Specialist Natural Stone Restoration: How & Why?
Different stones require different procedures in order to restore them to a factory finish or to remedy an undesired pre-existing problem. It is very common for us in the industry to receive requests from clients who require their marble, travertine ,Terrazzo or other natural stone floor to be ‘cleaned’ when they realise it no longer has the lustre or reflective quality it once showed. Now in most cases these floors will be lacking a shine due to minor scratches in the stone which have damaged the natural crystals on the surface. These need to be removed using a process known as ‘Diamond Abrasive Grinding’.
Another common situation is for an architect or builder to call us due to a floor being laid unevenly because the client wanted a ‘flat hotel floor look’. Again, the floor will require diamond grinding restoration in order to remove lippage where the tiles meet at the grout lines.
A client recently called us to survey the limestone floor in their Edwardian conversion flat which had a very high shine compared to the same floor in the communal areas of the building. This had happened over a period of about 6 months due to a maintenance procedure known as vitrification being carried out on the floor. The floor was diamond grinded and left with a smooth honed finish which was more natural looking and in keeping with the rest of the building.
There are a range of different procedures that can be carried out to remedy a huge range of problems associated with natural stone. Please click any of the links below to see a more detailed description.
Diamond Abrasive Grinding
This is a process whereby the floor is grinded down with a heavy rotary machine which has diamond pads attached to it. Diamonds are used because they have a rating of 10 on Moh’s scale of hardness.
The point where tiles meet at the grout line is usually not completely level. If you run your hand over the grout line you will notice a definite dip. Sometimes this can be very uneven with a tile being a few millimeteres higher than the adjacent tile which is known as lippage. The first stage in the diamond grinding process is to remove this lippage so that the floor is completely even and flat at the grout lines. This is achieved with metal bonded diamond plates which coarsely grind away at the stone leaving it flat but with a very rough finish. The next step is to repeat the process with finer grades of diamond which are resin bonded. Each grade of pad is progressively finer which serves to remove the scratches which are left in the stone by the preceding grade. The number of grades which are used depends on the type of stone and what finish is required.
Diamond grinding can be continued to a very fine grade until a polished finish is achieved. These final grades reduce scratches which are not even visible to the human eye allowing the natural crystals on the surface to reflect light more effectively. This is an extremely skilled task which requires patience and experience. If individual scratches are not removed effectively in the early stages then the finer grades will only serve to magnify them.
To create a honed surface means to leave it smooth and flat with a matte finish. This is achieved in a number of different ways. A stone which is being diamond grinded and having lippage removed will eventually show a honed finish as the medium resin grades of diamond are used. At this stage a honing powder will be used to enhance the smoothness of the surface. These honing powders are made from a blend of abrasives compounds and can also be used to remove ring marks on a table or counter left behind by a glass or mug. Some manufacturers produce a whole range of powder grades which will remove minor scratches and also etching as well as producing a fine smooth finish. Some limestone will not polish and so grinding it with very fine diamonds will produce an ultra honed surface and so powders may not be required.
It’s worth knowing that the concept of honing stone has been around for generations and any process of using an abrasive to smooth stone can be described as honing. The Venetians honed Terrazzo in the 15th century and since then stone has been honed with sand or any other abrasive which is effective on the stone being worked on.
Powder Polishing & Maintenance Polishing
After diamond polishing the floor can sometimes be enhanced further with the use of polishing powders which usually contain oxalic and aluminium acid. This is a specialist procedure which requires skill and experience when carried out with certain types of powder. Good concentration is required to maintain an even polish over the whole floor as over application can result in the stone ‘dulling off’ in places.
Another procedure we sometimes carry out is maintenance polishing with the use of diamond impregnated pads. These are similar to pads used in general resilient floor stripping and polishing however they have diamonds embedded in them to act as a fine abrasive. This procedure will only be effective if there are no harsh scratches already showing in the stone and is generally carried out as a more natural alternative to vitrification.