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Liquid Rubber can be sprayed using airless equipment. The fluid characteristics of Liquid Rubber produces a considerable pressure drop in the hose; therefore, choosing the correct equipment is key. The pump size, hose diameter and hose length must be carefully chosen in order to achieve satisfactory results.

The following recommendation is for Graco equipment. Other manufacturers with comparable pumps may also be used.

Liquid Rubber must be thinned with solvent to achieve a sprayable viscosity. See recommendations below.

Equipment capable of spraying Liquid Rubber

Pump Model Max. Pressure Fluid Flow Hose ID Maz. Hose Length
Graco GH733 3500 psi 3.0gpm 1/2 inch 150 feet
Graco GH3640 36000 psi 3.8gpm 1/2 inch 150 feet

Roof Rig
Gun should be rated for spraying mastics. A 30-40 inch tipextension is recommended
Tip Size .017 to .021with a 12 inch fan width

Note: Do not use a "whip" between hose and gun. This reduces flow and pressure which results in poor atomization.

Thinning Liquid Rubber

The as shipped viscosity of Liquid Rubber is 34-37,000 cp which is too high for spraying. By adding one gallon of Xylene Solvent to a 5 gallon pail the viscosity drops to 10,000 cp at 75° F. More solvent may have to be added at lower temperatures.

The spray atomization can be improved using a smaller tip size or adding more solvent to reduce viscosity.

Wash solvent from previous pump cleaning can be used for thinning after it is strained to remove dirt


Caulking around fasteners is usually not necessary.The physical properties of the EPDM Liquid Rubber will produce a longer lasting seal around fasteners than caulks will. Caulks can later become brittle with age causing loss of adhesion and crack.

It is good practice to brush the rubber into the fasteners after spray application to ensure complete coverage. This procedure will be less time consuming than caulking.

Fabric Reinforcing of Seams and overlaps

Tight overlaps and standing seam joints do not need to be reinforced. Overlaps with greater than 1/ 16" or corroded edges should receive fabric reinforcing.

  • Apply a light coat of Liquid Rubber.
  • Center the fabric on the overlap and roll it out taking care not to create wrinkles.
  • Press the fabric down with a squeegee or wide spatula
  • Spray a full coat of Liquid Rubber to seal top surface of the fabric.
  • Roll back over with a short nap roller to ensure complete surface coverage.


Overspray can travel a long way when carried by a breeze. Vehicles should not be parked downwind near the work area. Overspray landing on a vehicle can be easily removed with Mineral Spirits even after 24 hours. Thereafter, stronger solvents such as Xylene will be effective in removing the rubber but may dull some finishes.

Rain Showers or Freezing Temperatures

Unexpected rain showers after application may affect the surface appearance but will not wash the material off the roof. Temperature drops below freezing will arrest the cure but will not damage the Liquid Rubber. The cure reaction will resume again whenever adequate temperature returns.

Cleaning Equipment

A three stage Hushing is recommended.

  • Add Xylene on top of the remaining rubber in pail and continue pumping until Xylene reaches gun. Reduce pump pressure; add 2-3 gallons of Xylene to pail and spray into pail. With tip removed for about 30 seconds. Then remove gun and recirculate solvent for 3-4 minutes. Tilt pump out of solvent and let air pressure purge the material in hose.
  • Put clean pail with clean Xylene under pump and circulate at low pump pressure 3-4 minutes. Connect gun without tip for another short flush, then remove gun. Again tilt pump out of solvent, let air pressure purge the line.
  • Put another bucket with clean solvent under the pump and circulate for 3-4 minutes. The solvent should be a little stained by now. Connect gun with tip and spray about 10 seconds with rag over the tip.

The equipment is now ready for the next use. lf work is to continue another day the solvent can remain in the line if gun is attached. Clean up solvent should be strained and used for thinning as application continues

On some materials, such as EPDM rubber sheets, some swelling may occur due to solvent absorptions after applying EPDM Liquid Rubber ®. This is normal. This swelling will recover with time and heat. In 80° F or so, allow 7 to 14 days to recover. In colder temperatures, recovering will take several weeks, as much as 6 to 8 weeks in 60° F.

The information presented herein is furnished free of charge and is based on technical data that Pro Guard believes to be reliable. It is intended for use by persons having technical skill and is at their own discretion and risk. Since conditions of use are outside our control we make no warranties, express or implied, and assume no liability in connection with any use of this information. Nothing herein is to be taken as a license to operate or a recommendation to infringe any patents.

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