Salt Problems in Egyptian & Turkish Marbles

INTRODUCTION TO EGYPTIAN & TURKISH MARBLES

Egyptian marbles are the oldest and the finest marble products in the world and are available in abundance while Turkey has many assorted types and large volumes of marble reserves due to its geographical position on the Alpine Belt. Both marble types are famous for high lustre and visual appeal in terms of quality, appearance, designs and patterns of numerous sizes and utility. The marble of superior grade do not need any chemical reinforcement like other marble products But, there are certain types of marbles which do have high salt content.

In India, there has been significant increase in the use of such marbles owing to different qualities and factors. But, we have explored some serious problems while installing these stones. 

MARBLE PROPERTIES

• These marble slabs have very low percent of iron content
• They have some disadvantages like the cracks, salt, efflorescence and dis-colouration & low polish durability in certain marble tiles but this can be avoided by using various chemical products

• The qualities and attributes of the various varieties of marble can be identified from the patterns and grains on them

• Densifiers (RachTR Stone Power), Penetrating Sealers (RachTR Top Seal & Back Seal) & Epoxy  Systems are main products to look for while consolidating and finishing the marble slab

EFFECT OF SALT ON MARBLE SURFACES  

The degradation of Egyptian, Turkish or other stones is due to several types of water-soluble salts of minerals such as iron, copper etc. Salt crystallization in porous materials constitutes one of the most frequent causes of decay, in a wide range of environments. These salts can be observed directly as efflorescence and appear and disappear periodically according to the presence or absence of moisture sources. 

Pressures created by crystallization of salt in pores weaken the substrate until its mechanical strength is diminished and damage occurs. Inhibiting or reducing the salt crystallization would therefore prevent or slow down the degradation. This problem represents aggressive deterioration forms that take place on all stone surfaces, mortars and renderings through salinity solutions that are transferred to the stone pores.

  

 

This may be understood from the salt concentration that can be attributed to repeated dissolution and crystallization. When water evaporates, the salt will deposit either on stone surfaces "efflorescence", beneath the surfaces "sub- efflorescence" or within the pore of the stone itself" crypto efflorescence", especially with repeated wetting and drying cycles which finally lead to stone deformation. 

The formation of salt crusts on calcareous stone is the most important chemical reaction involving salinity ground water to cause stone degradation. When these crusts are formed on a porous stone, it disintegrates to a powdered material, while limestone and marble develop thick crusts instead. Furthermore, they are formed when calcite in calcite-cemented sandstone, limestone and marble react with different oxides in the presence of moisture sources through several kinds of chemical reactions.  

Salts manifest themselves in different ways depending on the type of marble used. The problem is not confined to Egyptian marble only. The manifestation of the problem depends on the type of marble used. For example, if the marble has veins, the veins open up when attacked by minerals. On the other hand, if the marble does not have veins, sometimes a layer of white powder can be formed on the surface. Luckily, the powder can be easily wiped off, but could reform again every now and then. Salt forms are aggressive deterioration problems, which occur on all stone surfaces, mortars and renderings through saline solutions transferred to the stone pores. Deterioration of Egyptian & Turkish stones is primarily due to water-soluble salts. The formation of these salts on calcareous stone is the most important chemical reaction involving saline water to cause stone degradation. The studies show that there are aggressive forms of salt affecting the weathered samples; especially those subjected to Na₂SO₄ followed by samples exposed to 1:1 NaCl and Na₂SO₄. The high level of Cl and SO₄, concentrations found on the decayed stone surfaces give an accurate evidence of salt migration. The degradation phenomena resulted from salty decay actions occurs directly through complex mechanisms depending on certain specific factors such as mineralogical composition of stones, stone reactivity and adsorption of some salty ions as Cl-and SO₄.

SOLUTIONS FOR SALT PROBLEMS

Before Tiling

• Marbles being natural products variations in color and veining must be expected

• Prior to laying any tiles inspect the tiles for any defects, correct quantity, color, shape and size

• Experienced tillers /stonemasons are strongly recommended to avoid damage to the material

During Tiling

• All natural stone must be sealed with impregnator such as RachTR Back Seal & laid using specialized stone/marble adhesives. Always clean any adhesive, grout and wax from the surface area of stone

• Adhesives/sand or cement with salt content will re-act with some natural stone and should not be used for stone applications

• Natural Stone should not be cleaned with acid or acid based industrial cleaners

• During the laying process, adhesives and grout must be cleaned off the stone immediately 

Polishing Procedure for Turkish & Egyptian Stones

• Grind the marble using Grit no’s 60 or 100 in Diamond Polish or Grit No. 1 in Granite Polish(Diamond and Granite Polish are two prevalent polishing methods)

• Apply RachTR Back Seal (http://rachtr.com/images/pdf/protection/rachtr-back-seal.pdf) to the substrate so as to harden the surface, enhance the adhesion between stone constituents & make the surface water repellent

• Apply RachTR Epoxy 201L ( http://rachtr.com/images/pdf/epoxy-systems/rachtr-201-l.pdf), on the substrate to fill microscopic minor pinholes, cracks and fissures

• Apply Grit no. 200 (Diamond Polish) or no. 2 (Granite Polish)

• Apply second coat of RachTR Back Seal

• Apply Grit No. 400 (Diamond Polish) or 3 (Granite Polish)

• Apply RachTR Stone Power to further strengthen the stone (http://rachtr.com/images/pdf/polish-systems/rachtr-stone-power.pdf).

• Use next grit, i.e. Grit no. 800 (Diamond Polish) or no. 4 (Granite Polish)

• Apply second coat of RachTR Stone Power

• Use further Grits (no. 1200,1500, 2000, 3000, 5000, 8000 & 12000 in Diamond Polish) & Grit No. 5 & 6 (Granite Polish)

• Apply RachTR Top Seal (http://rachtr.com/images/pdf/protection/rachtr-top-seal.pdf) to prevent absorption of oil, water and other stain causing things

• Apply RachTR Pro-Shine+ (http://rachtr.com/images/pdf/polish-systems/rachtr-pro-shine+.pdf), to further enhance gloss and surface finish

 

STONE MAINTENANCE 

Proper care and maintenance ensures beautiful appearance of natural stone

Cleaning

Only use a mild cleanser such as RachTR XC 1 as harsh chemical cleansers 

can eventually breakdown the sealer.

Acids

Products such as fruit and fruit juice, milk (lactic acid), coffee, tea,household

cleaners contain either natural acids or harsh chemicals that eat away natural

stone and the sealers that are used to protect them. Whenever spills occur wipe

them up. Always use coasters under glasses to prevent unseen spills from

remaining on the stone.

Protection from Heat

Never place a hot dish directly from an oven onto the natural stone - always use

protective mats or trivets. This also protects the stone from chipping that could

occur. 

Stain Removal

• Wipe up spill immediately

• Try to identify what caused the stain

• Use a mild detergent or soap first to try and remove the stain

• No usage of vinegar, lemon juice or other acid based cleaners on natural stone.

• Be aware of “Natural” and “Organic” products – always read the labels.

• Avoid cleaners that contain acid. Read product labels carefully of any bathroom  or grout cleaners.

• Don’t use abrasive cleaners or scourer pads or household grade steel.

• Don’t mix chemicals together. Some combinations could create a toxic gas

The Advantages of Epoxy Resin versus Polyester In Marbles & Stones

The Advantages of Epoxy Resin versus Polyester

In Marbles & Stones

Introduction

In any high-tech structural application, where strength, stiffness, durability and light weight are required, epoxy resins are seen as the minimum standard of performance for the matrix of the composite. This is why in stone and structural applications, epoxies have been the norm for years. However 95% of stones today are still processed with polyester resin. The main consideration for materials selection for most stone processors is cost, with performance and more importantly value for money often being a secondary consideration. As a general rule epoxy resins are twice as expensive as vinyl ester resins and vinyl ester resins are twice as expensive as polyesters. Since the resin can constitute 40 to 50% of the weight of a composite component, this price difference is seen as having a significant impact on the cost of the substrate.

However, when considered against the cost of the whole substrate (Stone) the cost is relatively insignificant, and the value of higher quality and long term gain of better durability (therefore better resale value) can be tremendous.

What contributes to this better value…..?

Epoxy resins have performance advantages over polyester and vinyl esters in five major areas:

1. Better adhesive properties due to better penetration (the ability to permeate and bond to the reinforcement or core)
2. Superior mechanical properties (particularly strength and stiffness)
3. Improved resistance to fatigue and micro cracking
4. Reduced degradation from water ingress (diminution of properties due to water penetration)
5. Increased resistance to osmosis (surface degradation due to water permeability)

Adhesive Properties

Epoxy resins have far better adhesive properties than polyester and vinyl ester resins. However many times have you known a polyester putty marble filler peel out during polishing? The superior adhesion of epoxy is due to two main reasons. The first is at the molecular level, where the presence of polar hydroxyl and ether groups improves adhesion. The second is at the physical level - as epoxies cure with low shrinkage, the various surface contacts set up between the liquid resin and the reinforcement are not disturbed during cure. The result is a more homogenous bond between fibers and resin and a better transfer of load between the different components of the matrix.

High adhesion is especially important in resistance to micro-cracking (see later) and when used as filling. The bond between the core and the top layer is usually the weakest link of the substrate, and the superior adhesive properties of the epoxy resin greatly increase the strength of the interface between skins and core.

 

Mechanical Properties

Two important mechanical properties of any resin systems are its tensile strength and stiffness. The figure below shows results of tests carried out on commercially available polyester, vinyl ester and epoxy resin systems, either cured at room temperature or post cured at 175°F.

After a cure period of seven days it can be seen that the tensile strength of the epoxy resin is 20 to 30% higher than those of polyester and vinyl ester. More importantly, after post cure the difference becomes ever greater. It is to be noted that stones processed with polyester resins are rarely post cured in the workshop while stones processed with epoxy quite often are. However, in practice all stones can quite often see “natural” post cures.

The consequences are twofold:

Structurally

A post-cured epoxy laminate will exhibit tensile strength and modulus (stiffness) close to double that of a non-post cured polyester or vinyl ester laminate.

Cosmetically

Polyester and vinyl ester resins shrink up to 7% volumetrically and because the resin continues to cure over long periods of time this effect may not be immediately obvious. This cure accounts for the print through effect observed on a lot of older polyester processed composites. In comparison, epoxies shrink less than 2% and an epoxy laminate will be a lot more stable and have better cosmetics over a long period of time than a polyester one.

 Fatigue Resistance and Micro-Cracking

In most cases a properly processed laminate will never be subjected to its ultimate strength so physical properties of the resin matrix, although important, are not the only criteria on which a selection has to be made. Long before ultimate load is reached and failure occurs, the laminate will reach a stress level where the resin will begin to crack away from those fiber reinforcements not aligned with the applied load. This is known as ‘transverse micro-cracking’ and although the laminate has not completely failed at this point, the breakdown process has commenced.

The strain that a laminate can take before micro cracking depends strongly on the toughness and adhesive properties of the resin system. For relatively more brittle resin systems, such as many types of polyester, this point occurs a long way before laminate failure, and so severely limits the strains to which such laminates can be subjected. In an environment such as water or moist air, the micro-cracked laminate will absorb considerably more water than an un-cracked laminate. This will then lead to an increase in weight, moisture attack on the resin and fiber sizing agents, loss of stiffness and with time, and an eventual drop in ultimate properties.

The superior ability to withstand cyclic loading is an essential advantage of epoxies vs. polyester resins. This is one of the main reason epoxies are chosen almost exclusively for most of the structures.

 
Degradation from Water Penetration

An important property of any resin, particularly in during rainy and winter seasons, is its ability to withstand degradation from water penetration. All resins will absorb some moisture, adding to a laminate’s weight, but what is more significant is how the absorbed water affects the resin and resin/fiber bond in a laminate, leading to a gradual and long-term loss in mechanical properties.

Both polyester and vinyl ester resins are prone to water degradation due to the presence of hydrolysable ester groups in their molecular structures. As a result, a thin polyester laminate can be expected to retain only 65% of its inter-laminar shear strength after immersion over period of one year, whereas an epoxy laminate immersed for the same period will retain around 90%.

Osmosis

All laminates in a marine environment will permit very low quantities of water to pass through them in vapor form. As this water passes through, it reacts with any hydrolysable components inside the laminate to form tiny cells of concentrated solution. Under the osmotic pressure generated, more water is then drawn through semi permeable membrane provided by the gel coat in an attempt to dilute this solution. This water increases the fluid pressure in the cell. Eventually the pressure will distort or burst the gel coat, leading to a characteristic “chicken-pox” surface.

To delay the onset of osmosis, it is necessary to use a resin that has both a low water transmission rate and a high resistance to attack by water. A polymer chain having epoxy linkages in its backbone is substantially better than polyester or vinyl ester systems at resisting the effects of water.