Runs when Spraying Paint-Their Causes and How to Fix Them

If you are painting, runs in the finish can be a major problem. After all, runs will create a poor appearing end product. In this article will cover how you can fix runs that have occurred as well as reduce the potential for runs to occur in future paint jobs, espeically when spraying your coating.

Fixing runs that have occurred

If you are already finished painting your surface and you notice that there are runs in the coating, there are a few steps you can do to potentially fix the run. If the paint is still wet, you can consider using a nap roller to smooth out the run (though this may not give you the same smooth appearance that the original sprayed coating had) this can be a solution for certain projects where the appearance doesn’t have to be perfect (this is often the case in industrial paint applications).

If the coating is dried, you’ll typically need to use an appropriate sandpaper based on what the products surface is to remove the runs. If the area with runs is significantly large and you are painting a metal product you may need to consider blasting the product surface to remove all the paint. By sanding or blasting and then repainting you will ensure a more uniform surface compared to rolling out the run.

After removing the runs using an appropriate option above whether it’s sandpaper or sandblasting you will then need to re-spray the area and areas immediately surrounding the affected area with the coating system you applied to the product.

Preventing runs that you don’t experience them again

Rather than trying to treat runs after they have occurred, it is always ideal to stop them from happening. Follow these tips to stop runs from occurring.

If using airless paint sprayers–

If you’re getting runs with an airless paint sprayer you can either move the sprayer further back from the product surface and or consider using a smaller tip size. Airless tips are given in numbers like 417 or 315: the first number refers to the fan pattern size and the second number refers to the opening of the tip.  In general, a larger tip opening will provide more coating. The same opening size will end up with less coating in a particular area when it has a larger fan pattern.  If you are using a particular fan pattern size and need that size for your production but you notice you’re often getting runs, you’ll want to consider using a tip with a smaller opening. If you try smaller tips and you are still having problems with runs regularly occurring, your product surface may not be large enough to justify using airless sprayers and you may be better off considering using an air spray gun.

If using spray guns–

Spray guns, in contrast airless paint sprayers use opening sizes that are listed in millimeters and often range from anywhere from 0.6 up to 2.3 mm in size. The bigger the opening the more fluid your delivering in a given time. If you notice that you’re getting runs frequently with a spray gun, try using a smaller nozzle size than the one you are currently using.  You can also use the fluid needle adjustment on the back of the gun to fine tune the amount of material that is being applied. In general, you want to try to keep the fluid needle as open as you can.

General considerations

Regardless if you using an airless sprayer or spray gun, you want to try to spray in an environment with relatively consistent temperatures and humidity (the best temp and humidity is usually found on the technical data sheet from the coatings manufacturer). If there are significant fluctuations in temperature and humidity in your facility this can create changes in your coatings viscosity.  With changes in viscosity will come different rates at which a coating will be applied which can lead to issues like runs. In particular, higher temperatures in your facility, as well as higher humidity levels, will often create thinner viscosity materials. If your fluid nozzle is the same size that you always use and you find you are getting runs you want to see if it is significantly hotter or more humid than normal in your facility. If it is the environmental difference is most likely contributing to the runs that are occurring.

In addition to the environmental conditions, you want to ensure you’re monitoring the volume of thinner you use. If you had more thinner than you typically do, the material would come less viscous and flow rapidly which can create additional potential for runs.

Ultimately, if you experience a run in your paint, you want to try to fix the problem as early on as you can and do everything you can to eliminate the future potential for runs in your finish.