gaps in masonry foundation, expanding foam or mortar
I am currently working on my basement and am in the middle of re-pointing my the 120 year old granite foundation. Much of the mortar has turned into something that looks like plaster dust, so I am removing and replacing it. After removing some of the old mortar, there are some large gaps inside between the blocks, like that I can put my arm into. I guess they didn't do much dressing of the blocks on site but just stacked them up and mortared them into place. I have used some great stuff to fill some of the gaps, but I think I need a much larger volume product if I'm going to fill all of them.
There has never been any issue with water in the basement, and some of the gaps are obviously continuous to the outside, so the drainage must be good enough to prevent leaks. Even so, I think it is a good idea to fill these gaps since I have it all open. It will also be allot easier to re-point if the bigger gaps have been reduced considerably.
I have added some pictures below.
The first picture is a section of the wall I am working on. All the the loose mortar has been removed.
The second picture is of a common gap I am seeing. This vertical gap runs for about 2 feet and is about 1-3 inches wide and about 1 foot deep.
The third picture is of a horizontal gap that is 1 foot deep 18 inches wide and about 5 inches tall. There are two loose pieces of granite sitting at the front of the gap. In the last picture, I have removed the loose pieces and you can see all the way into the gap.
There are two places where there is an ~8x8 inch gap that runs all the way through. I can see the underground dirt on the other side. I have no idea why there isn't water coming in here, but there is a cantilevered section of the house over that area and the grade slopes away from the house pretty well. I guess the overhand is keeping it dry enough to keep the water out. There are some signs of moisture in this area though, but nothing like standing water.
I found this video
by a group near here called the mended wall. They do allot of conservation/restoration of homes much older than mine. The video shows Andrew doing most of the same things I have been doing, removing loose mortar and stone, using a vacuum to remove dirt and debris, etc. He just filled all the gaps with a mixture of sand mix and type N lime. He didn't specify the proportions, so I'm not sure where to go with that. These are also restorations that aim to preserve the historical significance of the home and I don't know if that affects the techniques I would want or not.
advised what I was thinking about, which is to inject closed cell expanding foam into the gaps, which would be much quicker. The article didn't specify the type of foam to use or where to get it.
I have also thought of just shoveling concrete into the large areas to fill as much as possible and then using standard mortar mix to finish the pointing, or using cement to fill as much as possible, adding an inch or two of spray foam to seal and insulate, and then pointing. One of the problems is that some of the gaps have narrow openings, but get fairly large as they go back. It would be pretty difficult go get any kind of mortar back in there without some kind of pump. I also know there are other expanding hydraulic cement like products that are used for filling and sealing applications.
I don't really know if this wall need structural reinforcement or not. It has been where it is for more than 120 years with no shifting, so I suspect that it does not need much more than would be provided by replacing the loose rock and re-pointing enough to fill the gaps. Adding additional structure isn't going to do any harm however, and it would be nice if this remained stable for another 120 years.
There are allot of possibilities and I am a bit in the weeds here, so I would really appreciate any suggestions.
This site seems to have a reasonable selection of expanding foam,
If I do use foam, I'm not really sure what to get, 1-component, 2-component, fire block, etc. I'm not sure which of these would qualify as "structural". The products at this site range in price from $90-$800 and I don't want to spend allot here unless it is really necessary. It is hard to tell how large the largest gaps are, but I can always make repeat applications if necessary. Most of these things are advertised as waterproof, but I don't really know what that means in practice.
I'm not really sure what to get, or where to get it, so suggestions would be appreciated. Is there a standard for this sort of application?
I wouldn't use any type of spray foam to fill those gaps. Won't properly seal when the time comes, and certainly provides no structural strength. Stick with mortar, and maybe consider Type S if you want it to be stronger.
Is there some reason why I can't just fill the large gaps with concrete? I'm not completely sure on the difference, other than different proportions of sand, gravel, and Portland cement. I was thinking about spray foam because I don't think that these large gaps have even been filled with anything. The mortar was only about 1" deep and just held the small stones in place and sealed the gaps. I thing that there have always been large internal cavities. I thought that foam would be better than nothing and would provide a decent water tight seal. There are some foams that are considered "structural", but I don't really know what that means.
I can certainly fill everything up with mortar, but it will take longer. I'm also not sure what to do with the large gaps the have very narrow openings. I could always break out the diamond grinder and open the gaps some, but that is no fun. Also, how clean do I have to get the rock before re-applying mortar. Do I need to clean with water and detergent, or will just a dry brush be alright?
I have attached a picture of what this looks like on the outside. It's surprising how much cleaner it looks on the outside, thought I'm sure it was re-pointed at least once.
Well I guess I am going to be using type S mortar, since there have been no other suggestions. What is a good ratio to use? I would guess 1 part type S to 2-2.5 parts mason sand, but I could also see using sand mix instead of just sharp sand. If I use something like QUIKRETE type S Mason Mix, would I add anything or just use it straight?
Any suggestions on this?
Since you are trying to fill the voids and hopefully do some sealing foam is a wast of time.
Use mortar or masonry grout to fill the voids. Obviously concrete will not work. A wet, soupy grout (Portland cement and sand) would be best if you can contain it since it will fill all voids. A second choice would to use a lower strength wet mortar that you can force into the voids and keep it there. It will seal somewhat and provide great stability and work well since you do not have a leakage problem, any minor shrinkage would not be a problem. As in all masonry, you use the lowest strength mortar possible (Type N), since mortar strength is really immaterial, especially with you situation.
Type N masonry cement is not as readily available as Type N premixed mortar, so you could use either Type S cement or just Portland and sand, depending on your learned skills.
If I can buy straight type S cement, what ratio would I use with the masons sand (I wouldn't use play sand here)? What is the difference between type S cement and portland? I was trying to avoid getting into the more complex mixtures of cement, lime, and sand, even though that was traditional. I'm not sure what the difference is between these mortar mixes and cement. I have always just thought there were different ratios of ingredients.
I did another part of this earlier, but it was in much better shape so I didn't have to remove as much of the old mortar. I did use some spray foam to fill some of of the cavities that I couldn't get to. I believe that these cavities have always been there (empty), so I thought that adding some insulation couldn't do any harm. This part of the foundation has an edition with a full basement on the other side, so it's not exposed to whether any more. I just used bagged mortar mix to re-point where the mortar was loose or missing. That part turned out really well, at least it looks good. I am going to be painting this in the end. I probably would have done the same here, but this part is in bad shape and needs a much more complete treatment. It was behind the oil tank at one point and I think the rest got redone, and this wasn't.
At this point, I have 4 bags of QUIKRETE type S Mason Mix and 1.5 bags of Portland. I can get pretty much anything else if I am going in the wrong direction here. I guess I will be skipping the expanding foam, but that would have been really fast compared to using mortar. Fast isn't that helpful if it's the wrong method I guess.
I do have a grout bag that I could use to get a wet mix back into some of the places that have large cavities with narrow openings. Would there be a problem using more than one thing in combination, since I probably won't be able to fill all the voids with a single solution?
This stone is granite in case I didn't mention that at some point. I know that sometimes the material has an impact on the kind of mortar to use.
I am planning on painting the wall, but with all the water in this mix I guess I would want to wait at least 2 months or so before doing that.
It would be helpful to know if I am in the process of turning my foundation into the Okefenokee Swamp, so I would really appreciate it if someone would let me know if they think I am.
I will try to put up some more pictures for the next round of filling I do.
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