Proper Concrete Curing Doubles Surface Durability.

Matthew T. LeComte, CEO | Cornerstone Coatings Global, Inc. – August 13th, 2020

Matthew LeComte is a second-generation owner of the worldwide concrete coatings manufacturer Cornerstone Coatings founded in 1999, which over the past 21 years, has directly manufactured every product mentioned in this article at some time. – Cornerstone Coatings is known for its disregard of industry norms in favor of real-world results and product efficacy.

◢ Underperforming Concrete From Incorrect Product Selection:

I believe concrete in the form it is today is vastly underperforming at a minimum of 50% its true potential due to so little understanding of the curing process and how essential using the correct product categories are for getting dependable performance out of concrete.

Concrete is amazingly resilient but will consistently fail and need to be entirely (or partially) replaced after just one year if left untreated or if the incorrect products are applied.

Many companies in the residential [driveway] industry are consistently only trying the same categories of products year after year and wondering why this new membrane forming sealer is not performing better than the last without going back to first principles and considering if they should even be using a membrane forming sealer in the first place.

◢ The Key Issues in Concrete Today:

Most processes that are standardized within the process of curing concrete actually produce enormous amounts of hazardous waste, create significant health hazards, and give poor curing performance due to nearly every construction company specifying the wrong products for their intended results, and the standardized product formulations of coatings changing in the background because of new VOC compliance laws without most engineering and construction companies realizing that their specifications are no longer helping the concrete but instead now directly causing issues.

It is a major issue in the concrete industry, especially in several areas with "hard specifications" that can quickly become obsolete and damaging to an entire sector of concrete finishing, such as curbs and sidewalks, or driveways and garage pads.

For example, in many large cities concrete contractors have no choice when curing sidewalks but to use products that meet the specifications of being membrane forming (ASTM C309) sealers, and also being pigmented to be white in color, disregarding that color does not affect the curing performance (despite the common misconception) and that sealers make poor performing cures because they are trying to do something that sealers are not designed to do.

An average concrete sidewalk’s lifespan can easily be doubled if the correct products are properly used.

◢ The Latent Specifications as a Problem:

Products being reformulated due to new VOC compliance laws and regulations conceives new products that still meet existing "hard" specifications without any of the original ingredients that made them work in the first place still being in the product (this is a drastic change in solvent-based acrylic sealers and "white cure/resin cure" sealing products), having specifications staying the same without a review after huge shifts in manufacturing regulations has become a problem in many coating categories, especially any products that contained solvents previously (as any decorative coatings installer can attest to).

As such, there are few ways to remedy this problem other than education, and testing of that new information to create new best practices and standards.

◢ Water Curing (Moist/Wet Curing):

Water curing is possibly the most traditional method of curing concrete. Still, at a certain scale, it becomes completely unsustainable and will start to create enormous amounts of construction waste per square foot.

Water curing, although adequate for eliminating plastic shrinkage cracks and curing it still has two major issues regarding resilience and sustainability, curing concrete via water curing will generate vast amounts of waste per square foot of concrete placed, and will increase surface carbonation as a layer of alkaline sludge is brought to the surface during curing, once that residue dries it will cause a carbonated and dusty surface unless professionally cleaned and treated with a densifier or other similar product.

Generally, the only way to effectively scale curing concrete past a few hundred thousand square feet is to use a densifier to cure the concrete surface, which actually costs up to six hundred percent less than water curing depending on the water curing method used.

After the concrete is finished water curing, it will remain extremely susceptible to dusting, carbonation, and surface deterioration as well as being less reactive with any densifiers that are usually specified to be later applied to halt the surface from such dusting and quick deterioration. This essentially makes the entire water curing process an unnecessary waste generating cycle that consumes plastics, water, gas in the winter, and requires additional cleaning crews that wouldn't be necessary if the concrete was cured with a densifier which is what Amazon uses in the majority of their warehouses.

• In the following section, I will focus solely on the products that are considered on-par in safety with water curing or better, for the reasons that solvent-based products would simply be much too hazardous for practical use on any project of significant scale, or number.

◢ Environmental Hazards of Coatings:

Few things are talked about less than the environmental impact of the most commonly used LEED 4.2/VOC free products on the market that are considered to be the best in the categories of sustainability and environmental impact.

One major perpetrator of producing hundreds of gallons of hazardous waste per job site is Sodium Silicate densifiers, which require scrubbing of the product on the concrete for application, this, in turn, mixes cementitious material into the applied product creating a gel that is hazardous waste afterward, of which is commonly dumped onto the job site grounds at an increased volume of about double the amount of product delivered to the project (as witnessed consistently by concrete finishers).

◢ Health Hazards of Coatings:

A common health hazard of another of the "safest" products is Colloidal Silicas, which usually are not a health risk unless they are applied onto the surface of finished concrete without being incorporated into the surface (one of the most common applications).

As Colloidal Silica is a product unable to seep into average power trowel finished concrete, it will mostly stay on top of the finished surface and dry, leaving a layer of fine silica dust across all treated areas of the concrete, which not only leaves the surface an unsightly dusty white appearance but also hinders the proper adhesion of flooring adhesives.

This fine silica dust also presents a significant air quality risk and worker health hazard, and precautions should be taken to prevent or minimize any product being applied after the initial finishing operations.

◢ Let's Solve The Problems:

Now that we know a bit of background, we can now compare some new information against the current norms.

I would like to start educating you on what options are currently available to improve concrete resilience by selecting the correct products that improve concrete curing quality effectively in today's concrete, and in turn, how to finish and cure concrete that lives up to its full innate potential.

Not having to replace concrete every year due to improper concrete coating selection can easily save billions of yards of unnecessarily produced concrete made to replace improperly cured concrete that has quickly deteriorated from preventable failures caused by improper product selection.

◢ Degrading vs. Non-degrading Finishing Aids:

Using a non-degrading finishing aid made of a densifier is the best way to not only maintain workability in the concrete paste but also in preserving surface strength and preventing surface cracking as there is a high limit to the amount the concrete surface will accept as densifiers are actually one of the only categories of coatings that can reliably create workability without deterioration of the finished concrete surface, especially when finishing in hot and windy conditions.

When large amounts of a densifier are used as a finishing aid, the surface will actually become denser and increase in resilience once the surface is fully finished rather than a deterioration of the surface taking place as more degrading finishing aids are used (up to around 300-400 square feet per US Gallon for some products that are non-degrading finishing aids can be used), as is the case with current "best practices".

◢ Degrading (Standard) Finishing Aids:

Commonly used finishing aids such as water, sugar, or solvent-based products work via breaking down the bonds of the concrete surface to improve workability, and to allow proper finishing of the surface. These products do work as intended, but as more and more of a degrading finishing aid is used, the surface strength will begin to be significantly compromised as the cement paste is broken down repeatedly.

Using a degrading finishing aid will result in a weaker surface in areas where more finishing aids were used, along with developing surface issues related to breaking down the concrete surface, such as dusting and low surface strength, resulting in such problems as concrete popping or spalling.

With decreased surface strength from breaking down the cement paste to maintain workability during finishing, the surface becomes easily eroded when compared to non-destructive finishing and will be prone to irreversible surface-related issues.

◢ Non-degrading (Densifying) Finishing Aids:

There's a way you can non-destructively add workability to concrete when finishing without the use of finishing aids that directly decrease the surface strength after application.

That method is using a category of concrete coatings called non-membrane forming densifiers (also known as hardeners), which can be used as fully functioning finishing aids when placing concrete.

Densifiers work by chemically binding with calcium in concrete; this, in turn, creates what's called a finishing gel, which is similar to normal cement cream except for the distinction that this gel is actually stronger and slower drying than normal cement paste. When finishing with a cement gel, inherent surface-wide moisture retention will be occurring across the entire surface, and regularly occurring drying hazards such as gusting winds and high heat will be negated for up to a 40% increase in finishing time.

Using the right densifier as a finishing aid will give you workability usually much higher than a degrading finishing aid, as the surface paste will not crust up or break down (like with water or degrading finishing aids); instead, the cement paste will turn into a workable gel via an actual chemical reaction with the calcium in the concrete to maintain moisture within the surface, rather than the traditional method of breaking down the surface.

It's ordinarily intentionally unclear how finishing aids work, which is no surprise, as advertising your product breaks down the surface to maintain workability is not good marketing, so instead, you will see mentions of how great it maintains moisture, inhibits evaporation, or increases workability.

From an actual chemistry point of view, densifiers are actually one of the only classes of products that can be used in a non-destructive manner to maintain moisture in concrete while also increasing workability when used as a finishing aid, which either no one is talking about intentionally or they just don't know.

◢ Does making concrete last longer a risk for concrete production volume?

The short answer is no. Instead, it's an opportunity to reduce expenses from warranty claims, replacements, but also the additional employees solely needed to service defective concrete surfaces.

As a ready mix company said to me in a meeting once: "production volume is like a table full of marbles, you can take marbles (volume) from other concrete companies, or they can take marbles (volume) from you, but you cannot add more marbles (volume)."

If a ready mix company's concrete suddenly lasts twice as long as their competition, they could take market share, but once everyone's concrete lasts just as long as everyone else the industry will create a new definition of how resilient concrete should be, giving mainly early adopters the opportunity to grow their reputation of having the best concrete, leaving the late adopters the reputation of being second best or eventually the worst option as more early adopters gradually take all the marbles (volume) from the late adopters, similar to if a ready mix company was refusing to use plasticizers or accelerators up to this day.

Production volume will enviably slightly decrease from better concrete not needing to be replaced. Still, as construction demand increases and the early adopters grow from having better concrete, there will be a slight increase in early adopters' volume, which is actually not the most substantial benefit. Instead, the actual gain from better concrete is stopping the unnecessary expenses from replacing concrete. If a company could drastically reduce concrete they replaced from a warranty failure; they would already be leagues ahead of every other producer due to how lean they run; it is risky to not look at why around 10% of a company's concrete is failing and getting replaced.

◢ How To Properly Identify Coatings:

To fix the problem you will need to find the correct tool for the job, which is quite easy once you understand what's happening in the coatings market and what the different categories of products will do best.

Essentially the central aspect of curing concrete to focus on for increasing surface durability is to decrease the speed of surface dehydration and to strengthen the surface with coatings or treatments to increase its longevity.

To do this the most effective method is to use a product that can maintain moisture in the concrete on-par or better than water curing, to find such a product you will first need to understand what product categories can achieve this, and past that you will need to know a little bit of industry vocabulary to find the correct product for your desired result.

In the coatings industry standards in naming products and their functions can frequently be incongruent, unregulated, and a headache to sort through without extensive research and real-world experience. As such, the following sections will guide you through how to find the correct product(s) to get your desired results.

*First, it's best to figure out what a product can and cannot do to be able to categorize it yourself from its key literature including, the application instructions, technical data sheet, and safety data sheet, as these comprise the most trustworthy information you can use to categorize any given product.

There are essentially three main categories of concrete cures being used:

• A membrane forming coating that creates a seal on the concrete surface.
• A chemical densifier/hardener that works by reacting with minerals.
• A water repellent coating that is claiming to be a sealer.

◢ Sometimes It's just marketing:

Generally, every company will claim their product is a sealer even if it's just a densifier, which is mostly due to wanting to check that box for the buyer that needs a "cure and seal", even if the product has no actual membrane forming or sealing ingredients in the product.

It's similar to using terms such as "nano" or "micro" to imply that the product is super small and will penetrate into your concrete because it's exceptionally small, which is a checkmark for the consumer to confirm it's a "penetrating" product.

This word "penetrating" is so prevalent in the industry that every product will say that it "penetrates" even when it's not physically possible for it to do so, such as with a sealer.

You do not say paint "penetrates" your house, but that is what's happening in the coatings industry.

Now, on the other hand, some densifiers are going so far as to say that their product will "Impregnate" your concrete, manufacturers know "penetrating" means nothing in the industry, so you should too.

As you are reading all of this, you are probably wondering how to find the facts, so here is a detailed introduction to the prevailing product categories.



◢ 1. A densifier will have the following:

Can have two or more coats applied, has a PH of around nine or more (all silicas are alkaline), and will commonly be referred to as a chemical cure, densifier, or any permutation of "it's making magic crystals".

Also mentioning the product will close or fill the surface's pores, prevent freeze-thaw damage, will dustproof and harden/strengthen the concrete, or mentioning it is reactive in any way such as "it reacts with _____, to make _____" are go-to indicators that what you have is something with a densifier in it.

A minority of concrete densifiers will also claim to "waterproof" the concrete without containing any waterproofing ingredients, most of these claims of "waterproofing" are only based on the product category's innate ability to fill and close pores within the concrete surface, as such it is a good practice to check the SDS to see if any waterproofing ingredients are actually in the product that you are buying.

• Densifiers will also not have any VOCs, or noticeable scent unless something is added.
• The three most common types are Lithium Silicates, Colloidal Silicas, and Sodium Silicates in order of product efficacy.

Due to Lithium Silicates being highly sought after out in the concrete polishing sector of the three most common types of densifiers companies commonly price gouge when selling this sub-category of densifier at 500-600% or more than it costs to produce, with the additional practice of Lithium Silicate and Sodium Silicate blends being sold at Lithium Silicate densifier prices, which is the equivalent of selling a product that costs 35 dollars per pail to produce for 450 dollars per pail before shipping.

◢ 2. A sealer will have the following:

Usually, sealers will accurately self-proclaim being a sealer, will commonly have VOCs (Volatile Organic Compounds, commonly found in solvents), and will create a "membrane",

or other types of "seal" on the concrete surface, along with claims to change the concrete's appearance immediately after applying (densifiers and water repellents will not change a surface's appearance just after applying the product unless they are blended with something).

Generally, all sealers should be considered the final coat on any bare concrete floors, as ideally, no other products should be applied after an actual membrane forming sealer.

*You should not use a sealer if you plan to install any type of flooring, as a stripping of the sealer will be required for proper adhesion, which is rarely talked about in the industry.

It's important to distinguish between solvent-based and water-based acrylic sealers, as it is not just a difference in solvent content, but also a difference in end results and appearance. Solvent-based acrylic sealers will darken the concrete, giving a "wet" look to the surface, whereas water-based acrylic sealers will not darken or create a deep "wet" look on the surface, instead, a water-based acrylic sealer will likely have a subtle matte appearance.

Sealers generally make poor concrete cures, and should mainly be used as a way to add an additional layer of protection after curing has finished, or to change the surface's appearance such as to add shine, or change the surface's color.

• There are solvent-based sealers, and water-based sealers, and both perform in distinctly different ways.
• Generally, water-based sealers do not give a "wet look", as this is a trait that solvent-based acrylic sealers possess, water-based acrylic sealers normally will not give a "wet look" type shine. Hence, it is important to take note of this when specifying. Water-based sealers also cannot be redissolved in solvents when resealing the surface as they do not contain the same solvent-soluble resins that solvent-based sealers do.
• Sealers will commonly have a pretty noticeable odor from the solvents and other ingredients in the product, such as acrylics, polymers, emulsifiers, or drying agents.

◢ White Cures (A Sealer Sub-category):

Pictures below are of a commonly used water-based "white cure" concrete sealer, a widely specified sub-type of membrane-forming concrete sealers that have the strange requirement to be pigmented white in order to be approved for city use.

Any type of sealing product that is pigmented white and meets the membrane-forming specification of ASTM C309 is approved for use essentially, regardless if they are the right product to be used for curing concrete, which surprisingly is the most common reason white cures are specified.

Without recognizing what the intended end result is, and understanding what the correct product category to use to get your desired result is, you'll be left repeating the same mistakes year after year.

We see the "common knowledge" that in order to properly cure concrete, you need to use a concrete sealer that is specifically white in color.

Which will make it very interesting to know that all solvent-based sealers (like white cures) needed to be drastically reformulated a few years ago (in Canada) to no longer contain the high VOC solvents that made them work in the first place (because they would exceed the new limit for VOC content in sealers), when you apply these newly reformulated white cures to concrete they will no longer degrade after 30-60 days due to the acrylic resins now needing to be suspended in water instead of solvents (which means they needed to switch to completely different water-soluble resins), this, in turn, creates an entirely new product, causing the specification of "white cures" to no longer be temporary, leaving them to remain on your concrete for years as portrayed in the preceding photo.

It is so common that almost every company trying to find a way to stop concrete popping or sealer discoloration is only testing different types of white concrete sealers like water-based acrylic cure and seals, and solvent-based acrylic cure and seals, attempting to solve the same problem endlessly.

That's why it is so important to not only look for products that "seal" and which happen to be white in color, especially if you're trying to solve a problem that the current category of products are not succeeding in.

◢ 3. A water repellent will have the following:

Water repellants will claim to make water bead up, and have numerous claims of repelling or protecting against all sorts of things like stains, oil and grease, anti-freeze, and anything else that fits in the sentence "repels ____".

Water repellents leave the treated concrete surface looking natural or unchanged and should have a claim to the effect of "will make water bead" in the product details.

Water repellents almost always inaccurately claim to be a "sealer" and will be a one-coat application or have special wet-on-wet second coat application instructions. Water repellents will repel a second coat after the first coat has dried.

Generally, water repellents are very easy to make last 2-3 years, but despite there being notably more effective water-repelling varieties available such as silicone-based products, a sub-category of water repellents called Silane Siloxanes is commonly used, which are notably ineffective at water repellency over time compared to silicone-based products.

• Concrete should not be cured with a water repellent.
• Repelling moisture is not the same as maintaining moisture in concrete; thus, concrete should not be cured with water repellents as they have no inherent moisture-retaining or surface strengthening properties unless they also contain a densifier.
• Water repellents will usually not have any noticeable smell unless something additional is added.

◢ Product Combinations:

Common combinations include a densifier plus a sealer (a true "cure and seal" product by definition), and densifiers mixed with a water-repelling ingredient.

Usually, sealers are not combined with water-repelling agents.

It's important to know that not a single product you put on your concrete will "penetrate" more than a realistic maximum of 1/4-1/8 of an inch unless it is an acid.

Products will commonly say they penetrate up to 6 inches, which is not possible unless you have specialized fast-draining concrete.

◢ Mislabeling and Ingonguent Labeling:

One quick topic to mention is the prominence of the mislabeling of products where words are used with no clear definition being recognized, as such, these products can add another layer of confusion into the industry as to what these products actually accomplish.

◢ Unregulated Industry Terms:

The most common example is the word: Guard.

"Guard" Products can be anything from a waterproofer, a sealer, or even just a straight densifier.

All of these "Guard" products are labeled without discretion of what's actually in the products.

Some are acrylic polymers that are misted on at 2,000 Square feet per US Gallon, some are water repellents applied at 300 square feet per US Gallon without any membrane forming ingredients in them, and some are densifiers as they will "Guard" against chemicals or even a completely temporary coating for preventing graffiti that will "Guard" your concrete from vandalism.

All of the issues with this product designation make it an entirely unreliable product definition. As such, when you intend to achieve a definite result, you should instead use the prior categories, as they will be much more effective definitions to categorize and specify products with.

Such as: "A VOC free water-based membrane forming acrylic sealer with a densifier for curing new concrete just after finishing" VS. "A Guard to protect concrete".

With no other definitions to go on, a "guard" could result in 12 or more possible product types in different categories with completely diverse functions and end results.

✓ To Correctly Define Your Desired Product Include:

1. Membrane forming sealer or a non-membrane forming sealer? If a sealer, what is the intended effect and purpose?

2. Should it be a densifier or not? Should the densifier be of a particular variety?

3. Should it make water bead off? Sealers and densifiers can sometimes claim to "repel" water away, so you need to be prudent to define this accurately in order to get the correct product.

4. What's the VOC (Volatile Organic Compounds) Content?:

"Low-VOC" content is not specific wording, Instead, use a measurement such as a maximum VOC content of 0-50 grams per liter, or # of grams per ____.

• Note that nearly all solvent-based acrylic sealers are dead on arrival if they are using acetone as a carrier for the acrylic resin in the sealer, so go with sealers containing solids of 30% or higher, and that have a blend non-acetone solvents or a mix of xylene and pure tert-butyl acetate if available for purchase as these are higher quality solvents that won't break down the acrylic resin that is so critical to performance.

5. The intended end goal the product is trying to achieve? How you intend to use the product (what is your tangible desired effect), and what time in the concrete's curing process or overall lifespan do you want to use the product?

◢ Developing Resilience and Stopping Efflorescence In the Precast, and Concrete Block Industry:

A lot of precast concrete companies, and concrete block and paver companies have major efflorescence issues, especially on colored concrete because most precast concrete is water cured and then usually not densified, leaving the majority of the surfaces on the concrete to inevitably form efflorescence from exposure to moisture or rain if there is not already efflorescence present on the surface from being previously water cured.

• This can especially be a problem if any concrete products are stored outside to be rained on (especially if shrink-wrapped).
• Most efflorescence issues can be resolved by applying densifier coatings early in the product curing process, as a densifier will stop the free mineral salts before they can seep out of the concrete from exposure to water by binding with them, yet most companies will use a solvent-based acrylic sealer, which does not directly stop efflorescence but instead blocks moisture that draws efflorescence out.

◢ Efflorescence:

Efflorescence is a mixture of water-soluble salts that seep out of concrete exposed to water. As the surface of the concrete interacts with water, it brings out any water-soluble mineral salts from within the concrete.

When the salts reach the surface, they react with CO2 in the air and form insoluble calcium carbonate, or efflorescence.

This white, dusty, scaly salt can be dramatic depending on the amount of free soluble mineral salts present within the concrete.

When concrete is not adequately densified and is exposed to rain or standing water (water curing), it will cause the process of efflorescence to start.

Efflorescence is not as noticeable when it occurs on regular concrete, but even a little efflorescence on colored concrete can be extremely visible, especially on dark colors like black colored concrete.

The bad news is that unless you do something preventative, it can take as long as 15-20 years for the efflorescence to go away naturally (if you can wait).

◢ Removing Efflorescence Without Abrasive Blasting (Post Issue Arising):

Glycolic acid (also known as hydroxyacetic acid) is a generally user safe and slow working acid that can be used at a starting dilution of about 20% acid to 80% water and applied to the efflorescence for removal in about 10-15 minutes.

If efflorescence is still present, simply repeat the process with either a slightly higher concentration of the acid or a longer duration between the application and the rinsing process.

This is treating the symptoms, not the problem, and it is a completely unscalable option, especially in the precast and tilt-up walls world, but in the right situation, this could save you a lot of money when compared to abrasive blasting an entire building's outer walls.

Efflorescence should never be an issue in the first place, as there is such an easy solution to this problem as mentioned in this article, though in short, if you react the water-soluble salts in the concrete with a water-based penetrating chemical densifier, you will preemptively react those water-soluble minerals with silica, making them inert and insoluble, solving the problem before it starts.

◢ Closing Remarks:

So in closing, the results you get from concrete are directly correlated to how the concrete surface is cured and finished, and not all methods are the same, each has its unique uses and qualities that can either make or break a project, especially in the areas of durability and longevity, sustainability and presentation over time.

◆ I hope I've cleared up how to not only increase the sustainably and durability in the process of curing concrete, but also how to find the correct product for the job in the world of "our product does that too" concrete coatings industry.

— Matthew T. LeComte, CEO | Cornerstone Coatings Global, Inc. – August 13th, 2020