Coat the cinder block walls with concrete sealant using a paintbrush or roller. Allow the sealant to dry for at least 30 minutes, and then apply a second coat of sealant.
Coat one side of a sheet of R-Tech rigid foam insulation with construction adhesive using a paintbrush. Place the insulation sheet on one wall so that one side meets the corner of the wall. Press the board against the wall, and hold it in place for two to three minutes to allow the adhesive to bond the sheet to the wall.
Continue coating the R-Tech rigid foam insulation sheets with construction adhesive. Press the sheets against your cinder block walls, fitting the edges of each sheet tightly together to prevent insulation gaps. Cut the sheets with a utility knife as necessary to obtain the proper sizes and accommodate ductwork, electrical outlets and other obstacles.