Replacing a floating slab garage floor

[Kpaige]

Ok so I built this garage probably 15 years ago. The people I had prep the ground and pour the slab messed it up good. The garage moved that first year had the slab crack had it mud jacked Etc Etc. Well time to do it right. I am going to hire someone to do it so it gets done quick. Will need to disconnect electrical and gas then raise the garage and Lean to up then demo prep the ground re pour the concrete lay a course of block and re attach the building.

Any advice?

 

[DougWil]

Well you have the idea, but make it sound easy. It isn't.

I moved a 25x40 shop over 80' or so and placed it on a new footing, stemwall then poured the slab after placing the building.

Moving it wasn't easy, but sure would be easier than trying to remove a slab and turndown, compact, form and pour another with the building in the way.

 

[Kpaige]

Not trying to make it sound easy as it is definitely not it will be labor intensive. I have two companies I am working with for bids they both have very inginuos processes they have develooed. I might mention I am in MInnesota so seasons are hard on concrete.
If I had time and a goid back I could do all the lifting of the building and demo work but Those days are gone time to pay

 

[Dick in Wisconsin]

How big is the garage?

 

[ford33]

Is it just the slab that needs to be replaced? Could you cut the slab at the footings, remove it and just pour a new slab?

In my garage, the slab is separate from the footings.

 

[Kpaige]

Its not huge 26 by 32 with a lean to off the back.

Cant cut to the footings as its a floating slab so to do it we need to remove it all

 

[D45]

Is it just the slab that needs to be replaced? Could you cut the slab at the footings, remove it and just pour a new slab?

In my garage, the slab is separate from the footings.

Same here

 

[The Cobbler]

OP is talking about a monolithic slab where the footers are part of the pour. basically a floating pad with thickened edges .

to the OP, after I poured my pad I formed a curb around the perimeter (not including where the doors etc are) and poured a curb. I found it easier & cheaper to deal with than to lay block

 

[Ironhorse74]

Years ago I worked with a now ex-father in law. We jacked up one of the old Maytag houses. Raised it probably a foot off the foundation. Put bridging and cribbing under the floor. Supported the house on the all four sides. Then we cut a ramp and ran a bobcat under the house and dug out the old three layer brick foundation. Once we had it deep enough we used a rototiller to dig footings. Poured concrete level and then laid up a block foundation. Once that was done we poured a floor and then let the house back down. Pretty much the same thing you need to do. As I recall he rented the bridging and cribbing from a house mover.

 

[Kpaige]

Correct it is a monolithic slab.
I was going to talk to them about block verse poured wall I like the idea of a poured wall.

The original slab is fiber reinforced with no wire or rebar. I wanted wire but the concrete crew swore by this. I now know that is because they make the same but have less work!!!

 

[The Cobbler]

.... I like the idea of a poured wall.

.....!

the top of my form was a 2x6 laying on the flat ,except for door locations , that created a step on the top of the pad where the curb wall was then poured. rebar into the pad every 18" or so . after the pad was poured removed the 2x6 and formed the curb. wired rebar to the stubs sticking out of the pad.
poured a 6"x6" curb around the perimeter of the pad and set the walls on that.

Only thing I would have done differently would be to get extra long anchor bolts & place them in the pad pour instead of just in the curb pour. (not that it's an issue , just hindsight)

 

[The Cobbler]

the top of my form was a 2x6 laying on the flat ...

edit, after thinking about it I used full 1" rough pine ripped so it created a ledge for 6" walls

 

[Orionrising]

unless you use a bunch of steal beams, not sure how that's gonna work. Might be easier to change it from a monolithic poor to a conventional footing and slab. ( jack it off slab, install temporary jack walls about a foot in, cut off perimeter of slab to install footings, lower back down, remove jack walls then pull out the interior slab.

 

[DougWil]

The original slab is fiber reinforced with no wire or rebar. I wanted wire but the concrete crew swore by this. I now know that is because they make the same but have less work!!!

Many have learned that hard lesson. Fiber is no substitute for rebar or heavy wire mesh. No not that dinky wire in rolls either!


You would save a lot of time and labor if you have the space to roll the garage out of the way while doing all that work.

 

[Kpaige]

I have the space to move it to the side or back but all that will be up to the contractor.
And yes Fiber is not a substitute I learned my lesson.

 

[demeter008]

Not trying to make it sound easy as it is definitely not it will be labor intensive. I have two companies I am working with for bids they both have very inginuos processes they have develooed. I might mention I am in MInnesota so seasons are hard on concrete.

If I had time and a goid back I could do all the lifting of the building and demo work but Those days are gone time to pay

Moving it was difficult, however beyond any doubt would be less demanding than attempting to evacuate a piece and turndown, minimized, frame and pour another with the working in the way.

 

[Boilerhouse]

Ok so I built this garage probably 15 years ago. The people I had prep the ground and pour the slab messed it up good. The garage moved that first year had the slab crack had it mud jacked Etc Etc. Well time to do it right. I am going to hire someone to do it so it gets done quick. Will need to disconnect electrical and gas then raise the garage and Lean to up then demo prep the ground re pour the concrete lay a course of block and re attach the building.

Any advice?

You are sure the issue is the slab and not the original site prep. Before I poured my floating slab about 15 years ago, I had 4 feet of top soil/clay removed and replaced with pit run gravel, compacting between each truck load. Slab is holding up well and it was no better reinforced than yours. (Central Ontario)

 

[lakeroadster]

You are sure the issue is the slab and not the original site prep? ..... (Central Ontario)

...The people I had prep the ground and pour the slab messed it up good. ..

............

 

[wssix99]

The original slab is fiber reinforced with no wire or rebar. I wanted wire but the concrete crew swore by this. I now know that is because they make the same but have less work!!!

Your original concrete crew was correct. Reinforcement in shallow slabs only protects you against cracking from shrinkage. In your case, it would have done nothing for your structural cracking or subsidence other than hold the moving sections of slab together a little better.

Correct it is a monolithic slab.
I was going to talk to them about block verse poured wall I like the idea of a poured wall.

I would recommend that you do this. As Lakeroadster points out, ^ your issue is with the ground prep. In order to be able to rely on a new monolithic slab, you'd need to move the entire building aside, dig up all that loose dirt underneath, and then put it back in properly compacted layers.

A traditional foundation going down to solid ground (with a floating slab) should perform better for you going forward.

I would recommend reinforcement in your new floating slab, though. Your floating slab won't see the same stress that your old monolithic slab did, but the dirt underneath could still be suspect. Putting down a good bit of compacted high quality gravel under the slab will help you distribute the loads on to your dirt. In the event that you do have problems with the floating slab, the reinforcement will hopefully lessen them for you to the point where you don't need to make a big expense to fix it. (I did this for my slab because I had very shaky ground underneath and didn't want to get in to the expense of digging up 6' of poor fill to get it perfectly solid.)

 

[matt_i]

You'd have to do some study on the weight of the garage, but moving it on a gooseneck or semi trailer would be how I'd try to proceed getting it out of the way. Then you can actually work in the dirt.

A big thing would be to make very careful measurements & drawings now while the walls are still presumably square and parallel. The new foundation will have to match that as exactly as possible. I would not wait until its cut apart and up in the air to start measuring as things can obviously move.

Last thing I would not set any J-bolts/studs otherwise it will be pure hell trying to line them all up. Instead I would set the framing back on the new foundation, tweak to adjust if necessary, and then drill the wood and the concrete in a single shot. Very careful prep to remove dust and then do epoxied anchors.

 

[Kpaige]

I completely agree the original site prep was not done correct. First they did dig a lot out but it was tough using the largest bobcat made at the time with tracks and it struggled to dig the earth but here is the big issue they filled it all with sand and from what I gather talking with people Etc that seen them work (I was not here) there was no packing of the sand. Un fortunately fo me it was my first concrete expierience.

I will not be going with traditional below grade footings time, money, and soil will prevent that. There are no less then 20 floating slabs in my direct 1 acre neighborhood and they are all fine. My neighbors that I did for him one year after mine identical garage but I did all the prep and used a diffrent concrete contractor with heavy wire mesh not one crack.

 

[Kpaige]

Ok got the bid to lift the garag move it out of the way, tear up the concrete and dispose of, remove old fill? Apply new fill and raise it up a foot, then move a place garage back after mason work is done $5500 not bad. Just waing on the mason price. I will do all electrical and gas

 

[the GOAT]

That seems like a reasonable price to me.


Is there any possibility of having the new slab poured behind, next to or in front of the current location and moving the garage location. That way the moving contractor has less to do and can complete the job in one go.

 

[Kpaige]

I think it is a very fair price.
Unfortunately when I built it it is precisely placed. It is exacty 20 ft away from my main house which is the requirement for fire here. The septic field is right behind it so cant go there. And to the side it is exactly sitting on the edge of the easement. If I could I would do it that way.

 

[matt_i]

There's a good article in the latest issue of Fine Homebuilding #262 (Oct/Nov '16) with details about the frost-protected shallow foundation. Paraphrasing, they reference ASCE 3201 as a design guideline.

the link is not for promoting anything, just info.
http://www.standarddescription.com/asce-3201-p-397368.html

My interpretation is there is more detailing involved to setup the forms and prep the site in a "platform" area. But less digging, filling, and working down in a muddy hole.

 

[370]

OP is talking about a monolithic slab where the footers are part of the pour. basically a floating pad with thickened edges .

to the OP, after I poured my pad I formed a curb around the perimeter (not including where the doors etc are) and poured a curb. I found it easier & cheaper to deal with than to lay block

Forming and pouring a curb is easier and CHEAPER than laying a course of block? A block costs $1 a piece 3 block covers 4'. Where are you getting concrete that it costs less than $3 to pour 8x8x48 section. Including the limber to form it? Oh I forgot mortar. A bag is what $6 + sand at 10 a yd. and you can lay 40-50 block. So your looking at how many feet of block from 1 bag? Like 52' of block... so $66 for 52' of block. With sand left over a yard of sand goes quite q ways. There is no way concrete is cheaper.

 

[DougWil]

Forming and pouring a curb is easier and CHEAPER than laying a course of block? A block costs $1 a piece 3 block covers 4'. Where are you getting concrete that it costs less than $3 to pour 8x8x48 section. Including the limber to form it? Oh I forgot mortar. A bag is what $6 + sand at 10 a yd. and you can lay 40-50 block. So your looking at how many feet of block from 1 bag? Like 52' of block... so $66 for 52' of block. There is no way concrete is cheaper.

Concrete has much higher strength than CMU so it doesn't need to be 8" thick,,,and lost floor space.
Plus you didn't include having to grout those empty CMU cells so the wood has more bearing area and something to embed anchor bolts in.

Forms are the big factor in concrete vs CMU if you can borrow, rent or build and sell the forms when done, concrete would be way faster and as they say 'time is money'.

That said when I moved my shop, with winter closing in I poured a footing, went up 3 courses of block because I didn't have time to make forms, couldn't rent them, had no help, and the concrete company (the only one) was difficult to schedule.

 

[mike93lx]

This thread is 7 years old and the OP hasn't logged on since October. Don't hold your breath

 

[NUTTSGT]

This thread is 7 years old and the OP hasn't logged on since October. Don't hold your breath

Yep and the spammer has been banned and your post edited to remove his spam.

I'll be closing this thread, however if the OP comes back and wants to reopen, it will be.