problems with a concrete foundation

We are adding a sunroom on to our house and the foundation for the room was done in a sloppy and hurried manner. The cement truck arrived late and they poured the concrete in a messy way and finished the job in the dark. The resulting foundation is not a level surface. It has small bumps and dips. Also there is one edge which is not a straight line, it bulges out.

The sales guy from the company agreed the job was not done properly but not to worry, it would be completely fixed. The sales guy spoke about flashing the surface to level it. One of the workers spoke about using thin set. They also spoke about chipping away the extra concrete on one edge to straighten it out.

Ultimately, this foundation will be covered with tile and will not be visible so perhaps it is not such a big deal as long as the floor is smooth.

Unfortunately, I don’t know anything about construction, so I am looking for information about what should be done before I call to raise hell. How should they fix a foundation like this? Thanks in advance.

If you are not familiar with it, thin-set is a type of mortar. It works pretty well in smoothing out uneven surfaces like small bumps and dips. Basically, you spread it on thinner where there’s a bump and thicker where there’s a dip, and the tiles on top will all be even.

Thin-set has its limits, so if there are bumps and dips that are too big then thin-set won’t help you. But you did say “small bumps and dips”, so by the time they get the tile done, you probably won’t even be able to tell that the concrete underneath isn’t even.

A walk behind concrete grinder will smooth a slab. I’ve seen them used many times on DIY shows like Holmes on Homes.

Any company that does a lot of concrete work will be familiar with them. They either own one or rent the machine.

The contractor levels the concrete and it leaves a rough surface. The rough surface bonds to a thin finish coat of concrete.

There is self-leveling mix for just such problems.
You mix it, pour it on the surface, and let it spread out like any liquid, then then it will harden into a flat, smooth surface.

Thanks for the feedback so far. I am still trying to understand what should be done. Thin-set seems straightforward if it will suffice. While a concrete grinder sounds a lot more involved. Is “flashing” a possible solution?

On edit: Just saw the self-leveling mix post which also sounds good. I guess there are multiple ways of handling this.

The bond between the new concrete and old is the concern.

Thin layers of concrete or thin set can lift up off the slab.

Is this going to be a covered sun room? That makes a difference.

Wet slabs freeze and that’s what can lift up a patched area. If the slab is covered and stays dry then that won’t be an issue.

A tile floor in a heated space can protect it to. I’d use leveling compound in that situation and then tile.

Yes, this will be an enclosed, heated room. Thanks for your recommendation.

Put your foot down, as it were. Don’t let them scam you. I had many tense and loud conversations with our contractor when we built this house. That man, I cannot tell you how maddening he was. And he liked to scrimp and cut corners. I was paying a substantial amount for this house and I wasn’t taking shoddy work. He hated me. But inthe end I got what I contracted for. Read your contract see if there is a clause for disputed/crap work. Not sure the legal term.

I will lawyer up if I need to but we’re not at that point yet. From the feedback so far, this seems fixable.

Perhaps you should get an in-person opinion from someone not employed by the concrete contractor?

It sounds like a botched job. Leveling compund can only do so much. That’s why I initially recommended the contractor use a concrete grinder to smooth it down. Then leveling compound would fill any remaining problems. But, I haven’t seen the concrete to say for sure.

Tile has to set on a reasonably level surface. Otherwise the tile can crack where it’s not supported.

I agree it’s worth paying another contractor to look at it and give his advice.

The bag says it’ll level 1 1/2" in one pour.

I’d be leery of using this material to correct anything beyond that.

There’s a primer that’s used to get a good bond to the old concrete. Easy to apply and something a good contractor should use.

We have fairly strict town inspectors. I hope they will have to sign off on the foundation before anything further is done.

Thanks. I didn’t measure but I think the variations are not more than 1 inch.

I tried some self-leveling concrete patch in my garage about 15 years ago. The patch looks like new. I wish I could say the same for the concrete around it. If you can, get them to use self-leveling compound. Based on my limited experience it is very good-though more expensive.

What kind of reinforcement was used in the slab? You don’t want the wire exposed on the edge. If the grinding reveals the metal, make sure that is properly sealed-or make them do the entire job over.

It seems like self-leveling compound is the way to go. I’ll see if I can get them to use it.

I don’t know what kind of reinforcement was used. Unfortunately, I wasn’t watching the whole time.


In my old house I had a garage floor that was pretty wavy. The previous owner said he’d done it himself with the help fo friends; his advice - don’t break out the beer until the job is done. In the end he and his son worked very late to try and tamp things down to a level surface but didn’t manage to do the final tamp-down and smoothing.

I’ve seen Holmes on Homes where he’s used that self-levelling mortar to take a very sloped concrete floor (all sloping toward a drain) and make it a proper level surface for tile. I guess the question will be whether the solution they use will in fact properly level without waves, and if it needs to be smoothed or anything like that while setting. (If I remember, HoH did nothing but pour and it was smooth and ready to use.)

Thanks, self-leveling compound is sounding like the best option.

I just spoke to the company. There are planning on fixing the foundation using self-leveling compound this week.

I’ll provide an update after they do the repair.