Slip Form ( slipform ) Masonry Stone Wall

Slip Form Masonry Stone Wall

Here's my attempt at a slip form masonry stone wall. I wanted to install a new door to my basement, but before I could I had to fix the CMU wall that had failed. It was built without a footing, with no reinforcement, and without grout filling the blocks. On top of all that it wasn't even built to the depth of the stairs, so soil was passing under the wall and into the stair area.

After doing this one wall I'm not sold on the idea of slip forming a stone wall. I bought the book referenced here and tried to follow the instructions. What I didn't like in the book were that the stones appeared to be set on edge. With the bedding plane perpendicular to the wall. This doesn't usually look like a real stone wall and can lead to spalling as water can get in behind the layers of stone and then freeze/thaw will pop parts of the stone off. So that was one thing I did different. I also didn't "slip" the form up, instead we built enough forms to do the whole wall. We had to do that since it was getting cold (right around the magic 5 degrees C for concrete) and I didn't want to remove the forms before the concrete had time to set. So I didn't get to see how things were going with each layer. If I did maybe I could have changed things a bit. While I don't hate the look, it sort of looks like "stone stuck in concrete". None of my friends will see any difference to a real stone wall, so it's good enough for the stairs to the basement. What I do like about slip formed walls is the ability to form the wall with reinforced concrete.

Click on Pictures to see larger image.

Since I wrote the above I have come across Tomm Stanley's web site and book Stone House - A Guide to Self-Building with Slipforms, which has some great photos and techniques, like using rags to help stop the concrete from running down the front of the stones. His photos also showed that the chipping of the dried concrete is part of the job. When I first removed the forms I thought I had screwed up.

There were two walls, a "decorative" CMU wall, which we removed as one piece with the crane on the dump, and the one that failed which was supposed to be a retaining wall for the stairs to the basement.

The failed wall after half removed. No reinforcement and all block cores are empty.

View of the failed wall from the basement.

The last section of the old wall, note the lack of a footing.

Before pouring the footing I drilled the footing of the house so I could tie into it with some rebar.

Getting ready to pour the first part of the wall, I got a ton each of concrete sand and GA stone (1/2" minus), my dad shovelled it right from the truck into the mixer. We used a 1-3-3 mix for the concrete.

The first slip form in place. Vertical rebar was placed in footing when wet.

I added the stone up against the form, then poured the concrete over and in-between, I tried to keep the concrete about 1" back from the front of the stone/form. I would suggest 2" to 3" if you wish to point with mortar afterwards. Live and learn. I made the wall about 18" thick for the first 2 feet and about 11" thick for the remaining 4.5 feet.

Something not covered in the book, with the concrete in place it may be hard to see the joints in the stones below, I put some screws in place of the joints before covering the stone with concrete. That way I could (well try) to avoid vertical joints in the stones. The screws were moved for each layer of stone.

All the stone in place and concrete poured, blankets on top to keep the concrete warm. We did the first 2' on Sunday, the next on Monday, and the last on Tuesday. I removed the forms on Saturday. Temperatures were around 5-6 C during the day. In warmer weather you could remove the forms sooner.

Aaaa! The forms removed. Well that's not what I wanted. A few hours of chipping later...

I chipped away the concrete with a brick hammer and cleaned up with a wire brush.

Picture with the stone wet.

Another picture of the finished wall. See other projects - here