The Magnificent Membrane
The manufacturing and installation of low slope- polyurethane foam membranes (LS-SPF) takes place simultaneously, resulting in an emphasis is on manufacturing and processing controls. LS-SPF systems are formed by the resulting reaction created between mixing two liquid chemical components “A” and “B” while spraying to a prescribed substrate. The two liquids are packaged in individual containers, usually 55 gallon drums. The set, containing 500 lbs of Resin-“B” component and 500 to 550 lbs. Iso-“A” – are sold by the pound. They are processed in a 1:1 mix ratio or mixed equally in parts by means of plural component airless spray. Similar to airless spray painting and coating applications, the two materials are kept separate just prior to spray applying to the prepared surface. From the drums, the two liquid components are displaced or transferred equally from their individual containers to a processing machine called a proportioning unit for its ability to place both products under relatively equal pressure (proportioned equally). The proportioning unit is equipped with individual pumps and heaters that places the components under “prescribed” relatively equal, pressure (1000-2000 psi) and heat (110 to 160 degrees f).
The two components, still remaining separate, are then directed thru individual heated- high pressure hoses to a plural component air-actuated spray gun. Once the spray gun trigger is engaged both chemicals are continuously forced from the pressure provided by the proportioning pump- thru separate ports into a mixing chamber which atomizes (mixes) the components just before they exit out of the spray tip.
The resulting spray mist comes in contact with the surface and begins to grow expanding roughly 30 times its size in volume to form the SPF membrane or a monolithic spray applied rigid closed cell polyurethane foam thermo-set cellular plastic membrane or more simply put SPF. Processing these membranes is said to be a “technical art” and very specific manufacturing guidelines need followed in order to obtain a quality end product. The two most emphasized areas are; skill of the applicator and atmospheric conditions required to properly process product – typically humidity, wind and temperature.
Three main knowledge points of a “Spray Mechanic”:
- Proper procedure in handling a spray application job
- What the urethane foam should look like at application
- What to do if there is a problem with equipment and ability to correct
Basic manufacturing guidelines:
- Apply when ambient air temperatures are between 50-120 degrees
- Do not apply in inclement weather (rain, snow)
- Substrates must be dry at time of application
- Do not apply when humidity is in access of >85%RH
- Do not apply when wind velocities are greater than 15 miles per hour
- Protect adjacent surfaces from overspray
- Store product 65-85 degrees
- Materials in containers maintained 65-75 degrees during processing
- Utilize plural component equipment capable of supplying product within + 2% of ratio
- Dynamic pressures > 1000 psi
- Pre-Heater temperature setting 120-130 degrees
- Hose heat setting 120-130 degrees
- Mix ratio 1:1 by volume
- Maximum pass thickness 1.5”
- Wait 10 minutes between subsequent passes
- Become familiar with the hazards involved with the use of these products.