Stone Sealers

 

Marble & Stone Sealers

Stone installations undergo problems such as picture framing, mineral stains (for example from soluble pyrite, iron sulphide), and water marking and even primary and some secondary efflorescence are well known. Although not all natural stones are prone to these issues there is still a significant number that are. Sealing of a stone has been advocated by some people in the industry as a fix-all for these problems. There have been numerous studies and products for sealing stones, but there is always a apprehension among professionals and customers about different types of Sealers available in the market. Broadly, Sealers can be divided among 3 different categories.

1. Topical Sealers
2. Penetrating Sealers
3. Impregnators

All the products across various categories have their own unique advantages and shortcomings. So, choosing the right kind of Sealer requires a great deal of understanding of the substrate as well as chemical composition of Sealers.

In this article, our emphasis is on imparting a basic understanding about Sealers.

Types of sealers

1.      Topical sealers

Topical Sealers are coatings designed to protect the surface of the stone against water, oil, and other contaminants. They are formulated from natural wax, acrylic, and other plastic compounds. They will significantly change the look and slip resistance of the surface, especially when it is wet.

Advantages

• Some topical sealers contain additives that produce non slip characteristics. This is great for natural stone flooring.
• They create a protective barrier between water and oil contaminants, foot traffic, and the stone.
• They protect the stone from surface scratching and etching caused by acidic materials such as orange juice and coke.
• For the shiny, glossy look, a topical natural stone sealer can produce a gloss that can be buffed. This allows for the maintenance of a high gloss surface.

     Disadvantages

• They alter the appearance of the stone by adding a gloss sheen and may also deepen the color of your stone. This is not so great for a honed natural stone surface.
• Moisture is trapped within the stone. The protective barrier doesn't allow the stone to breathe.
• As they create a film on the surface of the stone, it tends to show scuffs, marks, and paths in heavy traffic areas. But, these marks are removed during the reapplication process.
• These sealers are not breathable i.e. do not allow the escape of water vapors and other gases, and are not effective against salt attack, such as efflorescence and spalling.
• These sealers may be effective at stopping stains but, being exposed on the surface of the material, they tend to wear out relatively quickly, especially on high-traffic areas of flooring.

2.      Penetrating sealers

These sealers penetrate the surface of the stone enough to anchor the material to the surface. They are generally longer lasting than topical sealers and often do not substantially alter the look of the stone, but still can change the slip characteristics of the surface and do wear relatively quickly. Most of them use siliconates, fluoro-polymers and siloxanes, which repel liquids. They often require the use of special cleaners which both clean and top up the repellent ingredient left on the stone surface.

Advantages

• The sealer penetrates into the stone and attaches its protection to the stone walls within the pore structure. This allows the stone to breathe.
• It does not alter the color or sheen of the stone.
• It doesn't need to be reapplied after each cleaning.
• The sealer is not on the surface so the coating won't scratch or scuff.
• A penetrating sealer does not need to be reapplied as often as a topical sealer because there is no surface coating to wear off.

Disadvantages

• Penetrating sealers do not protect the surface of the stone from scratching or etching.
• They do not penetrate deeply enough (generally less than 1mm) to be effective against salt attack, such as efflorescence and spalling.

3.      Impregnating sealers

Impregnators are water-based or solvent-based solutions that penetrate below the surface and become repellents.

They keep contaminants out, but do not stop the interior moisture from escaping. They are considered “breathable,” i.e. they have vapor transmission.

Some modified silane sealers impregnate deeply enough to protect against salt attack, such as efflorescence,spalling, picture framing and freeze-thaw spalling. Some silane stone sealers based on nanotechnology claim to be resistant to UV light and higher pH levels found in new masonry and pointing.A good depth of penetration is also essential for protection from weathering and traffic.

Advantages

• Most impregnators will not change the appearance of the stone.
• Most impregnators do not require frequent applications. Since the impregnator is below the surface, it will generally last several years before reapplication is necessary.
• Most impregnators are not affected by UV light since they are below the surface where UV light cannot penetrate. For this reason they can be used outdoors.
• They are generally hydrophobic (water-repelling), but are also oleo phobic (oil-repelling).

Disadvantages

• Impregnators that are solvent-based produce noxious and flammable vapors during application.
• Solvent-based impregnators are harmful to the environment producing high VOCs (volatile organic compounds). Always check the Safety Data Sheet (MSDS/SDS).
• Impregnators require a semi-skilled person for application. Proper training is highly recommended.
• The initial cost of most impregnators is relatively high.
• Impregnators in general cannot be used below grade to resist hydrostatic pressure. Since the stone is still capable of breathing, water can be forced through the stone by pressure.When choosing the proper product for protection, the above guidelines should help. Always talk with the manufacture or distributer, and let them know where you plan to use their product. They can be very helpful if you tell them all the conditions that apply.

 Comparison Chart of Sealers :

Sealer Type	Use on	Primary Applications*	Type of finish	Performance
Penetrating Sealers	Exterior applications, and thick, smooth or polished stone types such as granite or marble	Exterior concrete surfaces subject to corrosion and freeze thaw damage. Where a natural, matte finish is desired	Provide invisible protection without changing the surface appearance or leaving a sheen	Provide excellent protection against outdoor exposure conditions. Most products are breathable, allowing moisture vapor to escape
Water based Impregnating Sealers	Best on stones with open pores,i.e. marble, limestone, slate, etc.	Indoor/outdoor use	Moderate to reasonable reflective values.	Easy to apply. Very absorbent due to nature of stone
Solvent based Impregnating Sealers	For stones with hard, highly polished, tight pores, i.e. granite, ceramic, porcelain, etc.	Recommended for outdoor use for its resistance to ultraviolet rays from sun. Used in interiors to repel organic and inorganic stains	High gloss, depth and enriched colour	Deep penetrating and long lasting. Initial solvent odor
Topical Sealers	Not for Exterior uses, forms layer so not suitable porous stones		Sheen is observed	Limited durability as they form film on the substrate

*Always check with the sealer manufacturer to verify the compatibility of its product with the decorative surface you plan to apply it to.

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Six side Sealing of stone – Breaking myths of Debonding

Six side Sealing of stone – Breaking myths of Debonding

For years the use of sealers has been expressly for the protection of the stone or tile surface. Most, if not all, adhesive companies warranty their adhesives only if the back of the stone is free from any sealer as sealers are seen as “bond breakers” adversely affecting the integrity of the adhesives ability to bond to the stone or tile surface. However this situation has meant that many of the problems created by water absorption through the back and the sides of stone have gone unresolved. New and current technology now offers sealers that can successfully be applied to the bonded surfaces of stone without becoming bond breakers. To look at these and how they work I firstly want to investigate the problems and issues relating to porous stone and specifically water absorption through the sides and back.

Picture framing, efflorescence, soluble mineral contamination (for example iron Sulphides such as Pyrite) and prolonged water marking are some of the problems created when water is absorbed by the back and sides of some types of stone. The mechanics are as follows. When a stone is installed over a concrete substrate the concrete can contain potential soluble contaminants such as salts and other minerals. The underlying cement based screed or topping as well as the cement based adhesive and grout also have the potential to hold some of these contaminants. In most cases the contaminants will not react unless there is water present. Water is both the catalyst as well as the transport mechanism. The initial and most important source of water that triggers much of the reaction originates from the hydrating adhesive or mortar bed that is even more aggressive due to its high ph. With water the soluble minerals travel to the surface by way of evaporation and capillary action working their way through the stone and grout. In many cases the grout is more porous having higher water absorption than the stone creating an easier exit for the evaporating soluble minerals. This explains why in many cases the resulting stains are revealed as picture framing or at least concentrated around the sides of the stone and grout joint. Once on or near the surface the contaminants further react with the increasing rate of oxygen and ambient air temperature to form various compounds or simply evaporate or dissolve only partially leaving behind the unwanted stain or compound.

A good example of this mechanism at work is the soluble iron salts found in the granites and marbles across various projects.

The water from the thick mortar bed under the stone once absorbed into the stone body easily reacted with the soluble salts to form highly visible iron blooms. In some cases the iron salts would turn the complete stone a light shade of yellow. The solution to this problem is simple – if the stone’s natural water absorption could be reduced close to zero then the risk of iron contamination would be similarly reduced. The best and most cost effective way to reduce the stones water absorption is to seal the stone on all six sides. 

We have all known for many years that the trick to managing many of the water related problems of soluble mineral staining such as the iron salts is to lower the stones natural water absorption by sealing it on all six sides while still maintaining good vapor transmission. (The ability for the sealer to breath is very important as any trapped water can create other issues such as surface debonding by way of excessive moisture expansion. However the formation of the contaminants is not only due to the presence of water but also the quantity of water and rate of evaporation. If the amount of water is reduced and the rate of evaporation high enough that the water does not condense then the soluble minerals will also exhaust through the surface rather than solidify ). The problem however is that most sealers either did a poor job of repelling water in a high alkaline environment as that found at the interface between stone and cement mortar, or reduced the bond strength of the adhesive system. The latter is the reason why most adhesive manufacturers only warranted their adhesives when applied to clean unsealed stone. This claim in turn made clients reject any sealer solution to the problem as well as making sealer manufacturers uninterested in developing specific sealer technology. However as stone’s use increased globally so did the problems related to the high water absorption and chemistry of certain stones. All of this at last led to the development of sealers that could in fact both reduce a stone’s water absorption as well as maintaining the adhesive’s bond.

RachTR has designed the sealer specifically for application to the back and sides of stone called RachTR Back Seal. It is designed to hit the main market requirements for such a product – low cost per m2 (or sq ft), highly water repellent, good vapour transmission and of course not being a bond breaker for the adhesive. However we realized that the best way to apply sealers to the sides and back in a cost effective manner was to dip the entire stone. However this presented a problem in that many clients wanted a low cost sealer for the back and sides such as RachTR Back Seal but wanted a premium product for the actual surface, which would be exposed to long-term dirt and contamination. Therefore any specialized back applied sealer had not only to be compatible with a premium sealer but also needed to allow the premium sealer to penetrate it so the correct quantity of premium sealer could be applied to the surface. RachTR Top Seal is designed to satisfy both these conditions. The sub surface sealers will penetrate right through the RachTR Back Seal enabling the complete and correct quantity of premium sealer to be applied guaranteeing the long term performance of the final sealer.

Both of these sealers are tested regarding shear bond to ensure they do not act as bond breakers.

The contemporary existence of sealers that can be applied to the sides and back of a stone or tile now help to manage and greatly reduce the risk of the long endured problems created by moisture moving through the stone especially during installation and the process of final cure. The argument by both clients and adhesive manufacturers to not seal all sides due to the possibility of the sealer being a bond breaker is no longer valid now the technology exits to do so. 

Using a suitable sealer on all six sides is part of a total water management system that should be implemented to fully control the uses around leaching of soluble minerals. These include for example the use, where appropriate, of waterproof membranes, epoxy remediation systems, proper falls, factory prepared adhesives and grouts etc.