Does this concrete need repair (and how should I do so) before installing tile?

[SUPERFORD]

Hi guys,

This is related to a previous thread:

http://www.garagejournal.com/forum/showthread.php?t=112828

But I didn't want this possibly important question to get burried on page 3 or 4 of that already complicated/lengthy thread.

While removing a botched tile job in on the concrete slab in my garage bathroom, the concrete cracked at the very edge near the wall.

My question is. Is this a significant problem? Will it adversely affect the tile that i'm about to reinstall. (keep in mind, i'm using very small approx 3/4" glass tiles)

Is there a product that I can apply to perform a repair.

I just don't want the tile job to crack or come loose down the road due to loose concrete underneath.

Thanks,
Chris

 

[dcs Inc]

I was looking at this trying to figure out "why" it cracked like this. the only guess I could come up with that the outer edge of the slab was poured onto an L block or there was a wider block under the slab that the concrete was poured on. If that's the case then the fill under the slab has compacted not leaving a good support..... at least to match the 4inches that's setting on the foundation.

If there's actually 4" thick concrete above whatever this is sitting on then I would repair it. If it's only a couple inches thick then it will keep showing it's ugly head. If your garage is constantly heated there shouldn't be a problem.

 

[SUPERFORD]

I was looking at this trying to figure out "why" it cracked like this.

I THINK that it had more to do with the "jackhammer" chisel tool that I used to strip off the thinset, and the fact that it was near the edge of the slab. That combined with the angle of the blade and the concrete just "fractured" on the corner.

sorry for the rudimentary "paint" drawing, but like this:

at least I HOPE it's not an indication of larger problems.

 

[dcs Inc]

The drawing helps a bunch. I was seeing a "line" fault there and was thinking in a different direction. These are fractures and now are divorced from the slab it's self. they will move independently from the rest of the concrete in any temperature change. In this case I think it may be best to remove the loose stuff and fill with a good filler. Dependable crack fill is a big no no. A non shrink grout that can feather may be the way to go.

 

[Edger]

I very much doubt that the jackhammer caused the cracking. A jackhammer will just dig a bit of the surface out, but you have I believe some unstable concrete at the edge as Gene first indicated. What can happen is that the inside pour is against the concrete wall and one or the other moves. Say the floor drops a little and it is adhered to the wall. As it drops the outside edge has to give somewhere.

This can also happen with temperature differences between the two, not that I am saying it did. If you fill it after digging it out it might pay you to put a barrier between your repair and the outer wall so the two can slip a little. Maybe thick plastic film would do the job. When you dig it out see if there is a foundation issue too as Gene suggested because I used to see that a lot in floor edges near support columns. In that case I would think you just clean it thoroughly and fill it, cross your fingers and hope is lasts, otherwise it would be a big job to concrete cut, insert rods for strengthening etc. and it may not be necessary.

In short it looks like the cracking was caused by two slabs moving against each other vertically.

 

[SUPERFORD]

I should point out that I actually SAW the crack occur while using the hammer. As I worked my way down the wall I saw it spread.

I'm not saying that there couldn't be some underlying problem. The soil in my area is like swampland.

But I'm certainly hoping this was just operator error. I think I should have been hammering parallel to the wall working my way down the edge as opposed to perpendicular (at a 90 degree or going straight towards the wall/edge). it was just difficult to do because of the tool's proximity to the wall as well as the door frame behind me.

 

[dcs Inc]

I couldn't jack hammer that straight of a crack line.

 

[SUPERFORD]

So assuming for a moment that this crack is NOT the sign of some bigger structural or slab failure issue...

Did anybody have a suggestion as to a specific product that I should use to fill the crack before I re-install the tile?

I'm going to Sherwin Williams this morning to get something to paint or at least prime the block wall since somebody in the other post suggested that this could be messy and should have been done prior to tile installation anyway.

Once that's out of the way I'd like to fill this crack with something and hopefully lay tile tomorrow.

Or should I just fill it in with a little extra thinset when I start tile application and hope for the best?

I guess I'm trying to figure out if I need a hardening product or a flexible product or what?

thanks for any advice!

-chris

 

[dcs Inc]

Is this area heated? Does it stay pretty much the same temp?

 

[SUPERFORD]

Sorry, I meant to include this info.

Yes, the garage is heated and air conditioned.

It MIGHT get as cold as 60 degrees in the winter,
and MAYBE as warm as 75 in the summer.

 

[SUPERFORD]

also took a couple more photos to better show scale:

 

[dcs Inc]

The coins helped a bunch. I was thinking it was larger. I see some settlement from the slab which is telling me this is not sitting on a ledge. You have a pretty consistent temp so you don't have to worry too much about major expansion and contraction of the concrete.

Not being a tile guy (I've layed a bunch but decided that wasn't any better than pouring concrete), I'd worry about the tile cracking if ANY movement of this fracture. hopefully a tile guy will jump in here and give you a thumbs up/down.

If it were me.... (not always a good thing) I'd either pull this stuff out and re-pour a pre mixed product that has a higher level of adhesion and compressive strength with no shrinkage, use a thick piece of plastic against the block so it doesn't adhere to them or, clean well, pour some epoxy down the fracture line and keep pouring as it drains into the crack line. Level off and be done with it. I don't know which one would be faster, or less expensive. gene