Many older homes have foundations made of field stone that may have sagged or warped over time due to elements pushing on the stones. Since mortar as we know it today was not used, the stones can be easily moved. If there has been a serious total collapse of the stone wall, it is necessary to replace it completely. If the problem is less serious, a new concrete reinforcement wall may be necessary. If you have a dirt basement floor, the job is even easier. Starting inside the basement, you must first dig a trench along the existing wall to lay a new foundation for the bracing wall. I would make the base at least two feet wide, but three feet wide is much better. Make the base one foot deep. The top of the new base should meet the bottom of the stone wall and the new flooring will sit on top of the base. Be careful not to disturb the ground under the stones. You will not be able to jog under a stone wall. Once you have finished digging, form the base and install the rebar. Use bars that are at least 5/8′ in diameter. Lay them out along the base and on a base three feet wide there should be three continuous bars. Now take four foot long cut pieces and bend a one foot curve at one end to form a she. These bars shall be tied to the innermost and outermost reinforcing bar of the base to form two rows of dowels extending the entire length of the base, no more than thirty-two inches apart. When the base is poured, you will only see the vertical part of the bars sticking out. Once the base concrete is dry, remove all forms leaving no wood for termites to latch onto for dinner.

Now, using the same size rebar, install horizontal bars starting three inches up from the base and placing one every twelve inches along the new wall. Do this on both rows of tacos. These, when finished, are called wall mats. Using some small pieces of rebar, tie them together with wire between the two mats to keep them apart when you pour the heavy concrete. The new wall thickness will depend on how thick the stone wall is and how arched the stone wall is. My last wall was basically twenty-four inches thick, but twelve inches thick is the minimum you should build. Your rebar wall mats should be as close as possible to three inches from both faces of the wall. The interior carpet can be a bit more depending on the amount of arch in the stone wall. I used Symonns concrete form panels from my rental shop to make it easier to form the new wall, but you can also build the forms with wood. The advantage of concrete panels is that they come in all sizes, heights and widths, they have clips to easily attach them, they have prefabricated anchors, etc. You must remember that this is a one-sided form. The most difficult type to build. You need to brace it all the way and then add some more bracing to keep it from moving under the weight of the wet concrete. Installing what is called a whaling brace will keep the forms from bending, but will add a lot of reinforcement. Specifically per day, you will need additional help. Pouring through a foundation window is no joke, as those inside can’t see the one outside in the ready-mix truck.

A man has to stand outside and shout orders through the window. Faster, slower, more, too wet, and so on. Inside, a man does not have to do anything but observe the forms. If something moves, he must immediately stop pouring. Being buried under wet concrete and shattered formwork panels is no joke. Another person has to vibrate the forms with a mechanical vibrator to ensure there are no voids in the concrete. Another person can tap the forms with a hammer to make sure there is concrete in all the spaces and look down through the top of the form to make sure they are filled as level as possible. This eliminates putting too much pressure on one point of the forms at a time. Excess pressure can cause forms to fail. Wet concrete exerts what is called hydraulic pressure laterally against the formwork and can amount to tons of pressure. I’ve seen forms fail that flew a hundred feet from the job site. Depending on the thickness of your new wall, a two-day wait to remove the formwork is more than enough. Twenty-four hours is even better. Any concrete spill will harden very hard and make form removal much more difficult if you let the concrete sit too long. Again strip all the remains of wood from the work. Fill in the base and level the floor area to prepare it for the new basement floor.

Peter

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