Bad Slab...Good Garage?

[Tom R]

Hi All...I have a reasonable large garage...I think 32'x32' plus. My problem is that the concrete slab was done very poorly and it has two major problems...moisture seeps up from below...and the floor is breaking up in an increasing amount. It has to be dealt with.

I ahve read a few discussions about how you should build up a floor slab but am wondering what issues I will have with the process of removing and then replacing my current slab?

I am not an expert but will try and explain the construction...I think it is basic? I have a block wall foundation...I think the floor is poured "inside the block...but am not sure and I am not at that location right now. The garage also as a 1/3 2/3 dividing wall with its' own block base...may be more likely to be on top of the cement floor?

I thought it might make sense to start with the 1/3 stall that is the primary "parking" stall and has the most deteriorization (from road salt). BTW...there is mostly good drainage on the outside of the garage and I would plan to redo the drainage to make sure all rain, etc. drains around and past garage...but the slope will assist that step.

One cement guy suggested the current floor be "sawed" an inch or two away from the block and then dug out. Not sure if I like the idea of leaving any of the old floor?? I then assume I would need to have the base dug out (after the old floor is removed) deep enough to build up the correct base prior to having a new floor poured?

How deep from final floor level will I need to go to have a great moisture barrier and proper preparation for the cement? How think cement for a "normal" garage floor...no lifts...just cars/storeage and stuff???

I live in the country and plan on putting a gravity floor drain...maybe with a sump and a pump? Thoughts?

I probably have left out important info...what do you think? Tom R

 

[Tom R]

No one had to do this type of repair? Tom R

 

[PatrickR]

Hi Tom
I had asked about slab once and got a super reply. Check it out
http://www.garagejournal.com/forum/showthread.php?t=12160

 

[BillK]

two major problems...

moisture seeps up from below..

Fix that problem or you are wasting your time trying to fix this one.

and the floor is breaking up in an increasing amount.

 

[Mr. Welsh]

I can give you some basics. Yes, the floor should be poured using the block wall which is sitting on the foundation as the formwork. There should be a vapor barrier under the slab, which it sounds like there is not. Similarly, there should be a disconnect between the concrete and the block walls to prevent the concrete from binding to them. The purpose of this is to prevent shrinkage cracks as the concrete hydrates. If there is no vapor barrier, there may be no disconnect either. Thus removal could be difficult without damaging the block wall.

You could DIY the concrete removal and sub grade fix using rented equipment if you have a free weekend or two. Then hire someone to do the final leveling, vapor barrier, reinforcement, and finishing.

 

[Kevin54]

It has been done a few times around here. I don't know what area you are in but the standard in my area is to lay block, backfill with crushed stone, tamp solid, then pour the floor. So basically the floor floats inside the block walls. Some floors have rebar and some just have the reinforced concrete. If it has rebar, then it will need to be sawed before removing. If it is a considerably older floor it may be pretty tough concrete. The easies way to see how it is made is to but a section out of there with a concrete saw to see what it consist of as far as rebar then go from there. They will bust the floor with a jackhammer then use a skidlloader to remove the concrete. But you will be repainting afterwards as the exhaust from the skidloader will discolor. What you want to make sure is that after everything is out, that everything under the concrete is tamped down really tight before a new floor is poured.

 

[Tom R]

I don't know what area you are in but the standard in my area is to lay block, backfill with crushed stone, tamp solid, then pour the floor. So basically the floor floats inside the block walls. Some floors have rebar and some just have the reinforced concrete.

Assuming the floor was poured after the block and with the block as the sidewall to the floor...will it be difficult to clean off the cement floor where it sits against the side block? If I remember correctly, it looks quite tight against the block...does that "bond" cause you to end up damaging the block...or does the cement chip away reasonably cleanly?

As far as the current moisture problem I would plan on doing two things...1) first have the outside drainage worked on a bit to be sure it drains away from the garage foundation...it has a general slope pattern that will assist in improving what already is good natural drainage past and away from the garage. 2) use the moisture barrier and probably the foam boards with foil on both sides (like the "retirement" garage post in Michigan).

I will not spend this money w/o doing it right...drainage/appropriate packed base material/moisture barriers/insulation/rebar/cement. I hope it will work to dig out to the depth I will need once the "old" floor and base is out.

All info/input is appreciated...Tom R

 

[Mr. Welsh]

does that "bond" cause you to end up damaging the block...or does the cement chip away reasonably cleanly?

This is presumably why the contractor you spoke to wanted to saw cut around the perimeter of the concrete. It's likely that the bond will be quite strong, as I said above. If done correctly, there should be a disconnect to keep the concrete from bonding to the block.

 

[havi]

Two outfits you can contact in the TH area....
1: www.hollowrockdesigns.com
They were willing to remove the top 2" of my slab, pour a new overlay, and go from there. I didn't do it though.
2: Huseby garage movers.
They do garage moving, and you could have them move it, pour a completely new slab (I'd add the pex just in case) and move the garage back onto the slab. I was gonna do this with my garage, but decided to just build a new one later on.

As far as water in the floor, welcome to Spring weather. Cold mornings and warmer days leads to dew forming on the garage floor. I bought a digital dehumidifier from Menards and it keeps my floor dry.

I second the vapor barrier, too.

 

[Kevin54]

This is presumably why the contractor you spoke to wanted to saw cut around the perimeter of the concrete. It's likely that the bond will be quite strong, as I said above. If done correctly, there should be a disconnect to keep the concrete from bonding to the block.

If you look close, most slabs will drop a bit over time. You may be able to see where that has happened. This has to do with ground settling over the years and also shrinkage when curing occured. So the bond is not as tight on the block as it seems.

As far as water in the floor, welcome to Spring weather. Cold mornings and warmer days leads to dew forming on the garage floor. I bought a digital dehumidifier from Menards and it keeps my floor dry.

I second the vapor barrier, too.

We have had rain for almost a week straight. I do not have a vapor barrier and my garage floor has never sweat. Don't get me wrong, I am all for a vapor barrier, but my garage has been built for 10 years now and I have never had that problem. So a lot must have to do with the base under the slab. My walls are block but not sealed, and my base stone is 8's crushed limestone compacted and probably 2' deep and 3' at the edges. Soil is hard clay. But I have seen garages (my sons for one) that looks like someone has turned a hose loose in there and has to squeegee it out every hour. Same foundation, same fill, but a little different soil. But my garage is also well insulated, drywalled, etc so maybe that also has something to do with it. As a matter of fact, the other day we had 95% humidity, and it was raining. I washed out the garage and it was dry withing an hour without a squeegee and just a small box fan.

 

[havi]

I'll explain my situation regarding the dehumidifier. My slab is only 3-4" thick, no rebar, no mesh, no footings... so it is cracked pretty bad. The neighbor told me about the slab when he was helping the PO that poured it. (no contractor) It sits on flat ground and has MN red clay underneath. Maybe it was raised up 10 years ago, but it sure has settled since, then. I have a high water table in the Spring when the snow is melting, thus the moisture is near the surface all of May. Temperature gets below freezing or atleast below 40F every night, and then warms up during the day. With all the moisture from Spring thaw in the air, it gets really wet oneverything that is steel. With a project car parked in the garage, it seems to attract the dew that forms under the car and in return covers the floor. By running my 60 pint dehumidifier, I empty it every morning on my way to work, and it keeps everything nice and dry in there. I recently built my new house/shop (someday) and went with a vapor barrier, 2" HD foam, heated pex, raised up 2', and 5" thick slab with slightly deeper footing all around, along with 4' of 2" foam around the perimeter, and drainpipe all around too. Not a drop anywhere, and it's only 8 feet from the old garage. In all, I agree with Kevin54, as the base is most important in keeping it dry. Tom, depending where you are at, some areas are solid clay, and some areas are solid granite, depending which side of Hwy 2 you are on, lol.

PS: I live outside TH on Hwy 3.