Airless paint spraying is basically a gun-like tool connected to a hose which is powered by an electric pump. The machine draws paint directly from the paint pot and produces a fine mist as you press the trigger.
Paint spraying is an excellent and cost effective method of painting large areas quickly but also dries to a perfectly smooth finish, unlike brushes and rollers. It is an incredible way to rapidly paint garden fences, external brickwork such as walls or houses, roofs, garage doors but can also be used internally to rapidly paint ceilings, walls and even woodwork. While there is a little preparation time involved in masking certain areas so they don't get over-sprayed, the result is that entire rooms can be fully painted in a fraction of the time without compromising on quality.
Many high-end hotels and buildings now elect for paint spraying due to the better quality of finish. It's also a very common practice in the US on homes.
Training is required however to master the technique so be wary of DIYers offering the same service.
The machine we use easily handles different thicknesses of paint, varnish, creosote up to even thick paints.