# Exterior spalling on cinder block foundation wall



## pkendron

Sections of the parging on the cinder block foundation wall outside started to fall away over the winter, so this month, I started to knock it away to replace it. Underneath, I found that some of the cinderblocks are starting to spall.

In some cases, about 1/8 an inch of the block face would come off with the parging.

So my question is, is it OK to just cover this up again with the cement I'm using? (QuickWall from Quikrete) Or do I need to do other repairs first?

I'm relatively new to this whole repairing thing, so any help anyone could give is welcome.

Thanks!


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## ChrWright

Parging on any outside masonry usually doesn't last very long in climates that are subjected to heavy freeze & thaw. It's likely to be something you have to keep up on a yearly basis. Just make sure you get everything loose off, and follow the directions of your product closely. Most recommend you wet the masonry a little before application so it will bond better.

Is this a mortar troweled directly to the block or a stucco over a wire mesh?


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## DDEENY

I've had this same exact problem with spalling cinder block foundation walls. The crux of the problem is that cinder block is inferior to concrete block and is softer, so when the surrounding mortar (which is harder than the cinder block) is dampened by winter moisture and freezes, it expands at great force and pinches the surface of the cinder block and forces it to shear off in a thin layer, thus causing the cement plaster to fall off with it. If the basement is finished with interior wall finish and/or insulation, that worsens the problem all the more because the warmer interior basement air is unable to migrate through the masonry wall and provide a small amount of heat to prevent the mortar from freezing and expanding.
I've been patching my foundation walls for years and even had a mason install metal diamond mesh lath and cement plaster over the existing surface and even that hasn't helped, although the lath supports the plaster to keep it from falling off. The contractor also wasn't careful enough to fold the lath over the corners to brace the plaster and now I have cracks at all of the corner locations. I've considered several possible solutions, including the most drastic which would be to replace the upper 3 courses of cinder block with concrete block in strategic 4-foot sections at a time to keep the house sufficiently supported, or possibly breaking out half the depth of the block and filling the cores solid with concrete (perhaps also using rebar), then re-plastering. But these solutions would require the approval of a licensed engineer and the local engineering dept.  I've also considered cutting the mortar from the outer surface joints and replacing it with a type of mortar that's softer than the cinder block to prevent spalling. The problem is that if the existing mortar freezes, the spalling will recur regardless of anything so long as the cinder block remains. I've also considered covering the foundation with rigid insulation with the hope that its R-value would suffice to prevent the mortar from freezing and then with cement board panels and plaster, but I have only about 1-1/4" from the face of the foundation to the edge of the siding and the result would never look right depending on the thickness of the insulation panels. Finally, perhaps one last solution would be to build a brick or stone knee wall on its own footing in front of the foundation wall with insulation behind to protect and conceal the foundation, and the new surface would of course protrude and I'd need to place a Z-flashing under the edge of the siding to prevent water from seeping behind the new surface. Tough problem to address, that's for sure, not to mention uncertain results and cost.


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## nealtw

Welcome to the site. If that is the problem, then the foam on the outside would keep it dry amd maybe stop the wicking action from below but then inspection is impossible. You can go thicker foam with the Z flashing


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## mudmixer

DDENNY -

I suggest you bone up on terminology and materials.

I doubt if "cinder block" are even available now and they have been rare for about 60 or 70 years. You may be confusing they by using a colloquial inaccurate term because of the shape or experience. Generally cinders are waste product that is variable and consequently difficult to use, but it does work well for running tracks if coarse enough.

I only cinder block that have seen in the U.S. were and may still be available and use natural volcanic cinders for color and texture on plain and split face architectural cinders.

You may be confusion "cinder block" with lightweight concrete masonry units (CMUs or block) that use manufactured lightweight aggregate for fire resistance, acoustics/texture reduced weight. - They are more costly than normal weight CMUs, but have desirable properties. All CMUs for the past 60 or 70 years have to meet the same specifications - ASTM C90 (Specification for Loadbearing Concrete Masonry Units). The specification is essentially the same for all CMUs, and is broken down into density categories for specifying purposes and identification. All have to meet the same strength requirements, but it is rare to find a block that is not at least 30% over the minimum strength because of the manufacturing processes. - Quite simply, it is too expensive to make a weak block because a contractor would not buy or lay it.

Dick


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## slownsteady

Mudmixer: Real good explanation. I appreciate the knowledge. Cinder blocks may not have been available for 60 years, but I bet some are still around. Many homeowners on this site are dealing with older homes. DDenny didn't say how old his house is. If he's right about his wall, what to do?


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## mudmixer

The best approach, if you desire to cover up the block is to attach lath/mesh to the block from the top of any exterior below grade "waterproof" coatings and then stucco over it.

This way, you can have the finish/pattern you desire and provide a break between the coating that sees the short term weather from the massive thermal sink or storage that is more stable. - You need a break because of the different materials and their properties. A mechanical break and connection is a good approach if you want to cover the block ("cinder" or modern).

Dick


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