, which should appeal to you depending on the protection and finish you wish to achieve.
Characteristics of varnish
In essence, varnish is a paint without pigment.
The majority are polyurethane and solvent-based resins (like oil paints).
Acrylic varnishes, although water-based, are becoming increasingly popular because of their environmental and health benefits.
As with most paints, there are three main ingredients in this material:
This is the ingredient that will harden under the effect of air to form the protective layer that constitutes a varnish.
The variation in the proportion (and types) of oil to resin affects the properties of the varnish.
This can range from glossy, hard (but brittle) varnishes used on furniture to softer, flexible, weather-resistant varnishes that are better suited to outdoor use.
The choice of oil will affect the eventual appearance of the varnish. Some oils may have a certain colour that will tint the varnish.
The gloss of the varnish will be determined by the oil, although additives can be added to reduce the gloss effect.
This is the component that adds strength and body to the finished varnish.
There is a wide range of compounds from natural products (tree resins or insect secretions) to organic chemicals (polymers and plastics) that are used as varnish resins.
Like oil, the choice of resin can affect the varnish, so resins that do not colour the varnish are preferred.
How they react or act with the oil will affect the properties of the final product.
The thinner (or solvent)
This is the ingredient that dilutes the oils and resins to allow the varnish to be applied easily.
Once the varnish is applied, the thinner must evaporate and allow the resin and oils to solidify.
The thinner may be a solvent (e.g. white spirit), although water may be used in some coatings.
Characteristics of the stain
This material is similar to paint.
It is designed to colour the wood but does not leave a protective film as it is designed to be absorbed by the substrate.
As the stain is absorbed, this means that the wood grain will be visible through the colour, and the extent of this absorption depends largely on the opacity of the stain pigment.
Like varnishes, a conventional stain is made up of three ingredients:
This is the ingredient that gives the colour.
Suspension pigments are large molecules, which do not penetrate intensely into the wood structure, making them more opaque.
The colour range is generally from browns to woody effects, although there are very colourful stains that have nothing to do with brown.
This is the ingredient that brings the pigment or stain into the substrate.
When it evaporates, it leaves the pigment or stain in the grain, accentuating it and leaving the colour of the wood close to its natural state.
Unlike conventional paints, the binder is a very small part of the ingredients but is always present.
It helps to retain the pigment in the wood once the stain is applied.
Stain or varnish: what are the differences between these two materials?
The main difference is that the varnish combines a transparent polyurethane with wood protection. It adds rich colour to wood while protecting it with a highly durable clear finish.
Designed with superior clarity, varnish enhances the natural grain characteristics of the wood and intensifies furniture and interior woodwork with rich, classic tones.
Stain, on the other hand, is mainly used for exterior or construction wood, which is subject to the elements. It is water-repellent and microporous, preventing water penetration while allowing the wood to breathe.
How do I apply a stain or varnish with a spray gun?
Every good varnishing job starts with a good base.
Regardless of the age of your wood, you can follow these steps for preparation and application:
1. Remove dust and any rough fragments. Remember to wear a mask for paint spraying and appropriate clothing.
2. Sand the wooden surfaces until they are smooth. If possible, perform this step outdoors to minimise dust in your work area (if you do not have a ventilation system with exhaust).
3. Dust the wood with a clean, dry brush.
4. Clean your workspace. This step is particularly important so that no dust will stick to your fresh paint afterwards.
5. Use a clean, damp cloth to clean the area to be painted.
6. Allow the area to dry for a few hours before applying your coating.
Video of mechanised application
In the following video, you can see an example of work with an Aircoat pump : the Wagner SuperFinish SF 23 Plus AirCoat
The model of pump used, the paint as well as the necessary accessories are all indicated in the link above.
In general, we recommend the use of a compressed air system, otherwise known as Aircoat, for carpentry work.
With this method, the transfer rate increases and the formation of paint mist is even lower than with airless.
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