How to fill a big crack/gap in concrete?
September 25, 2022 1:21 PM Subscribe
We have a 1-2 inch gap between the concrete sidewalk on the side of our house and the house itself. I would like to fill it with something like a self-leveling sealant. What specific product/method do you recommend? Other questions inside.
We have a city house with a ~5 foot gangway between houses. On our side, the gangway is covered with concrete - like a sidewalk - with concrete blocks that are about six inches deep and maybe 4ft long by 2.5 feet wide. The concrete used to run flush with the house, but a developer knocked down the house next door and dug a new basement, causing our cement sidewalk blocks to subside/shift. The blocks are now at a slight sloping angle, with the slope running downhill toward our neighbors house. The block have also shifted about 1-2 inches away from flush against the house, so there is a gap about 1-2 inches wide and about 6 inches deep running along the side of the house. The side of the house at this spot is concrete - it's basically the top of the foundation for our basement. Here are some pictures.
I would like to fill the new gap between the concrete and the house, for aesthetics but also to try to keep water/ice from building up in the gap against the foundation, which can't be good.
Here are my questions:
1. Do you recommend a specific product or method for doing this? My plan so far is to try to push a foam backer into the gap and then use a product like self leveling sealant on top.
2. What should I do about the "vertical gap" at the front of the stair/sidewalk shown in the first photo above? I am worried that there will be an ugly view of the foam backer and sealant from the front unless I do something to close the vertical part too, but how to do that?
3. Because the gap is so deep, do you think I should do multiple layers of backer? Or is Ok to have one piece of backer shoved about halfway into the gap, with nothing under it?
4. Any ballpark estimates for how much sealant product I need to buy? The gap is between 1-2 inches wide (it varies) and it is probably 80-90 feet long.
Thank you DIYers!
We have a city house with a ~5 foot gangway between houses. On our side, the gangway is covered with concrete - like a sidewalk - with concrete blocks that are about six inches deep and maybe 4ft long by 2.5 feet wide. The concrete used to run flush with the house, but a developer knocked down the house next door and dug a new basement, causing our cement sidewalk blocks to subside/shift. The blocks are now at a slight sloping angle, with the slope running downhill toward our neighbors house. The block have also shifted about 1-2 inches away from flush against the house, so there is a gap about 1-2 inches wide and about 6 inches deep running along the side of the house. The side of the house at this spot is concrete - it's basically the top of the foundation for our basement. Here are some pictures.
I would like to fill the new gap between the concrete and the house, for aesthetics but also to try to keep water/ice from building up in the gap against the foundation, which can't be good.
Here are my questions:
1. Do you recommend a specific product or method for doing this? My plan so far is to try to push a foam backer into the gap and then use a product like self leveling sealant on top.
2. What should I do about the "vertical gap" at the front of the stair/sidewalk shown in the first photo above? I am worried that there will be an ugly view of the foam backer and sealant from the front unless I do something to close the vertical part too, but how to do that?
3. Because the gap is so deep, do you think I should do multiple layers of backer? Or is Ok to have one piece of backer shoved about halfway into the gap, with nothing under it?
4. Any ballpark estimates for how much sealant product I need to buy? The gap is between 1-2 inches wide (it varies) and it is probably 80-90 feet long.
Thank you DIYers!
I have this issue and my previous fix lasted about 10 years. Next time I'm just going to use sand, backer rod and then Akonaflex/Sikaflex or some other polyurethane concrete sealer.
The sand is to make it levelish - there is special locking sand for pavers that I'm going to press in after cleaning the void out. The backing rod is just to provide flexible support to the sealer - it comes in different sizes. for my gap isn't uniform so I'll be getting a couple of sizes. I'm getting more sand than I think I need- it's cheap and any extra can just. be added to the lawn. I expect the sealer to take 3 tubes for 45 feet. Here it's about 7$ a tube for the 10z tubes, but I'm leaning to 2 giant ones to seal up some other spots as well.
posted by zenon at 3:01 PM on September 25, 2022 [1 favorite]
The sand is to make it levelish - there is special locking sand for pavers that I'm going to press in after cleaning the void out. The backing rod is just to provide flexible support to the sealer - it comes in different sizes. for my gap isn't uniform so I'll be getting a couple of sizes. I'm getting more sand than I think I need- it's cheap and any extra can just. be added to the lawn. I expect the sealer to take 3 tubes for 45 feet. Here it's about 7$ a tube for the 10z tubes, but I'm leaning to 2 giant ones to seal up some other spots as well.
posted by zenon at 3:01 PM on September 25, 2022 [1 favorite]
I just went through this. After endless Googling I settled on Sikaflex self-leveling sealant as the best product. I can tell you that my gap was as wide as yours but nowhere near as deep or long, and I ended up using a shocking amount of sealant. Also, despite meticulous prep and jamming it full of backer, it kept finding ways to disappear into Mother Earth.
With a gap that deep, I would definitely pack it full of sand and then put the backer rod in, to eliminate as much air space as possible. FYI, backer rod that wide exists but was impossible for me to source, even online--however this was last year and things might be better now. If it happens to you, you can take two lengths of narrower backer rod and twist them together.
Also, be prepared to come outside in the morning expecting to see the beautiful results of your labors and find that a good amount of the sealer has been sucked into the vortex. Buy extra (a LOT extra) and you can return it if you get lucky.
posted by HotToddy at 3:10 PM on September 25, 2022
With a gap that deep, I would definitely pack it full of sand and then put the backer rod in, to eliminate as much air space as possible. FYI, backer rod that wide exists but was impossible for me to source, even online--however this was last year and things might be better now. If it happens to you, you can take two lengths of narrower backer rod and twist them together.
Also, be prepared to come outside in the morning expecting to see the beautiful results of your labors and find that a good amount of the sealer has been sucked into the vortex. Buy extra (a LOT extra) and you can return it if you get lucky.
posted by HotToddy at 3:10 PM on September 25, 2022
Why not just fill it with concrete? All you need is a bag of just-add-water concrete mix. Something like this.
posted by EndsOfInvention at 4:16 PM on September 25, 2022
posted by EndsOfInvention at 4:16 PM on September 25, 2022
I would definitely use something cement based. The challenge with using regular concrete is that the gap is too narrow for the coarse aggregate. You can get gap filling concrete or just do a type S mortar which is just sand and cement. Dirt cheap, easy to mix, rather than leveling it you can just joint it with a putty knife or masonry jointer and it will look like it was part of the sidewalk
posted by goingonit at 4:51 PM on September 25, 2022 [1 favorite]
posted by goingonit at 4:51 PM on September 25, 2022 [1 favorite]
Gypsum self leveling concrete about 40$ a.bag sets smooth ,good adhesion, made for smoothing uneven floors.
posted by hortense at 6:20 PM on September 25, 2022
posted by hortense at 6:20 PM on September 25, 2022
Use structural grout. It's a high strength concrete mix that's meant to pour thin and penetrate cracks, among other things. Mix it to a pancake batter consistency per the instructions. You can find it at big box stores.
You'll need to seal the end temporarily so it doesn't flow out the vertical crack. If there's a gap under the slab, this will flow into it, so it's possible you'll have to top up the crack as the liquid settles.
posted by Pantengliopoli at 7:36 PM on September 25, 2022 [1 favorite]
You'll need to seal the end temporarily so it doesn't flow out the vertical crack. If there's a gap under the slab, this will flow into it, so it's possible you'll have to top up the crack as the liquid settles.
posted by Pantengliopoli at 7:36 PM on September 25, 2022 [1 favorite]
Response by poster: Thanks, everyone. My thought with using sealant instead of cement/concrete was that perhaps there will be some movement or expansion/contraction in the gap because of weather or settling/etc. I also thought that cement/concrete might look bad, because I won't be able to match the color or texture of the existing slabs. My previous attempts to use concrete have resulted in some crumbling/cracking and messiness, so I thought the sealant might be a cleaner/neater way to handle. That said, the gap or void is very deep for sealant (about 6 inches), which I planned to handle with some foam backer, but HotToddy's point that the sealant can seep down into the gap is a little concerning. Just pouring a ton of grout/cement would be a lot easier from that perspective.
posted by Mid at 7:54 AM on September 26, 2022
posted by Mid at 7:54 AM on September 26, 2022
I would explore filling it with a lawsuit. If you can document that the development on the adjacent property was responsible for the subsidence and gap, they can be held responsible for making things right -- perhaps not with a patch but with a full replacement of the pavement they damaged.
posted by Scarf Joint at 9:13 AM on September 26, 2022 [3 favorites]
posted by Scarf Joint at 9:13 AM on September 26, 2022 [3 favorites]
I have filled such cracks and bigger on remodel projects, and am also working on a tennis court right now. A couple points.
1) Don't fill it with concrete! You don't want it adhering your house to your sidewalk.
2) Don't use self-leveling sealant! You will end up using a ton of it and it will slip through tiny holes. Also, any unsecured backer rod will float in it.
No matter what method you use to fill most of the crack, use something like a grey polyurethane waterproof caulk to fill the top of the gap and outside of the vertical crack. It won't flow through small holes, and it will look nice too. You might need to practice a bit with how you want to tool/smooth it. It may shrink a bit at first, so you may need to do two coats.
For the bulk of it, I'd either slip a concrete expansion joint (usually a roll of flat closed cell foam, or slightly rigid fibrous sheets) in to just below the top, then backer rod on top of that, and then polyurethane caulk. Another bulk fill approach would be pea gravel, then backer rod, then polyurethane caulk.
posted by MonsieurBon at 12:33 PM on September 26, 2022
1) Don't fill it with concrete! You don't want it adhering your house to your sidewalk.
2) Don't use self-leveling sealant! You will end up using a ton of it and it will slip through tiny holes. Also, any unsecured backer rod will float in it.
No matter what method you use to fill most of the crack, use something like a grey polyurethane waterproof caulk to fill the top of the gap and outside of the vertical crack. It won't flow through small holes, and it will look nice too. You might need to practice a bit with how you want to tool/smooth it. It may shrink a bit at first, so you may need to do two coats.
For the bulk of it, I'd either slip a concrete expansion joint (usually a roll of flat closed cell foam, or slightly rigid fibrous sheets) in to just below the top, then backer rod on top of that, and then polyurethane caulk. Another bulk fill approach would be pea gravel, then backer rod, then polyurethane caulk.
posted by MonsieurBon at 12:33 PM on September 26, 2022
While researching a different but related problem a while back, I found a flexible vinyl filler product (two brand names I've found are trim-a-slab and slab gasket). I'm not sure if it would suit your problem - it's quite expensive and requires a fairly even width hole (presumably a 1.5in gap as would be left by a 2x4, given its purpose) - but it's another jumping off point as you research.
ETA: I'm actually looking at the polyurethane caulk over expansion joint option for my own purposes, now...
posted by How much is that froggie in the window at 9:45 PM on September 26, 2022
ETA: I'm actually looking at the polyurethane caulk over expansion joint option for my own purposes, now...
posted by How much is that froggie in the window at 9:45 PM on September 26, 2022
This thread is closed to new comments.
posted by Lanark at 2:54 PM on September 25, 2022