Why Your Spray Pattern Falls Apart in the Summer Heat

Hot-weather spraying begins long before the trigger is pulled. The entire path from the drum to the gun has to be considered.

You are spraying along normally when the pattern starts to break apart. Instead of a clean, even cone, the gun begins throwing narrow fingers in different directions. You stop, pull the module, drill the ports, clean the screens, put everything back together, and pull the trigger again.

The pattern is still bad.

Maybe the fingers move. Maybe the pattern looks decent for a moment and then breaks apart again. You clean the module a second time because everything about the problem looks like a restriction at the gun. Eventually, though, it becomes clear that you cannot drill out a blockage that is not there.

In extreme summer heat, the real problem may be farther upstream. The B-side resin can become hot enough that its physical blowing agent begins forming vapor before the material reaches the mix chamber. Instead of feeding the proportioner as a steady column of liquid, the resin becomes frothy and unstable. Once that happens, the contractor may start chasing pressure problems, changing temperature settings, cleaning the gun, and replacing parts without ever touching the source of the problem.

The foam is supposed to start after the A-side and B-side meet at the gun. When the B-side starts foaming before it gets there, the entire process begins moving in the wrong direction.

What Is Actually Frothing?

Closed-cell B-side resin is more than a simple polyol. It is a formulated blend containing polyols, catalysts, surfactants, fire-retardant ingredients, and a physical blowing agent. That blowing agent is one of the ingredients responsible for creating the cellular structure and expansion contractors expect from closed-cell foam.

During normal processing, the blowing agent remains within the liquid resin as the material moves from the drum, through the transfer system, into the proportioner, and down the heated hose. The A-side and B-side meet inside the gun, the chemical reaction begins, pressure drops as the material exits the module, and the blowing agent helps expand the reacting mixture into foam.

When the B-side becomes frothy before reaching the gun, it is generally not cured polyurethane foam forming inside the line. The A-side has not mixed with it yet, so the normal polyurethane reaction has not begun. What the contractor is more likely seeing is vapor or gas bubbles forming in the resin as part of the blowing agent begins leaving the liquid phase.

Honeywell, which manufactures the Solstice liquid blowing agent used in many HFO foam systems, compares the behavior to opening a warm bottle of soda. When a liquid containing a low-boiling material becomes warm and then experiences a pressure reduction, dissolved material can be released quickly and create froth. Honeywell also identifies high temperature, agitation, viscosity, surface tension, blowing-agent concentration, and its solubility in the polyol blend as factors that can affect frothing.

The soda comparison is not a perfect chemical match, but it explains the basic idea well. A warm, disturbed liquid is less likely to keep a volatile ingredient quietly contained when the pressure around it changes.

HFO Blowing Agents Are Designed to Change Phase

The physical blowing agent needs to vaporize at the proper point in the application process. That phase change is part of what creates the foam’s closed-cell structure. The problem is not that the blowing agent can become vapor. The problem is that it can begin doing so too early.

Solstice LBA has a boiling point of approximately 66°F in its neat, unformulated state. That does not mean any B-side resin above 66°F should begin boiling. Once the blowing agent is blended with polyols and the other ingredients in a foam formulation, its vapor behavior changes. Temperature still matters, but so do concentration, solubility, pressure, viscosity, and the rest of the formulation.

That distinction is important. Contractors routinely process closed-cell materials at temperatures well above 66°F. The resin may pass through preheaters and a heated hose at more than 100°F without frothing under normal conditions.

The key phrase is under normal conditions.

Material moving through the high-pressure side of a proportioner is not in the same environment as resin sitting in a drum or low-pressure transfer hose. The pressure, length of heat exposure, movement, and amount of agitation are all different. A temperature that works properly in one part of the system can create trouble in another.

Drum Temperature and Hose Temperature Are Not the Same Thing

This is where the issue becomes confusing on the jobsite. A contractor looks at the proportioner and sees that the preheaters and hose are set around 100°F. That does not sound excessively hot for closed-cell foam, so heat gets ruled out as the cause.

But the number on the display is not necessarily the temperature of the resin in the drum.

Owens Corning’s Natural Polymers guidance for Natural-Therm HFO tells contractors to prepare the drums between 65°F and 80°F. The same guidance notes that excessive drum temperature and agitation can create frothing. At the same time, applicators may need higher processing temperatures farther downstream to get the product properly dialed in.

There is no contradiction there. Bulk chemical conditioning and high-pressure processing serve different purposes.

Inside a drum or on the low-pressure feed side, the resin may sit for hours under relatively little pressure. The drum can absorb radiant heat from the sun, while the rig itself traps heat around the pumps, feed hoses, and proportioner. If the material is being circulated or disturbed, that movement may make frothing more likely.

Once the resin reaches the high-pressure side, it is confined, moving, and approaching the point where it will be mixed and sprayed. Heating it there helps control viscosity, mixing, atomization, reaction, and finished-foam quality.

A 110°F heated hose may be exactly what a particular product needs. A 100°F B-side drum may be exactly what it does not need.

The manufacturer’s product-specific application guide should always control the actual temperature ranges. The larger lesson is that the word temperature does not mean much unless you also know where in the system that temperature is being measured.

Why Turning the Heaters Down May Not Solve It

Once the contractor suspects excessive heat, the natural response is to shut off the preheaters or lower the hose setting. That may prevent the equipment from adding more heat, but it does not actively cool material that is already too warm.

A proportioner is not an air conditioner.

If the drums, transfer pumps, low-pressure hoses, proportioner inlet, and chemical inventory have been heat-soaked inside a hot rig, changing the heater setting does not remove the heat already stored throughout the system. The display may be set to 95°F while the resin entering the machine is already warmer than that.

The heated hose also cannot refrigerate material. Turning the hose down only reduces or stops its heat input. The chemical already inside the hose still needs time to lose heat, and the next material entering from an overheated drum may continue feeding the same problem.

Once vapor bubbles have formed, the system may need more than a small temperature adjustment to stabilize. The bulk chemical, pumps, feed hoses, proportioner, and rig environment may all need time to cool. In severe conditions, that can mean moving the rig out of direct sun, improving ventilation, allowing the equipment and material to cool overnight, or scheduling the work early enough that the sun has not yet reheated everything.

Sometimes the correct temperature setting is a different time of day.

The Spray Pattern Is Often Where the Problem Shows Up

For the applicator, frothy resin may first become obvious at the gun.

Instead of a smooth, balanced pattern, the module begins throwing fingers. One side of the cone may look heavy while another looks thin. The fingers may change direction from one trigger pull to the next, or the pattern may appear acceptable for a few seconds before breaking apart again.

The first suspect should still be the gun. A partially blocked module, dirty impingement port, plugged screen, worn component, or restriction near the tip can absolutely create a bad pattern. Graco lists partial blockages, dirty mixing-module ports, plugged filters, low or excessive pressure, and excessive temperature among the common causes of inconsistent spray patterns. Graco also advises contractors to stop spraying when the pattern or foam appearance continues to fluctuate until the cause has been found.

That is why drilling out the module is a reasonable first response. The mistake is assuming that the module must still be plugged after it has been thoroughly cleaned and the pattern continues changing.

A plural-component proportioner is designed to receive two stable liquid supplies and meter them at a controlled one-to-one ratio. The A-side and B-side pressures need to remain reasonably balanced for that process to work properly.

Frothy resin does not behave exactly like a steady liquid supply. The vapor bubbles introduce compressibility and can interfere with consistent transfer-pump and inlet delivery. Mechanically, it follows that changing B-side delivery can alter the velocity and consistency with which the two components meet in the module. That can contribute to an unstable cone or fingers that seem to move around even though the ports have just been cleaned. This connection is an inference supported by Honeywell’s frothing guidance and Graco’s identification of excessive temperature and pressure variation as causes of inconsistent patterns.

A physical blockage often creates a more repeatable defect. If the same port remains restricted, the same area of the pattern may remain weak. An unstable material supply can be less predictable. The pattern may change because the condition of the material entering the module is changing.

That is not an absolute diagnostic rule, but it is an important clue. When a clean module keeps throwing different fingers, the gun may only be showing you a problem that began back at the drum.

Why Frothy Resin Threatens Pressure and Ratio

A proportioner cannot meter vapor bubbles as confidently as it meters liquid resin.

The transfer pumps are supposed to keep the proportioner supplied with material so the high-pressure pumps can deliver equal volumes of A-side and B-side. When the B-side feed contains gas, the pump may not receive the consistent liquid supply it expects. Inlet pressure can become unstable, material delivery may fluctuate, and the proportioner can begin working with a compromised feed condition.

That does not mean every visible bubble instantly creates off-ratio foam. The machine may continue operating, and the high-pressure gauges may still look reasonably close. Froth does, however, increase the risk that the B-side will not be delivered as consistently as it should be.

The results can include an uneven pattern, pressure imbalance, changing output, poor mixing, reduced confidence in ratio control, and finished foam that varies from one pass to the next. The applicator may also spend more time cleaning the module because hot processing conditions can increase material buildup around the air cap and mixing chamber. Natural Polymers specifically notes that excessive material buildup and unusually frequent chamber cleaning can be signs that the product is being processed too hot.

The contractor may think the gun keeps plugging. In reality, the gun may be receiving material that is increasingly difficult to spray consistently.

What It Can Do to the Finished Foam

Frothy B-side does not guarantee that every inch sprayed during the condition is failed foam. It does mean that the process is no longer as controlled as it should be.

If the blowing agent begins escaping or changing phase before the resin reaches the mix chamber, part of its expansion potential may be lost before it can do its intended work inside the reacting foam. Unstable B-side delivery can also increase the possibility of resin-rich or iso-rich application, irregular rise, inconsistent density, poor cell structure, reduced yield, adhesion problems, or foam that changes in texture from one section to the next.

Some bad foam announces itself immediately. It may be soft, brittle, unusually dark, slow to react, pulling away, or visibly off ratio. Other material can rise and fill the cavity well enough to look acceptable from several feet away.

That is why the spray pattern matters so much. A changing, fingered pattern is not only an inconvenience that makes the wall harder to spray evenly. It can be evidence that the application process itself has become unstable.

When the pattern will not stay consistent, continuing to spray and hoping the foam looks better after it rises is a poor gamble.

“Summer Blend” Does Not Mean Unlimited Heat

The name summer blend can create a false sense of security.

A summer formulation is designed to provide an appropriate reaction profile over warmer ambient and substrate conditions. It may react differently from a winter blend so contractors can maintain control as temperatures rise. That does not mean the drum can sit inside a baking trailer at any temperature without consequences.

Reaction temperature and bulk chemical temperature are not the same specification. Natural-Therm’s HFO transition guidance still calls for drums to be prepared between 65°F and 80°F and warns that excessive drum temperatures can create frothing, even though the product is available in summer and winter formulations.

Summer blend describes how the foam reacts. It does not make the B-side immune to heat.

Not Every Bubble or Bad Pattern Is Heat

Excessive heat should not become the new answer for every inconsistent pattern. Several other problems can produce similar symptoms.

A drum running empty can introduce air into the feed system. Loose fittings, damaged seals, or suction-side leaks can do the same. A partially plugged Y-strainer or feed hose can starve the proportioner. Cold, overly viscous material can contribute to poor transfer-pump performance and cavitation-like behavior. Contamination during a product changeover can alter the resin’s appearance and behavior. A dirty module, plugged screen, damaged side seal, or worn gun component can still be the real cause.

The diagnosis becomes stronger when several clues appear together: the B-side is visibly frothy, the problem worsens as the rig and chemical heat up, the spray pattern keeps changing after the module has been cleaned, B-side delivery appears unstable, and the condition improves after the chemical and equipment have had time to cool.

Heat-driven frothing is not the only possible cause. It is simply one contractors should recognize before they spend half the day drilling a clean module.

What to Do When the B-Side Becomes Frothy

When material delivery, pressure balance, or spray pattern becomes questionable, the first step is to stop spraying. Continuing to install foam while hoping the condition clears on its own can turn an equipment problem into a removal problem.

Check the actual bulk-material temperature rather than relying only on the preheater and hose displays. Inspect the transfer pumps, inlet pressures, strainers, drums, feed hoses, fittings, and seals. Confirm that the drum is not empty and that air is not entering the system somewhere else.

If excessive heat appears to be the cause, the resin and equipment need to be returned to the chemical manufacturer’s approved processing range. That may require moving the rig out of direct sun, increasing ventilation, using an approved cooling method, allowing the chemical to rest, or postponing the application until the rig has cooled.

Avoid unnecessary recirculation or agitation unless the product manufacturer specifically permits it. Honeywell notes that severe agitation and high ambient temperature can contribute to frothing, while Natural Polymers warns that excessive drum agitation can create the same problem.

Do not improvise by casually opening a hot or pressurized drum, cracking fittings, or venting material without following the chemical manufacturer’s safe-handling procedures. Heated B-side drums can build internal pressure, and the correct response should come from the product supplier’s application guidance and technical service team.

If the drum is bulged, the material will not settle, or stable processing conditions cannot be restored, stop and contact the manufacturer.

Keeping Heat From Taking Over the Rig

Hot-weather spraying begins long before the trigger is pulled. The entire path from the drum to the gun has to be considered.

The drums should be conditioned within the product manufacturer’s recommended bulk-temperature range before the job. The rig should be parked in shade when possible, with enough ventilation to keep it from becoming an oven. Drums, transfer pumps, and feed hoses should be protected from direct radiant heat, and actual drum temperature should be checked instead of estimated from the air temperature outside.

The contractor should also watch how the system changes throughout the day. A setup that sprays well early in the morning may become harder to control after several hours of sunlight and heat buildup. In extreme weather, beginning earlier may be more effective than continually lowering machine settings after the entire rig is already hot.

Keep watching the pattern. Keep watching the inlet and spray pressures. Pay attention when chamber cleaning becomes more frequent or when the product begins behaving differently from the way it did at startup.

The proportioner display tells you what the machine is trying to do. It does not tell you everything that has already happened to the chemical before it reached the machine.

Final Thoughts

Frothy B-side is not just an odd texture in the resin. It can be a sign that the blowing agent is beginning to form vapor before the material reaches the place where that phase change is supposed to happen.

The preheater and hose settings may be within a normal processing range. The module may be clean. The pressure gauges may not immediately show a dramatic imbalance. The problem can still begin farther upstream, where the drum, transfer pump, or feed hose has been absorbing heat for hours.

That is why contractors need to watch more than the numbers on the proportioner. Watch the bulk chemical. Watch the pressure behavior. Watch how often the gun needs attention. Most importantly, watch the spray pattern.

When a clean module keeps throwing different fingers, stop assuming the blockage is hiding deeper inside the gun. The gun may be perfectly capable of spraying what it is being given.

The problem is that hot, frothy resin is no longer giving it a stable liquid to spray.

by Gage Jaeger, Owner and Founder of Foambid