Slippery Rock Gazette

Bob Murrell 

Special Contributor

Photos provided by Bob Murrell

Above: Wear from constant foot traffic on black granite in front of an elevator cab. This can be considered a high traffic area.

Above: Black granite wear restored and polished

Above: This granite flooring in a hallway is starting to show wear patterns: note the dull areas.

Above: This office building lobby is a challenge in restoration: a floor that combines both dark and light granites in a polished and honed design. Remember that stock removal on granite can be very slow. Lippage removal is very important, especially if the granite is black or dark. “Picture framing” flaws can be very obvious when working on black granites.

When it comes to tough restoration jobs, being able to successfully restore granite is definitely a big feather in the cap. It is a milestone of a sort when a contractor completes his first granite project. It is almost like you have arrived, even though you know there will still be many trials and tribulations ahead.

Granite is much harder than marble and most all other natural stones as well. Granite is a loosely used terminology as most of these stones are gneiss, anorthosite, basalt or some other igneous material. However, the stones are grouped together and called granites as a common commercial term.

Granites are generally about a 7 on the Mohs scale. Most marbles and other similar stones tend to be generally less than 4.

We use specialized acids combined with micro-abrasives to polish marble. These same acids do not help when polishing granite. Only the fine micro-abrasives work to mechanically shine the granite.

Grinding, honing, and polishing granite is a slow process compared to that of marble. Because the granite is so hard, stock removal can be very slow. Lippage removal is slow but very important, especially if the granite is black or dark. “Picture framing” flaws can be very obvious when working on black granites.

It helps to have granite-specific diamonds and heavy machinery when doing granite projects. Because granite is so hard, softer bonded abrasives are needed. Remember, when working on “soft” material like travertine or limestone, hard-bonded abrasives are required so that they won’t wear prematurely. When working on hard material, the opposite is true: soft bonds are necessary to achieve good cutting rates. If significant lippage is present, a total restoration will be required. 

Also, remember that granite normally doesn’t wear too much because it is so hard. There are always exceptions, of course. However, if lippage is not a major issue, blending can be achieved by feathering out in traffic wear lanes. For example, starting with the use of an 800 grit diamond to smooth the heavy wear areas followed by a 1,500 (or 1,800) grit overlapping by a good amount, and finally by a 3,000 (or 3,500) grit, overlapping all by at least a foot or two. Try using foam spacers under your diamonds to allow for maximum flexibility which definitely helps with minor lippage. 

It’s best practice to use granite specific diamonds on large granite projects. However, regular marble-suitable diamonds should work satisfactorily on mixed material surfaces or small granite projects. Just remember– if you are not removing stock as fast as you think you should, you will probably need to use softer bond diamonds.  

Speed and weight will help with many aspects of the process. Stock removal is faster with more weight and the higher RPM of a planetary-type machine. Polishing is also certainly faster and better with more weight. Standard heavy duty floor machines are also capable of successfully finishing granite.

Current granite polishing procedures utilize granite polishing powder combined with crystallizer or a ready-to-use granite polishing compound. 

Either type of polishing process typically uses a #0 or #1 steel wool pad. When the granite polishing powder (normally the dark variety as most granites contain some black elements) is used, a 1/4 -1/2 cup amount is applied in a small pile. Several squirts of the crystallizer is applied on top to wet and lubricate the powder. The steel wool pad is laid on top of the mixture and the machine is run spreading the mixture over about 9 square feet or so. It is best to use a buffing pad of some type between the steel wool pad and the pad driver. This will keep steel wool fibers from getting stuck in the pad driver. 

The mixture will initially become a paste as you spread it over the polishing area. It will then start to dry out and turn back to powder. When this happens the machine will encounter resistance and become hard to handle. Apply more crystallizer to rewet and lubricate. Repeat this going from wet to dry procedure until the polish develops as required.

I had always heard that getting the granite hot when polishing is what helped it “pop.” That may have been somewhat true back in the day when a lead and felt head was used to polish. Most granite has open microscopic surface pits where small crystals have been ejected from previous honing steps. The lead would actually fill in these pits making the surface more uniform and helping with the overall polish appearance. Today, the polymer in the crystallizer helps provide this same effect. Getting the granite hot is just a byproduct of polishing correctly. 

Polishing can be used to maintain a floor, but normally will not repair wear satisfactorily when it has become noticeable. 

This will require the use of some diamond honing. The amount of honing needed is usually minimal, and in most cases can be blended or feathered into the existing polish– provided the lippage is not too severe, of course.

Small tight areas and borders are accomplished using a variable speed right angle hand tool, or a specialty machine like WerkMaster Scarab. When honing entire floors with diamonds, always lead with the hand tool or edging machine on the edges or borders. Overlapping the edge work with the floor machine on each grit step will blend it well. Otherwise, a noticeable picture frame will develop around the edge of the room. If you use a hand tool, there are 7-inch steel wool pads available for just for this purpose. 

Some granites have been dyed at the production facilities to improve color or just to help keep it consistent. Stones from different areas of the quarry can vary. If you encounter this type of issue, there are color intensifiers available which can help with getting these stones back to their installed color.  

One of the biggest issues with polishing granite can be the surrounding materials. Polished granite combined with honed or flamed granite, carpet, wood, and other materials can make restoration and polishing very difficult.  

I have given out just enough information to get you into trouble, here. So, please always do or submit a test area prior to general work. This will confirm the necessary procedure and results. In this way adjustments can be made as necessary to be successful when doing granite. Doing granite is not rocket science but it can be more difficult than most marble.

As always, I suggest that you consult with a reputable distributor and solicit their input for specific products to help with your granite projects. You can utilize their experience in supporting and dealing with others who have successfully completed granite projects.      

Bob Murrell has worked as a supplier of products and technical support to the natural stone industry for over 35 years. He has written numerous articles for various trade publications and has also trained thousands of contractors over the last 25 years.