Sign In to join the community | Help
Build & Remodel

Losing warm air through block walls

I am renovating my bedroom as a DIY project.  I am no expert.  I have a 1952 Cape Cod build from cinderblock.  There is no insulation and drywall was nailed into furring strips.  I plan on puttting up rigid foam board.  After tearing down dry wall I am noticing rather large gaps/chunks in my cinderblock which is letting a lot of warm air escape.  Most of the air is exacting from where they have the electrical boxes cut into the block.  There are two more on the other wall.  They do not fit snug and look like the one in the picture.  There are no cracks and gaps on the exterior. What would be the best method to seal these up?   Would it work to hit it hard with a bunch of spray foam? I have attached a picture.  Thanks in advance for your help.

Not what you were looking for ? Try posting a question
Posted 2017-02-14T12:38:56+0000  by Kinger06 Kinger06

Hello Kinger06 and welcome to the Community.


Before you get started installing your rigid insulation you must make sure walls are in good shape and that no moisture is infiltration from the outside.  This could lead to an environment for dangerous and unhealthy mold growth. 

Perform a moisture test by attaching a 2’x2’ plastic sheet to the wall with duct tape and keep in place for a week or so.  If moisture appears under or on top of the plastic sheet you must seal the walls.

You will need to remove the furring strips and outlets before you install the ridged insulation.  This will expose your cinderblock wall and you will be able to repair and seal the wall. 

Fill in any cracks and holes by removing any loose material and apply hydraulic cement. You could use foam spray foam insulation to fill in large voids in your walls. 

Here are some block wall sealers, Seal-Krete rated to stop up to 15 PSI, Drylok Withstands up to 10 lb. of hydrostatic pressure  and Behr  Basement and Masonry waterproofer Withstands up to 10 lb. of hydrostatic pressure

After all the wall repairs are made and sealed then you will be ready to install your ridged insulation, studs and electrical boxes.

Click here to view one way of installing rigid installation.  Here is a series of videos for insulating a basement with rigid insulation, but principles still apply.

Thanks for your inquiry.


Posted 2017-02-14T16:06:22+0000  by Char_HD_CHI
Not what you were looking for ? Try posting a question