How to Fix a Cracked Basement Wall from The Inside

Here’s a long post (questions) from one of my blog readers. I will outline and write my response (Answer) below it. Let’s get going.  

Reader’s Questions

So we have this house we are fixing up. Downstairs in the basement, we have some block work repairs we’ll be doing. The pictures are one room I’ll be attaching.

How to Fix a Cracked Basement Wall from The Inside How to Fix a Cracked Basement Wall from The Inside

I’ve already taken all the shelving out, saturated it with a 50/50 bleach/water mix, scrubbed the crap out of it, rinsed with water, swept/scrubbed all the loose stuff off the walls and floor. There is a little bit of grime left in a few spots on the interior walls.

And the house had an old wood burning furnace; there was a bucket that collected the water that came down the chimney and there’s some nasty soot-water on the wall (it sat for ~3 years). I’m hoping to start with the hydraulic cement in the big cracks, holes, and wall-floor corners next week, then crack filler in small cracks. After that, paint the exterior block walls with DryLok. After paint, we’ll frame out the walls, insulate, and Sheetrock to be a finished room. 

How to Fix a Cracked Basement Wall from The Inside

Here are my questions and what I need help with. 

  1. What is the best way to clean the nasty soot water residue off the block? Any certain chemical, soap, or degreaser?
  2. Would the bleach water and scrubbing be suitable for prep for block work? Does it need to be ‘washed?’ (There’s no efflorescence on any of the block).
  3. Do the interior walls need to be painted with DryLock prior to framing/drywall?
  4. Any TIPS for working with hydraulic cement? I’ve never touched the stuff before.
    *Any other tips for the process?

Oh, we have no heat/air or water at this house. I have a generator for power. Sorry for such a long post, but I really only want to tackle this once with as few problems as possible. I’m sure I’ll be back with more questions.

My Responses

1. First, you can use a proper mold killer like RMR-141 RTU Mold Killer, Disinfectant and Cleaner that actually works. RMR kills mold and disinfects the area as well. 

2. If you seal the wall with dryloc or similar, you will also stop the wall from “breathing” (weather vapor permeable, aka moisture from outside evaporating through the wall. this is not a bad thing, but an essential part of building physics).

I’m doing architecture / reno in Europe and sealing the interior basement walls is a major no-no in our building codes, but I read it a lot in diy posts from the US, so i’m wondering if this is a trend due to a company trying to promote easy fixes without explaining the physics behind moisture evaporation.

When we have basements that are slightly damp, we recommend preparing the walls the way you did with heavy scrubbing and a vinegar solution. then painting it with a paint that is made from chalk (antimicrobial properties that inhibit mold) and that is also water vapor permeable. it is also important to leave 3 inches of space between the wall and any closed shelf, in your case, if you want to put drywall up, you should consider leaving an inch space at the bottom and at the top, so the airflow is still functioning.

A sure fix, but also a labor intensive one is to run a drain around the perimeter of the house, by digging a trench to the lowest point of thee foundation. But by looking at how the paint is not completely flaking of in the lower half of your wall, I’d say your moisture levels are fine and there is no water backlogged on the outside of your walls.

as to the soot….

It will never come out. the only thing you can do is lavishly spread wallpaper glue-paste on the spot and then spread regular kitchen tin foil over it, smooth it out and firmly press down, make sure to overlap the edges and spread glue again on the outside. let dry. it then can be covered with regular wallpaper and painted. here it is important to see this as a fix only in the areas where actual soot is occurring. you cannot do this over an entire wall, because it will mess up your building being able to regulate moisture levels.

Here’s my friend’s experience

Our basement is freezing. I think there are 3 culprits:

1) It’s a spit level and the basement is only cinder block with sheet rock over it. We noticed this when we were painting and took the covers off the plug ins.
2) There is a small but steady cold breeze coming from some cracks around the sliding glass door. This is where all the frost on the trim has built up.
3) we have a wood burning fireplace that has only a thin metal damper and glass doors with a small open space between them. Is there something we can do ourselves to fix these issues? If we have to hire a contractor, what’s our estimated cost?


1. Test for radon, keep an eye out for moisture and any major vertical shift (bowing up or down at the crack).

2. They make a putty that comes in strip form, you can use it to temporarily seal any cracks around your sliding glass door. Bubble wrap will cling to your windows as an added layer of insulation.
3. As long as you aren’t using your fire place I would cut pieces of insulation and put a couple layers in there, followed by a piece of foam insulation cut to fit. You should be able to set them up in and make it nearly invisible. As long as you can seal big drafts you will notice a big difference. They also make foam insulation that goes behind outlet plates and those are helpful as well!

4. We just hired a basement contractor after doing tons of research and got two of the best companies we found to bid against each other let me go over some key issues we learned and work that was done to our house and others. Ours looked just like this but is now bright white, dry and cheery…..

Cracked Basement Wall 6

Okay first things first……do not finish this basement until any drainage issues/mold issues are tackled. what are your exterior walls and what are your interior walls or are all of these facing the perimeter of the house?….

We started from the top down. Gutters/roof…is everything draining as they should…do gutters need cleaned? do down spouts need cleaned? Are there any trees or landscaping too close to downspouts or the house? How is the grading of the exterior of the house?

Where is that water from in the basement? Do you have a sump pump? In order for the mold to STOP growing it needs to be dry. In order for the Current mold to dry, it needs to be physically removed and/or treated by a mold killer in this part.

The company we hired sandblasted or scaled back the cinder block 1/8 in to a 16th of an inch/a very thin layer to expose fresh clean block again…then it was treated with mold spray…cracks were sealed and then the dryloc….but that was after the moisture issues were fully addressed. We had water sitting in our cinder-blocks because our old French Drain when the house was built was clogged…so we installed a new system. the cement was jack-hammered around the perimeter so we could dig to the footer tiles and a new drain was installed flush with the foundation.

Weep holes were drilled in the blocks to prevent the wall from storing the water/eroding brick….that drains into the sump pump and out a discharge pipe into the downspouts. That drainage system has since been covered with cement again. If your walls have been bracing/ holding water you will also want to check to see if any bowing exists. 3/4 inch or less was considered a monitoring phaze but we took action because if you ignore it until the walls bow to 1″ or more then you could be shelling our more money in foundation repairs.

We had carbon fiber straps installed at $200 a beam from the footer to the sill plate with a lifetime guarantee. the carbon fiber straps are thin and less intrusive to finished basements than steel beams. I can’t say from your photos what the full extent of your water issues may be but all i can do is compare some photos to mine.

Outside photos are just as helpful! Looking at the moisture lines outside of that fireplace drain thing it looks like your mold growth lines are congruent with where downspouts would be and drains should be on the exterior or interior of the house.

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