When it comes to maximizing yield, you must first understand the conditions that affect yield. There is no standard test when it comes to “yield,” therefore, we interpret yield through density. In regards to spray polyurethane foam (SPF), “density” is the weight of one cubic foot of the foam. Through density, we can extrapolate the theoretical yield from a liquid chemical. For example, if the stated core density of a half-pound foam is 0.5/ft3, then a set of chemical weighing 1,000lbs should produce 2,000/ft3 of foam. Since there are 12 board feet in a cubic foot, theoretically, a half-pound foam should achieve 24,000 board feet. In reality, we can never achieve a perfect yield, so where does it all go? If we examine where the yield disappears to, we can have a better understanding of expected yields and how to maximize yield.
Conditions That Affect Yield
There are several factors and conditions that may affect yield. Although we can’t eliminate these factors, we can certainly limit the amount of yield lost overall. By following specific parameters, per the foam and manufacturer that you use, you will be able to maximize the yield on every spray foam job!
Factors to Consider:
- Starting Drum Chemical Temperature & Storage
- Substrate Type
- Substrate Temperature
- Substrate Contact Layer & Surface Skin
- Mixing Chamber Size
- Spray Mist
- Lift/Pass Thickness
- Number of Lifts/Passes
- Uniformity
- Off-Ratio
- Dialing in the Correct Temperature Settings
Keep reading, as we look at each factor to understand how they can affect yield, and how you can lessen the effects of each! Remember, there is no way to achieve a perfect yield, however, you can minimize yield loss by the conditions you set up for yourself before starting your next SPF install!
Starting Drum Chemical Temperature & Storage
Temperatures, you will find, are very important when it comes to several factors. Knowing what temperature your chemicals are at before starting, will be helpful when looking at the loss in yield. Starting drum temperatures account for 0-10% of loss in yield.
When starting your spray foam job, be sure to NOT start with cold chemical in the drum. Colder temperatures increase the viscosity of the ISO (A side) and Resin (B side). This throws your A and B side out of alignment which can cause the pumps to cavitate with cold, thick chemical. If the thick chemical transfers into the proportioner and pressurizes cold, as the chemical heats up, the volume changes, resulting in off-ratio chemical and a reduced yield.
To avoid this, use blanket heaters to warm the drums to the manufacturer recommended temperature(s). UPC open cell and closed cell foam drum temperatures are as follows:
| Closed Cell SPF | A-Side | B-Side |
| UPC 2.0 HFO | 50℉ – 75℉ | 50℉ – 75℉ |
| UPC 2.0 HFO Max | 50℉ – 75℉ | 50℉ – 75℉ |
| UPC 2.0 High-Lift HFO | 50℉ – 75℉ | 50℉ – 75℉ |
| UPC 2.0 | 50℉ – 75℉ | 50℉ – 75℉ |
| UPC 2.0 Max | 50℉ – 75℉ | 50℉ – 75℉ |
| UPC 2.0 High-Lift | 50℉ – 75℉ | 50℉ – 75℉ |
| UPC 2.0 Premium HFO | 50℉ – 75℉ | 50℉ – 75℉ |
| Open Cell SPF | A-Side | B-Side |
| UPC 500 Classic | 75℉ – 100℉ | 75℉ – 100℉ |
| UPC 500 Max | 90℉ – 100℉ | 90℉ – 100℉ |
| UPC 500 OCX | 90℉ – 110℉ | 90℉ – 110℉ |
Keep in mind that closed cell foam is susceptible to frothing. Frothing happens when the drum temperature gets too hot (>75℉). This will cause the blowing agent to expand too much, throwing the pressures between A&B out of alignment.
The warmer the starting chemical, the more aligned the viscosities will be! The use of band heaters or torpedo heaters are not recommended. This is due to the fact that they do not heat evenly and can scorch the blowing agent. Scorching the material reduces the reactivity and growth of the foam.
Substrate Type
The substrate is the surface or medium that you are spraying. There are several substrates that you may work with as a SPF installer. These may include concrete, metal, and wood, etc. Concrete and metal will reduce yield (0-10%). These two materials have a greater conductivity and suck the heat out of the chemical, thereby lowering reactivity and creating a thicker contact skin.
To reduce the amount of yield lost, if spraying onto concrete, pre-heat the substrate as close to 70℉ as possible. If spraying onto metal, preheat to no more than 50℉, as condensation may accumulate on the substrate. If spraying concrete and metal, use a sacrificial flash coat of ¼” to create a thermal break between these substrate types and the subsequent full pass layer.
Substrate Temperature
Above, you have learned what the substrate is…and here we are talking about temperatures again. The substrate temperature greatly impacts the chemical reaction and growth of the foam. As the substrate temperatures drop below 70℉, yield will begin to fall. If temps start to fall below 50℉, yield declines exponentially more. This factor accounts for 0-30% yield lost in a spray foam job.
Properly pre-heating a building can dramatically increase the yield. With the use of diesel or electric heaters (avoid propane), you can heat the building. If it’s a large building/structure, focus on heating the sections being sprayed. Using the sun to heat your substrate can be a great help too! An infrared thermometer may be used to gauge the substrate temperature.
Substrate Contact Layer & Surface Skin
Understand that when the SPF initially contacts the substrate, a dense layer of the foam forms which creates a dense skin on the surface. These dense layers cause 5-10% of a loss in yield.
Heating the substrate helps improve the density of that initial contact layer. A cold substrate cools the chemical reaction and reduces the reactivity, thereby limiting its expansion. Heating the ambient temperature improves the density of the skin formation. Heat the ambient temperature and substrate temperature as close to 70℉ as possible.
Mixing Chamber Size
The larger the mixing chamber the harder it is to control. Too large of a mixing chamber can result in 0-10% of a loss in yield. Larger mixing chambers increase flow of gallons per minute (GPM), which in turn, reduces the ability of the chemical to heat up properly in the proportioner. The mixing chamber size must be able to handle the delta T of the proportioner.
A greater yield (5-10% greater) has been noted when switching from a 02 to a 01 mixing chamber in experienced sprayers. Additionally, a 01 mixing chamber will allow the chemical more time to pass over the block heaters if the drums are still too cold. Remember to check the temperature of the chemical coming out of the gun, while also making sure the ratio of A and B sides are correct.
Spray Mist
Out of all of these factors, the smallest amount of yield lost is through spray mist. A fine mist of chemical is emitted from the gun that never makes contact with the substrate. Therefore, you can never fully prevent a loss in yield with misting. This mist is lost chemical (3-5% yield lost). This factor will ALWAYS account for some lost yield, but you can achieve less product lost here by lowering your pressures.
By lowering the pressures, the installer can spray closer to the substrate. For example, with the use of a 01 mixing chamber, the sprayer can lower the pressures between 1,000-1,200 psi to reduce the amount of mist, which improves yield.
Lift/Pass Thickness
A thinner lift will not generate enough exothermic reaction, which is necessary to fully expand the foam. An application that calls for a thin thickness will experience significantly less yield, therefore, bid the job accordingly! This factor alone, can result in 0-30% of yield lost.
If using UPC open cell SPF, a thicker lift will result in a greater yield. More exothermic reaction is generated, which helps to fully expand the foam. When using UPC closed cell SPF, make sure the formula you are using is designed for the applicable pass thickness. For example, a High-Lift formula when spraying at a 2” lift will not provide the desired yield. Spray as close to max pass thickness as each formula will allow in order to achieve optimal yield. BE CAREFUL! As spraying more than the formula permits risks excess exothermic reaction that will affect the physical properties and dimensional stability.
Number of Lifts/Passes
Each pass will produce another layer of dense skin (mentioned above) and will increase overall density. Each additional pass will reduce yield by 3-6% (overall, 0-20%). For example, it is common to see the in-place density at 3lb/ft3 for a 2lb/ft3 closed-cell foam when multiple thin passes have been applied. Overtime, a sprayer can minimize yield lost here.
Perfecting the technique of spraying will take practice. The sprayer should attempt to hit the manufacturer desired lift in a single pass. If using UPC open cell SPF, try and spray as close to the full thickness required as possible. As for the UPC closed cell SPF, spray as close to 2” in a single lift for the regular formulas, and 3-4 inches for the high-lift formulas.
Uniformity
Technique and skill will dictate how flat the sprayer can apply the foam. If the thickness of application is uniform, then less overall foam will have to be applied to achieve minimum required thickness. In other words, the more passes a sprayer does, the more yield that is going to be lost on the job (0-10%).
UPC open cell foam should be sprayed side-to-side. A thicker application that requires more than one pass should be applied as follows: first layer, side-to-side; second layer, up-and-down. The best application for UPC closed cell foam is the up-and-down technique. This motion will provide a more uniform and flatter application.
Off-Ratio
With this category, the installer, whether novice or experienced, may expect to see 0-30% of yield lost. Being off ratio can not only result in lost yield, but can also have your end product looking less than acceptable and physical properties of the foam may be diminished. Some factors that affect the foam ratio include, but aren’t limited to:
- Cavitation
- Clogged Y-Strainers
- Clogged Check Valve Screens
- Mixing Chamber Clog
- Cold Chemicals
- Worn Pump Seals
The best way to prevent becoming off-ratio is simply by maintaining your spray foam equipment. Keep a detailed track-record of your equipment, and when different parts were last serviced. It may seem like a hassle to keep up with equipment maintenance, however, improperly working equipment and/or off-ratio foam will give you a much larger problem!
If you don’t typically do maintenance checks, start by cleaning the mixing chamber(s) daily. Valve screens should be checked daily while Y-strainers should be checked weekly. The dry portion of stick pumps should be rebuilt each year while the wet portion of stick pumps should be rebuilt every 2 years. Additionally, rebuild the pump seals every 2 years.
A great benefit of newer equipment is that several brands utilize flow meters. Flow meters monitor the ratio of the A-side & B-side and provide assurance that your equipment is working properly. Remember, you will still need to maintain other parts of your spray foam equipment!
Dialing in the Correct Temperature Settings
Here we are talking about temperatures again. This is a major factor and may account for 0-30% of yield lost. If your temperatures are too cold, then lack of heat will generate poor chemical reactivity, resulting in poor yield.
Start by finding the desired temperature you want the foam coming out of the gun at and setting your hose at that temperature. The hose heating element is not meant to be a primary heat source, only to maintain the heat. If using UPC foam, set your A-side 2-5℉ higher than the hose and set your B-side to 2-5℉ higher than the A-side. The B-side should be set higher than the A-side because the resin has a lower viscosity versus the ISO. Understand that the A&B temperatures are set higher than the hose as the chemicals will lose a few degrees as it travels to the gun.
If spraying open cell, starting temperatures must be high enough that the foam shrinks slightly from the studs, then lower the temps 3℉ at a time until the shrinkage stops. This is known as the yield sweet spot! When using a closed cell formula, it is better to start with lower temperatures. A “wet line” must be established. The “wet line” is the dark, unreacted chemical. This line should last for 1-2 seconds to achieve maximum yield. If the wet line lasts for more than 2 seconds or the liquid is drippy, the chemical is too cold. If the wet line isn’t visible, the chemical is curing too quickly and the foam is too hot. Again, these tips are meant for open and closed cell UPC spray foam.
UPC 500 Max In-Field Yield Simulation
UPC created a data sheet that provides two hypothetical scenarios for the open cell formula, 500 Max. Each Factor is broken down to see how much yield was lost, comparing an experienced sprayer versus a novice sprayer.
As you can see in scenario A, in optimal conditions with an advanced sprayer, hypothetically, a near perfect yield was achieved versus scenario B.
Conclusion
Throughout this post, we have gone over several conditions that can reduce the amount of yield you see on your job. All of these factors affect the amount of yield differently for each individual sprayer. Remember, it is impossible to achieve a perfect yield. The more experience a sprayer has, the better yield they will get.
As you start your next SPF job, consider these factors and make adjustments to be able to produce a better yield!