Classic Hard Water Stain Removal

[Craig 111]

This is a job we did a few months ago. There are so many different (BAD) things going on in this picture.

Do many of you come across hard water stains like this?

By looking at the picture what do you think is happening with this concrete?

[Christopher 102]

It looks like there are planter boxes there that when watered by tap water, the hard water stains are left under them and are getting worse over time.

That hard water stain removal chemical you have looks to be great.

Great job Craig.

[mick m 19]

I'm thinking it's due to being constantly wet over a long period, then the sprinkler has been turned off & as it dried, it's left the salt's etc to dry on the surface to the point where it's starting to calcifiy.

[Craig 111]

Chris and Mick,

Both are good answers but there are more things to notice than just that.

What kind of finish does the concrete surface have? Troweled? Salted? Sanded? Any ideas?

If any of you do concrete coatings you might have a better idea or have run across this in the past. This is going to be good education for everyone.

[mick m 19]

Not 100% sure, but I'd say it's a troweled finish.

[Christopher 102]

Hard to tell but I would guess troweled since it does not have the broom marks.

[Ron Musgraves 240]

Hey Craig Join this Group on FB , you would be a Great Help in there. Log In | Facebook

[Craig 111]

Joined! Thanks.

[Chappy 138]

broom troweled finish. Calcium buildup deposits from hard water.

[Craig 111]

What are all of those little holes in the concrete?

[Ron Musgraves 240]

Salt finish guys, Craig driving by you tues night.

[Craig 111]

Salt finish guys, Craig driving by you tues night.

Incorrect. Not a salted finish- thank you for your guess and that was the answer I was looking for. I'll explain below and that is the reason I posted this picture is because concrete exists like this and we all need to keep it in the back of our minds and it is something everyone should be aware of.

What time are you coming by? I live right off the 10 and Washington- about a half mile down the road. You should stop by and I'll give you some product to try...and dinner somewhere?

- - - Updated - - -

Edited July 2, 2012 by Craig

[AAPaint 14]

It looks like a hard troweled finish. I don't know what they call it, but it's smooth and shinier than the other concrete in the before pictures. I've done acid staining, color staining, and a few other things with concrete. I know when it's that smooth (first pics) it's hard to get a finish to take. Maybe it's power troweled smooth finish. Can't think of what that's called. Ahh, maybe it's just wet...but that's positively calcium and magnesium buildup on the surface. That's what the white stuff in hard water is.

Educate us some more.

[Craig 111]

HERE IS YOUR ANSWER:

This is a job in a food court area of a strip mall. The entire 13,500' of concrete had calcium, calcium carbonate, efflorescence and mineral stains. At first, just like Ron had posted, the concrete looks like salted concrete. It actually looked like a pretty poor salted concrete job and the concrete had been over watered for years. What we had to do was strip the calcium off to expose the concrete and create a surface that was profiled and porous to accept a polyurethane top coating.

The concrete had over 60 above-ground planters, many palm trees and bushes on both sides that all got water every day. After we spent 3 nights (from 7PM to 7AM) stripping the concrete, we put in a moisture barrier in the concrete and then applied a very strong colored polyurethane. Within a week of our application, the coating failed... and failed miserably. It was popping and flaking everywhere. Then the investigation began...They got experts, we got experts... They had attorneys, we had attorneys...

HERE IS WHAT WE ALL NEED TO BE AWARE OF, especially if we are applying coatings or sealing concrete. What appeared to be salted concrete were actually "pop-outs" from small little aggregates that weren't screened for and filtered out at the quarry. When moisture contacts these little rocks, the rocks breakdown and release what is known as "silica gel." Silica gel can rise up through the concrete and "pop" the concrete out resulting in small holes.

These holes are only small if there is not a coating or something on the top layer of concrete that prevents them from coming up. When a coating is applied in areas with alkali-aggregates and moisture is present, disaster happens. The more solid and adhered the coating is, the more violent and destructive the pop-outs are. Silica-gel reactions can have pressures coming up through the concrete with 1000's of pounds of pressure behind them. After this job and after I had gained my reputation back as more of a concrete "expert" I got more and more phone calls to help people out in similar situations. I have personally seen alkali-silica reactions create pop-outs that are the size of small paper plates.

Did you notice that the "hard water staining" is stained evenly? This is an indication something is wrong. Hard water staining is rarely stained that evenly because the water mainly stays in low areas. The concrete was stained evenly because the alkali silica rising up through the capillaries in the concrete were all close enough together that it turned the concrete black very evenly. Then look at the little holes (alkali-aggregate pop outs). Around most of them (if you ever have this in person) you can feel a very slippery fluid. This is the silica gel. It feels oily and slippery. So in a sense, this concrete had hard water stains on top and hard water stains under the surface of the concrete too.

So, after a year of meetings, conference calls and research on my part, this job turned into a 33 Billion dollar a year company tearing out and replacing all of the concrete. We evaluated over half a dozen core samples, ph tests, hydrostatic testing and more. We had essentially "won" our case and learned a BIG lesson in concrete.

They call this "Concrete Cancer."

Edited July 2, 2012 by Craig

[Craig 111]

It looks like a hard troweled finish. I don't know what they call it, but it's smooth and shinier than the other concrete in the before pictures. I've done acid staining, color staining, and a few other things with concrete. I know when it's that smooth (first pics) it's hard to get a finish to take. Maybe it's power troweled smooth finish. Can't think of what that's called. Ahh, maybe it's just wet...but that's positively calcium and magnesium buildup on the surface. That's what the white stuff in hard water is.

Educate us some more.

Calcium can be both white or black. It can even take on the colors of the landscape rocks if the rocks are watered and then flows down the side of the concrete. Most of the time it will eventually turn black from impurities.

Magnesium staining usually looks gray- light and dark. I've had HOA's give tickets to their homeowners for magnesium stains in their concrete because they thought they were oil stains.

The white you see in the picture is from cigarette disposal bins. I remember thinking, "why is there calcium buildup around these things.. they don't have water coming out of them.." It was very strange. The reason that rings were forming under the bins was that the alkali-silica reactions were coming up through the concrete and not forming from topical water exposure. I think the employees were baffled too. You can see where they kept moving the bin all the way around the palm tree, but the reactions were happening everywhere.

Edited July 2, 2012 by Craig

[AAPaint 14]

Very interesting to say the least. Concrete is probably one of the most complicated surfaces to deal with cleaning and sealing, staining, or painting. Concrete is made by a chemical reaction, treating it involves chemical reactions, and those reactions can rear their heads in many coatings situations, and if you're not sure what you are dealing with, you can really lose your rear over it. Over and above every other substrate, concrete is the hardest to deal with. I know from coating thousands upon thousands of square feet of concrete that one wrong move, can cost big money.

Glad to see it worked out in your favor this time. Not every contractor who's dealt with concrete has been so lucky, like the installer in this case!

[David Phillips 14]

Great read Craig! This is exactly the kind of education we need. Thanks for sharing.

[Craig 111]

Great read Craig! This is exactly the kind of education we need. Thanks for sharing.

Thanks, David.

[Christopher 102]

Craig, do you have an email address to send a few pictures to for your advice?

Thanks.

[shefferz 14]

I agree, thank you for this information.

It seems that concrete has a way of "maturing" contractors in their early years.

I had a mix up with concrete and learned over one night of research of what I previously knew with 3 years experience. It has laid the foundation (no pun intented) to always research/ask/learn then practice before accepting a new type of cleaning project

[Chappy 138]

Thats the reason I don't work with concrete sealing. Too many problems that I don't have the time to spend on.

Thanks for the education Craig. That is something that I have never heard before.

[starbrite 14]

good lesson

[Kristopher Pettitt 23]

I just was googling "Hard Water Stains on concrete" images and this one was one of the top pictures. Absolute fantastic read. I actually have a job removing hard water stains tomorrow.

[attsux 14]

So these aggregates that produced silica gel...like whats in tge shoe boxes?...what are they? I thought concrete was made with agregate n portland...so there's a specific stone or rock that produces this? What is that rock called..I imagine thats what they were looking for intge core samples. .. so if we see this happening ...remove the staining. .and attempted to put a protective coating. .do you think an impregnating non film forming sealer would still increase the back pressure of these pop outs. . Thanks for posting this

[Craig 111]

So these aggregates that produced silica gel...like whats in tge shoe boxes?...what are they? I thought concrete was made with agregate n portland...so there's a specific stone or rock that produces this? What is that rock called..I imagine thats what they were looking for intge core samples. .. so if we see this happening ...remove the staining. .and attempted to put a protective coating. .do you think an impregnating non film forming sealer would still increase the back pressure of these pop outs. . Thanks for posting this

The silica in shoe boxes is different than the reactive aggregates sometimes found in concrete. What you are referring to in shoe boxes is silica sand. The reactive aggregates in concrete are mostly formed from argillite, greywacke, chert, quartzite, opal and strained quartz crystals. The reactive rocks are supposed to be screened for at the quarry but sometimes make it through.

In the core samples all we looked for was silica gel.. no need to diagnose the rocks. Once we know that there is a reaction between the hydroxyl ions in the alkaline cement pore solution and a reactive form of silica in the aggregate, then case closed.

So, as far as sealer goes there are some lithium sealers that work fairly well. These are super expensive and no one would be willing to pay for it in the work that we do.. like upwards of $200 a square foot. If you put down a breathable penetrating sealer it can help to slow down the reaction but most still have a 2% vapor transmission rate so water vapor can still escape. Basically, if you run across this type of concrete you can clean it but that's about it. A penetrating sealer will help and you can even tint it, but within a short time the aggregates will release their fluid and still permanently stain the penetrating sealer.

If you want to learn more, here is a 90 page article on the basics of ACR's: http://books.google.com/books?hl=en&lr=&id=p8--3BiBbYMC&oi=fnd&pg=PP1&dq=alkali+silica+reactive+aggregates&ots=TDKVnWWmuK&sig=912i9YE1ieo3rm57qJccSsP_hrs#v=onepage&q=alkali%20silica%20reactive%20aggregates&f=false

Edited May 18, 2013 by Craig