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!

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.

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?

http://www.youtube.com/watch?v=WJM1537rp8s

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

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).

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!