The weather has been very cool, damp, and rainy recently, and I have this concrete efflorescence at the base of my slab. The house is only about 1 month old since the construction was completed. It seems to do this mostly on the sides of my house that are downhill from the opposite sides. It seems like the moisture is wicking up from the ground into the stucco finish they put around the slab. Is it a concern?

Cannot post pics yet, but it is linked below.

https://b.l3n.co/i/mqzFSA.jpeg

I tend to agree with the Google search mantra ....

Here ya go...

It almost looks like you have a cold joint. Basically the concrete below that line was almost set (hardened) or already hardened when they poured over top. Thus making a joint without properly waterproofing it.

That and no vapor barrier. Water/moisture below the slab is coming out of that opening

When was the slab poured and what temps?

kubiak03 said:

---

It almost looks like you have a cold joint. Basically the concrete below that line was almost set (hardened) or already hardened when they poured over top. Thus making a joint without properly waterproofing it.

That and no vapor barrier. Water/moisture below the slab is coming out of that opening

When was the slab poured and what temps?

---

The slab was poured all at once 6 months ago, so around May. Not sure the temperature but this is the Boerne area. Regardless, there were no signs of cold joints in the pics I have before the stucco finish was put on. Other houses built in the neighborhood around the same time as mine don't appear to have the same efflorescence issue, so I wonder could it be that they didn't mix the stucco finish properly when they applied it? Just a cosmetic issue rather than a concerning foundation issue?

Going to ask my partner on this as he is the expert, but it could also be the askim coat the put over the rough foundation is wicking up water and minerals from the lawn. That would be my best guess.

You should not have a horizontal cold joint unless something when very wrong or the foundation was capped for some reason (which would also indicate something went wrong.

But the consistency above grade seems like wicking. That skim coat is going to generally be more porous and prone to that action.

Just saw your update. Yes, you are on the right path with the skim coat / stucco being the issue.

If yours is the only house doing it, then something likely not right with their mixture when they coated it. New house, I would make the builder fix.

They may want to paint it "concrete" or gray color. Not sure I would agree to that.

Purely cosmetic but its a pretty big cosmetic and they should fix (in my opinion).

Thanks! Yeah it is consistent in height like that around most of the house. Not sure how they could fix it? I read that sealing it in any way could be bad because then the concrete won't breathe properly.

Would they have to chip away all of the skim coat and redo it? I would be worried they might chip the actual foundation.

Edit: On a related note, I noticed the skim coat is fairly brittle. I chipped some of it off a corner of the house with my weed eater. I wouldn't think a weed eater should do that.

Thunderstruck xx said:

---

Thanks! Yeah it is consistent in height like that around most of the house. Not sure how they could fix it? I read that sealing it in any way could be bad because then the concrete won't breathe properly.

Would they have to chip away all of the skim coat and redo it? I would be worried they might chip the actual foundation.

Edit: On a related note, I noticed the skim coat is fairly brittle. I chipped some of it off a corner of the house with my weed eater. I wouldn't think a weed eater should do that.

---

Common for that stuff to fleck off and the solution be to recoat it. It's pure cosmetic. Heck, I had a lightning strike that blue out about 4-6 inches off the corner of my slab at old house. No issue.

I co own a foundation company and my partner who handles the dirty work confirms effervescence from hardware. Do you have sprinklers or hose that would be hitting that consistent all of there? If not, it's wicking up.

What do you mean by "efflorescence from hardware?"

There are sprinklers around the house, but they haven't been running lately. It has been cold and rainy for the past week, so plenty of moisture on the ground.

Hardwater. Fing spellchuck.

This is an intriguing phenomenon I'm gonna follow with interest. It would seem to be the result of a chemical reaction that is manifesting upon the surface of your foundation, perhaps from lawn fertilizer…? The uniformity suggests it could be leaching from the stucco formulation, but that's just a guess. Very intriguing! Try scrubbing a section off with a brush, or power washing and see if it returns…?

Quote:

---

Common for that stuff to fleck off and the solution be to recoat it. It's pure cosmetic.

---

Happens with natural stone, brick, concrete & mortar underpinning like the OP has.
Recoating would result in the same thing with a little time since the underlying issue is still there.

I would suggest removing with a diluted muratic acid wash.... but it's going to come back until all the salts have leached out.

Better still, get rid of the grass there & install some plants to hide the foundation & beautify your home.

Apache said:

---

Better still, get rid of the grass there & install some plants to hide the foundation & beautify your home.

---

Excellent rec and probably the best if not only true long term fix. Bonus if you get the builder to pay for it as a remedy, but do not sign anything from them if they try to absolve themselves from future issues.

Looks like they had a wavy form board on the top edge!

fka ftc said:

---

Apache said:

---

Better still, get rid of the grass there & install some plants to hide the foundation & beautify your home.

---

Excellent rec and probably the best if not only true long term fix. Bonus if you get the builder to pay for it as a remedy, but do not sign anything from them if they try to absolve themselves from future issues.

---

The builder said they would use a stone (or something) to scrape off the skim coat and redo it.

I don't know much about how the foundation should have been built, but I know my slab has a vapor barrier under it. So since my house is the only one with this kind of issue, I have to assume it's a bad mix of slim coat and redoing it should fix?

Here's a pic of the back porch foundation where there was some skim coat missing. You can still see moisture coming up the exposed slab and causing efflorescence there too. Does this indicate some other issue? Vapor barrier didn't extend out under the footings? Should it have extended beyond the footings?

Apache said:

---

Quote:

---

Common for that stuff to fleck off and the solution be to recoat it. It's pure cosmetic.

---

Happens with natural stone, brick, concrete & mortar underpinning like the OP has.
Recoating would result in the same thing with a little time since the underlying issue is still there.

I would suggest removing with a diluted muratic acid wash.... but it's going to come back until all the salts have leached out.

Better still, get rid of the grass there & install some plants to hide the foundation & beautify your home.

---

What could be the issue other than a bad skim coat mix?

We just had a lot of heavy rain, and the bottom edge around my house is noticeably damp and darker in color now. Other houses have their skim coat looking bone dry and uniform in color.

If this skim coat continues to wick moisture is that going to cause the foundation wall behind it to fail over time?

I'm going to be pushing my builder to fix this soon, and I want to know as much as I can about how critical the issue is.

Quote:

---

The builder said they would use a stone (or something) to scrape off the skim coat and redo it.

---

Take this as a win, he is fixing the cosmetic issue.
No potential for long term problems here, just moisture wicking up from the ground & drawing out calcium and other minerals from the underpinning.

Quote:

---

What could be the issue other than a bad skim coat mix?

---

Nothing that I am aware of.

I'm still working to get the builder to fix this issue. I noticed today that there's all these spider web like cracks appearing. Is this probably just surface cracks in the skim coat, or could be a bigger concern? The water you see is from me recently running the sprinkler.

Bumping this. Does anyone know a civil or structural engineer in the San Antonio area that could inspect this issue and provide advice? I am looking to get an independent engineer's opinion so I can make sure the builder will do the proper fix.

The cracks are cosmetic only.
The underpinning isn't even necessary on a slab, it's icing… serves no function other than aesthetics. This is not a big deal. At all.

You are throwing money away if you get an engineer out IMO.

Apache said:

---

The cracks are cosmetic only.
The underpinning isn't even necessary on a slab, it's icing… serves no function other than aesthetics. This is not a big deal. At all.

You are throwing money away if you get an engineer out IMO.

---

I guess my larger concern is why my slab continues to wick moisture up the side. Will this not cause damage over time?

I've seen older houses (10+ years) in my neighborhood with similar stains on the side from efflorescence, but they no longer appear to be wicking up moisture or having efflorescence. I was reading that the parge coating/stucco/skim coat/whatever you want to call it is partially there to protect the slab from moisture intrusion, but mine is attracting any water on the ground.

Edit: This is what I'm talking about in the below pics. Any time it rains, the bottom parts get all soaked up to a certain point, but I see other houses not doing this. After the weather dries, it will then cause efflorescence in some spots as the water dries from the slab.