crumbling foundation

[gbick]

Recently, after a hard rain, I noticed "rabbit holes" next to the cement block foundation. Digging down to investigate, I found the outside of the blocks crumbled away below grade and the dirt was falling into the hollows. The blocks look fine from inside and above ground outside.
The house is "L" shaped The original section is over 100yrs old, 2 story with cellar and full stone foundation. It is in fine shape. The 1 story problem section was added on in the 70's. It sits over a dirt crawlspace. The block frostwall was never sealed on the outside and the paved driveway slopes right to it. The backyard also slopes toward the house. (The JD 4310 will remedy this.)
The immediate issue is to replace this foundation before that part of the house falls. Lifting the whole house is out of the question and as they are connected, this section can't be lifted much. The plan is to knock out and replace the blocks a small section at a time. This, I can afford and and can work as I can. Not having laid block before, I'm wondering how to get the blocks hard up against the sill. Should anything go between the blocks and the sill?
I was wondering how I would ever get the time to do this. Well be careful what you wish for- the paper mill I've worked at for 22yrs. suddenly shut down last week. I could lament about America's evaporating industry, but that's a different thread. I will be paid for 60 days or until called back by a different owner. If the mill isn't sold by then, GP will close it permenantly. So I will be starting on this job right away. Any advice, guys and girls? Thanks, Greg.

[Pat]

gbick, I have helped a friend replace a block stem wall a section at a time but have a different idea for your consideration. Dig out a trench all around the "BAD" section to expose the broken blocks. Place forms parallel to the block wall and pour in concrete. Use a water reducer plasticiser admixture added to the concrete as per the manufacturer's directions (not very long before pouring.) This water reducer-plasticiser will make the concrete very runny without having to add excessive water which reduces strength.

The object is to fill the hollow blocks with concrete as well as slightly widen the concrete block wall with the concrete pour. I recommend adding rebar to "dowel" the concrete inside the broken blocks to the concrete outside of the blocks. There are pre-bent (pre-formed?) right angle corners of rebar wich would make that a lot easier.

If I were doing it I would consider placing forms on the inside of the defective block as well as on the outside and "open" up passages ever few feet to let the concrete flow to the inside cavity. This would bolster the original wall from both sides in a sandwich. You would want rebar runing parallel to the original wall in the new concrete on both sides of the wall and rebar in the connecting passages through the original wall tieing to the rebar parallel to the old wall. You should also use "stirrups" of rebar in the new concrete.

The above assumes a useable crawl space. It also demonstrates a certain degree of overkill as you could do a completely satisfactory repair that would be stronger than the original wall when new from the outside of the wall without going under the house (assuming there are no large holes that will drain the concrete through the wall to the crawl space. You could do this job in segments if you choose, mixing the concrete in a portable mixer or all at once from a redi-mix truck. "Cold" joints should be no problem as the original wall was ALL cold joints, the block being cured when used.

A plus to this approach is that you don't have to lay blocks. Block laying is not as simple as it may seem and a DIY beginner would likely not get a strong wall.

Another consideration is to not dig any deeper in the access trench than you intend to pour concrete as you want undisturbed earth under the footprint of your widened secton of stem wall/foundation. You could, of course, rent a plate compactor... but why?

I hope you can make sense out of my description.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]