General things about polishing marble.
Before I get into some technical details, I just want to discuss some basic things about polishing marble in general. I figure that not all my readers may be familiar with the shop floor, machinery and tools used in polishing marble.
Polishing marble, using a slab polisher or even a small manual system, you'll use in the majority of the cases a Frankfurt system abrasive. What does this mean? The Frankfurt system is specially designed abrasive, it looks rather like a horse shoe and fits into to the slot in the polishing heads plate.
On our right you'll see a couple of Frankfurt abrasives, all Frankfurt are similar in shape, although some have a plastic base to fit into the machine. Normally the plastic base is for abrasives that break easily, when fitting them on the polisher, it needs a little bit of hardness to be able to secure itself onto the polishing plates.
The Frankfurt abrasive sequence is made up with different coloured abrasives, or even different type (configuration/moulding). Many manufacturers relate colour to grain size, so you'll be fitting into your polisher several grains of abrasives, from the lowest to the highest ... and at the end, you'll need gloss/shine abrasives. Polishing marble requires a chemical polish, so the yellow abrasives are normally the gloss/shine abrasives, these are very soft and the least resistant abrasives, although they have an important role in polishing marble.
I've mentioned slab polishing machines, well just to get you familiarized with them, there are several types, namely differing in width and in polishing heads. The width varies significantly, you will find machines that work 60 cm materials, 80, 100 and then you'll find 180 and 240 ... the width is very important as it limits the width of the material you are able to polish. I have a photo of a polisher for slabs:
A marble slab polisher can weigh up to 30-40 tons, the more heads available will guarantee speed and quality to your polish. A machine like the one in the picture may use more than 90 frankfurt abrasives simultaneousely, which becomes a serious production problem to manage, as each type of abrasive has a different usage time, so constant set-up times are needed during the day. (I haven't mentioned the diamond based abrasives which last for a few thousand sqm and are better for production flow)
I also mentioned the manually polishing equipment, I've included a picture of a blue machine on the right, so basically it uses a dish on the end, which normally has 4 Frankfurt abrasives attached. To reduce set ups and other productivity issues, normally you'll have several dishes one for each abrasive grain in the approved sequence.
Why is polishing cultured marble such a big deal?
In truth, each type of texture and colour in cultured marble has their particular polishing sequence. So, unlike most marbles, you'll have several grain sequences and pressure defined for your cultured marble. One thing that is at the base of the polishing problem is the polyester resin from which the cultured stone is made with. The resin in the cultured stone is the main reason for many polishing problems regarding cultured stone. Some of the abrasives themselves also use polyester resin for their bonding which does not facilitate polishing cultured marble.
The cultured marble that uses fine grain in it's texture is more sensitive to polishing, a little too much pressure, or too little cleanliness of the water .... and you'll have shade problems and micro scratches.
Cultured marble should havea measured gloss between 70 and 85 points, when we relate to engineered quartz the numbers go lower and in most colours you'll have gloss index of 50-60 points.
Being cultured marble sensitive, shade problems sometimes can be hidden due to lighting, direct lighting on the polished cultured marble will not help you detect the polishing defects.
In my opinion, cultured stone shade varies significantly due to polishing, if you polish one slab using one abrasive sequence and particular machine parameters, to reproduce the same shade in future productions, you should maintain all these variables stable.
Another typical problem, related to thickness of the slabs, especially regarding tiles, when the 10 mm or 12 mm slabs are polished, the machinery has to be top maintained to get a good job done. It has to be very well levelled and stable. Imagine the weight of the polishing heads, they are in constant movement, and the slab underneath being thin may have tendencies to react. (to check if a polisher is stable I usually use a coin a put it on it's side, when the machine is working it should maintain still, even with the bridge movement, that's how stable you need your polisher)
Now I'm on a roll here, another thing that may cause dreadful problems in non calibrated slabs, or warped slabs, you can imagine a warped slab being polished, it's almost impossible to get a top and even gloss on the whole surface, and frequently the slab will break.
Polishing cultured marble requires a lot of testing of different types of abrasives, and on the production floor abrasive sequences testing. Just a hint for my readers, you may need for some delicate textures soft abrasives, the Italian manufacturers classify them as T type or even TT. T for tender, and TT tender tender ... very soft. In most cases, the abrasive sequence is not standard, which means ... it gets complicated after the grain 400. And the gloss abrasives at the end, are the ones responsible for the shiny look of the cultured marble, these are very difficult to find (good quality at a good price).
Most European manufacturers of cultured stone will sell you polished slabs, which you can avoid most of the problems they have to deal with on a day to day basis, but you can buy blocks from some manufacturers and then you'll need to really look seriously at your machinery and production.