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I would like to refinish an old wall of previously finished CMU blocks and bricks. See these pictures:

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(full-size images also available at https://www.dropbox.com/sh/ryr4m5adx6cd22c/AADFZKSiNORkaFE8bO6gDscoa?dl=0)

The wall is original (from 1939) it doesn't appear to be sagging and the cracks are probably just on the surface. The finish layer has cracked, among other things, possibly due to water leaking from within the wall.

As you see in the picture, there are a few other things going on:

  • a layer or two of bricks at the top
  • a section of concrete that was done more recently (strong, reinforced with rebars)
  • an area of concrete to fill a whole underneath the above concrete, also done more recently
  • 1/2 inch holes at the very bottom of this wall to release the water that may be within the wall, also done recently

In general, I have no concerns with this wall other than the aesthetics.

I recently learned about the properties of surface bonding cement. For example: https://www.homedepot.com/p/SAKRETE-50-lb-Surface-Bonding-Cement-in-Gray-65300845/100321221

It has fibers in it and allows you to build walls out of CMU blocks without using mortar.

I am thinking of applying a layer of surface bonding cement on top of all of what I have at the moment (including the bricks, the concrete, the cracked layer) without removing any of it. Is it a good idea? I don't see much discussion about surface bonding cement on the internet.

What I see regarding bonding, however, is advice like this: https://www.swimmingpoolsteve.com/pages/bond-concrete.html which, in a nutshell, is:

  1. Remove grease and oils
  2. Acid wash
  3. Rinse and neutralize the concrete
  4. Apply a bonding slurry
  5. Apply the new concrete layer

Seems like solid advice. Is this advise compatible with surface bonding cement? That is, does it make sense to do 1 through 4 above before applying surface bonding cement? Or is that not needed when using surface bonding cement (as opposed to concrete which is what the advice is about).

Or what is the best advice in general for my situation?

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    Please edit your post to upload the images directly to this site. Not everybody can access Dropbox in all locations, whereas Imgur (this site's hosting partner) seems to be available to almost everybody. You may have to resize images to smaller than 2MB, but that's not difficult.
    – FreeMan
    Oct 5, 2021 at 17:11
  • Will do when I get to a computer. I tried actually but they got rejected - too large. I can resize though. However, note that the link should not require Dropbox client, it’s just a web link.
    – Peter
    Oct 5, 2021 at 23:38
  • @FreeMan Done. Thanks for the note.
    – Peter
    Oct 6, 2021 at 1:31
  • Thanks! Some places block file sharing services but not photo sharing services - web-based or installed client-based alike.
    – FreeMan
    Oct 6, 2021 at 12:20
  • Also (sorry for not noticing this the first time), please include some quotes of the relevant items from your last link. Web sites die all the time and if that one goes down, nobody knows what advice it is that you're referring to.
    – FreeMan
    Oct 6, 2021 at 12:32

1 Answer 1

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I have used surface bonding cement. I like it because it looks good and helps hold everything together, but it is not a miracle worker. Surface bonding fibered cement doesn't last forever and needs maintenance now and again. Your wall appears to have been previously surfaced. The water that pushed through the wall is going to give the coating a hard time, but go for it anyway.

Your wall is in much better structural condition than mine. Your wall could also be cleaned really well. Go for it. You'll be happy that you did because it will help the wall last longer and it will look good. Just don't expect it to last forever. There really isn't anything else you can do.

More Details as per comment:

  • Nothing sticks to dust, dirt, or flakes. A solid clean surface is necessary.
  • Nothing sticks to smooth, so a rough surface is necessary. A chisel or whatever can be used to scratch a smooth surface.
  • The water in the cement will evaporate causing shrinkage as it dries. The big deep holes will have to be filled in stages. Filling a big hole all at once means that the top will shrink (dry) first which causes the rear to pull away and release from the wall behind as it shrinks.
  • Water must be stopped at the point of entry, not at the point of exit. Water seeps through the wall with a pressure required to push it down and through the weep holes at the bottom. Most of it evaporates off of the top and you don't even know it is happening. But, the water pressure against the back of the cement will pop the surface bonding cement off.
  • The wall will have to be redone every 3 to 10 years or more or as often as it needs redone. It will depend upon the measure of water pressure from the rear, general movement, and how bad it can get before you want to repair it.
  • The fiber in the cement will not cause the cement to stick better, but will will cause the cement to remain on the wall until a big section fully releases.
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  • Thank you @Paul this is helpful! Does it make sense to chisel out the previous surface before application? Does it make sense to use the 1 through 4 in that bonding advise I pointed to? Finally, how often do you think maintenance will have to be done? And what? Apply another layer?
    – Peter
    Oct 7, 2021 at 5:38
  • I appreciate the clarifications. I'll go ahead and accept this answer although there are a few things that are still unclear to me: Would acid wash be necessary? Maybe I'll skip that part? I was thinking of chiseling the previous layer not to roughen the newer concrete - but that's a good point.
    – Peter
    Oct 7, 2021 at 23:11

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