Concrete Joints on Basement Walls 6

[sigma1]

I have a 27 ft x 50 ft x 9 ft deep basement. How often and at what locations we need to provide joints to avoid future cracks. The walls are 12" thick.

 

[JAE]

For concrete walls, not sure you need or want joints. The idea of a joint in concrete is to control the location of the joint and allow for sealing to occur either with joint sealants or waterstops...not to avoid cracks.

For a 50' wall - not sure I'd use any joints and if the concrete cracks, patch or inject the crack and provide waterproofing on the outside....or ignore the crack and just waterproof the wall which is what most often happens.

 

[kenvlach]

In addition to waterproofing the outside, insulate it. Saves heating $$$ and protects the concrete from freeze/thaw cycling.

For a cold climate, use 2" thick 4 ft wide extruded polystyrene boards lengthwise, up to the bottom of the siding. Attach with an exterior adhesive sold by the PS vendor. Use metal flashing from under the siding to over the polystyrene, & paint any remaining exposed PS to protect from sunlight. I suggest also using 1" thick PS insulation below the 2".

The exterior insulation is far superior than applying inside -- protects the concrete (I have seen frost on inside of concrete behind a 'finished' basement wall in Wisconsin), saves space & avoids fire hazard (although can use fiberglass inside, it has a lower R value).

 

[kenvlach]

When I lived in SE Wisconsin, the no. 1 cause of failed basement walls (mostly, push-in concrete block) seemed to be water-logged soil. Presume that swelling of the clay subsoil & frost-expanded soil contributed, but these are also excess water. Is this basically true?

So, I consider the root cause to be insufficient drainage alongside the basement wall. The drain tile was typically covered with about a foot of crushed stone, then the remaining excavated area was filled with soil for growing shrubbery, flowers, etc.

My idea for improved drainage: Place a cardboard partition in the excavation, about parallel to and the height of the basement wall. Then backfill inside with crushed stone or sand/gravel, and outside with soil. So full height drainage. Perhaps cant the cardboard so as to have the width of the drainage region widest at the bottom.
Would this be a good idea? Has anyone done similarly?

 

[boffintech]

kenvlach They make a fairly inexpensive drainage mat for what you describe. The mat is plastic waffle with felt on one side to keep soil out. The mat is placed on the wall with the felt side towards the soil so that water can run directly to the drain tile through the waffel.

 

[MichSt]

Kenvlach-
I’m a bridge guy, but for drainage behind foundation walls in bridge applications we do something similar…we use a felt like fabric (we call it filter fabric) to separate the drainage stone from the rest of the backfill. This keeps the fines from the backfill from clogging the drainage stone. For placing the backfill I’ve seen bridge contractors place steel plates vertically to separate the two types of backfill and then pull the steel sheets once he’s backfilled the full height of the wall.

We usually bring the drainage stone to 1’ or so below finished grade and wrap the top surface with the filter fabric. They we place top soil and grass.

 

[apetr26542]

Sigma1, If this is a request of your client, I would venture to say the joints may eliminate shrinkage cracks to some degree, they always seem to appear at re-entrant corners of basement windows or other knockouts. However, concrete will crack if not through shrinkage curing cure it will through settelment, don't make any guarantees.