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Calcium based stones have three main factors which relate to maintenance, they are porous they etch and scratch easily. Although a penetrating sealer cannot stop etching and scratching, it can reduce the stones porosity which will improve the stones stain resistance.
WHAT TYPE OF SEALER SHOULD I USE?
With very few exceptions, every porous mineral building material, including stone, tile, masonry, concrete and grout, will benefit from being well sealed. To maximize these benfits the selection of the most suitable sealer is critical. There are two main types of sealers, namely, surface topical sealers and impregnating sealers. A surface topical sealer will provide a physical film or barrier over the surface. The result is a darkening of the surface. These coatings are less hard than the origianl surface and will wear and weather relatively quickly, often make the surface more slippery when wet and must be completely stripped off when re-coating. Salts and water may also build-up under the surface, causing the coating to appear cloudy and peel. Impregnating sealers can be classified as those that repel water and those that repel both water and oil based stains (the ones germs cling to). Impregnating sealers usually have little effect on the frictional properties and appearance of the surface but will not completely stop dirt and rubber getting into the open pores of the surface. When comparing similar sounding impregnating sealers the two most important questions are: (a) is it permanent? and (b) how deep does it penetrate below the surface? A good depth of penetration is critical to provide protection against traffic wear and weathering.
SHOULD I USE WATER-BASE OR SOLVENT-BASE?
Sealers need a carrier to evenly spread and take the active ingredients onto or into the surface. This carrier is either water and/or a non-water based solvent. There is no doubt that “water-based” sounds like a more desirable product but this term can be misleading. Many water-based impregnators still contain a considerable amount of solvent such as n-butyl acetate. As a general rule, non-water based sealers are more effective than water-based sealers. The main reasons they perform better include: they are able to wet and penetrate into the surface – this gives the sealer protection from weathering, cleaning, traffic, freeze-thaw, picture framing (critical on kitchen counter tops where water may by-pass any surface treatment) and efflorescence. Non-water based sealers can also be used over a previously impregnated surface and are suitable to treat resin treated stone, which is the norm for granite kitchen counters.
DO I NEED TO PRE-SEAL MY TILES?
Pre-sealing is the process of sealing a tile or stone before it is installed and helps protect the tile from installation water damage such as that caused by grouting between the tile joints. Pre-sealing also helps reduce the amount of impregnating sealer required once the tile is installed as it reduces the amount of sealer penetrating too deeply into the tile. One other important benefit of pre-sealing is to reduce the effects of grout migrating into the side of the tile causing an unsightly discolouration. Some tiles arrive on the job already pre-sealed, often with a relatively weak sealer in the factory. To check if a tile needs to be pre-sealed place a tablespoon of water on it’s surface for 30 seconds. Blot up the water with a tissue, pressing hard to soak up any water in the texture of the surface. If the water is absorbed or leaves a dark mark the tile should be pre-sealed prior to their laying. Pre-sealing the sides of a tile is not an issue since a strong bond between the grout and the tile is not essential. The main purpose of the grout is to fill the gap and provide lateral support. Both of these outcomes are achieved by pre-sealing the edge of the tile.
WHAT IS ‘PICTURE FRAMING’?
This is a term used to describe a discolouration that may occur to the outer rim of the surface of the tile. The source is usually either the seepage of grout into the tile or, for cement based materials, an uneven curing of the cement in the tile or, water. Picture framing is usually irreversible and it is best to prevent it from occurring. Preventive measures include pre-sealing the upper-surface of the sides of the tile.
IS IT NORMAL TO GET SCUFF MARKS ON A SURFACE THAT HAS BEEN TREATED WITH AN IMPREGNATING SEALER?
Yes. Since impregnating sealers do not fill the surface pores, marks from the likes of rubber soled shoes or tannin from tree leaves can still discolour the surface. The good news is that the sealer holds the contaminating agent close to the surface. Usually, a diluted acid free bleach and light scrubbing will remove most marks caused by organic inanimate contaminating agents such as oil etc. impregnating sealers are bleach tolerant.
Marble, travertine, limestone & onyx are all soft materials which are prone to marking as a consequence of their calcium carbonate structure. Acidic liquids react with calcium carbonate and literally eat away a tiny piece of the polished/honed surface, creating dull spots which are typically called an etch. Contact from acidic materials like lemon juice, wine, coffee, fruit juice etc can create an etch. The more acidic the liquid the faster and deeper the etching occurs.
An etch is not a stain; like a scratch it effectively changes the surface of the stone. It generally appears as a light, dull mark. Penetrating Sealers cannot stop etching as they are beneath the stones surface and not a physical barrier between the acidic liquid and the stone.
HOW TO REPAIR AN ETCH?
If the etching is minimal (you can see it, but is not rough enough to feel) you might be able to polish it out using a marble polishing creme. If the etch is deep and you can feel the surface is rough, you will need to have it mechanically removed.