How To Densify Concrete

With CARRcrete PROhard

Hybrid Silicate Densifier

For Awesome Polished Concrete

Polished concrete is an awesome floor surface when processed correctly, and we stress correctly as there’s a lot involved in process. Polished concrete is not simply a matter of grinding down a floor and applying a sealer, if only it was that easy.

A silicate densifier is required to convert any calcium hydroxide in the surface of the concrete to calcium silicate hydrate. Otherwise the concrete will remain porous and possibly dusty. The densifier needs to be applied thoroughly to saturate the surface, to help ensure a good chemical reaction.

In order to get the very best finish from concrete, you need to incorporate a variety of elements, grinding, honing, grouting, polishing and of course densifying.

Unfortunately densifying of a concrete slab during the polishing process is often over looked because many contractors either don’t see a real value in, don’t fully understand the mechanisms of the product or have the time available to do the process thoroughly.

When floors are correctly densified they are somewhat transformed, they appear more complete, homogenous and thickened out for want of a better term.

Burnishing a polished concrete floorBurnishing a polished concrete floor

Reasons To Densify A Concrete Floor

Calcium hydroxide or free lime is the really porous portion of the concrete, the bit that gets stained, is attacked by acids and refuses to polish to the same level as the rest of the concrete.

So I bet, like myself you are thinking it would be a great idea to do something with this less than optimal part of the concrete? Fortunately this is where silicate densifiers come into play.

Densifiers or concrete hardeners in general transport silica molecules to the concrete using various liquid solutions of lithium, sodium or potassium to sites where there is calcium hydroxide. 

The different silicate solutions all have their strengths and weaknesses, some manage to attach silica to more sites, some penetrate further, some react quicker, some enrich the colour more. There’s a massive debate which one is best.

Our simple answer is that there isn’t one singular silicate densifier that is best for the greatest majority of concretes. There’s just too many variables the liquid solution has to cater for.

CARRcrete’s solution to this problem is to not rely on just one type of silicate densifier to harden our concrete. So I formulated a product which uses multiple silicates; sodium, potassium and lithium with advanced ingredients such as rheology, prewetting and penetration agents to help get the product deep into the surface and for it to work really quickly.

By getting a premium densifier into the concrete, you are not only performing the conversion calcium hydroxide, you are in turn hardening the surface so that it polishes more effectively and becomes less porous as crystals form within the surface.

You also get a very fine layer of silica left in all those minute pores and aeration holes which helps fatten out the concrete surface when dry polishing. This ultra fine layer increases the overall gloss of the polish, our PROhard densifier does an excellent job of this.

A CARRcrete PROtop concrete overlay in high gloss finishA CARRcrete PROtop concrete overlay in high gloss finish

Very Brief Chemistry Of Concrete For Floor Polishers

In the most basic of terms, concrete is essentially a mix of cement, fine aggregates such as sand, large aggregates and water. 

During the hydration process where the cement molecules are activated by the presence of water, a gel is formed which coats the other elements of the mix.

As the gel transforms from a soft and pliable material able to bind to other objects through to a hard crystalline structure other byproducts are produced.

Calcium hydroxide or free lime as it also known is one of the more prevalent.

Calcium hydroxide when in the presence of carbon dioxide causes carbonation often seen as dusting across the surface, carbonation is everything you don’t want in a concrete surface.

A high gloss polished concrete factory floorA high gloss polished concrete factory floor

The Right Way To Densify Concrete

Are there different ways to apply concrete densifiers? Yes most definitely, although there are more incorrect ways than correct ways to do the deed.

Here’s where I have issue with a lot of the videos currently online, that show the application of a densifier.

For example, how many times have you seen a youtube video where the contractor or sales rep is demonstrating the application their silicate densifier by spraying down the product in a nice fine layer.

Are we to think, ooh look how convenient their product is, look how far it must stretch, just how quick and easy it is to apply.

I can even recall being at a seminar when a sales rep sprayed down a fine mist of product over a red hot external concrete slab that had been baking in the sun all day.

Naturally the densifier just evaporated instantly, upon asking if that was okay, the rep simply replied it was supposed to work like that because of its advanced formulation. Oh how I wish that was the case.

Well I can tell you honestly, having spent years working with polished concrete and developing our own densifiers, that that those kind of demonstrations are absolute nonsense when it comes to effectively conditioning a concrete surface.

That tiny amount of product sprayed to the surface really doesn’t achieve anywhere near the products true potential. It doesn’t matter how much the company protests with quotes of advanced ingredients and prewetting agents.

You simply need more product applied to the floor, no if’s no buts. 

A diamond polished power trowelled concrete floorA diamond polished power trowelled concrete floor

How To Correctly Apply Concrete Densifier

We always recommend applying our own CARRcrete PROhard densifiers until the surface is fully saturated. Floors which have been placed and cured correctly will have a lower level of porosity and in doing so, will need far less product applied. Fingers crossed you have luck on your side you’ve a nice tight floor.

Because soft concrete floors or those which have not had the proper care during curing, will need considerably more product and time to bring up standard. Often they will seem to drink product, but multiple applications will cure this problem.

For either type of slab, we always recommend applying the PROhard densifier by pouring the liquid onto the floor and spreading out with either a microfibre or a T bar applicator moving the product across the surface so that it can be worked into the pores of the concrete.

If the liquid should be absorbed instantly, don’t worry it has not been wasted; it will have been drawn down into the capillaries where it will react and start creating a tougher, less porous structure. Think of this rapid absorption as a primer for any additional coats.

Simply continue to apply the liquid to the remaining areas of the floor and allow the completed areas to react with the densifier for at least 30 minutes, before reapplying a further coat of PROhard densifier.

You will notice that with each application, the densifier will go much further than the previous coat. Keep applying until the slab will take no more product. You should notice that the slab is starting to look fuller and enriched, like it’s on a full fat diet lol

Ensure that you do not leave puddles of product on the surface, as it is very difficult to remove.

Close of diamond tools fitted to a concrete grinderClose of diamond tools fitted to a concrete grinder

What Stage Of Concrete Polishing Is Densifier Applied?

This again depends what kind of floor you have. If you’ve a nightmare super soft floor then you’ll need to grind away that useless laitance on the surface with some sacrificial diamond tools and get densifier into the ground surface.

You need to use the densifier to begin pulling the surface together if you’ve any hope of polishing it and not wearing away your tools.

So for soft floors, densify as early as you can and build it up before progressing further into the process with finer tools.

For decent, hard slabs we like to apply at 100 grit and if required apply a fine lick coat at 200 grit. The key is to apply thoroughly otherwise you’ve wasted an opportunity to get the best out of the floor.

A polished concrete floor in a kitchen
A polished concrete floor in a kitchen

Why Use CARRcrete PROhard Over Other Densifiers?

There are literally a whole host of concrete hardeners and densifiers out on the market and have been for years. 

And by and large we have tried, tested and used the greatest majority of them.

What we have found is that one type of silicate solution doesn’t work at full efficiency on all floors.

This is why we chose to make a blend of sodium, potassium and lithium silicates to create a hybrid solution that would bring the best qualities from each.

The difference with our product is that is works on pretty much any cementitious surface, doesn’t need scrubbing down like sodium based densifiers.

It also works really quickly and the application is pretty difficult to screw up. It’s not rocket science to get a great result.

Applying a sealer to a concrete floorApplying a sealer to a concrete floor

Do I Still Need A Guard Or Sealer?

Whilst I would always recommend the use of a solvent penetrating sealer such as our PROseal on any polished concrete surface, its requirement is greatly reduced by the densification process.

It is important to remember that the crystals being formed by the densifier take weeks, months and potentially years to fully mature and stabilise, so until that process is complete the fully will always have some level of porosity.

So the use of PROseal is highly recommended, plus burnishing PROseal produces a gloss like you’ve never seen.

Grouting a polished concrete floor to fill aeration holes
Grouting a polished concrete floor to fill aeration holes

Tricks And Tips

Besides fully densifying the concrete, there are a few tricks and tips that I can give you when using our PROhard densifier.

The first tip is that you can effectively use a many coats as you want as now as you don’t leave excess unreacted material on the surface. 

So you could apply a coat at 50 grit, another at 100, and 200 for example, you could even start way back in the metals if the concrete is soft and porous enough to require that kind of densification process.

You can do something called lick coats. Lick coats are for when you’ve already done a full densification of the slab, preferably grouted the floor and want to pop the floor to a gloss like appearance. 

So for example, you’ve removed your grout with 100 grit resins, and you’ve already densified the floor.

You can now spray down a fine mist of PROhard and immediately run the machine with 200 grit resins over the wet surface to combine even finer dust with densifier to fill those minute pores that maybe the grout didn’t fill.

Allow this very fine slurry to dry and remove with 400 grit pads.

Another tip is to not apply further coats too soon after the previous application. If you apply in under 30 minutes of the last coat, you are simply dissolving the previous. 

So let the coat before soak in, react for at least 30 minutes and then reapply more; don’t throw your time and money away. 

Here’s a tip for very soft and dusty floors. If you turn up at a job site and the surface is really soft, and you just know it will kill your tools.

Before you even break out your machine, simply vacuum away any loose debris and apply a heavy coat of PROhard densifier right there, let that penetrate and react. 

Apply another heavy coat if necessary and if still really soft, too soft to work on, Leave overnight to react fully and harden through before grinding away the surface.

I know this may sound like wasted time, but it saves your diamonds.

Dave Carr of CARRcrete Polished ConcreteDave Carr of CARRcrete Polished Concrete

Written By Dave Carr

As we mentioned right at the beginning of the video, polishing concrete is a highly involved task consisting of many different disciplines, densification just being one of them.

If you take just one thing away from this video, remember to apply plenty of product to the concrete, without saturation you are not reaching anywhere near the floors potential.