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Stone foundation wall problems/repairs


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Recently I have come across a few stone foundation walls that are failing because of improper construction and deterioration of mortar. These are often early 20th Century walls constructed with sand/lime mortar. they are typically constructed essentially like a two-wythe wall with some larger stone bonding the inner and outer wythes. Often they do not have many larger stones and as the rubble fill and mortar deteriorated they can separate. When they support brick walls the brick bears on the outer part of the wall and sometimes significant lateral displacement of bowing/bulging occurs.

I evaluated one a little while ago and was hired to design a repair. One part of the repair involved dealing with the voids that developed inside of the foundation wall. I found a masonry contractor who was willing to try something new. I had him create some openings at the top of the foundation wall and a few near grade level. We then cleaned out a lot of the loose mortar. At some openings it flowed out like sand (well, it was sand). He then poured a grout mix into the wall cavities/voids. He did a section about 10 feet wide by 4-5 feet high (above grade level). I don't have the number on the amount of material used, but it was probably about 25 to 30 buckets.

The next step will involve pointing the stone and then installing tie rods with steel plates at the exterior and connected to floor joists at a spacing of about 4 feet on center.

The photos show gaps where a basement window frame was removed, debris removed from inside of the wall, various voids, and grout installation.

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Really strong. Depends on the type and mix. Some grout is the consistency of heavy cream, but still sets like a rock, bonds like glue, with no shrinkage.

This is an interesting repair method. Good pics.

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I'm wondering how strong a grout mix can be when it's watered down to flow like that?

By typical mortar standards, it may not be considered high, but its a lot higher than the sand/lime mortar that was used. Its main purpose is to provide some lateral stability to the stones and hopefully bond the wall together. The mix was quite high in lime to keep the water in the mix and help it flow.

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Just wondering if gunite (or shotcrete) would of helped with a repair like that.

Marc

I have read of cases where shotcrete was installed over welded wire fabric as interior reinforcing for stone walls. It would not have been an use in this situation.

If you were thinking of pumping into the walls, I would not use any method that applied pressure to the walls. They could easily blow apart.

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Do you know the actual materials and the proportional mix? Grouting mixes are really weird; some of them set up exothermically in minutes. Was this one of those types, or was it primarily a lime mix?

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Do you know the actual materials and the proportional mix? Grouting mixes are really weird; some of them set up exothermically in minutes. Was this one of those types, or was it primarily a lime mix?

About 2 parts sand; 1 part portland cement;1/2 part lime.

Here is today's progress.

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Different building and older (1860's). Probably seeing the same condition here, but

I would not try grout with this one.

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It sounds like the only damage was above grade. Was there no damage below grade?

Were you concerned with stones popping loose during the void-clearing process?

Just out of curiosity, were these kinds of walls constructed as straight vertical structures or is the below grade portion battered back into the earth?

We don't have stone foundations out here. . .

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It sounds like the only damage was above grade. Was there no damage below grade?

Were you concerned with stones popping loose during the void-clearing process?

Just out of curiosity, were these kinds of walls constructed as straight vertical structures or is the below grade portion battered back into the earth?

We don't have stone foundations out here. . .

Usually where I see this the outer portion above grade rotates out, so below grade is not much of a concern. In other cases, such as the last photos I posted, the foundation wall is entirely below grade and in that case the interior is bulging inward. There can be a slight increase in width from top to bottom, but generally they are pretty much the same width (usually 18-20 inches).

The stone construction varies depending on the area. In my area there is a lot of shale, so stones can be big and flat. That makes a better foundation wall because the bearing can be more uniform and stones can tie the foundation wall together. In the city there is a lot of mica schist. There can be many small irregular stones with a lot of mortar fill. Also, they sometimes set bigger stones on edge, which is not good for stability or weathering. Some mica schist crumbles with age.

Good stone foundation walls, even with nothing but sand/lime mortar, can last hundreds of years, if built correctly and reparged on the inside periodically. Most of the bad walls are getting close to 100 years old, but age is taking its toll.

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Were you concerned with stones popping loose during the void-clearing process?

I was not concerned about stone popping loose during the cleaning process. The mortar at the exterior was in relatively good condition. I was more concerned about the force developed during the grouting process. But since the grout was poured in one bucket at a time we could monitor the wall as we worked.

While we poured a lot of grout in the wall after the contractor removed the old mortar to repoint I was able to look into the wall at several areas. I would say that I think we did a good job grouting the top 2 feet or so of the wall I could still see voids below there. In the future I would make sure the contractor did more work cleaning the voids, and would probably limit the lifts to 2 feet.

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Very interesting problem and solution. Would you consider a gypsum based grout in the future to reduce weight and pressure?

I don't think it would make a significant difference. Also, I am hoping the grout has some bonding action, which should be better than gypsum.

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Did you vibrate it?

No. The voids were irregular at most areas, so a pencil vibrator would probably not fit. I though about banging on the stone with a rubber mallet, but figured that the stones would dampen out any vibration. I did try pushing wire, rebar, and a long spike into the voids. It helped to clear some blockages. When the grout seemed a bit thick or stopped flowing we poured some water down the hose. That did help.

After the grout was poured there was about a 4 to 6 inch void at the top of the wall. The contractor packed stiff mud into those voids. I deemed the job a success, but I know there is room for improvement.

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It's a very interesting approach and solution. It's got me thinking about grouting mixtures.

Have you ever worked with that fast set stuff that's like heavy cream? It goes off exothermically, and sets in about 15 minutes, and it bonds like glue. I was wondering if you could do lifts of that stuff....it would flow and possibly be better at filling voids.

Or, it might be too soupy and run out all over the place and be total ****ing mess.

Do you think the soupy stuff could work?

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It's a very interesting approach and solution. It's got me thinking about grouting mixtures.

Have you ever worked with that fast set stuff that's like heavy cream? It goes off exothermically, and sets in about 15 minutes, and it bonds like glue. I was wondering if you could do lifts of that stuff....it would flow and possibly be better at filling voids.

Or, it might be too soupy and run out all over the place and be total ****ing mess.

Do you think the soupy stuff could work?

I think the soupier (is that a word?), the better. I am not familiar with it. If you have a idea what it is called let me know. One problem may be that if a contractor can't get it tomorrow at wherever he does business, he is not interested in trying it.

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I buy it in 50 lb. bags at the depot. I forget the brand name; I recognize the bag and buy it. It's expensive as hell. It's about $26 for a 50 pound bag.

Now that I think about it, it would be ridiculously expensive for this application. It'd be thousands of dollars just for material.

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This process reminds me of how we installed steel door bucks after opening a hole for them in a concrete or a block wall. Once the buck is set, you tape the sides to seal them, and pour a slurry from the top until the sides are filled, then pack the opening at the top.

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In Chicago, it's a frame inside a rough masonry opening that a door or window is installed in.

Since masonry wall openings are usually AFU'ed, it's a way to square up the opening before mounting the door/window, and it provides the fastening member for the door/window.

That's what we call them anyway.

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Gary is talking about a welded steel door frame. Commercial industrial stuff. They are mother f***er to to remove when installed like that.

Yeah, but they don't move when you slam one.

You set the buck / frame, brace it, seal the sides with good old duct tape, and pour the mud from the top down.

What about the hinge screw holes, and a place at the top to tap for the closer? No problem. Just tape in some styrofoam block outs before you set the frame.

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