how would you seal space where new / old cinder block walls touch?

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Old 04-18-10, 04:08 PM
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how would you seal space where new / old cinder block walls touch?

Previous owners to our house built on a sunroom to the house. The original house has 8' hight basement, cinderblock walls. the sunroom has a concrete floor, cinderblock walls, 5' high (they didn't dig down as far as original basement). ABout 2' of basement cinderblock walls are visible around the house.

We recently had a guy run pipes outside to collect downspout water and run to the woods. Now we are getting some water in crawlspace, right where the addition's cinderblocks butt up against original foundation. We had that a little in heavy rains before but now it's worse.

I ran water in the downspouts / new pipe - the water isn't leaking out of those pipes. It's just coming in from the ground.

There's a crack visible on the outside where the old / new cinderblocks met, that originally was covered with concrete? I am thinking they disturbed the crack between the old foundation and the new addition. How would you seal that - where new cinderblocks touch the old foundation? Now that it's built already - we're not talking about new construction. I guess we have to dig down on the outside to the bottom of the crawl space to seal the entire crack? can't do it on the inside cause that will get the water still coming into the cinderblocks and leaking out somewhere else?

THANK YOU!
 
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Old 04-21-10, 10:09 PM
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Hey Babaganoosh. Very common problem. Good news: easy fix. Bad news: gonna have to dig. I have fixed theese alot, and here is what i do. Dig out the erea where the two walls meet down to footing level. Make sure to remove enough soil to be able to work and apply materials to corners. I would suggest a 1 foot minimum. You need to do this when the forecast is clear of rain for a few days in a row. Ok, now the block will more than likely be damp. Let it dry out overnight. next day block should be dry, and any dirt on block surfaces will easily be removed with stiff brush. Get a couple tubes of a good quality concrete caulk. run a very large bead of this caulk into the corner from the footing to the height of the backfill or just a bit higher. You will need to immediately force this caulk into the corner smashing it out onto the surfaces of both walls. You can use your fingers for this, but its very messy. I use a patch of denim from some old jeans. Now, let this caulk cure for 24 hours or till it is quite firm to the touch. Next you need to get a bucket of Trowelable Roofing Cement. A good quality foundation tar would probably work, but this is what i use. It is very thick, like paste. I usually use a margin trowel or pointing trowel to apply this over the caulked corner and to cover as much block as you have exposed, including down onto the footing. Lastly get some self adhesive sticky back flashing and stick it into the corner over everything else. You can get this at brick or masonry supply stores. If you cant find this stuff, you can get by with tar paper. Remember to stop all this at the height of the finish grade. You wont want to see this. Now you can backfill your holes and remember to tamp the dirt in one foot lifts with the end of a 4x4 to the top. That is it. if you still get water after this, its not coming in from your corners. From your grade on up, run a small bead of your gray concrete caulk. done. I have done this many times.
 
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Old 04-22-10, 04:21 AM
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thanks. but not hydraulic cement? caulk instead?
 
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Old 04-22-10, 10:35 PM
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Hydraulic cement might work if you can be sure there is no movement at the joint. Once cured, hydraulic cement will crack with movement. Caulk will flex and maintain a seal. Its just what I use. I have never had it fail, so i have never tried anything else.
 
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