gaps in masonry foundation, expanding foam or mortar

House Repair Talk

Help Support House Repair Talk:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

LMHmedchem

Well-Known Member
Joined
Aug 20, 2012
Messages
92
Reaction score
5
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
[ame]http://www.veoh.com/watch/v17334188sxcp6K25[/ame]

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.

This article,
http://voices.yahoo.com/adding-struc...558.html?cat=6

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,
http://www.energyefficientsolutions....amproducts.asp

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?

Thanks,

LMHmedchem



under_window.jpg

vertical_joint.jpg

horizontal_joint_filled.jpg

horizontal_joint.jpg
 
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.
 
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 the use of type S going to present any problem in painting it (on the inside)? I guess I would have to let it cure and dry for at least a month before painting.

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.

LMHmedchem

foundation_outside2.jpg
 
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?

LMHmedchem
 
Last edited:
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.

Dick
 
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.

Dick
I started using type S because this is below grade, but that is just a guess. The easiest thing for me to get was the QUIKRETE type S Mason Mix. I also have Portland around and sand. I have been basically skim coating the old "moon surface" concrete floor with a 2-1 mix of Portland and play sand. I have mixed it to the consistency of drywall mud and applied it more or less the same way, pre-treating the old concrete with concrete adhesive. The results have been very good so far, but I am only able to so small sections at a time.

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.

LMHmedchem
 
Last edited:
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.

Dick
Well I am moving along a bit, mostly trying to get the technique right. I have been filling up the outside joints with the smaller pieces of granite that I removed with the old mortar and filling about 3 inched in with mortar. I am using the quickerete type S mason mix. After that sets up, I have a well behind it that is contained by the new mortar. I have been using the same mix, but making it wetter, about twice at thick as paint. Then I have just poured that into the open well behind the replace mortar. Some of the voids lower down are large and I have poured many gallons of this mix into some of them. Eventually they fill up and top off the well. Even though the mix is so wet, it seems to set up reasonably well just overnight. I am working along the wall, starting at the bottom. By the time I have gone all the way across, the wet mix will have had several days to set up and I will repeat for the next level up.

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.

LMHmedchem
 
LMHmedchem,

Hi, I found your posting in my search to address exactly the issues/questions that you describe. I have a granite foundation (house built in 1835), where I need to fill lots voids behind the first layer of granite, followed by pointing, and wondered about using foam for the voids. This thread has been quite helpful, particularly the conclusion about using a wet-soupy mix of type S mason mix, poured into the voids. I'm wondering now, seven years later, how this has worked out for you? Seems like the perfect solution to my problem, as injecting foam into the voids just doesn't sound that effective (as discussed in this thread). I suspect I will also require gallons of mix to fill the voids in my wall.
 
Argh….another thread with no closure! Epic thread bump anyone? I too have wondered the same…our house was built in 1790, and we also have some really large holes behind our foundation. Either the op or Nick get anywhere here?
 
Argh….another thread with no closure! Epic thread bump anyone? I too have wondered the same…our house was built in 1790, and we also have some really large holes behind our foundation. Either the op or Nick get anywhere here?
Sorry I never closed this thread out. I posted some of my results at another site but for some reason never did here.

Yes, I was able to do repairs implementing some of the methods suggested here (and other sites).

Here is an explanation of what I did and some pictures.

I used an air hammer and chisel tip on a compressor to remove the old mortar, though most of it could be removed with a vacuum cleaner and large screw driver. At the time I was considering using foam to fill the interior gaps which can be big enough to put a basketball into. Just to note, this mortar is entirely non-structural. The wall will stand as is with or without the mortar.

Here is a picture of one area after the mortar was removed.
01_wall_under_window.jpg

Some of the gaps are really quite large,
02_large_gap_1.jpg

On advice, I ended up using type S mason mix to re-point the interior to a depth of about 4"-6". I did this across an entire wall for the first 2 coursed of stone, which is about halfway up to grade.

This is a picture after re-pointing some near the bottom, (sorry the pictures are not great)
04_re-pointed_first_2_courses.jpg

I then mixed up a liquid "soapy grout" and poured it in to completely back fill all the voids.

Under the left side of the window you can see the holes where I poured the mortar in for this area. I poured in several holes across the wall to make sure I was filling it all up. After the liquid set, I re-pointed up to about 1-foot above grade and back-filled again.

05_pour_hole_under_window.jpg

This picture shows the liquid mortar filled up to the top of the holes.
06_pour_hole_under_window_filled.jpg

The space between 1-foot above grade and the mortar cap (top of the foundation) I filled with 1-component fire-block expanding foam leaving at lest 2" free depth for mortar. I pointed over the cured foam, let it sit for 60 days, and then put on 2 coats of drylock and then interior paint.

I replaced the window and did some re-pointing on the outside as well. It turned out well as far as I was concerned. I can't find any pictures of it finished so I will have to take some new ones.

More or less you remove the old mortar, clean out all the dirt and junk, wash off the stone where you will be repointing, and then repoint with type S. You need to repoint sections to create contained bathtub spaces that you can backfill with liquid mortar. This means closing it off so that the liquid won't flow out into the basement anywhere or into other sections of the wall you are not ready to fill yet. When you get above grade, you also have to make sure the liquid won't flow outside anywhere.

I found this to be a reasonable process, excepting that all masonry involves working with a large quantity of very heavy material.

I am actually getting ready to do some of this again so can give more details when I do that. I will be making up my own type S instead of buying bags as it is very much cheaper and you will go through allot of it. I will also be adding a bonding adhesive to the soapy grout and possibly a waterproofing additive so that the center of the foundation is waterproof. I am also looking at adding some percentage of polystyrene beads to reduce the weight and quantity of mortar needed. I will also try to find some fireblock foam panels that I can cut up and stuff in the upper area so I only have to use expanding foam to fill in around the cut up panels.

the big issue around here now is termites. They have done allot of damage to my house and I need to seal thing up. Termites can easily build mud tunnels up through the large gaps in the interior of the foundation and get into the framing without there being any external evidence. Backfilling the foundation with liquid mortar is one of the best options to prevent this.

LMHmedchem
 
Sorry I never closed this thread out. I posted some of my results at another site but for some reason never did here.

Yes, I was able to do repairs implementing some of the methods suggested here (and other sites).

Here is an explanation of what I did and some pictures.

I used an air hammer and chisel tip on a compressor to remove the old mortar, though most of it could be removed with a vacuum cleaner and large screw driver. At the time I was considering using foam to fill the interior gaps which can be big enough to put a basketball into. Just to note, this mortar is entirely non-structural. The wall will stand as is with or without the mortar.

Here is a picture of one area after the mortar was removed.
View attachment 31798

Some of the gaps are really quite large,
View attachment 31799

On advice, I ended up using type S mason mix to re-point the interior to a depth of about 4"-6". I did this across an entire wall for the first 2 coursed of stone, which is about halfway up to grade.

This is a picture after re-pointing some near the bottom, (sorry the pictures are not great)
View attachment 31800

I then mixed up a liquid "soapy grout" and poured it in to completely back fill all the voids.

Under the left side of the window you can see the holes where I poured the mortar in for this area. I poured in several holes across the wall to make sure I was filling it all up. After the liquid set, I re-pointed up to about 1-foot above grade and back-filled again.

View attachment 31801

This picture shows the liquid mortar filled up to the top of the holes.
View attachment 31802

The space between 1-foot above grade and the mortar cap (top of the foundation) I filled with 1-component fire-block expanding foam leaving at lest 2" free depth for mortar. I pointed over the cured foam, let it sit for 60 days, and then put on 2 coats of drylock and then interior paint.

I replaced the window and did some re-pointing on the outside as well. It turned out well as far as I was concerned. I can't find any pictures of it finished so I will have to take some new ones.

More or less you remove the old mortar, clean out all the dirt and junk, wash off the stone where you will be repointing, and then repoint with type S. You need to repoint sections to create contained bathtub spaces that you can backfill with liquid mortar. This means closing it off so that the liquid won't flow out into the basement anywhere or into other sections of the wall you are not ready to fill yet. When you get above grade, you also have to make sure the liquid won't flow outside anywhere.

I found this to be a reasonable process, excepting that all masonry involves working with a large quantity of very heavy material.

I am actually getting ready to do some of this again so can give more details when I do that. I will be making up my own type S instead of buying bags as it is very much cheaper and you will go through allot of it. I will also be adding a bonding adhesive to the soapy grout and possibly a waterproofing additive so that the center of the foundation is waterproof. I am also looking at adding some percentage of polystyrene beads to reduce the weight and quantity of mortar needed. I will also try to find some fireblock foam panels that I can cut up and stuff in the upper area so I only have to use expanding foam to fill in around the cut up panels.

the big issue around here now is termites. They have done allot of damage to my house and I need to seal thing up. Termites can easily build mud tunnels up through the large gaps in the interior of the foundation and get into the framing without there being any external evidence. Backfilling the foundation with liquid mortar is one of the best options to prevent this.

LMHmedchem
THANK YOU! For responding…I appreciate the information without a doubt. There’s so much info to weed through, I think I’m going to end up going the more traditional route. Watching, reading, chatting with a guy that’s experienced…….. I guess if you read through the comments on this, this old house video, it kinda sums up where I’m heading. Thank you again for your follow up, I hope to be getting underway this winter, next winter at the latest. I have an awful lot of cleaning to do before getting started.



Enjoy! (Don’t forget to read the comments, great info in there)
 
There’s so much info to weed through, I think I’m going to end up going the more traditional route. Watching, reading, chatting with a guy that’s experienced…….. I guess if you read through the comments on this, this old house video, it kinda sums up where I’m heading.
I will try to watch that video when I get a chance. I have been watching This Old House since it went on the air.

The only video I was about to find at the time was the repair of a barn with a field stone foundation. That mason just tuck pointed the mortar all the way in to fill all the interior space. There were two reasons why I went with the back-fill method instead of that.

The first is that if your foundation is anything like those around here, you will go through an unbelievable amount of mortar. Just in the sections I did, I went through 80, 80lb bags of type S mason mix (about $800 with today's prices). Mixing all that up to a paste and tuck pointing it into the voids would have taken absolutely forever. These foundations were originally designed with empty voids that were often filled with yellow clay below grade and nothing above grade. The mortar was only about 2 inches deep and it entirely absent below grade on the outside. Making it up in buckets and pouring it in was so much faster, as long as your did enough pointing to contain it.

The second, and most important I mentioned before. Termites only need a 1/64 inch gap to make their way in. With no mortar between the stones below ground on the outside, the only way to stop them from getting in is to completely seal off the voids. One of my neighbors had to replace 2 of the main sills on his foundation because of termites. You can only imagine what it costs to jack up the house, crib it, and remove and replace beams like that. I lost most of my front porch last year and another neighbor list his garage. I have had the ground around the house treated but that only helps if the termites have to come up through the surface to get to the foundation. If they can go in 4 feet down, that is below the level of the treatment. There will be many voids that you just can't reach by tuck pointing. Pouring in a liquid it the only way to fully seal the area.

Other points are that I can add polystyrene beads to the liquid to lighten it quite a bit. I was a bit concerned about all the weight I could be adding with the type S. That is one reason I used foam for the upper section above grade. I can also add waterproofing to the liquid to make the lower part of the foundation waterproof.

In Maine, you may still be far enough north that termites are not an issue yet. That could affect my decision but I would likely still use the liquid for the speed of the method. Either way, you are filling the base with mortar, one method just uses more water.

LMHmedchem
 
I am going to do a similar project in spring but am going to use foam as mortar to tuckpoint and closed cell spray foam to insulate the wall from the inside. Based on all the info so far I have not seen any cons of doing this. Or are there?
1. Foam will expand into places mortar wont reach
2. Foam is waterproof, durable and offers good buffer for expansion and contraction
 
Back
Top