Know Anything About Concrete?

[HoneyBadger]

I'm thinking of adding a concrete wall or two in my unfinished basement. I have a new home and the basement floor is a floating slab (I think that's the right terminology). Are there any special considerations I need to take before, during, or after pouring the concrete? There is a limited possibility that the floor could shift a little over time. What is the best defense against this? How should I anchor the new walls into the existing concrete floor and walls?

Thanks in advance! [Beer]

[gnihcraes]

Full sized walls? Floor to Ceiling? (like a gun vault?) :)

Walls should float with the floor if it were to move.

[HoneyBadger]

Full sized walls? Floor to Ceiling? (like a gun vault?) :)

Walls should float with the floor if it were to move.

8ft walls with a few inches to spare under the main floor trusses.

[Jamnanc]

The product you want at the bottom of the wall is surevoid. Basically cardboard boxes that squish if the slab moves. Might ruin some of the purpose of your walls though. If my guess is right.

[ChunkyMonkey]

Consider wood frame w/ heavy gauge sheet metal instead?

[ChunkyMonkey]

The product you want at the bottom of the wall is surevoid. Basically cardboard boxes that squish if the slab moves. Might ruin some of the purpose of your walls though. If my guess is right.

To keep it simple..anchor to the bottom but build it w/ its own roof 4 inches short of the basement ceiling (like a safe room), so you don't have worry about settlement.

[HoneyBadger]

To keep it simple..anchor to the bottom but build it w/ its own roof 4 inches short of the basement ceiling (like a safe room), so you don't have worry about settlement.


I was planning on leaving a few inches to spare at the top anyway, but I'm a little concerned because the slab has cuts in it (to guide cracks) and one of them is right in the middle of the room I was planning.

ChunkyMonkey, you're thinking in the right direction. I considered steel, but in my limited research, it seemed that concrete was easier to work with and had a better strength to cost relationship. I could be convinced otherwise... I haven't done enough research yet.

[newracer]

Use cinder blocks

[davsel]

To do it "right"
Bust out the floor where you want the new room.
Dig down four feet
Pour a 16" wide by 8" tall footer where you want new walls
Pour walls on top of footer
Fill in and pour floating floor inside room
Patch floating floor outside room

That 4" floating slab you currently have may not support the walls you want to pour on top without cracking.

[newracer]

I assume this would be to make some type of secure room. Why not use steel studs to frame the wall and then steel security mesh before the drywall? Then you could build a floating wall that is typical used in basements.

[HoneyBadger]

I assume this would be to make some type of secure room. Why not use steel studs to frame the wall and then steel security mesh before the drywall? Then you could build a floating wall that is typical used in basements.

Yeah... Drywall sure doesn't sound very secure... I'm looking for fire and storm resistence as well. Safety and security all in one. The room will be about 150 sq ft.

I am considering 8"x16" cinder blocks filled with concrete and rebar as an alternative to poured concrete walls.

[newracer]

Anyone can get into anything with enough time and tools. It depends on how secure you want to make it. You also have to remember to secure the ceiling too or someone can just get in that way. To do it right you would need to do what davsel posted, even with cinder blocks.

[tmckay2]

my two cents with a little bit of experience. you're better off to dig a hole and build this off your basement, then cut through the concrete wall to make a door. its just going to be easier and you can do the roof of it right. you can also hide the door quite easily if wanted.

building concrete on concrete is problem laden.

[patrick0685]

the two things i know about concrete are this:
1) it will get hard
2) it will crack

outside of that i am no help

[cofi]

why not build a secret room instead of a secure room?

[tmckay2]

also, having a room off the side of the basement will allow you to make an escape tunnel/hatch which is very important. if you have in a safe concrete room and your house collapses in front of the door, well, not good.

[Hunter12]

Be the cool kid on the block and build secret ROOMS not a secret room. Build it like "Mexwell Smart" had in Get Smart (tv series). That is when you know you have reached a new level of greatness!

[HoneyBadger]

my two cents with a little bit of experience. you're better off to dig a hole and build this off your basement, then cut through the concrete wall to make a door. its just going to be easier and you can do the roof of it right. you can also hide the door quite easily if wanted.

building concrete on concrete is problem laden.

Well my budget is limited... Otherwise I would have just done this in the first place.

[cofi]

http://www.youtube.com/watch?v=8T6rpT5_XXE

no way robbers breaking in would find something like that vs robbers breaking in and finding a locked bunker room that they tell all there buddies about and someone coming back with the right tools to open it up

[HoneyBadger]

http://www.youtube.com/watch?v=8T6rpT5_XXE

no way robbers breaking in would find something like that vs robbers breaking in and finding a locked bunker room that they tell all there buddies about and someone coming back with the right tools to open it up

Don't think that I would give all my secrets away on the internet! ;)

[Hunter12]

If your serious about building a secret room. I would start simple check with City and County and Public works to make sure you are clear of all utilities and right of ways. Then once that is all in the clear see if building permits apply and how that will effect the value of your investment "house". Then you should probably contact and engineering firm to ask them for advice on the "type" of concrete needed or other building materials. Because the concrete in your basement is extremely dense. This is to help prevent water and other things that go through the ground. You will also need to consider vent ports. Because, you will need to fresh air! Your best bet is to seek a professionals help when taking on a task like this. You can also look into different bomb structure designs from the "Cold War" era. You can do alot of this research on your own if funds are tight. But, with new technology and materials. You will probably find it cheaper to get it done by hiring someone in the field with reputable references. For something like this. You are gonna want to get it done right the first time around.

[Eric P]

Talk to a licensed geotechnical or structural engineer and find the plans for your floor. You are right to be concerned about doing this. If you have swelling soils, the slab was engineered to float and move uniformly. Adding the weight of concrete walls (145 lbs per cubic ft) can cause the slab to shift in ways you may not want. Even enough to shift the wood frame to keep windows and doors from opening.

[HoneyBadger]

If your serious about building a secret room. I would start simple check with City and County and Public works to make sure you are clear of all utilities and right of ways. Then once that is all in the clear see if building permits apply and how that will effect the value of your investment "house". Then you should probably contact and engineering firm to ask them for advice on the "type" of concrete needed or other building materials. Because the concrete in your basement is extremely dense. This is to help prevent water and other things that go through the ground. You will also need to consider vent ports. Because, you will need to fresh air! Your best bet is to seek a professionals help when taking on a task like this. You can also look into different bomb structure designs from the "Cold War" era. You can do alot of this research on your own if funds are tight. But, with new technology and materials. You will probably find it cheaper to get it done by hiring someone in the field with reputable references. For something like this. You are gonna want to get it done right the first time around.


"Okay"

[def90]

You will need footings period.. You cannot build a concrete wall on top of a floating slab.

[HoneyBadger]

You will need footings period.. You cannot build a concrete wall on top of a floating slab.

Thank you. This is the kind of stuff I need to know.

[HoneyBadger]

I wanted to do as much of this as possible by myself to keep costs down and keep it low key, but it's looking like it might not cost a whole lot more to excavate and add a room to the basement... which is still a lot more project than I can afford at the moment.