Applying water-based damping coatings by airless spraying
Airless spraying atomises the coating by mechanical pressure alone, with no atomising air added. It suits water-based damping coatings that must be applied over large areas in an even layer. This article covers the principle, pre-spray checks, film control, a troubleshooting path and safe clean-down; equipment settings always follow the product's technical data sheet and the equipment maker's manual.
Principle and limits of airless spraying
A pump pressurises the coating and the liquid is sheared and atomised as it passes through a small nozzle orifice. "Airless" means that no atomising air is needed; it does not mean the equipment uses no compressed air: a pneumatic pump still runs on compressed air, while electric and hydraulic pumps do not. Damping coatings carry a high content of fillers and binder, so whether they pump and atomise smoothly depends on how well the coating's flow behaviour matches the equipment set-up. With suitable equipment, tip and technique an even coating can be obtained, but the result depends on those conditions and is not a given of airless spraying itself.
There is therefore no universal answer to how a given coating is sprayed. Equipment type, pump capability, nozzle and filter arrangement and the permitted ambient conditions should be checked against both the technical data sheet (TDS) of the product and the equipment maker's manual; where neither covers a point of equipment or material compatibility, ask the supplier or our technical team and do not assume. Plan for the limits too: overspray needs masking, the equipment must be kept in good and clean condition, and narrow gaps and corners usually need touch-up.
Before spraying: substrate and compatibility
Start with the substrate. It should be clean and dry, free of oil, loose rust, flaking old paint and release agents. Whether an old coating or primer is compatible and will hold should not be assumed; confirm it on a representative test panel.
Then the environment. Substrate and air temperature, humidity, ventilation and the drying conditions after application all affect film formation and adhesion, and the permitted window is the one in the TDS. If site conditions fall outside it, contact the technical team first instead of trying to rescue the job with faster drying or an ad-hoc change to the coating.
Equipment selection and readiness check
Selection rests on checking the coating's TDS and the equipment maker's manual together, not on rules of thumb; missing compatibility information has to be asked for. Before starting, confirm item by item: the pump type and capability suit this coating; the pump body, seals and hoses in contact with the coating are suitable for water-based systems; hose length and bore will not cause a large pressure loss; nozzle and fan choice match the maker's advice for this coating; and the filtration is set up as the maker and the TDS require, not removed or altered on your own initiative.
Also check that the equipment is clean and free of dried residue from the last job, whether and how the coating must be stirred, and that earthing and protective equipment are in place. If any of these cannot be backed by the manual or the TDS, ask before you start.
Film control and drying
Film quality comes from a steady travel speed, a steady distance and sensible overlap. Do not try to build the whole thickness in one pass: a heavy pass runs, and after drying it can crack or stay wet inside. Number of coats, time between coats and total thickness follow the TDS.
Before production, spray a test panel, measure the wet film, then measure the dry film after drying and check adhesion and appearance; write the results down. Dry under the conditions given in the TDS. Any forced drying must be one the TDS permits; forcing it to save time can skin the surface while moisture is still trapped and lead to blistering or cracking.
Defects and a troubleshooting path
Before working on the tip, a filter or a hose, stop spraying and relieve the pressure as the equipment manual prescribes; never work on a pressurised system. After that, change one variable at a time and record the effect. A streaky, tailing or pulsing spray: check that the supply is continuous, whether the nozzle is worn or partly blocked, and whether a filter is clogged, then compare the pressure setting with the manual. Sagging is usually a heavy single pass, too short a distance or too slow a pass, so also check the temperature and humidity. Orange peel or poor atomisation: check nozzle and fan choice, the state of the coating, and whether pressure is inside what the manual and TDS allow.
Pinholes and bubbles: look at moisture in the substrate, drying that is too fast, and air drawn into the coating. Cracking after drying: look at single-coat and total thickness and at the drying conditions. Poor adhesion: go back to surface preparation and the compatibility test. If the same defect keeps returning, do not change pressure or adjust the coating (including thinning with water) on your own; follow the TDS and the equipment manual and send your records to the technical team.
Shut-down, pressure relief and cleaning safety
Before cleaning, or before touching the tip, filter or hose, relieve the pressure as the equipment manual prescribes. Engaging the trigger lock alone does not relieve pressure. High-pressure fluid can penetrate the skin and cause serious injury; if it happens, get medical help at once and say that it is a high-pressure injection injury. Keep hands away from the front of the tip and never remove the tip guard or other safety devices.
Cleaning medium and method follow the coating's TDS and the equipment manual and must be carried out before the coating dries, taking in the hose, filter, tip and pump; dispose of waste and rinse water as local rules require. Equipment makers such as Graco publish detailed pressure-relief and cleaning guidance, but the manual of your own equipment is what governs.
Process record and what to send the technical team
Keep a record that can be checked later: product model and batch, the TDS edition used, equipment model and set-up, substrate and preparation, ambient conditions, wet and dry film on the test panel, drying conditions, and the appearance and adhesion results. It makes problems traceable and keeps different crews consistent.
When you contact us, include the coating model and batch, equipment and nozzle, site conditions, the substrate and any old coating, photographs of the defect and where it occurs, and the adjustments already tried with their results.
Sources
Current edition of the TDS of the product used, and the manual of the equipment used: the only basis for application settings, filtration and nozzle choice, and drying conditions
Graco: Basics of Airless Spraying (equipment-maker article, general background on the principle only): https://www.graco.com/us/en/contractor/solutions/articles/basics-of-airless-spraying.html
Graco: How to Clean Up a Paint Sprayer (equipment-maker article, general reference for pressure relief and cleaning only): https://www.graco.com/us/en/contractor/solutions/articles/how-to-clean-up-a-paint-sprayer.html
Graco: Airless Sprayer Safety (equipment-maker article, general reference on injection-injury safety only): https://www.graco.com/us/en/contractor/solutions/articles/airless-sprayer-safety.html