fixing crumbling mortar around blocked in basement window

janeskitchenApril 1, 2012

I have tried finding some solutions to my problem in this forum and while I have learned so much about how to approach my basement finishing, i cannot find any reference to my specific problem. If you can help I would really appreciate it! FYI we live in Minneapolis!

We removed all the drywall from our what we thought was finished basement, which we started because we found some mold along one of the baseboards. As we began tearing away the wall we found more mold, growing on the drywall and 1x2s which they were attatched to. The house was built in 1960..there was no insulation, some vapor barrier in random places, and lots of rotting wood! Behind one wall we found a window which had been filled in with cement blocks, to accomodate the deck/patio behind the house, and the mortar around these blocks is crumbling and missing in places. It has been leaking, there is evidence of water stains running down the wall.

We have never had pools of water in the basement, but did see dampness in a few spots where the wall meets the floor in the back corner and wall of the house after a big spring rain since we have removed all the walls. We have graded, fixed drainspouts, installed a closed interior drain system and have an additional sump pump in the center of the house which was original.

We plan to either use xps or spray foam, as repeatedly suggested by Worthy...thanks for all the tips!

I want to patch this window area properly, and make sure that it does not leak before we begin finishing the basement. In addition to the leaking, there are a couple of areas missing mortar at the top where I can actually see daylight. The top line of the blocks seems a bit lower than the rest of the basement and I wonder if it was sealed properly to the exterior. The way the deck and brick patio are built prevent us from accessing this area from the outside.

For the window area repair, we have some ideas...spray foam, hydraulic cement, caulking...but I wanted to ask the experts before we start. Can anyone head us in the right direction to make sure this old window opening does not leak!

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Concrete and mortar are porous materials--more or less depending on the chemicals and aggregates used in making them. So you can never use concrete as waterproofing, but only as a way to slow bulk (liquid) water.

Remove the crumbling mortar and repoint with a new proper "mortar mix" available at any hardware/big box/building supply centre. If you can access the blocks from the exterior, you can either dampproof them with asphalt cutback or waterproof them with Platon or similar plastic membranes. It wouldn't be surprising that the POs filled the window but didn't take that extra vital step.

There are crystalline waterproofing materials that can be effective from the inside, but I believe they now come in mostly industrial sizes and the preps using sulphuric acid are not a diy job.

    Bookmark   April 4, 2012 at 10:46AM
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Thanks Worthy,

You suggest mortar mix - not hydraulic cement, can you tell me why? I read about Hydraulic Water-Stop Cement by Quikrete.. any thoughts on this?

Also, we can't access the exterior without tearing up the back deck and brick patio.

    Bookmark   April 5, 2012 at 12:25AM
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If you're a really quick worker, you might get it done before the hydraulic cement becomes unworkable. Depending on the formulation, hydraulic cement sets in three-10 minutes. However, since this is only a "leak" because there is no mortar to begin with--not a crack or hole in otherwise solid material--I'd personally use conventional mortar mix.

    Bookmark   April 5, 2012 at 9:49AM
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Be careful with hydraulic cement.

It is designed to expand when setting to seal cracks, but in softer material it can produce new cracks form the expansion.

There are even high expanding grades that are used to break up concrete (drill holes, fill with high expansion cement, concrete cracks when cement expands).

    Bookmark   April 11, 2012 at 10:00AM
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Thanks for the info...we are going to go with a mortar mix as Worthy suggests. Brickeyee, I do not want to take a chance we make a crack where we don't have any!!

Would it be helpful to cover the whole repointed area with something like parging that you do on the exterior, or not? Thanks for your help with this!

    Bookmark   April 14, 2012 at 1:58PM
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