expansion joint between wall and surface bed? really needed?

[BauTomTom]

Hallo

In the books you find every time the same detail. Between the wall and the surface bed you should have the expansion joint. Here in South Africa it is 12mm.

It is a problem because it must be sealed and 12mm is somehow to much. ants could also come through this joint into the building

when you cast concrete just against the wall, the concrete will shrank anyway and you get a small joint anyway there.

What is your experience with this detail? See attached PDF

BauTomTom

 

[OHIOMatt]

Since it is interior, there will likely never be any chance if expansion. The concerete at placement will be at its largest. In my opion you really only need a bond break. My typical detail is for a 1/4" (6 mm) joint. I have, simply had them turn the vapor barrier up and cast it tight to the wall.

 

[Ron]

BTT...this is an isolation joint, as OHIOMatt notes. It is there to prevent slight settlement or wall movement from transferring stress to the slab on grade.

The most common method used for this is to fasten a strip of asphalt impregnated fiberboard to the wall, and place the concrete up to the strip. That will prevent bonding to the wall.

 

[BauTomTom]

-- to OhioMatt –
I agree, just a bond break which comes by a but joint actually automatically. Ok the Idea of the vapor barrier just to pull it up would be also good.
Are you not taking the vapor barrier then into the wall?

-- to Ron –
Is a isolation joint not the same as a expansion joint? Hhmm ok bit different, you are right.
But to allow different settlements is not really such an huge joint of 12mm needed, or?
The solution from OhioMatt is alright or?

BauTomTom

 

[csd72]

I have never used an expansion joint for an internal slab and would only imagine that they would be necessary in extreme cases.

As others have said, turn up the plast or use a bond breaker. 12mm is too high in my opinion.

 

[Teguci]

There have been times where I wanted the slab on grade poured tight to the wall without any bond breaker or expansion material. Just need to eliminate the possibility of differential settlement.

I don't see a reason for a wide expansion joint at this location.

 

[BauTomTom]

Now I got a answer from four engineers, which I wanted to hear, very good and not even one person with a other opinion.

So now for me is clear

NO EXPENSION JOINT at this spot, only a bond breaker, but even this one is probably not even needed.

Thanks a lot guys

BauTomTom

 

[ToadJones]

Nah, bond breaker is all you need. If the slab was cast directly on the footing (as in the case of most residential basements) you dont even need that. If the slab is on fill, I'd use the bond break. It would mitigate the cracking caused by the slab settling and getting hung up on the wall.

BTW, is there anything better than that crap asphalt impregnated fiber?? I have used that stuff 100's of times and I still think it is garbage. When used out doors it lasts about two years.
Is there a good material it can be replaced with after a few years?
I used it between my driveway and garage slab and the driveway slab heaves a little in the winter. I'd like to replace it. Any ideas?

 

[Ron]

TJ..agree the asphalt impregnated fiberboard is crap. I prefer any bond breaker, with a styrofoam blockout at the top (1/2" x 1") to create a sealant reservoir....then backer rod and sealant.

Although none of that is really necessary unless you have water or vapor issues from below. If all dry, paint the wall with a little form release and move on.

The only advantage to the fiberboard is that is can act as a screed point.

 

[ToadJones]

Ron,
What do you think about the conditions I have outside?
If I tear out the fiberboard and replace with a Sika flowable sealer, what's going to happen when the concrete heaves?

 

[Ron]

TJ.....Nothing. Dig it out, put a backer rod in there and use Sikaflex 1c SL or Sikaflex 15M SL.

Keep the sealant thickness over the backer rod to about 2/3 of the width...that pretty much guarantees more bond area at the sides than cross section in the center of the joint, so the sealant will stretch (vertically or horizontally) before breaking the side bond.

 

[ToadJones]

so even if the outdoor slab were to heave as much as 3/4" relative to the garage floor slab you dont think the sealant will break free?

 

[Ron]

TJ...if you are getting that much heave, I would use a preformed traffic joint.

Here is info for Emseal...

http://www.emseal.com/Products/Architectural/DSMSystem/DSMSystem.htm

 

[msquared48]

Ron:

Toad gets that much heave only after his garage parties.

Mike McCann
MMC Engineering

 

[Ron]

Sounds like party time, Mike!

The better solution to his issue would be to move somewhere that doesn't have frost heave!

 

[ToadJones]

thanks for the "input" guys

 

[larsacious]

Be careful if you have any re-entrant corners in the building. The nice thing about the expansion felt is that when the slab shrinks it can be compressed at the re-entrant corners. If you only place the vapor barrier between the slab and wall then the slab can get restrained at these corners and cracks will develop in your slab.

If you have a nice rectangular building this shouldn't be an issue though...

 

[ToadJones]

Ron-
I know I am just a dumb former nail bender (as few here love to point out) but I tried everything I could to mitigate the heaving with proper fill and drainage.
It apparently didn't work.

 

[JennyNakamura]

Hi everyone,

Don't mean to hijack the OP's thread, but a related question that I think the OP will appreciate. I have done this joint many times without the expansion joint as everyone suggest, but all my previous supervisors and probably my current one would ask me to provide a dowel into the CMU or concrete wall. ToadJones brings up point that I think about often, but fortunately have not had problems with yet, regarding "...cracking caused by the slab settling and getting hung up on the wall."

When do you dowel into the wall and when don't you? Not only for interior basement type slabs but even for a concrete walkway around the perimeter of a building or where a residential driveway butts into a driveway slab? Everyone who suggests to me about doweling into an adjacent wall or slab talks about preventing differential settlement, but what about cracking in the slab that is settling? Isn't that worse?

 

[Ron]

TJ...there's not much you can do to mitigate thin slab heave relative to a footing that is not subject to the same heave. Differential will occur.

The joint either has to accommodate the full movement or you have to resign yourself to yearly maintenance on the joint....even the full movement approach will require attential periodically.