Applying polyurethane or putting a topcoat on a sealed or painted surface is always tricky! But, since the process is highly protective to wood, you’ve to do it. A slight mistake in application can ruin the surface outlook or even the entire project. Rollers and brushes are great for applying poly, but sprayers can maximize the efficiency. That’s why professionals recommend using an advanced gun or sprayer while applying complex things like polyurethane or paint for a flawless result.
What is a Spray Gun?
As the name implies, a spray gun is used to spray polyurethane, paint or similar finishes. They work much like aerosol spray cans, but they’re more powerful and suitable for larger-scale projects. They can process a lot more poly or paint and give a much better finish, although never an alternative to brushing or wiping, particularly for touch-up works.
Types of Sprayer (Gun)
When it comes to spraying systems, there are two main types, and they have their subcategories also:
|1. Pressure Based|
-Manual low pressure
-Manual high pressure
-Automatic low pressure
-Automatic high pressure
|2. Transfer Mode Based |
-Air Assisted (Compressed air)
However, considering both the pressure and transfer modes in general, the three subordinates of the second type are fundamentally recognized as functional spray guns. Here the manual pressure guns are categorized as conventional models.
As said, all devices or systems have their own characteristics and applications, to summarize-
i. Airless Sprayer – An airless gun works by pumping polyurethane at quite a high pressure (up to 3000 psi), fanning out the droplets through a hose and a very small hole in the tip of the gun. Great for spraying larger surfaces, including indoor and outdoor wood walls. The only shortcoming is – it may be messy with overspray sometimes. But caution can give you relief. But, they are excellent overall, as for instance – Graco Magnum X5 or Titan ControlMax.
ii. Compressed Air Sprayer – Also known as Pneumatic or Air-Assisted sprayer, it uses compressed air to push the paint or poly forward to a surface, offering an even and smooth finish. It’s great for finishing furniture and cabinets. But for noise and tricky set up (as it requires connection to a compressor), it may bother you. And, with a little tendency of overspray, it can mess the project if not maintained carefully. But still they are popular, e.g. Dynastus 33.
iii. HVLP Spray Gun – Standing for High Volume Low Pressure, the HVLP sprayer works by using a very high air volume to aerosolize and propel the polyurethane at lower air pressure. To date, this is the best gun type for spraying most wood finishes, including polyurethane. It minimizes overspray while maximizing the possibility of error-free finishing. Performs extraordinarily at small to medium projects (but detailed works) with a capacity of serving multiple purposes (use of HVLP is so wide – home, DIY, and professional). But thick coatings may not be atomized well always. It should not be your first choice while dealing with very large projects, as it works slower than airless guns. But of course, it is about twice as efficient as manual spray guns. To test, the Wagner Spraytech is an unparalleled unit.
Some Excellent Guns for Applying Polyurethane & Paint
As there’s a thorough research protocol, we usually end up with some quality results, so did we in terms of polyurethane sprayers. Let’s check the best polyurethane sprayers, one of which should be in your arsenal.
Best Pro-Grade Sprayer – Graco Magnum ProX19
A Note – Not only for polyurethane or paint, but these guns are also eligible for spraying lacquer, varnish, stain, sealer, and other contemporary wood finishes.
HVLP, Conventional, or Airless – What’s best for Polyurethane?
High volume, low pressure – HVLP spray guns have a reversed similarity to conventional spray guns, as both use pressure from a compressor (built-in for HVLP in most cases, while bought separately for conventional guns) to move air through the gun. But HVLP models can generate a higher volume of air at a lower pressure, where typical or conventional models use air at higher pressure, just opposite to each other.
Fluids or finishes like polyurethane are pretty sensitive and complex. Overspray, inconsistency and delay in spray, uneven pouring, and similar things can destroy the project. An HVLP ensures higher precision at each of these aspects. Naturally, it gets priority over conventional guns that overspray or make delay at spraying.
An airless gun is better in many aspects, but they also face the overspray problem sometimes, so not suitable for small-scale, detailed finishing jobs. But yes, they are indeed better for applying polyurethane at larger flat projects. A significant benefit of HVLP is that it reduces paint or poly waste by about 50%, thanks to the minimized overspray! Moreover, they are less expensive than airless guns, and even the typical spray gun requiring a separate compressor.
Air Compressor for Spray
Airless spray guns have their air tanks, so they require no extra compressor. But HVLP sprayers need an abundance of air volume at low pressure, while the conventional spray guns need low to medium air volume at high pressure. In both cases, assistance from an air compressor is a must. For conventional spray guns, you have to manage the compressor separately. On the other hand, HVLP guns may sometimes come with a built-in compressor or without it.
Whatever the case, the gun manufacturers recommend a 3-HP and 5-CFM compressor with a 20-Gallon tank standard for most fluid spraying jobs, including professional projects. For home-doers, DIYs, and small-scale applications, anything over 1-HP, 2.5-CFM, and 6-Gallon is acceptable if the spray guns are pretty efficient. But anything shorter than 2.5-CFM is completely incompetent for spraying tasks.
Check some of the suitable and efficient air compressors for spraying paints and finishes:
- California Air 20020
- California Air 10020
- Dewalt Pancake
- Craftsman Pancake
- Bostitch Pancake
- California Air 60040DCADC (for Professional Spraying)
Hose is an essential tool for spraying any finish, whether you’re using an airless or HVLP sprayer. It carries the required compressed air to the sprayer from the pressure tank. Being the connecting component between tank and sprayer, or compressor and spray gun, it must be suitable and robust enough. Currently, you’ll find hoses manufactured from different materials like Rubber, PVC, and PU. Internationally, the approved diameter for spraying fluids is between 3/8-inch and 1/2-inch.
Correct Gun Pressure to Spray Finishes
Either you’re giving the base coat or just applying a clear coat. When it’s the base coat, you should maintain at about 26 to 29 PSI. It means dial reading any PSI between that and pull the trigger for base coats. But for clear coats, we always prefer increasing it by 2 or 3 PSI. This gives better atomization and flow-out.
Some Essential Tips – When Spraying with a Gun
- Always use user-friendly (easy to apply) finishes;
- Measure and ensure right viscosity of finish;
- Set up the place where you are going to spray;
- Maintain the humidity and temperature based on instruction of finish manufacturer, especially for high VOC fluids;
- While working for outdoor projects, do not spray under direct sunlight;
- Never spray the final project without practicing it earlier;
- Maintain a straight line while spraying the gun;
- When it’s conventional or HVLP, hold the gun closer to the surface. But for air assisted, hold the gun less close to the surface;
- Spray the interior upright first when it’s a case-type structure, later the interior horizontal parts, and finally, go for outer parts;
- Screwing the shelves to support will give you better result at spray;
- Spraying in a horizontal orientation to the parts (as much as possible) will reduce drips and runs;
- Access to the interior and tight corners will be easy if you leave the backs of structures like cases and cabinets;
- Sanding between coats will help to knock out the dust nibs;
- While spraying, never do it standing in between an exhaust fan and your project.
Use of guns to spray polyurethane, paint, lacquer, sealer, stain, or other applicable finishes dates back shorter than wiping, brushing, or rolling. But it has gained much popularity because of more technical precision and ability to cover a large area shortly. It minimizes the labor, reduces the waste of finishes, saves the finishing time, and gives a well-treated surface simultaneously. But getting the right sprayer for your purpose is the big challenge that we probably have solved in this article. And, we are always here to assist you with information.