Layered Cement Basement Wall

[Desert_Sasquatch]

Googling around I see folks here have experience with having cement walls or foundations poured. I've got a question about that:

I'm thinking of building a house on some fairly sloped land, and it seems like one way to make that work would be to have a walk-out basement. Since so much of the wall would need to be concrete anyhow, I am wondering about, instead of going to the effort and expense of covering that concrete with another wall system, just making the concrete look attractive. The best way I can think to do this would be to imitate a rammed earth look, perhaps one like this:



In other words, I would ideally want a layer of concrete every 4-12 inches, and the layers would alternate colors. I have heard that cement trucks may not like using colored concrete, so I imagine I'd have to add an intermediate step where concrete goes from the truck mixer into one of maybe 2-4 smaller mixers where color is added in, and then those mixers dump their concrete into the pump truck in sequence.

Maybe this'll be where I figure out why this isn't done. There's a lot I don't know about the practicalities of pouring concrete.


My questions are:

1). How high is a normal lift? Four feet?

2). How long does one have to wait between pouring one lift and another? It sounds like maybe just an hour or two, usually? What if no accelerant is used? (Assume the weather is warmish, say at least 40 F at night and 70 F during the day.)

3). In your opinion, how insane is this idea ? Seriously, most of the time when someone asks "why haven't people done this before" there winds up being an actual reason. I'm open to hearing what it is.

Thanks everyone!

PS. FWIW the foundation exterior would be insulated, waterproofed, and drained. This would be a proper basement for living in, not a cold damp basement I just happened want to make pretty.

 

[billconner]

Very appealing ideas. Just following. I've always been interested in the concept of fancy form work. like those early and mid century buildings and structures.

 

[ConCretin]

I'll take a shot at your questions;

1). How high is a normal lift? Four feet?

Four feet is generally considered the maximum allowable lift on spec jobs but it's not uncommon for contractors to exceed this.

2). How long does one have to wait between pouring one lift and another? It sounds like maybe just an hour or two, usually? What if no accelerant is used? (Assume the weather is warmish, say at least 40 F at night and 70 F during the day.)

An hour would be too long and probably result in a cold joint. Ideally you place and vibrate each lift shortly after the prior lift depending on the formwork's load capacity, ambient temps, concrete temps, etc.

3). In your opinion, how insane is this idea ? Seriously, most of the time when someone asks "why haven't people done this before" there winds up being an actual reason. I'm open to hearing what it is

I suppose anything's possible but there are multiple challenges to what you are considering. Ready mix suppliers are generally willing to provide colored concrete but the challenge of timing the delivery, placement and consolidation of multiple colors in a single placement is daunting. It's possible but I suspect you'd have a hard time finding a contractor and if you do, you'll pay a steep premium for labor and materials

The bigger issue with architectural concrete of any type is the cost of the formwork. All the fancy color in the world isn't going to look very good if the formwork produces a standard rough surface. Smooth or textured concrete is very expensive.

At the end of the day, if you don't like the appearance of as-cast gray concrete, it's a lot cheaper to cover it up than it is to make it pretty.

 

[john.k]

If you want layered ,consider blocks.

 

[Desert_Sasquatch]

I suppose anything's possible but there are multiple challenges to what you are considering. Ready mix suppliers are generally willing to provide colored concrete but the challenge of timing the delivery, placement and consolidation of multiple colors in a single placement is daunting. It's possible but I suspect you'd have a hard time finding a contractor and if you do, you'll pay a steep premium for labor and materials

If ready mix suppliers (I guess that means the people with the concrete trucks?) are willing to provide colored concrete, then does that mean just ordering several truckloads of concrete is an option if I pay for them to sit around for a bit? Depending on how long it takes to pour an 8' or 9' wall, and how much they charge me per hour to just sit there... maybe that would be an option?

I assume the limiting factor when deciding how long it takes to pour a foundation for a medium residential home is how long it takes the concrete to dry, right? Because at some point you have to wait for the concrete to harden a bit before you pour more or else it will blow out the form. So... how long does it take for concrete to dry enough for another lift to be poured over it? And how tall can a lift be? (I'm mostly wondering whether with this plan of mine I'd be asking four ready mix trucks to idle around for an extra one hour or six.)

The bigger issue with architectural concrete of any type is the cost of the formwork. All the fancy color in the world isn't going to look very good if the formwork results in a typical, rough surface and smooth or textured concrete is very expensive.

At the end of the day, if you don't like the appearance of as-cast gray concrete, it's a lot cheaper to cover it up than it is to make it pretty.

Hmm, I guess my hope was that it would look enough like rammed earth that a rough surface would be acceptable. I think rammed earth often has a less-than-smooth feel. To be honest my biggest fear in terms of texture would be that it would be too smooth, which might give it away to be pure concrete rather than stabilized rammed earth. Or I guess that there's a noticeable difference in texture between the concrete and rammed earth just due to the mix of gravel, sand, and cement that has to be used.

All that said, I'd have to experiment with all this on a smaller scale (to see about texture and color) before I decided to build a basement this way. At this point I'm just kind of assuming that I'd be able to achieve a texture and color mixture that felt good to me.

But right now I'm more wondering about whether it could be done at all, and if so for what price.


[An example of the kind of texture rammed earth walls can have]

 

[Desert_Sasquatch]

If you want layered ,consider blocks.

I hear you--I am definitely a form follows function person, and I've certainly lived in some not-exactly-pretty-but-definitely-functional situations of my own making. For this project though, I'd prefer not to. Mostly because I love how rammed earth looks, but also because I think enough other people will agree with me (at least compared to, say, some painted cinder blocks) that imitating rammed earth well will also prove worth the money if I sell the home or rent out the basement.

 

[Adaylate]

What is your target R value and can you reach it with just your outside rigid insulation?
Good luck!

 

[Desert_Sasquatch]

What is your target R value and can you reach it with just your outside rigid insulation?
Good luck!

I don't have a number yet--I'd have to look at what is normally used in this climate. But my understanding is that, from a moisture control perspective, exterior insulation is much preferred to interior insulation for basements (or crawl spaces, if you are conditioning the crawl space, which again, seems to be the better thing to do from a moisture control perspective). The idea would be to use either mineral wool or foamed glass exterior to the concrete, depending on whether I was concerned about rodents getting at the mineral wool. On one hand one does want to use enough insulation. On the other hand the ground keeps a much steadier temperature than outside, and that means that cold winter nights and certainly hot summer days won't impact indoor temperatures nearly as much, so there may be room to use a bit less insulation than I'd use on above-ground walls.

I admit that I've not thought to ask whether it's ok to use multiple layers of a rigid insulation product on the exterior of the foundation... but I don't see why it would be a problem. The compressive forces exerted on the insulation from the earth mounded around the foundation wouldn't get larger if I added more insulation, right?

 

[john.k]

If you want rammed earth,use rammed earth.

 

[Adaylate]

I have had two homes with walkout basements. Both had an insulated stick wall inside the concrete wall and were quite comfortable. That was the reason for my question, to make sure you can meet the energy code without an interior insulated wall.
Good luck with your project!

 

[Desert_Sasquatch]

If you want rammed earth,use rammed earth.

The problem I see with rammed earth--apart from not knowing whether it's used at all for foundations at all--is that it is really expensive. I generally see estimates around $450 - $750 per square meter ($42 - $70 per square foot) of wall face or higher online, but according to the local company I talked to who specializes in this, that underestimates the cost significantly because it neglects the cost of all of the engineering and soil experts et you need to do it properly, so the real cost is something like 3-10X higher than that iirc (the conversation was a few years ago now, so all I recall was that it was several hundred dollars per square FOOT of wall face). Plus, most modern rammed earth uses 5-10% cement anyhow, so combined with the fact that rammed earth walls are typically thicker than concrete walls, even the environmental benefits are somewhat in question in my opinion.

Thus my interest in concrete that looks like rammed earth because a) I know concrete works for foundations; b) it should be way, way cheaper than rammed earth; and c) I think/hope I can get concrete to look close enough to real rammed earth or even just real layers of sedimentary rock that I'll be happy with it, and potential buyers or renters will too.

 

[Desert_Sasquatch]

I have had two homes with walkout basements. Both had an insulated stick wall inside the concrete wall and were quite comfortable. That was the reason for my question, to make sure you can meet the energy code without an interior insulated wall.
Good luck with your project!

Cheers, I appreciate the question, God knows it would be horrible design a whole basement around this idea of bare cement walls and exterior insulation only to find out that it won't work because I can't put that much insulation on the exterior.

All I can say is that the architect I've been taking home design classes from loves basements, lives in a cold climate, thinks that all basement insulation should be on the exterior, and doesn't seem to think that it's all that complicated to achieve with new builds. I'm not an architect myself, but that's where I'm getting my information.

 

[PopcornSutton]

There isn't a limit on how high a wall pour can be placed in a day's time. You have to have a pour plan, and experienced people. First your form work has to be designed right. Usually you don't pour a "full liquid head" in a wall form. A 2 foot lift is normal, it is vibrated as it's placed, and you start at one end and place that lift to the end, than fall back and start again with another lift. Each lift gets vibrated into the last lift, and so on. How many feet per hour is planned. As far as wall finish, there are a lot of ways to deal with it. One thing is a given, there has to be through wall ties, but you can place those in a pattern if it's critical, as long as the design is adhered to. Ties are broken off when the wall is stripped and holes patched. New plywood can be used and a very nice wall finish can be had. Form liners can be used to give a pattern and/or texture. Concrete will be a mirror finish to whatever the form is.

Now the pour method I described is standard for structural concrete walls. That concrete must meet a standard for strength, and is tested at the site. House builders don't necessarily have to meet structural criteria, they use high slump concrete and pour walls full height. Nothing wrong with that when a structural requirement doesn't have to be met.

 

[ConCretin]

If ready mix suppliers (I guess that means the people with the concrete trucks?) are willing to provide colored concrete, then does that mean just ordering several truckloads of concrete is an option if I pay for them to sit around for a bit? Depending on how long it takes to pour an 8' or 9' wall, and how much they charge me per hour to just sit there... maybe that would be an option?

I assume the limiting factor when deciding how long it takes to pour a foundation for a medium residential home is how long it takes the concrete to dry, right? Because at some point you have to wait for the concrete to harden a bit before you pour more or else it will blow out the form. So... how long does it take for concrete to dry enough for another lift to be poured over it? And how tall can a lift be? (I'm mostly wondering whether with this plan of mine I'd be asking four ready mix trucks to idle around for an extra one hour or six.)

You'd just order as much of each color you need for each lift with enough time between trucks to place the previous lift. The placement will be continuous so that the concrete doesn't harden between lifts and create a cold joint. If you're vibrating the concrete, I expect the colors would blend a bit between lifts. Most concrete forms are designed to place about 8' per hour.

Hmm, I guess my hope was that it would look enough like rammed earth that a rough surface would be acceptable. I think rammed earth often has a less-than-smooth feel. To be honest my biggest fear in terms of texture would be that it would be too smooth, which might give it away to be pure concrete rather than stabilized rammed earth. Or I guess that there's a noticeable difference in texture between the concrete and rammed earth just due to the mix of gravel, sand, and cement that has to be used.

All that said, I'd have to experiment with all this on a smaller scale (to see about texture and color) before I decided to build a basement this way. At this point I'm just kind of assuming that I'd be able to achieve a texture and color mixture that felt good to me.

But right now I'm more wondering about whether it could be done at all, and if so for what price.

The finish produced by formwork depends on ties, panel seams, facing material and condition. Your average residential form system is designed for speed and efficiency rather than appearance. I don't think you'd end up with a wall looking like rammed earth but rather a rainbow colored concrete foundation wall.

It's an interesting idea that I don't think I've ever seen tried. About anything can be achieved with custom forms and form liners but complexity and cost go up exponentially. I could see you paying $300 plus per yard for some colors plus the cost for small loads, truck cleaning, etc. Not to mention the premium a contractor would charge if you can even find one willing to take it on. I could see the total cost going into the thousands per yard. Unless you have very deep pockets, I can't imagine it's worth the cost. I think you'd be better off with some kind of lime wash or stucco.

 

[racecougar]

I think you'd be better off with some kind of lime wash or stucco.

You beat me to it. If I was asked to create the appearance the OP is after, I'd place the foundation as usual and work the 'art' side of it afterwards.

 

[DGersic]

If ready mix suppliers (I guess that means the people with the concrete trucks?) are willing to provide colored concrete, then does that mean just ordering several truckloads of concrete is an option if I pay for them to sit around for a bit? Depending on how long it takes to pour an 8' or 9' wall, and how much they charge me per hour to just sit there... maybe that would be an option?

You wouldn’t be paying them to sit around with concrete hardening in their trucks. You’d be paying for a bunch of small loads to show up on a very tight schedule. Each truck pours one layer of your layer cake, and goes away, so the next truck in the train can arrive.

I wouldn’t say that it’s impossible, but it looks to me like building your foundation with actual stacks of money would be cheaper.

If I wanted something like this, I’d pour a normal foundation and investigate how to dress up the inside of it to meet your artistic design goals. That has to be cheaper, easier, and a lot less likely to fail.

 

[Desert_Sasquatch]

Thanks for all of that PopcornSutton. That's helpful to know about what a typical lift height is. Any idea how long it takes before another lift is added, usually? FWIW I'm not trying to get an absolute rule--I assume it depends on how the concrete is formulated and the weather. And I know at the end of the day I'll find a company and leave the details up to them. I'm just trying to figure out whether, if I ask for four trucks to sit around waiting between lifts, if I'm asking for something insanely expensive or just a bit more expensive.

Now the pour method I described is standard for structural concrete walls. That concrete must meet a standard for strength, and is tested at the site. House builders don't necessarily have to meet structural criteria, they use high slump concrete and pour walls full height. Nothing wrong with that when a structural requirement doesn't have to be met.

Interesting. What do you mean that house builders don't have to meet these structural criteria?

Do you mean that these criteria are important for foundations, but that if you're using Fox Blocks or something like that to build above-ground concrete walls, that there is a bit more leeway in terms of concrete strength and the testing for it?

Or are you just saying that larger buildings--with more than 2-3 stories, the kind where you've got architects and engineers involved rather than just some dude building a single family dwelling where the details are scribbled on a napkin--have higher standards for checking concrete quality?

 

[Desert_Sasquatch]

You'd just order as much of each color you need for each lift with enough time between trucks to place the previous lift. The placement will be continuous so that the concrete doesn't harden between lifts and create a cold joint. If you're vibrating the concrete, I expect the colors would blend a bit between lifts. Most concrete forms are designed to place about 8' per hour.


The finish produced by formwork depends on ties, panel seams, facing material and condition. Your average residential form system is designed for speed and efficiency rather than appearance. I don't think you'd end up with a wall looking like rammed earth but rather a rainbow colored concrete foundation wall.

It's an interesting idea that I don't think I've ever seen tried. About anything can be achieved with custom forms and form liners but complexity and cost go up exponentially. I could see you paying $300 plus per yard for some colors plus the cost for small loads, truck cleaning, etc. Not to mention the premium a contractor would charge if you can even find one willing to take it on. I could see the total cost going into the thousands per yard. Unless you have very deep pockets, I can't imagine it's worth the cost. I think you'd be better off with some kind of lime wash or stucco.

Ah, thanks ConCretin, that's really helpful. 8' per hour is good to know, and seems plenty fast for whatever I'd want to do.

And oh boy, $300 per cubic yard is a bit more than I would want. I had assumed that earth tones would be quite inexpensive. I guess I need to look into that.

My original idea was to create this look using stucco over the concrete wall. I guess I had hoped that just adding color to the original concrete pour would be easier and cheaper. Alas, if what you say is true, that may not be the case...

 

[Desert_Sasquatch]

You wouldn’t be paying them to sit around with concrete hardening in their trucks. You’d be paying for a bunch of small loads to show up on a very tight schedule. Each truck pours one layer of your layer cake, and goes away, so the next truck in the train can arrive.

I wouldn’t say that it’s impossible, but it looks to me like building your foundation with actual stacks of money would be cheaper.

If I wanted something like this, I’d pour a normal foundation and investigate how to dress up the inside of it to meet your artistic design goals. That has to be cheaper, easier, and a lot less likely to fail.

Really? They couldn't pour half of it, wait for half an hour or an hour, and then pour the next half? Somehow I imagined there was more leeway in the timing with concrete trucks (but obviously I know very little about all this)...

 

[bluedog225]

Another vote for paint or stain or anything other than trying to pour different colored layers of concrete. I believe there are lots of full finish type products that will get you where you want to be.

 

[Desert_Sasquatch]

Another vote for paint or stain or anything other than trying to pour different colored layers of concrete. I believe there are lots of full finish type products that will get you where you want to be.

I did look into the stains that are out there. Seems like there are options, though I wonder how the layers would look, compared to stucco. I'm mostly concerned that overlapping two stains would give me a third color, and I'm not sure I want that. It might look nice though... I'd have to see.

Also I wonder about using stains on grey concrete. Obviously it would work in some cases, but in others I worry I would need more of a paint than a stain to get the lighter tones, and I very much want a stain rather than a paint...

 

[Steve W.]

How about using something like Gunite or Shotcrete?

After application, call in an artist with a large airbrush and color it to taste.

Will probably look a bit like stucco, but you can vary the thickness so it's not all flat.

.

 

[bluedog225]

Edit “faux” finishes.

I think if you use earth tones, the overlap and bleed might look natural.

 

[billconner]

I it were my job to produce what you like and want, I would go after finding the contractors who did the work in the photos you showed and want to mimic or come close to. They're going to say sure with fewer mistakes and less learning or they're going to say never again. If you want something that's been done before, find those people.

 

[Desert_Sasquatch]

How about using something like Gunite or Shotcrete?

After application, call in an artist with a large airbrush and color it to taste.

Will probably look a bit like stucco, but you can vary the thickness so it's not all flat.

.

I do want it to at least feel like the color is an inherent part of the concrete. Even if it isn't. I know it's kind of a weird distinction, but I gather it is mostly the distinction between concrete stains vs paints (or so I gathered, looking at the Keim concrete stains and paints), so I gather I'm not the only one interested in that.

The stain could definitely be applied after the stucco, but at that point I'm wondering why I would need the stucco at all if I'm happy with the basic concrete wall texture and I could have just asked for a lighter colored concrete to be poured for the foundation (that is an option...right?).

I don't know, I think I'd have to experiment with this myself a bit to see whether the result looked ok to me.

I have wondered about using colored shotcrete, but I've not quite figured out how to keep the lines between colors distinct. On one hand I'd be happy with that rough texture, but on the other hand I've no idea how to keep one color of concrete from blending in with the one below it. Which I guess is what folks here have been saying.

 

[Desert_Sasquatch]

I it were my job to produce what you like and want, I would go after finding the contractors who did the work in the photos you showed and want to mimic or come close to. They're going to say sure with fewer mistakes and less learning or they're going to say never again. If you want something that's been done before, find those people.

Unfortunately, those photos are of actual rammed earth. Which I'm only trying to mimic, not duplicate...

 

[Desert_Sasquatch]

Edit “faux” finishes.

I think if you use earth tones, the overlap and bleed might look natural.

Yeah, I agree. I've seen rammed earth where when two layers meet there will be a darker portion. Of course, that might be due to there being heavier stuff there that settles during the ramming, I'm not sure. But... it could be an interesting look, allowing for some overlap in stains. Definitely a thing to experiment with

 

[billconner]

Unfortunately, those photos are of actual rammed earth. Which I'm only trying to mimic, not duplicate...

Ahh! So this is all research and development for something that's never been done.

 

[PopcornSutton]

Thanks for all of that PopcornSutton. That's helpful to know about what a typical lift height is. Any idea how long it takes before another lift is added, usually? FWIW I'm not trying to get an absolute rule--I assume it depends on how the concrete is formulated and the weather. And I know at the end of the day I'll find a company and leave the details up to them. I'm just trying to figure out whether, if I ask for four trucks to sit around waiting between lifts, if I'm asking for something insanely expensive or just a bit more expensive.



Interesting. What do you mean that house builders don't have to meet these structural criteria?

Do you mean that these criteria are important for foundations, but that if you're using Fox Blocks or something like that to build above-ground concrete walls, that there is a bit more leeway in terms of concrete strength and the testing for it?

Or are you just saying that larger buildings--with more than 2-3 stories, the kind where you've got architects and engineers involved rather than just some dude building a single family dwelling where the details are scribbled on a napkin--have higher standards for checking concrete quality?

I worked commercial construction for over 30 years. Concrete work was part of it, but it's the backbone of a building (or structural steel). Commercial buildings are designed by architects and structural engineers, and they determine what it needs to be. I'm not knocking housing work, but it is a different ball game. Hundreds of thousands of houses have been built using masonry block as foundation walls, mostly none have any reinforcing in them. They get backfilled the house is built on top of them. In today's world, block work is rare and poured concrete walls have taken their place. They are probably stronger than block, but they don't have the structural requirements as structural reinforced walls. Commercial concrete is tested on every pour, and if it's a larger pour, tested at every 50 yards placed. The concrete is slump tested to be sure the design mix tolerance is met, air entrainment if specd is tested, and concrete samples are taken, placed in cylinders and cured. Those cylinders are broken on testing equipment that records how much compressive strength it took for it to fail. They are tested at 7 days, which is the first indication if there is a problem with the mix, but the deciding factor comes at 28 days. There is serious quality control done on this concrete. Oh, and to add to the process, weather conditions play a big factor in quality control, especially in cold temps.

 

[mike93lx]

The problem I see with rammed earth--apart from not knowing whether it's used at all for foundations at all--is that it is really expensive

If this approach was significantly cheaper, why hasn't it been done yet?

Sounds like an interesting idea, but looking at it as cost saving doesn't feel realistic

 

[Desert_Sasquatch]

If this approach was significantly cheaper, why hasn't it been done yet?

Sounds like an interesting idea, but looking at it as cost saving doesn't feel realistic

I'm not sure I understand.

If you're asking why my weird-*** idea hasn't been done yet, why people are still using more typical ways of finishing basements, then that is definitely one of the things I was wondering and asking about.

If you're asking why my "layers-of-colored-concrete-instead-of-rammed-earth" thing hasn't replaced rammed earth I think it's just that rammed earth has sustainability cred. As I said earlier, I think some or much of that is unearned, at least when it is stabilized with cement. But nonetheless, I think that many people willing to pay a premium for rammed earth won't be willing to pay a smaller premium for concrete that looks like rammed earth. If you are rich it is hard to brag about concrete walls, even if they look nice and feel and operate functionally the same as rammed earth walls. If you are less rich though, maybe it doesn't matter. At least that's what I'm thinking.

 

[WildBill]

I don't have a picture but about 20 years ago I helped do something like this with stain after the fact. Was a pain and took forever to put the stain on with brushes and let each layer dry for awhile before doing the next. And we spent a couple of days making the concrete look nice before doing the stain. It looked really great afterwards though. We patched all the holes in the concrete then used a 9" grinder to make long slow continuous passes down the wall, so it looked like layers of dirt. Was for a crazy expensive walkout basement swimming pool area. The owner wanted to look like it was just cut out of the hill without concrete walls around it. When I showed him a picture of what the dirt looked like before the wall was poured and asked if that's what he wanted he said no, he wanted it to look like nice dirt.

 

[Renegade1LI]

Maybe look into a 3d printed foundation,pretty cool how it's layered. They built a few here on long Island. Probably could add different colors to the layers, can't hurt to ask.