Switching to waterborne basecoat changed more than the paint on the shelf. Solvent paint flashes as its solvents evaporate; waterborne flashes as water evaporates. That puts the air coming out of your gun to work in a way it never was before. Air that's already carrying moisture can't pull much more out of the film, so the coat sits wet longer, and any liquid water or oil that rides along lands right in the finish.
This guide explains why "dry enough for solvent" often isn't dry enough for waterborne, what dew point actually means at the gun, and how to choose a point-of-use dryer that fits your booth. We carry the full RTi (Reading Technologies) line as an authorized dealer, so the examples below use their systems.
Dew point: the number that actually matters
Compressed air is judged by its dew point, the temperature at which the moisture in it starts condensing into liquid water. As long as the air stays warmer than its dew point, the water stays vapor. Let it cool below that temperature anywhere between the compressor and the gun, in a cold line, a hose lying on a concrete floor, or the expansion at the gun tip, and it drops out as liquid.
That's why a shop can have a dryer at the compressor and still get water at the gun. Air leaving a refrigerated dryer is typically dried to a dew point somewhere in the high 30s °F. That's fine for most tools, but it still holds moisture that can condense when the air cools further downstream, and it still carries water vapor into the spray pattern.
RTi's desiccant systems are built to deliver a -40°F dew point at the gun. At that point there's effectively nothing left to condense in a heated booth, and the air leaving your gun has room to absorb water from the paint film.
What wet or dirty air does to a waterborne finish
RTi lists the problems contaminated air causes in spray finishing: poor gloss, poor adhesion, uncured finish, cloudiness in clear, fisheyes, poor holdout and finishes that are hard to buff. With waterborne, the most common complaints are:
- Slow flash between coats. Humid air can't carry water away from the film quickly, so you wait longer between coats and before clear.
- Cloudiness and dieback in the clear. Moisture trapped under or in the clearcoat shows up later as haze or lost gloss.
- Fisheyes and adhesion failures. These usually trace back to oil, not water. Compressor oil carried as aerosol or vapor is invisible until it hits the panel.
RTi says its Perfect Air® systems hold compressed air humidity at 3% or less, and credits clean, dry air with flash times up to 75% faster. Your results will depend on your booth, paint system and air supply, but the direction is consistent: drier, cleaner air flashes waterborne faster and more evenly.
Oil and dirt deserve their own walk-through. See water, oil and dirt in your paint air for where each contaminant comes from and which stage removes it.
Two ways to dry air at the booth
RTi builds two families of point-of-use desiccant dryers for paint booths. Both finish at -40°F; they differ in how the desiccant gets renewed.
Perfect Air® paint air systems: self-regenerating
The PERF-25 (one gun, 25 SCFM to the gun at 100 PSI) and PERF-50 (two guns, 50 SCFM) pair a two-stage pre-filter with a twin-tower regenerative desiccant dryer and a final after-filter. One tower dries while the other is purged with a small stream of already-dried air, so the desiccant reconditions itself. RTi rates the filtration at 99.99998% at 0.01 micron.
- Why shops choose it: consistent -40°F air all day, no desiccant cartridges to swap, and no upstream dryer required. RTi calls it its best system for shops spraying waterborne.
- The trade-off: the purge uses 10–15% of rated airflow, so size your compressor with that in mind. It plugs into 110 V and mounts on the wall outside the booth.
- Upkeep: filter elements every 6 months; the desiccant beads themselves last 3–5 years before the towers need repacking or swapping.
Eliminator® II dryers: replaceable desiccant cartridge
The EH4000 series is a two-stage unit: an activated-carbon first stage pulls oil vapor, water and dirt, and a second stage holds a contained desiccant cartridge (DE401) that drops the dew point to -40°F. It's rated at 25 SCFM and RTi designs it for one paint gun. The three versions differ only in outlet regulator size: ¼" (EH4000), ⅜" (EH4000-3R) or ½" (EH4000-4R).
The EH7000-3R / -4R adds a third stage, a 0.01-micron coalescer between the carbon and the desiccant, and is rated at 30 SCFM. RTi positions it for body shops with high levels of contamination and designed it to stop fisheyes caused by compressed air.
- Why shops choose it: lower up-front cost, no electrical connection, compact wall mount at the booth, and no purge air.
- The trade-off: the DE401 desiccant cartridge is a consumable. Change it when the moisture indicator turns from blue to pink, or every 3 months, whichever comes first.
Which one fits your shop?
| Your situation | Good fit |
|---|---|
| One gun, high daily volume, mostly waterborne | PERF-25 Perfect Air® |
| Two guns in one booth | PERF-50 Perfect Air® |
| One gun, moderate volume, want the lowest upfront cost | EH4000 Eliminator® II (pick the outlet size your gun manufacturer specifies) |
| Known oil or fisheye problems from the compressor | EH7000 three-stage Eliminator® II |
| Painters also need supplied breathing air | BRAD-PERF combined paint and breathing air system |
Whichever you pick, install it close to the booth (but outside it), mount it vertical with the drain down, and keep the incoming air between about 40 and 70°F if you can. A point-of-use dryer works best when the air reaching it has already had its liquid water and bulk oil knocked out at the compressor.
If you're adding supplied breathing air for your painters, plan it at the same time. RTi's BRAD-PERF builds breathing air and paint air into one system.
Frequently asked questions
Do I need a desiccant dryer for waterborne paint?
Most paint manufacturers specify very dry, oil-free air for waterborne systems. A refrigerated dryer alone typically leaves a dew point in the high 30s °F, which can still condense downstream. A point-of-use desiccant dryer that delivers a -40°F dew point removes that risk and helps waterborne flash faster.
What dew point should paint air be?
RTi's Perfect Air® and Eliminator® II paint air systems deliver a -40°F dew point at the gun. At that level, moisture won't condense in the line, hose or gun in a heated booth.
What's the difference between the Perfect Air® and Eliminator® II?
Perfect Air® systems use twin regenerating desiccant towers that recondition themselves with a small purge of dry air, so there are no desiccant cartridges to change. Eliminator® II dryers use a replaceable desiccant cartridge (DE401) and need no power or purge air.
How often do I change the Eliminator® II desiccant?
RTi says to change the DE401 desiccant cartridge when the moisture indicator turns pink, or every 3 months, whichever comes first. The 4P-060 first-stage element is changed at least every 6 months.
Can one Eliminator® II run two paint guns?
No. RTi designs the EH4000 Eliminator® II for one paint gun only. For two guns, look at the PERF-50 Perfect Air® system.
Get the right dryer for your booth
Tell us your gun count, the paint system you spray and what your compressor delivers, and we'll help you pick between Perfect Air® and Eliminator® II. RTi can also build a unit around a custom requirement. You can read RTi's own technical literature at rti-pbe.com.
Dry Air, Faster Flash
We're an authorized RTi dealer, carrying their paint air dryers, replacement elements and maintenance kits. RTi orders over $1,200 ship free.
See the RTi paint air line →
Ask us which dryer fits your booth →
Filter element change schedule →