Advice for thinning paint to suit application methods
There is no rule of thumb when it comes to thinning paint to aid application methods; the reason the percentage of thinners required changes so much is there are lots of different external variants that affect paint. The best advice we can offer is when thinning is required, add thinners gradually as you can always put more in but never take it out. When ordering thinners and paint ensure they are compatible i.e. a White Spirit based solvent (usually brushing paints) will not thin a Xylene based coating (QD grade). A Xylene thinner will thin a White Spirit paint, but when over coating the Xylene will attack the resin and the film will craze and chemically breakdown.
What are the main factors that will affect the amount of thinners required?
- Temperature – All our products are manufactured to BS EN ISO 2008:9001. One of the quality control systems is to ensure the paint is at the same viscosity, this test is always set at 20°C to achieve consistency. When the paint is below 20°C it will be naturally thicker which will mean a touch more thinners may be required to achieve good flow and atomization and vice versa, when the paint is warmer than 20°C the paint will be thinner and less thinners will be required to achieve the same finish.
- If spraying, the figure will change dramatically depending on the equipment used i.e. Pot Guns, Pressure Pots and Piston Pumps. Most coatings will go through an Airless or Air Assisted Airless system with out thinning depending on the tip size used (this is why these systems are more efficient than conventional). Conventional and HVLP may required thinning up to 20-25%
- Gun set ups will also have a big impact on the amount of thinners needed, the bigger the tip the less amount of thinners required.
Here are some FAQs:
Q. Do I need to add thinners when applying by brush or roller?
A. It depends on the finish you require; when rolling a coating the roller adds air in to the film, when the air escapes it leaves small craters behind which gives the dimple effect. A small addition of thinners will help the flow and reduce the dimples. When brushing you may start to see faint brush marks in the film, again a small addition of thinners will help reduce it. We normally recommend thinning no more than 10%, be careful not to over-thin the coating as this will increase the risk of the paint running and reduced opacity.
Spraying Paint with conventional systems.
Q. How much thinner’s do I need when spraying with a gravity or suction spray gun?
A. We would normal recommend thinning around 5-10% to start off with, if more thinners are required add extra carefully until you achieve good flow, control and atomization. Some coatings may require thinning up to 20 – 25% depending on the build of the paint and the conditions applied. Be careful not to over-thin the coating as this will increase the risk of the paint running and reduced opacity.
Spraying with Airless or Air Assisted Airless Systems
Depending on the set up, most paints will go through these systems without the need of thinners. A small amount of thinners may achieve a smoother finish and better control when applying. Be careful not to over-thin the coating as this will increase the risk of the paint running and reduced opacity.