Elastomeric and roof coatings are made to be thick, flexible and durable. Those same qualities make them hard on spray equipment. A pump that handles a thin interior paint all day without complaint can struggle with a heavy coating, and a filter that is ideal for stain can clog in minutes.
This guide explains what thick coatings do to an airless pump, a filter and a hose, how to match the equipment to the coating and how to look after a high-volume pump during a roofing season. It draws on pump manufacturers’ manuals, on the troubleshooting tables for airless equipment and on the general rule that the coating maker’s data sheet comes first.
Key takeaways
- The coating data sheet is the starting point: it names the recommended tip size range, pressure, hose and filtration.
- Thick coatings need pump capacity, a larger tip and a short, wide hose. Long, narrow hoses lose pressure quickly.
- Filters protect the tip, but a filter that is too fine for the coating will clog. Follow the data sheet and clean often.
- Abrasive or highly filled coatings wear packings, rods and cylinders faster. Choose the packing material with the coating maker’s advice.
- Daily care, flushing and a check of the rod and cylinder at each service are what keep a high-volume pump running all season.
What makes thick coatings hard on equipment
Four things combine on a roof job.
- A thick coating resists flow. The pump has to work harder to draw it in on the intake stroke, and the intake valve has less time to seat. Manufacturers’ manuals list thick material as a cause of low output on the downstroke.
- Roof surfaces are large, so the pump runs continuously for long periods. That puts more strokes, and more wear, on the packings and valves each day.
- Solids and fillers. Many protective and elastomeric coatings carry fillers and pigments that are abrasive. Graco’s packing guidance for its high-volume pumps distinguishes between packing materials for abrasive and chemical applications.
- Heat and sun. A hose that lies across a hot roof, and a pump that sits in the sun, change how the coating behaves and how rubber parts age.
Start with the data sheet, not the sprayer
Coating manufacturers publish equipment recommendations on the product data sheet: a range of tip sizes, a working pressure, and often a minimum hose diameter and filtration advice. Those numbers are specific to the product and should come before any rule of thumb. If your equipment cannot meet them, the answer is different equipment, not a longer extension or a smaller tip.
The same principle applies in reverse. Sprayer manufacturers give maximum tip sizes for their machines, and a tip that is too large for the sprayer asks the pump for more paint than it can supply. Graco’s manuals, for example, give a maximum tip size for each model. If the coating needs a bigger orifice than your machine can drive, you need a higher-capacity pump.
Pump capacity: why high-volume lowers exist
High-volume pumps, such as Graco’s Xtreme lowers, are built for protective coatings. They come in displacements from 85 to 290 cc per cycle and are driven by air motors or electric drives. Graco’s manual for its NXT air-motor packages lists output figures that scale with the size of the lower. At 60 cycles a minute, an 85 cc lower is rated at about 1.5 gallons a minute and a 290 cc lower at about 4.6 gallons a minute, and the output halves at 30 cycles a minute.
The point of the large displacement is that the pump can deliver the volume that big tips and long hoses require without running at high stroke rates. A small pump pushed to the limit with a heavy coating wears faster than a properly sized one running comfortably.
Filters: protect the tip without choking the flow
Filters exist to keep debris out of the tip, and they are still worth having on a roof. But the filter and the coating have to suit each other.
- Follow the data sheet. Many thick coatings call for coarser filtration, or for limited filtration at the gun, and some specify none at all.
- Strain the material from the bucket if the maker recommends it. Skins and lumps clog tips and filters faster than the coating itself.
- Check the inlet strainer often. Thick material clogs it more quickly than thin paint does, and a restricted inlet starves the pump.
- Clean filters at every break and replace them when the mesh is damaged.
Because filter choice depends on the coating and the tip, filters, strainers and manifolds are normally offered in several mesh sizes. Choose the mesh that the data sheet and the tip size call for.
The hose: short, wide and cool
Pressure drops along a hose, and the drop is larger with thick material, a longer hose or a smaller diameter. Graco’s troubleshooting table for a sprayer that is not producing enough output lists a large pressure drop in the hose with heavy materials, and the remedy is to shorten the hose. Its guidance on hose size notes that on long runs a 3/8-inch hose loses much less pressure than a 1/4-inch hose.
- Use the shortest hose that reaches the work, and use a larger inside diameter for thick coatings.
- Avoid kinks and sharp bends, which restrict flow.
- Keep the hose out of direct heat where you can. A hose lying on a hot roof can change the viscosity of the coating inside it.
Packings and abrasive coatings
Packings seal the piston and the rod, and they are the main wear item in the pump. Graco’s high-volume pumps use three families of packings, and the catalog names reflect the materials.
| Packing family | Materials | What Graco says it is for |
| L/PE | UHMWPE and leather | Abrasive applications; standard in the Xtreme NXT packages |
| TFE | PTFE | Chemical resistance and higher temperatures; not ideal for abrasives |
| TFE/PE | UHMWPE and PTFE | Chemical resistance and durability below 140 degrees Fahrenheit |
The sources we reviewed do not give coating-specific recommendations. If you are spraying a heavily filled coating, ask the coating maker which packing family suits it, and confirm the choice for your pump size before you order. Part numbers for these kits run across the sizes and packing types, and older numbers appear on older pumps. A guide to repair kits and parts for Xtreme pump lowers shows how the sizes, packing families and numbers fit together.
Reading the symptoms on a high-volume pump
Graco’s manuals tie common symptoms on these pumps to specific causes.
| Symptom | Likely cause |
| Low output on the downstroke | An open or worn intake valve, or fluid too thick for the ball travel (the intake spacers can be adjusted) |
| Low output on the upstroke, or erratic, fast cycling | An open or worn piston valve, or worn piston packings |
| The pump cycles or will not hold pressure at stall | Worn check valves or seals |
| The pump will not run | Fluid that has dried on the rod |
Daily care that makes a season
- Check and top up throat seal liquid every day. Graco’s instructions are to fill the packing nut at set-up and to check, adjust and top it up daily.
- Park the pump at the bottom of its stroke overnight, so that fluid does not dry on the rod.
- Flush between jobs with a fluid that suits the coating, and never leave coating to cure in the pump.
- Inspect the rod and the cylinder bore for scoring and wear whenever the pump is serviced, and replace them if they are damaged. Graco publishes no hours or gallons interval for packings; it tells you to replace them when the symptoms point to them.
- Use all the new parts in a repair kit, which is Graco’s instruction, rather than replacing only the part you think has failed.
- Replace the filter-cap o-rings whenever the caps come off. They take a set at high pressure and should not be reused.
A short roof-day checklist
- Read the data sheet for tip, pressure, hose and filtration.
- Check the hose for wear and keep it as short and wide as the job allows.
- Clean or replace the inlet strainer and any filters.
- Top up throat seal liquid and check the packing nut for leakage.
- Prime, test on a scrap area and check the pressure and the pattern.
- At each break, check the filters and the output.
- At the end of the day, relieve the pressure, flush and park the pump correctly.
Frequently asked questions
Why does a thick coating clog my filters so quickly?
The mesh is fine compared with the particles and skins in a heavy coating. Strain the material if the maker advises it, use the filtration the data sheet recommends and clean filters often.
How do I know my pump is too small for the coating?
The signs are low output on the downstroke, a pump that runs at a high stroke rate and still cannot keep up, and a tip that must be smaller than the coating recommends. If those are constant, the pump is undersized for the job.
How often should packings be changed on a high-volume pump?
Graco does not publish a fixed life for packings. Replace them when symptoms such as leakage at the packing nut or falling output say so, and inspect the rod and cylinder every time you open the pump.
Can I use any packing material for a roof coating?
Not without checking. The packing families differ in what they tolerate, and the coating maker is the right authority on the coating. Choose the family on that advice and your pump size.
Between jobs: cleaning when coatings cure
Many roof and protective coatings are designed to cure, which is the whole point on the roof and a serious problem inside a pump. A coating that is allowed to cure in the lower, the hose or the filters can ruin all three. Before a long break, such as lunch on a hot day or an overnight stop, check the coating data sheet for its pot life and its recommended flushing fluid, and decide whether to flush or to keep the pump filled and moving. Never leave a curing coating sitting in the pump on the assumption that it will be fine.
The same rule applies to filters and the gun. Pull them, clean them and look at them before you put the machine away, because material that has skinned over in a filter is hard to remove the next morning.
What to bring to the roof
- A repair kit for the lower, matched to the pump size, and the pump’s ID plate number written on it
- Throat seal liquid and a clean funnel or bottle
- Spare filters, a spare inlet strainer and a spare tip in the size the data sheet recommends
- A short spare section of hose and the fittings to connect it
- The manual or a copy of the parts list for the lower
A pump failure on a roof is far more disruptive than one in a shop. Those few items fit in a small case and are the difference between a short delay and a day without a sprayer.
The short version
Let the data sheet set the equipment, give the coating a short, wide hose, filter sensibly and protect the pump every day. A high-volume pump that is sized correctly and cared for daily will carry a roofing crew through a season, and when it does need parts, matching the kit to the exact pump is the step that saves the most time.
About the author
The eRepairCenter parts team helps painters, contractors and maintenance crews identify and replace worn parts on airless paint sprayers. eRepairCenter is a Houston, Texas supplier of aftermarket, used and surplus replacement parts and an authorized Bedford Precision distributor, shipping across the United States.