Consolidation Agents for Stone (ie: preventing sandstone based rock from dusting/flaking)

[Stoopalini]

I've been researching different solutions to the deterioration concerns of sandstone based rock being used around pools, and thought I'd start a thread to open up the discussion, and get some input from folks who understand this much better than I do.

There seems to be a lot of discussion in the forums on the fact of 'low quality rock', or 'soft rock', or 'sandstone based rock', etc ... deteriorating over time when used as coping (and in other applications .. ie: waterfall, etc), around a pool. Sure, some folks attribute it to salt water, others say it's the water and not the salt, etc ... But in thinking through this, I'm not sure it really matters if it's water or salt water, or both ... and whatever solution is best to address it, should be best for both scenarios, correct?

I started thinking about all the work which is done in the realm of building preservation, where old stone structures (buildings, statues, monuments, etc ...) are preserved by historical societies and such. Certainly, they must have an approach that is better than applying some $30-$50 sealer to the stone.

@Dirk had mentioned in a previous thread that his mason friend suggested he use Prosoco OH100 on his flagstone coping to address dusting and flaking. I won't speak for him, but his reports have been that it worked very well on all but one of the stones they applied it to. So based on that, I was considering having this done to my flagstone and moss rock, but only if I start to notice degradation (my pool is only 25 days old right now).

Now I'm wondering if I should do something as preventative instead of reactionary though.

In my research on how historical structures are preserved, I can across some interesting information on nanoparticles, and how nanotechnology is being used to preserve cultural heritage sites. In this article, it specifically addresses using nanomaterials for stone consolidation purposes, but seems to use a different chemical compound than the OH100 product uses.

Here is a link to the article: How can nanotechnology preserve stone cultural heritage sites?

And here's a quote from the article, describing the chemical approach:

Consolidation

Nanomaterials used for consolidation can be thought of as “fillers,” like the packing peanuts that fill the empty space in a package sent in the mail. These nanomaterials fill empty pore spaces and mimic the original stone material. One common consolidation material is a product based on calcium hydroxide nanoparticles (Ca(OH)2 NPs). To restore damaged stone artifacts, we can spray the calcium hydroxide nanoparticles over the stone’s surface or apply them using a brush. The nanoparticles sink deep into the pores and cracks of the stone. The power of these nanoparticles is their ability to transform into calcium carbonate mineral phases such as calcite and aragonite, the major minerals of limestone, through a reaction with atmospheric carbon dioxide in the presence of moisture:

Ca(OH)2, aq + CO2, g → CaCO3, s + H2O

(Calcium hydroxide particles in solution plus carbon dioxide gas goes to calcium carbonate plus water)

In this way, Ca(OH)2 NPs are often used to restore stone artifacts and buildings made of limestone, because the properties and chemistry of the filler will match the original artifact. The Megalithic Temples of Malta, the Bust of Nefertiti, and St. Paul’s Cathedral are all examples of cultural heritage made from limestone. Ca(OH)2 NPs used for limestone consolidation are an excellent example of preservationists matching the filler material to the stone material to achieve better compatibility, effectiveness, and treatment durability.

Comparing that to the Prosoco OH100 product's approach:

PROSOCO Conservare® OH100 is a ready-to-use consolidation treatment that stabilizes masonry by replacing the natural binding materials lost due to weathering with silicon dioxide. OH100 penetrates deeply, does not form a dense surface crust, and retains the substrate’s natural vapor permeability. It is also an effective pretreatment for friable substrates that need to be strengthened before cleaning, patching or coating.

So it seems the OH100 product uses silicon dioxide as the binding agent, while the nanomaterial approach example in the article, uses calcium hydroxide nanoparticles, which after penetrating the stone, transform into calcium carbonate mineral phases such as calcite and aragonite. It seems the article suggests this approach was used for limestone, becasue the resulting binding agent is the same material. So does that mean there are other nanomaterials for other stone types? hmmm ...

Either way, I'd be very interested to understand which of these approaches would be better suited for stone which is in contact with pool water. Obviously, I don't have a strong enough chemical knowledge base to understand the impacts of either of these being used in and around a pool, so was hoping to get some input.

I also think this topic (ie: deteriorating stone around the pool) pops up with enough frequency where having a recommended treatment approach for the concern would be valuable to the community. As it stands today, when this topic pops up, the responses are pretty varying. Some say "use a good sealer", others say "you chose the wrong stone", some say "it's because of the salt (if SWG)", other say "it's natural water errossion and nothing you can do about it", etc, etc ....

Usually, the person with the concern will then research sealers, because that's really the only thing they can do ... but even the most durable sealers don't seem to address the root issue. Or if it does, it seems to be a temporary fix until the sealer wears off after a year or so. Not to mention sealers can also negatively impact the look of the stone as well.

So ... thoughts on these two different consolidation approaches?

 

[Newdude]

This is out of my lane but I applaud you for starting the discussion. It may not end the long standing debate but it very well may provide a better work around. Well done Stoop !!

 

[Dirk]

My understanding, based on what an expert in the field taught me: Water is the culprit, not the salt. Sealers are good for stone because they help with repelling the culprit. So the more you can keep water off sandstone, the better. But sealers will not solve for stone that is already flaking, and is not the best solution to keep it from happening (because sealers cannot guarantee against some amount of water intrusion, and that's true even before the sealer has begun to wear off).

So a consolidator is used. It penetrates the layers of the sandstone and binds them together. In effect, gluing them together. It's clear to me why just waterproofing the layers with sealer would not be as effective as gluing them together. What type of binding is best (as pondered by Stoopalini), is beyond me, and something definitely worth exploring. I used Prosoco OH100 based on the expertise of my stone guy, and nothing more. And it worked on my flagstone coping.

My coping was much worse off than the same stone just a foot away. Like night and day. And one stone in particular, by the pool steps, is the worst of all. That suggests to me that it's the pool water, and not other factors like sun or rain, that is to blame. I had this issue long before there was an SWG, but the previous owner's pool guy had let the salt build up in the water. So I have an instinct it is not salt related, but not definitive proof. What is clear to me, is that a typical pool's salt content is going to happen with or without an SWG, so whether the salt is causing the flaking or not is academic in terms of repair or prevention. By that I mean, if your stone is going to flake, it's going to flake whether you use an SWG or not.

That's about my sum total knowledge on the subject.

 

[JoyfulNoise]

A big part of the problem is availability. I’ve read plenty about Prosoco and other manufacturers and suppliers. But try finding the stuff...it’s not easy. You can‘t just go strolling into Home Depot to buy a few gallons and often vendors will only sell to commercial buyers that are looking to buy the stuff in pallets and 50 gallon drums. It’s hard to find vendors that are willing to sell you just a few gallons and not do so at exorbitant costs. One way to start is to talk to local masonry suppliers and see what they either have on hand or are willIng to get for you.

I would agree generally that sealants and consolidators provide different functions and that adding a consolidator to a stone installation is a good idea ... as long as it doesn’t cost an arm and a leg. My tile guy installs Saltillo tiles (it’s a southwest thing) and Saltillo is notorious for being a huge PITA when it comes to stains, chipping, etc. He follows a similar process where all of his tiles are dip coated with a heavy duty sealant prior to installation and he has no issues. BUT, you’d better be prepared for the estimate because all of that hand dipping and drying time adds to his labor and material costs.

 

[Dirk]

Yep. I got mine from my stone contractor, so didn't have to hunt it down. He warned me it would be hard to find for others. He suggested calling Prosoco so see if they could offer a solution to that problem (like pointing you in the direction of a local guy that's got it or sells it). I haven't tried that yet.

 

[Stoopalini]

I think the consolidation approach is definitely a better approach than sealer, at least from my research anyway. And I do understand getting something like OH100 is more difficult, most likely due to it's shelf life only being 1 year, and also probably due to it's flash point being so low (104*F). If you left a gallon sitting outside in the Texas summer, I think you'd have a problem.

But aside from availability, is the silicon dioxide approach of the OH100 a better fit for a pool, over the calcium hydroxide nanoparticles approach?

I'm sure there are other consolidators out there, but maybe the nature of them leads to short shelf life and low flash points ... I'm not sure.

I think I'll call Prosoco later today and ask them a few questions:

1. Is the OH100 product 'ok' to use on material which will be in contact with swimming pool water?
2. Are there any concerns for adverse affects to swimmers in the water?
3. Same questions about the H100 product ... which would be recommended for material in contact with swimming pool water?
4. Does the product need to be reapplied over time, and if so, would the chlorine environment of a swimming pool change the recommended reapplication schedule? ie: Will chlorine have any negative affect on the durability of the product?

Aside from Prosoco's reply to these questions, would silicon dioxide in the stones have any impact on the pool water chemistry directly? Their spec sheet says N/A for pH, so I don't suspect it'll change that. But will it have any other affect on the water, or cause test results to be skewed in any way?

I'm wondering if the treated rock is used as coping, vs. being submerged in the water (ie: waterfall, or boulder coping, or a grotto, etc ..) matters for the product having an impact on the water.

I also learned that there are other types of consolidation approaches. This article does a great job in explaining them: Stone Consolidation: halts decay and prolongs life

In the list of Siliane based materials, they state silicon hydrides as one approach, but also say this "- use presents many health and safety problems;". Does Prosoco's silicon dioxide fall under the silicon hydrates category?

So I think my questions related to what kind of consolidation agent would be good for swimming pools is something I'd definitely want to answer before applying anything to my pool .. considering my boulder coping dips into the water, and of course, my water fall is in contact with the water as well. I also think this would have to be fully vetted before TFP could have a tried-and-true recommendation for folks looking for a solution.

 

[Stoopalini]

So I called Prosoco .... The rep said they do not recommended the OH100 nor the H100 product for horizontal surfaces because "it'll penetrate too deeply and not do what I want" ... huh? She said it can only be used on vertical surfaces. Umm, ok? I asked what the adverse effects would be if used on a horizontal surface, and she couldn't answer. She said I needed to talk to their historical expert, and would transfer me. I then got someone's voice mail.

So I left a message ... we'll see if I get a call back.

 

[JoyfulNoise]

I don't really think the consolidation agent's binder matters too terribly with respect to pool water exposure. Silicon dioxide is simply a glassy material and it looks like they use volatile siloxanes (polymeric compounds containing silicon and oxygen bound to organic residues) to penetrate the pores of the stones and eventually leave behind silicon dioxide. Siloxanes are a class of organosilicate materials that have all kinds of properties; some will decompose into volatile organic compounds and leave behind silicon dioxide (aka, glass). Silicon dioxide is a great material in and of itself as it is essentially "glass" and is very resistant to most forms of chemical attack that would be found in aqueous environments. I have not read much about nanoparticles based on calcium hydroxide, but I suspect the effect would be similar - deliver nano-sized binder material using a volatile organic phase leaving behind the calcium hydroxide to convert slowly over to carbonates. This is similar to how cements cure - silicates and hydroxides undergo hydration and carbonation reactions forming hardened calcium carbonate cements with silicate materials and aggregates. SO using a consolidation agent based on calcium carbonate formation would be a more natural material for certain stone types (limestones and sandstones). Though I suspect silicates would work as well too.

Vertical versus horizontal application techniques or limitations are not something new. There are certain types of cement based waterproofing materials that can sometimes only be applied vertically or horizontally. It has to due with viscosity and curing times. If Prosoco states that their tech sheet requires a particular orientation for application, then I would adhere to it as it has been tested and certified to work in a specific way.

 

[Stoopalini]

So I got a call back from a VERY knowledgeable gal ... she is a University of Texas @ Austin grad though, so how could I expect anything different

She said the issue with horizontal application has more to do with contractors who expect miracles out of stone consolidation. Like those who want to strengthen a stone for traffic weight, and they think consolidation treatment will give the stone more strength to withstand traffic on top ... and it won't.

She did say that consolidation would not be a great choice for the pool stones though, and had good explanations as to why, which were kind of lost on me considering I'm just now trying to learn about this stuff .... She said nothing will help with the stone that is partially in the water (not even consolidation), as none of their products are designed for constant hydro pressure (ie: not designed for constant water contact). Being partially in the water means it'll wick the water up into the entirety of the stone.

She said even the coping stones would be better served with one of their other products, rather than a consolidation treatment, just based on what the treatment is designed to do.?.?

She was the Prosoco engineer who deals with building conservation, and I could tell she a chemical engineer .... she gave an example that when she works with fountains, she only treats the caps, and top areas which aren't receiving the water flow because treating areas which have constant hydro presure actually causes more issues. Something to do with vapor not being able to escape the rock.

I asked her about the nanoparticle tech, and she said they've done a lot of research on it and they found the nanotech is good, but it performs the same as the silicon dioxide approach, so they haven't seen a reason to develop a product using nanomaterials.

So after all of that, I asked what would be good to use then. She said for non salt pool, Prosoco Siloxane WB concentrate would be good.... and Prosoco Salt Guard would be good for salt pools ... but she reiterated that neither product should be applied to stones which are constantly under water, or receiving a constant flow of water over them.

The thing with consolidation is that it is permanent, while any other type of treatment is temporary and will wear off. I'm still not convinced a consolidation treatment wouldn't be good for this type of application, but maybe Prosoco's isn't the one. I'm going to see if I can find a product that uses the nanoparticles, and try calling them to have a similar conversation .... I'll keep digging ...

 

[Dirk]

Great report, though doesn't bode to well for what I did. I'll run all this by my guy and see what he says, as he can speak to real-world applications better than me (and maybe even her).

My take away, and what I had already concluded should I need to replace my deck, don't use sandstone for coping.

 

[Stoopalini]

Great report, though doesn't bode to well for what I did. I'll run all this by my guy and see what he says, as he can speak to real-world applications better than me (and maybe even her).

My take away, and what I had already concluded should I need to replace my deck, don't use sandstone for coping.

My take away was that what you did is fine, as it won't cause any harm ... but she was adamant that it wouldn't solve the deterioration problem (if the stones were prone to deterioration), and she thought my expectations wouldn't be met if I used it.

She said when using a consolidation treatment, you should 1st remove any loose or already flaking pieces, as the treatment won't solidity these areas. And that the treatment is only designed to penetrate 1/2 inch or so. This was part of the reasoning for the horizontal vs vertical application ... that applying to horizontal surfaces would cause the solvent to sink too deep into the stone and not remain within the outer areas, which is where the consolidation treatment is desinged to provide the protection. Her words were "gravity is working against what you are trying to accomplish".

I'd say if it's working for you, then great! No need to 2nd guess yourself.

 

[JoyfulNoise]

I will offer this from a discussion I had back in the day with a mason when I asked about using sealer and preservation products - he says the only way he’d change his warranty was if every stone he installed (I have flagstone coping) was pre-dipped in sealer and allowed it to cure BEFORE installing it. That would have doubled his labor and added days to the process. His point was that unless you seal every surface from contact with water, sandstone type materials will absorb and emit water all the time. This can then lead to thermal expansion and freeze/thaw damage. Most people wouldn’t want to spend the extra money on that and he figured it was just cheaper and easier to get 10-15 years of life out of the stone work and then renovate the pool down the road or let the next homeowner decide what they want to do.

 

[Dirk]

he figured it was just cheaper and easier to get 10-15 years of life out of the stone work and then renovate the pool down the road or let the next homeowner decide what they want to do.

And that's exactly what I figure I'm looking at. The stone is probably going on nine years. If I can replace a few of the worst one, I may make it to 15 years. Then I'll deal with it.