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Douger_F 04-14-2009 06:34 PM

Mortar bed removal from block wall
Is there an easy way to remove an old mortar bed from a block wall? I am renovating a 1950's bath where there was a pink ceramic tile shower. This is on 2 exterior walls made of concrete block and the mortar bed was about 1 inch thick. The tile has been remove down to the first coat with a hammer drill with chisel, but there is 3/8 to 1/2 inch of first coarse/scratch coat mortar still on the wall. Because the space is small, just building a wall in front of it is not a viable option. It is the intention to put 1x or 2x (on the flat) firring strips on the wall with foam between the strips to insulate the wall.

One possibility is to use a grinder and wheel to remove portions of the mortar bed and just shim the firring strip out, then insulate the space behind the firring strip with canned foam.

Any suggestions would be appreciated.

Tscarborough 04-14-2009 06:41 PM

Why do you need to further insulate it, and what is your final finish going to be?

Douger_F 04-14-2009 07:44 PM

The house is old, there is no insulation in any of the walls. Room by room, we have removed the drywall, added 1 1/2 foam board insulation to the walls and fiberglass bats to the ceiling. The house has a flat pitch roof, so we fill the ceiling cavity with fiberglass and have a radiant barrier. This is a single story building with block walls/hard coat stucco exterior, slab on grade floor. This is the last set of rooms to complete the whole house. This renovation has cost us materials only, but the energy cost reduction has been nice.

The room was and will be the master bath, however updated with normal colors, not pink and black. Final covering on this wall will be drywall as the shower will have been moved. This project was started because the shower pan is leaking (lead pan) and will be replaced. The shower floor must be removed down to the slab. Some of the wall tile were cracked, so there is plenty of reason for this remodel.

Tscarborough 04-14-2009 07:50 PM

I am not questioning your reasons, just your logic. A stuccoed 8" CMU wall with a 1/2" of parging is a pretty good thermal mass. I am not sure you will gain versus the effort required to remove it. It can be done mechanically, for certain, but what, in fact, will you actually gain?

Depending upon the climate and interior environment, you may well be creating a trapped moisture problem by creating an airspace.

Douger_F 04-14-2009 08:10 PM

The room is part of the north and west corner of the exerior of my house. Living in NC, in the winter the wall would sweat very badly because it was always cold. The tile was mounted directly to the wall on the mortar bed. The cold air could be felt leaving the walls to the point if the shower curtain was pulled wall to wall, it would buldge with the "weight" of the cold air. The room could not be kept warm easily, so the door was always shut to keep the heat in the MBR at a reasonable temperature.

PT2x3's are being placed against the outside wall to get 1 1/2 inches of gap for rigid foam insulation, Given the thickness of the mortar bed, it seems as if the most logical thing to do is to shim/space/support 1x3 firring strips at the proper depths to create an even wall. Then insulate the remainer, whatever the depth, using the 1/4, 1/2, 3/4 and 1 inch thickness boards. Another thought is to buy one of those spray foam kits, spraying the wall between the firing strips and cut it down to the right thickness.

Tscarborough 04-14-2009 08:19 PM

" Living in NC, in the winter the wall would sweat very badly because it was always cold"

This is your concern. If you do not properly address this, that sweat will occur inside the wall and you will have serious issues. Your current plan does not address it, unless you are planning on transferring the airspace to the (properly weeped) exterior barrier wall, in which case you just place a waterproof membrane against the pargecoat and sheetrock it.

Douger_F 04-14-2009 09:41 PM

The way I see it, the shower wall would sweat because it was significantly colder due to being a north or west wall with no insulation and in a bathroom. This alone would drop the air below the dew point in the house and cause the sweating on the wall. Additionally, there was no exhaust fan in the bathroom. All of the walls in this house would sweat in the winter. In this last set of rooms that are currently being renovated, there are streaks where water would run down the wall due to condensation. The cold cinder block wall coupled with the 3/4 inch air gap between the drywall and the cinder block wall made for a draft space, but also one where moisture would collect. Much of the drywall had mold on the back (some on the front).

In the rooms where the remodling has been completed, there is not the condensation because of vapor barriers and insulation installed. After being up for 4 years, one exterior wall of drywall was removed for a plumbing repair, and there was no signs of moisture.

Back on topic, so the only/best way to remove the mortar bed is mechanically?

Tscarborough 04-14-2009 11:13 PM

That is the only viable option.

jomama45 04-15-2009 07:47 AM


Originally Posted by Tscarborough (Post 260094)
That is the only viable option.


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