Sprayable Adhesive India: Why Does the Spray Gun Clog, Web or Spit? A Viscosity, Pressure and Nozzle Troubleshooting Guide

Quick answer: An adhesive spray gun may clog, web or spit when the adhesive viscosity, fluid tip, air supply and material-drying behaviour are not properly matched. Clogging can result from dried adhesive, contamination or an unsuitable fluid tip. Webbing occurs when the adhesive forms strings instead of a uniform film, often because of viscosity, atomisation or solvent-drying issues. Spitting can result from a blocked air cap, a poorly seated nozzle, damaged gun components or an inconsistent fluid supply. Start with the adhesive TDS and gun manufacturer's instructions before changing pressure or thinning the adhesive.

A spray gun that runs cleanly for an hour and then starts spitting or laying down strings is a recurring problem on foam, footwear and insulation lines that use spray application. The adhesive is often blamed first. In many cases, the adhesive is behaving exactly as its formulation predicts. The problem is that the gun setup has not been matched to the material.

Citifix Adhesives has been manufacturing rubber and polyurethane adhesives since 1994, with facilities in Sahibabad, Ghaziabad. The company supplies adhesives for foam, footwear and HVAC insulation applications, and the technical guidance that follows applies to any sprayable adhesive India system where viscosity, tip size and atomisation settings must be matched to the product. This guide breaks down the three most common spray faults, the role of viscosity, pressure and nozzle size, and the checks that solve them without guessing.

The Three Faults: Clog, Web and Spit

Clogging, webbing and spitting look like different problems, but they sit on the same chain of cause and effect: adhesive viscosity, atomising air, fluid tip size and solvent behaviour.

Clogging is a flow problem. The adhesive cannot pass through the fluid tip fast enough, or dried adhesive has narrowed the opening. Clogging can result from dried or partially skinned adhesive, contamination, a blocked filter, an undersized fluid tip or adhesive viscosity outside the gun's operating range. The result is a weak, pulsing or uneven pattern that gets worse over a shift.

Webbing (cobwebbing, stringing) is an atomisation and drying problem. Webbing or cobwebbing occurs when the adhesive forms strings or filaments instead of a uniform deposited film. Possible causes include excessive viscosity, unsuitable solvent evaporation characteristics, poor atomisation, incorrect air or fluid settings, and excessive spray distance. The threads land on the substrate as visible strings and a non-uniform film.

Spitting occurs when adhesive is discharged intermittently as droplets or blobs rather than as a consistent spray. Possible causes include dried material around the nozzle or air cap, an incorrectly seated fluid nozzle, damaged needle or tip components, air entering the fluid path, or an unstable fluid supply.

Viscosity: The Number That Decides Everything Else

Viscosity is the adhesive's resistance to flow, usually measured in centipoise (cP). Viscosity influences fluid delivery and atomisation, but it does not independently determine the fluid tip size or air pressure. The correct setup depends on the adhesive's flow behaviour, the gun design and the required application film.

Low-viscosity adhesives flow through smaller tips. High-viscosity adhesives may require a larger fluid tip, a compatible pressure pot or pump, or specialised application equipment. The required atomising pressure depends on the adhesive formulation and the spray gun design, so follow the equipment manufacturer's guidance rather than assuming that a thicker adhesive always needs higher air pressure.

Adhesive viscosity is not a fixed number. It changes with temperature. A solvent-based adhesive that sprays cleanly on a warm afternoon can thicken noticeably on a cold morning, and that shift alone is enough to turn a stable pattern into spitting or webbing. This is why the viscosity should be checked at the gun, not just read off the drum label.

Adhesive viscosity should be measured using a method suitable for the material's flow behaviour. ASTM D1084-16(2021) covers test methods for free-flowing adhesives, with limitations for thixotropic and plastic materials. A shop-floor viscosity cup can also be used as a process-control tool where the adhesive supplier specifies the cup type, test temperature and measurement procedure. Compare results with the product TDS rather than relying on a generic conversion chart, because cup measurements depend on the cup standard, temperature, test procedure and material flow behaviour. Newtonian and non-Newtonian materials do not necessarily behave alike.

Where an adhesive is thixotropic or otherwise non-Newtonian, use the test method and measurement conditions specified by the adhesive supplier rather than treating a single cup-time result as its complete viscosity profile.

Material condition and equipment considerations

Fluid tip selection depends on the adhesive viscosity and flow behaviour, the gun design and manufacturer, the feed system, the required fluid pressure and output, the solids content and film thickness, and whether the adhesive is shear-sensitive. Use the gun manufacturer's fluid-tip chart and the adhesive supplier's current TDS to select the correct combination. Confirm the final setup through a spray trial. An oversized tip can cause excessive fluid delivery, poor control and an unsuitable film, so sizing up is not always the right answer.

Pressure: Atomisation, Fluid Feed and the Webbing Trap

Two different pressures matter on a spray gun, and confusing them is another common source of faults.

Atomising air pressure breaks the adhesive into droplets at the air cap. Fluid pressure pushes the adhesive from the cup or pot to the gun. They are set separately and they solve different problems.

If atomising pressure is too low for the material and gun setup, the spray may become coarse or uneven. Depending on the adhesive formulation and fluid delivery, poor atomisation can also contribute to stringing or an irregular deposited film.

Excessive atomising pressure can contribute to dry spray, overspray or uneven deposition. On some solvent-based systems, the combination of air velocity, spray distance and solvent evaporation may also encourage the adhesive to dry before reaching the substrate. The effect depends on the formulation and equipment setup.

HVLP equipment is designed to operate with controlled air-cap pressure. The permitted air-cap pressure and required gun-inlet pressure depend on the specific gun and air-cap combination. Follow the manufacturer's manual and measure pressure under the specified operating conditions. For example, the Binks GPG Conventional, HVLP or High Efficiency Gravity Spray Gun Operation Manual gives different inlet-pressure limits for different HVLP air caps. Those figures apply to the specified equipment, not to every adhesive spray gun. This manual is an equipment reference; confirm that the selected gun and its wetted components are compatible with the adhesive being used.

An unstable or insufficient fluid supply can cause intermittent discharge or spitting. Check the fluid level, feed pressure, filters, fluid-line restrictions and air entering the fluid path before changing the pressure setting.

Pressure troubleshooting

Nozzle and Fluid Tip: Size, Wear and Cleaning

The fluid tip and air cap are small but important components in spray performance. Material build-up, wear, damage or an incorrect combination can distort the spray pattern.

Size. The tip must match the adhesive viscosity. A tip that is too small clogs; a tip that is too large delivers too much material and can cause runs, sagging or excessive penetration on porous foam. The correct tip is the one that lets the adhesive atomise cleanly at the pressure the gun is designed to use, as confirmed through a spray trial.

Wear. Fluid tips and needles wear over time. A worn tip changes the spray pattern gradually, and the change is easy to miss until the pattern is visibly distorted or the gun starts spitting. If the pattern has drifted and cleaning does not restore it, the tip is a likely culprit.

Cleaning and build-up. Dried adhesive around the fluid tip or inside the air cap restricts airflow, distorts the pattern and causes spitting. Material build-up inside the air cap between spraying operations is a recognised cause of guns spitting when the trigger is pulled. Check that the fluid nozzle is correctly seated and tightened according to the gun manufacturer's instructions. A loose, damaged or incorrectly fitted nozzle can contribute to inconsistent spray or spitting.

Needle and tip matching. A needle that does not match the fitted fluid tip can cause spitting and inconsistent flow. Check the gun manufacturer's tip-and-needle selection chart before changing either part.

Nozzle and tip checklist

• Confirm the tip size against the adhesive TDS and the gun manufacturer's chart.
• Check the air cap and fluid tip for dried adhesive before every shift.
• Confirm that the fluid nozzle is correctly seated and tightened per the gun manufacturer's instructions.
• Match the needle to the fitted tip using the gun maker's chart.
• Inspect the tip for wear if the pattern has changed and cleaning does not help.
• Keep a spare tip and air cap on the shelf so a worn part does not stop the line.

Solvent Behaviour and Webbing

Webbing on a solvent-based adhesive is usually a drying-rate or atomisation problem. Cobwebbing occurs when the adhesive arrives at the substrate as filaments instead of a continuous film. Several factors can contribute, and the cause has to be identified by changing one variable at a time.

Three common contributors are:

1. The adhesive is too thick at the gun. Cold adhesive, a high-solids product or a batch that has lost solvent will string rather than atomise. Bring the adhesive to its specified application temperature and check viscosity before adjusting the gun.
2. The solvent is flashing too fast for the setup. A fast-evaporating solvent or an over-thinned mix can dry in flight. Use the thinner recommended for the product and follow the TDS thinning guidance rather than adding a generic solvent.
3. The spray distance is too great. The further the droplet travels, the more solvent it loses before it lands. Reducing the gun-to-substrate distance within the recommended range gives the adhesive less time to dry in the air.

Some adhesives have flow characteristics that change under shear. If the product is identified as shear-sensitive in its TDS, confirm that the selected pump, fluid path and application equipment are suitable for it. Follow the supplier's recommended fluid pressure and handling conditions, and check the spray pattern during a controlled trial.

Spray-Pattern Diagnosis: What the Pattern Tells You

Reading the spray pattern is faster than guessing at settings. Test the pattern on a piece of scrap substrate at the production distance before adjusting anything else.

These are diagnostic possibilities, not definitive answers. Change one setting at a time and re-check the pattern so you know which change made the difference.

The Diagnostic Sequence: What to Check First

When a gun starts misbehaving, work through the chain in order rather than changing several settings at once.

1. Confirm the adhesive identity, condition, TDS and recommended spray method. If the adhesive is not intended for spray application, no gun setting will make it work reliably.
2. Check for contamination, skinning, lumps and blocked filters. Skin and lumps at the drum or in the line will pass through to the tip and cause intermittent clogging.
3. Inspect the fluid tip, needle and air cap. Check for dried material, wear and correct tip-to-needle matching.
4. Confirm the fluid supply and air supply. Check pot pressure, fluid filter, air leaks and cap pressure against the gun manual.
5. Set the gun according to its manufacturer's instructions. Do not adjust pressure before confirming the tip and material are suitable.
6. Run a controlled spray test and change one variable at a time. Record the setting and the pattern result so the fix is repeatable.

Before Changing Any Setting

This guide is a troubleshooting reference, not a replacement for product-specific guidance. Before changing settings, consult the adhesive TDS and Safety Data Sheet (SDS), and follow the spray equipment manufacturer's operating and cleaning instructions. Use the appropriate personal protective equipment for solvent-based adhesives, work in a ventilated area and control ignition sources where flammable solvents are present.

How Citifix Approaches Adhesive Selection for Spray Lines

Citifix offers adhesive products for foam, footwear and HVAC insulation applications. However, the suitability of an individual formulation for spray-gun application must be confirmed from its current TDS. Before selecting a product, check its recommended application method, viscosity, permitted thinning guidance and equipment requirements.

Citifix SR 500 HVAC is a high-strength synthetic rubber-based adhesive developed for HVAC insulation bonding, with adhesion to galvanised iron, aluminium, steel, nitrile rubber and EPDM. Citifix SR 500 FW is a synthetic rubber-based adhesive engineered for footwear, bonding rubber, leather, EVA, rexin, foam and canvas. Citifix FoamGrip is formulated for foam and mattress applications.

The broader solvent based adhesive India range covers related solvent-borne systems, and the foam bonding adhesive India and insulation bonding adhesive HVAC India guides cover the application side for those industries. Product-specific viscosity, recommended tip size, thinning guidance, spray pressure and confirmed application method should be checked against the current TDS before setting up a gun.

Frequently Asked Questions

1. Why does an adhesive spray gun clog?

Clogging can result from dried or partially skinned adhesive, contamination, a blocked filter, an undersized fluid tip or adhesive viscosity outside the gun's operating range. Check the material condition and the fluid path before changing the tip size.

2. What causes adhesive webbing or cobwebbing?

Webbing or cobwebbing occurs when the adhesive forms strings or filaments instead of a uniform film. Possible causes include excessive viscosity, unsuitable solvent evaporation characteristics, poor atomisation, incorrect air or fluid settings, and excessive spray distance. Identify the cause by checking the TDS and changing one setting at a time.

3. Why does a spray gun spit adhesive?

Spitting occurs when adhesive is discharged intermittently as droplets or blobs. Possible causes include dried material around the nozzle or air cap, an incorrectly seated fluid nozzle, damaged needle or tip components, air entering the fluid path, or an unstable fluid supply. Check the fluid nozzle tightness and air cap cleanliness first.

4. How do I select the correct fluid tip for an adhesive?

Start with the adhesive TDS and the gun manufacturer's tip selection chart. Tip selection also depends on the feed system, required output and film thickness, and whether the adhesive is shear-sensitive. Confirm the final combination through a spray trial rather than relying on a general table.

5. Does temperature change adhesive viscosity?

Many adhesives become more viscous at lower temperatures, which can affect fluid delivery and atomisation. Check the product's specified application temperature before changing equipment settings.

6. How do atomising pressure and fluid pressure differ?

Atomising air pressure breaks the adhesive into droplets at the air cap. Fluid pressure pushes the adhesive from the cup or pot to the gun. They are set separately and solve different problems. Atomising pressure that is too low gives a coarse pattern; unstable fluid supply causes spitting or intermittent flow.

7. Can adhesive be thinned to prevent clogging?

Only with the thinner and ratio specified on the TDS. Adding a generic solvent can change the drying rate, weaken the bond or cause webbing. If the adhesive is outside its sprayable viscosity range, correct the temperature first, then thin only as the TDS allows.

8. How often should an adhesive spray gun be cleaned?

Clean the air cap and fluid tip at the frequency recommended by the gun manufacturer and the adhesive TDS. Adhesive build-up around the tip between spraying operations is a common cause of spitting, so a quick clean at breaks and a full clean at the end of the shift prevent most pattern faults.

9. Why does a spray pattern change over time?

A gradual change in pattern usually points to tip or needle wear, or to a build-up that cleaning has not removed. If cleaning does not restore the pattern, inspect the fluid tip and needle for wear and replace them as a matched set.

10. What should I share with an adhesive supplier when troubleshooting a spray fault?

Share the adhesive name or code, the substrate, the gun make and model, the fluid tip size, the atomising air pressure, the fluid pressure or feed method, and a description or photo of the observed fault. That information lets the supplier recommend the right product and setup instead of guessing.

Conclusion: Fix the Setup, Not Just the Gun

A spray gun that clogs, webs or spits is usually telling you that one link in the chain is out of balance. Clogging says the material condition, the filter or the tip and the viscosity do not match. Webbing says the atomisation, the solvent or the spray distance is wrong for the adhesive. Spitting says air is getting into the fluid, the tip is not seating cleanly, or the fluid supply is unstable. None of these faults is solved by turning up the pressure without checking the cause.

A sprayable adhesive line runs cleanly when the adhesive, the tip, the pressure and the solvent behaviour are set as one system. Start with the TDS, measure viscosity at the gun, match the tip to the material, and clean the air cap before every shift. Put the material and the equipment together, and the gun stops being the variable you cannot explain.

Need Help Setting Up an Adhesive Spray Line?

The right setup depends on the adhesive viscosity, the gun, the tip size and the substrate. A configuration that runs cleanly on one foam or footwear line may not suit another.

Citifix Adhesives Pvt. Ltd. supplies adhesives for foam, footwear and HVAC insulation applications. Share your adhesive name, substrate, gun type, tip size, spray pressure and the fault you are seeing with the Citifix team to discuss a suitable product for evaluation.

Contact Citifix for adhesive information and technical guidance.