Basement Types

[billboe]

Yeah... I know the pool guys use "gunnite" (no, I'm not sure what is in it??). I was talking about the process... From the name and your description, it sounds like they use a "gun" to "shoot" the concrete onto a rebar structure...

 

[RobS]

Around here poured concrete is the norm. Our current house is 11 years old with a poured concrete basement. One minor crack has been there since about day 2, but other than that it's been fine. We're building a new house this year and it will be poured also, though deeper (9'). Our builder experimented with pre-cast basement walls a couple of years ago, but has returned to poured. I like the idea of the styrofoam forms, but it's more expensive (at least around here). Seems like every one and their brother in this area has a truckload of basement wall forms /w3tcompact/icons/wink.gif

The only thing we'd like to do differently, but probably won't due to cost, would be to cast in a brick ledge at grade level and brick the face of our foundation from grade to sill. This seemed to be the standard method when I was travelling to Nashville a few years back and it really looks nice. Up here, very few do it. Funny how construction details can be so regional /w3tcompact/icons/smile.gif

 

[buckeye]

Thanks for all the input so far. As for gunnite, I have experience with this in the chemical plant I work in. I have only seen it used as fireproofing for the protection of process vessel skirts and support steel. Around here they call it "pyrocrete." They build a wire cage around the steel to be protected and then use a gun to shoot it on the steel. They (contractors) say it is much cheaper, but sometimes it is just as cheap to trowel it on by hand. With pyrocrete you usually have to build a shelter around the area to be applied or you will splash the stuff everywhere, onto instruments, insulation, workers, etc.

 

[cowboydoc]

I've built and lived in quite a few houses and I haven't seen very much difference in the two. I think it all comes down to how good the guy doing the work is. I've seen five year old poured foundations crack and have to be repaired and block foundations 50 years old that were still as good as the day they were layed down. I've also seen the cracking in the block foundations as well. I don't think it matters much what type you go with as much as who is doing the foundation. If you have someone who's been around a long time and has good references you will alright either way. Another thing to consider is that if you ever do have any problems with the foundation it is much easier and cheaper to repair a block foundation than it is to repair a poured foundation or if you ever wanted to build on.

 

[Bird]

Gunnite is what's used to build most of the swimming pools in my area; don't hear much about its other uses.

 

[RobS]

One of the factors affecting cracks is the weather when they put in the foundation. Our current house was poured in February and I cannot remember what the conditions were at the time. We have one small crack.

Our new house will also be poured in Feb (next month /w3tcompact/icons/grin.gif ) but this builder is very conscious/concerned about the weather conditions during that time. They will look for a window where the footer/walls can be poured and cured without freezing. Sounds directionally correct to me /w3tcompact/icons/smile.gif

 

[radman]

Our area use almost exclusively poured concrete basement walls. Poured concrete used to be more expensive now that it is more common, the number of block layers have decreased and labor costs have gone up. The use of block or poured concrete does seem to be regional and I notice it even varies from city to city. It probably depends a lot on local contractors. I have had both and prefer poured.
Once the basement is excavated and footings dug, it takes about one day to pour the footings, wait 2 days then place the forms for the poured concrete, day 4 pour the concrete and then remove the forms is a few days.

 

[DVerbarg]

Its been my simple observation that labor costs have much influence on the block vs poured foundation debate. Like GlueGuy said about his area, labor costs are very high here and as a result poured foundations are more popular. And like RobS said about his area, it seems that everyone and his brother have forms around here and we get the benefit of supply/demand.

I'm not the physics mind but would assume that a rebar reinforced poured wall would have higher psi ratings compared to block. This would allow for deeper basements/higher walls which makes a basement much more usable. We had 10' walls when our house was built a year ago and love the space in the basement. There is still 8'10" clearance after ducting, plumbing, structural beams, etc.

When the beams are engineered be sure to look at support post locations in the basement. An extra few hundred dollars for a heavier beam might mean eliminating a few of those obnoxious support posts. Our basement is 2500 sq ft and only has 3 posts. My GC is now disgusted with his basement which has 5 posts in 1600 sq ft and is now spending over $900 in materials plus his own time to change out a beam to eliminate one post in the middle of the room /w3tcompact/icons/shocked.gif. Architects don't always get together with the engineers to talk about basement function.

Just my 2 cents...

 

[RonL]

Buckeye

My personal feeling is that poured concrete foundations will increase the future value of the house. It's probably my personal prejudice but my first impression of a house with a block foundation is that it was done " on the cheap". Codes, of course, also apply.
An area where many problems originate is in the excavation and forming of the footing. Some people form for the footing over disturbed earth that will, by its nature, settle. At the very least the area where the footing will go should be thoroughly compacted. On large projects soil engineers are brought in to check the compressive strength of the soil. Proper perimeter drains are also helpful.
Another area where problems occur is when pours are not allowed to properly "cure". Curing concrete is a chemical process that occurs over time. Proper moisture levels should be maintained. It is common for contractors to form for a footing, pour, strip the forms, form for the foundation, pour, and strip the foundation forms all in a very short length of time. This causes internal stresses that set the stage for cracking.
I have recently read a report that recommends that after a slab is poured and begins to set a perimiter
dam is set up and the surface is flooded. This allows the slab to cure slowly without inducing internal stress.
In some parts of the country it is common to pour footings and foundations without rebar. If you have ever tried to demolish a properly reinforced concrete stucture you would appreciate how tough and strong reinforced concrete really is. You could probably knock a block wall down with a sledge hammer. Try doing that with a reinforced concrete wall.

RonL

 

[MossRoad]

Yeah, it seems that there is always some truck sitting on some construciton site with all of the forms. You can rent the forms as well, down on main street. That's where I got all of my cross ties and rebar. I built my own forms for the future garage, but they were only four feet high.

Around here, poured is the way to go. If you go deeper than 8 feet, you might want to increase the wall thickness by 2 or even 4 inches. We will probably go with a 10' deep basement with 12" walls. Of course, a footing drain all the way around that will exit down hill from the house, and several inches of insulation on the outside of the walls. Some contractors recommend that you pour the basement walls in the fall and let it sit all winter to cure. They say that the cracking occurs when construciton starts before the concrete is completley cured. But then, some say cracking occurs no matter what you do.