Remove Thick set mortar on CMU wall?

Old 01-19-15, 07:13 PM
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Remove Thick set mortar on CMU wall?

We did some demo work this weekend and found out that the exterior wall of our bathroom is just CMU with thick set mortar applied to it, no lath in between. I'm nervous that removing the mortar will affect the integrity of the CMU since it chipped in one small location that we tried, but not sure we can leave it since it is so rough once we chipped the tile off. Should we attempt to remove the mortar, or is there a way to smooth it out enough to get a new tile bed on there? There is no room to furr out in front of the wall.


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Last edited by Jenfumuso; 01-19-15 at 07:20 PM. Reason: Added photo
Old 01-19-15, 09:20 PM
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You'll kill yourself trying to remove that mortar. It takes an experienced tile guy to correct it. I certainly couldn't do it.
Old 01-20-15, 07:48 AM
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That's a sorta common situation in parts of the world where cement is the most common building material. I'd go over the whole wall tapping with a hammer or the pointy end of a masons hammer listening for hollow spots and remove anything that's not solid. Then patch the damaged areas to be flush with the surrounding mortar. How rough the area is and your tile will determine if you need an intermediate skim coat or can go right over with tile.

Larger tile with a deeply notched trowel can go over a rougher surface while smaller tiles generally need a smoother surface. Watch out for bumps or ridges that will snag a notched trowel and grind or chip them down. Then give the wall a thorough wire brushing and a good cleaning to remove any dirt or loose material before proceeding with the next layer. It's also very helpful to thoroughly wet the wall before applying the next layer (thinset or skim coat) to prevent the old stuff from soaking moisture out of your wet mortar/thinset.

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