How do I self-repair a section of crumbling basement wall, or should I hire a professional?


How I discovered it:

I removed some exposed blue foam insulation from my basement walls to comply with my home insurer's request (part of the solution to the question I posted here). Unfortunately, I discovered a crumbling foundation wall hidden behind it in one corner.

About the house:

The house was built in 1928. The foundation wall is a mix of stones and mortar - and even some seashells (I’m on the east coast of Canada, and apparently this is very common). The basement is dry most of the time, but with very heavy rain/snow thaw in the spring, I get water seeping from beneath the concrete floor/walls (this corner is particularly bad and now I know why!). This does cause some puddles, but I have a sump pump that helps move water away. The point here is that the basement is not waterproof - which I accept for the time being.

Overall Questions:

  1. Should I, and how do I self-repair this section of crumbling basement wall?
  • 1b. What kind of mortar should I use? (my reading has suggested I should use a high lime mix - which is breathable and won’t trap moisture)
  1. Is this is a more serious problem than I'm assuming - should I hire a pro to assess it?

My expectations are not to create a perfectly watertight seal (that would be unrealistic without work being done on the exterior), I am simply looking to prevent further damage, without doing even more damage with the solution I choose. There are no plans to finish this basement.

My Ideas:

I was thinking about getting some stones and mortar to fill the voids.

To further secure that section of the wall I was thinking about getting some wire-mesh, securing it over the broken area, and then parging over the top for extra strength - is this a terrible idea?

Broken section of wall: enter image description here

Close-up of damage: enter image description here

This large section is fairly loose: enter image description here

This section is starting to experience the same issue: enter image description here

  • 10
    I'd be worried about additional deterioration that you cannot currently see. The "hire a professional" route seems like a good choice as even as it stands this appears to be well beyond more DIYer's capabilities. You'll also want to determine WHY this is happening and resolve that too.
    – jwh20
    Sep 7, 2021 at 12:00
  • 8
    Would go with a professional also. That wall is use to support your floor joist ends also. Just slapping on new mortar and stones won't do, need to clean out remove the loose stuff first, which might cause lost of support of joists/walls above.
    – crip659
    Sep 7, 2021 at 12:15
  • 1
    Re-pointing the wall could be an option but I hesitate to add it into my existing answer. youtube.com/watch?v=jgU245CbALc
    – MonkeyZeus
    Sep 7, 2021 at 14:19
  • 1
    @user3067860 This is not a concrete spalling issue because, as the question states, the wall is not poured concrete. This is just plain spalling, caused by the exact same mechanism (increasing acidity/decreasing pH); the difference here is that the delamination is happening because the bonds in the mortar are disintegrating due to the acidity, allowing water to seep in, which causes the acidity to increase, which disintegrates more bonds...
    – Ian Kemp
    Sep 8, 2021 at 8:27
  • 2
    Whether or not I finally ended up using a pro, I would call one out to look. Namely, I would probably have a structural engineer check it out first. Don't mess around with foundations -- the entire house relies on them being stable.
    – Bloodgain
    Sep 8, 2021 at 21:36

4 Answers 4


It looks like a cosmetic DIY patch-job was already attempted before. The current situation is exactly how you can expect your attempt to turn out.

This is a structural issue and I would hire a professional. Odds are very high that an entire section of wall will need to be removed and a new wall made of block will be installed.

Prepare yourself and your wallet for a hefty estimate.

If you want to sleep better at night for a small sum of money then frame out a load-bearing wall spanning the entire crumbling section as close to the foundation wall as possible without touching it. Just make sure your bottom plate is pressure-treated.

This shouldn't be treated as a permanent fix but it should hold up for years no problem until you can save enough money for a proper repair. Consider it "permanary".

The tangent wall looks like it is starting to crumble as well and you won't have the luxury of supporting it using a load-bearing wall since it runs parallel to the floor joists.

Definitely inquire about that wall while you're getting estimates. It would save money to do it all at once instead of staggering the repairs.

  • 2
    "Prepare yourself and your wallet for a hefty estimate." This was my initial thought. Was honestly wondering if they might suggest underpinning those existing sections for replacement. It doesnt look good, from the photos, sorry to say.
    – element11
    Sep 9, 2021 at 2:35
  • 3
    The sobering and financially scary answer, but it's the one I'm going with. I plan on staying here long term, so anything temporary I do now, will still be my problem later on. So, I want the solution to be permanent and safe. I have called out a professional and I will update my question with details of the proposed solutions
    – user138192
    Sep 9, 2021 at 14:31
  • @welshonabet I look forward to reading about your next steps! I'm sorry that the previous owner hid this problem from you.
    – MonkeyZeus
    Sep 9, 2021 at 14:45

The first step of repairing a deteriorated wall is to knock loose and remove the bad materials to the solid base. However, in your case, I suspect there is nothing solid that remains, as the cracks are likely to have penetrated through the thickness of the wall, the removal, and refilling of the defects will require significant efforts, so a professional is therefore recommended.

Please do not use seawater and sand/gravel that contains salt in the repair works.

  • Curious - why is salt an issue?
    – Vikki
    Sep 8, 2021 at 0:59
  • 1
    @Vikki 1) Salt is corrosive especially on metal. 2) In porous materials, the salt lowers the freezing point of water, attracts moisture, and increases the pressure of frozen water.
    – r13
    Sep 8, 2021 at 1:24
  • 4
    @Vikki, 3) Saltwater seeps into pores and evaporates, leaving salt crystals behind and forcing the pores open, causing cracks.
    – Mark
    Sep 8, 2021 at 2:07
  • @Mark Good adds on!
    – r13
    Sep 8, 2021 at 3:11
  • Based on the state of this section of wall on the outside (which I thought was just cosmetic), I'm almost 100% certain "cracks are likely to have penetrated through the thickness of the wall" is accurate
    – user138192
    Sep 9, 2021 at 14:33

Caveat: I'm not a structural engineer, or a builder.

If you want to answer the "how can I DIY this?" question, the answer is to get a structural engineer to draw up some plans for how you can temporarily brace the weight of the house so you can remove one portion of the wall at a time until you have a new foundation that will stand up to the elements. Once you have a structural engineer look at it and draw up a plan for temporary bracing (~$2k USD), you can dig dirt from the outside of the foundation wall (~$1k USD per section) and then cut out (~$2k USD per section) the compromised areas completely in sections about 5' wide. Build forms to hold your new wall (cheap if you DIY), lay rebar (cheap if you DIY), pour (not terribly expensive if you do a bunch of alternating sections at once), and repeat until you have a brand new foundation. It's unlikely an engineer will sign any plan that doesn't involve a complete replacement of all affected areas. Your slab may also need to be replaced if it is in bad shape or it won't be able to take the load of the temp braces.

Because this is such a niche area for a builder, it's likely you will pay a huge amount of markup for them to learn on your project. So you're doing the right thing by educating yourself on the various options. Then you can take any critical thought out of the hands of the builder, which always makes things cheaper and better in the end.

As mentioned by others, any attempts to patch will end up as they have in your photos.

EDIT - builders will just jack up your house, knock down foundation, and rebuild. Not sure price on that, but not a huge markup on that process AFAIK.

  • I'm handy, but this sounds like it's out of my skill level. Regarding "builders will just jack up your house, knock down foundation, and rebuild." - would they/I usually need to employ a structural engineer in this case, or is the structural engineer only really required in the scenario where I'd be doing some of the work myself? @rajan
    – user138192
    Sep 9, 2021 at 14:37
  • 1
    Yes they'll have to get structural engineers, you wouldn't want anyone working on your home's foundation that doesn't have a good structural engineer on speed dial. Side note - I agree with @MonkeyZeus "permanary" solution, which is basically to do what a temp brace would do, just much closer to the wall that is affected. Last thing - the issue with foundation fixes is that they tend to cause cracking in walls above, due to shifting of the house. Something to keep in mind.
    – rajan
    Sep 9, 2021 at 16:55

I seems the foundation isn't moving. The comment on salt may be the only reason for the concrete coating coming off. So I would say to remove loose material and recoat. There are materials that crystalize and follow water back through concrete and mortar to solidify any cracks but I don't see a need in these pictures to remove the foundation. I have replaces several myself but wouldn't waste that money on this one. It just needs maintenance.

  • Please post some photos Mar 21 at 12:22

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