How to Put Foam Insulation Behind Plaster

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Many older homes with plaster and lathe walls are not insulated. The Department of Energy estimates that insulating an existing older home can reduce energy costs as well as create a more temperate, comfortable environment for the home dwellers. Rather than remove the plaster and lathe -- an arduous, messy task -- you can insulate the wall cavities with sprayed liquid foam insulation. While foam insulation is more expensive than traditional blown-in cellulose or fiberglass batt insulation, foam offers twice the insulation value of fiberglass batts. You can reduce the cost of foam insulation by installing it yourself.

Things You'll Need

  • Stud finder
  • Pencil
  • Drill
  • Hole saw
  • Plastic tubing 5/8-inch diameter
  • Electrical tape
  • Liquid spray foam equipment
  • Locate and mark the position of each stud with the stud finder.

  • Drill a hole with the hole saw 3 feet up from the floor in between the stud cavities. Drill a hole 6 feet up from the floor, and drill another holr at the top of the wall. Each stud cavity should therefore have three holes, one at 3 feet high, one at 6 feet high and one at the top of the wall cavity.

  • Tape the nozzle of the liquid spray foam gun to one end of the plastic tubing with electrical tape. Connect the liquid spray foam gun to the foam dispenser.

  • Insert the other end of the plastic tubing into the bottom wall cavity 3 feet up from the floor. Feed the tube into the hole until you feel the tube hit the bottom of the wall cavity.

  • Press the gun trigger and spray the foam into the cavity. Swish the tube back and forth as you spray, to provide even coverage inside the cavity. Do not overfill the cavity. Stop spraying when you see the foam rising up to the level of the hole.

  • Insert the end of the plastic tubing into the second wall cavity 6 feet up from the floor. Feed the tube into the hole until you feel the tube hit the top of the spray foam portion already inside the wall cavity.

  • Press the gun trigger and spray the foam into the cavity. Swish the tube back and forth as you spray, to provide even coverage inside the cavity. Stop spraying when you see the foam rising up to the level of the hole.

  • Insert the plastic tube into the hole at the top of the ceiling. Continue spraying the foam into the cavity. The foam may ooze out of the holes as you spray. This is normal. Allow the foam to dry and slice off the excess foam even with the wall surface.

  • Continue filling the rest of the wall cavities in the room. Allow the foam to dry and slice off the excess foam from the holes so that the foam is even with the wall surface.

  • Patch the holes with joint compound. Allow it to dry. Prime and paint the walls.

Tips & Warnings

  • To prevent problems from overspraying and rapid expansion, select a slow-expanding liquid foam for your project.
  • Liquid foam insulation can expand five times in size very quickly. Never overfill a wall cavity or the plaster may expand or loosen from the lathe. Before applying to the wall, practice spraying foam in discarded cardboard boxes to accommodate to the expansion rate and installation procedure.
  • Do not insulate walls that contain operational knob-and-tube electrical wiring. This type of aged wiring overheats when surrounded by insulation. Many municipal building code regulations prohibit insulating cavities that contain knob-and-tube wiring.

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References

  • Photo Credit Brand X Pictures/Brand X Pictures/Getty Images
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