Technical Memo 107-DP
Written by Bob Rossiter
Sunday, 18 January 2009 09:35

Sodium Silicate Sealer Vs. Colloidal Deep Sealer

Technical Memo 107-DP issued 30th January 2007

The following letter was written by the inventor of our technology in response from a query from a distributor in the United States on the 16th of March 2000. Seven years down the track and with the popularity of existing or polished concrete floors, this issue of serviceability of our proven and superior products over commonly used poor performing high maintenance sodium silicates still confuses clients. Some clients say our products are expensive - we think they are priceless.

Dear Neil,

Pursuant to our recent telephone conversation, here are some very important differences between penetrating sealers for portland cement concrete, made using a sodium silicate base and Densi-Proof Moisture-Fix, made using a colloidal silicate base.

Sodium silicate is a crystalline substance which is marketed in viscous liquid form, also as a powder, and is especially known for it's powerful detergent and emulsifying properties. Sodium silicate is sometimes called "water glass", or "soluble glass", and has excellent adhesion, subsequently; large quantities are used in water solutions for industrial adhesives.

Since the early to mid - fifties, sodium silicate products have been marketed to the concrete industry, mainly as floor hardeners, temporary surface sealers, or curing agents. However, in recent years, some sodium silicate products have begun to make claims which sodium silicate products cannot possible live up to, i.e., it can provide a permanent deep penetrating integral seal in portland cement concretes.

Sodium silicates will probably always have a place for it's use in portland cement concrete, however, it's current roles should be limited to what it was in the mid-fifties. In explanation, let me point out, sodium silicate's transformation from liquid to gel in concrete is caused by contact with one or more, hydroxides, i.e., calcium, magnesium, potassium, and at least one of these hydroxides is always present at the tip of the surface of concrete to cause immediate, upon contact gel formation, not allowing penetration into the concrete, past the large upper surface porosity, as is sometimes claimed by sodium silicate sealer manufacturers. Plus, sodium silicate gel is a thixotropic weakly linked crystalline structure which causes penetration into concrete to be extremely hampered.

Densi-Proof Moisture-Fix is a catalyzed colloidal silicate which contains only natural ingredients, i.e., a precision blend of colloidal silicates especially designed for ultra-deep penetration into concrete, with concrete enhancement as its main objective. Sodium silicate solutions, applied to concrete, only harden a concrete surface, while incidentally forming a weak soluble seal in the concrete's upper-surface porosity. Densi-Proof Moisture-Fix, whose colloidal silicate molecule sizes are purposely controlled and are very tiny, as compared to sodium silicates' molecules, will also harden a concrete's surface, as well as, deeply penetrate into and beyond concrete's tiny micro porosity since it is virtually unaffected, short term, by the hydroxides in concrete, meaning, due to the above, it has the ability to enter and flow through concrete's paths of reticulation with relative ease.

Also, due to sodium silicates creation of thixotropic gel, upon initial contact with concrete, only the leading edge of this temporary gel becomes a fully cycled, or developed gel, leaving the rest of it in various stages of underdevelopment, and underdeveloped thixotropic gel has great affinity to carbon dioxide gas, which means, the major portion of this sodium silicate formed thixotropic gel, if not flushed out of the concrete's surface immediately, will prolifically absorb carbon dioxide gases from the earth's atmosphere, forming carbonates inside the concrete, promoting carbonation, and potentially detrimentally affecting the concrete's surface integrity.

Since sodium silicate solutions form thixotropic crystalline structured gel-like precipitate upon contact with portland cement concrete, let me explain what this means to the concrete itself. In thixotropic breakdown, upon contact with concrete and it's hydroxide(s), sodium silicate solution viscosity abruptly decreases, both with shear time and shear rate, taking a texture similar to a gel. Subsequently, no further decrease in viscosity occurs. The thixotropic materials, initially generated, belong to a group of concentrated sodium silicate suspensions, i.e., molecules, etc and show a characteristic yield point, indicating flocculated (tufted masses of molecules) structures of gel type. Under mechanical shearing, brooming, or squeegeeing his gel will gradually breakdown until all flocculated particles are completely dispersed, giving off liquid of minimal constant viscosity. However when such suspensions are left at rest, flocculated particles gradually form clusters, then thin flocs, finally, a solid gel. This may occur in hours, days or even weeks, however, during this period of transition several other factors may come into play, i.e., rainfall, mop water, traffic, and etc, have a significant bearing on the treatments outcome, which is why sodium silicate treatments are not recommended on outside concrete installations. Both size and shape of molecules and interaction forces (hydroxide concentration) the molecule of sodium silicate solutions to play an important role in the rate of thixotropic breakdown.


Sodium silicate's thixotropic gel possesses tremendous hydrophilic affinity, so if the humidity inside the concrete doesn't satisfy the gel's affinity requirement, gel will begin pulling moisture from the atmosphere, beginning slowly, maybe even unnoticeably, to the not so observant, the gel will eventually begin oozing out of the concrete, appearing as a glistening surface, detrimentally affecting concrete's surface traction quality, possibly over a period of years, until there is none of this gel left in the concrete.

In describing the structure of thixotropic gel, crystalline indicates that its structure has not developed to its final form, or composition, because the term crystalline, in reference to this type of polymer, indicates that it is still in transitional form. This means that it could, and probably will, evolve into another composition eventually. Tests have shown, crystalline structures inside of concrete tend to evolve into a mineral - looking particle, which only looks like, but does not act like, a mineral, and the time period for this to happen varies considerably since the concretes surrounding environment, to which it is exposed, plays an important role in this evolution process. The descriptive term used to describe this mineral looking particle is "pseudo morph", meaning particle resembling a mineral, in crystalline form.

This evolved pseudo morph's biggest significance in the sealing of concrete; through a crystalline process is that this particle, which evolved from a crystal, is smaller and lighter than the original crystal which initially occupied the concrete pore space, and will easily float out of the concrete, or allow water to leak past it, should water become available to carry it, once again leaving concrete vulnerable to leakage and contaminant penetration. Thus, the reason for placing a trowelable material on the concrete surface, in a lot of cases, following application.

Densi-Proof Moisture-Fix's internally generated precipitate formation, following its application to concrete, is mainly activated by the concrete constituent always available in a Portland cement concrete, free alkali and free alkaline hydrates, forming an especially designed colloidal silicate precipitate barrier which is immediately formed in its final form, never to evolve into any other shape or composition, Densi-Proof Moisture-Fix's nil solids liquid changes into a 100% solids precipitate deeply inside of concrete without generation of heat nor expansion pressure. Densi-Proof Moisture-Fix's initial encounter with free alkali/alkaline hydrates is well inside of concrete's interior, in the transition zone, between its surface porosity bottom and it's matrix component, this is usually where the internal barrier begins, Only a minute portion of Densi-Proof Moisture-Fix, in it's liquid form , is used in each free alkali encounter as concrete penetration is occurring, meaning the balance of product's liquid keeps penetrating deeper and deeper, with unique ability to pass through its own colloidal silicate precipitate.

There are three main reasons that ultra deep penetration occurs

  1. Colloidal base liquid consists of friction reducing agents coating the very tiny spherically–shaped molecules that roll into surface accessible paths of reticulation like tiny ball–bearings,
  2. The very tiny colloid molecules are hydrophilic and have tremendous affinity to internal free water or moisture always available on concretes interior,
  3. Unique colloid molecules have electrical attraction to the earth’s opposite charge magnetic pull and this same attraction becomes even more magnified where embedded reinforcement steel is inside of concrete being treated.

Unlike concrete surface-activated, thixotropic gel-producing, sodium silicate solutions, Densi-Proof Moisture-Fix deeply integrally seals the concrete, as well as, supplements, densifies, hardens, and strengthens it. Furthermore, Densi-Proof Moisture-Fix has unique ability to render harmless existent or potentially existent internal steel corrosive activity (if any), by neutralizing internal acids (if any), removing electrolyte availability, and etc. Product also has ability to arrest or, at lead, significantly retard detrimental internal chemical reactions that may exist, or potentially exist, i.e.. alkali- aggregate reactions, etc. Densi-Proof Moisture-Fix addresses all ailments, or potential ailments, associated with portland cement concrete, and provides numerous other benefits to concrete, many more than is derived from a sodium silicate solution, plus, a Densi-Proof Moisture-Fix application is permanent.

If I can be of more assistance please let me know. Thank you for your interest.

Respectfully Yours,

Bill Ward, Technical Dept.

Densi-Proof™ is a one coat spray on system that deeply penetrates ( up to 200 m/m and beyond ) providing permanent water proofing and protection. Withstands a minimum of 35 metres of Hydrostatic Pressure and can be effectively applied on the positive or negative side of concrete structures. There is minimum site disruption and provides early access to other trades. It is important to point out that Densi-Proof provides a permanent unique passive non destructive colloidal silicate gel barrier and should not be confused with temporary, soluble, weakly-linked large pore, thixotropic gels,that are formed using sodium silicates, through free lime reactions,which have proven detrimental to long-range concrete integrity. Densi – Proof technology is unique, it is not a Sodium, Potassium or Lithium silicate and has stood the test of time for over 26 years.

Last Updated on Wednesday, 17 February 2010 22:41