Stone Restoration Secrets, Tips 07; Mineral Buildup on Granite Water Features
by, Mike Marsoun
Here in West Hawaii we have extremely high mineral content in the ground water. To make matters worse, a lot of this mineral content is silica which is igneous, therefore not effected by the usual acids. The only acid types that will dissolve silica are hydrofluoric-acid and ammonium bi-fluoride. Unfortunately these two acids (although the latter is not technically an acid) will, for the same reason they will dissolve silica minerals, etch a polished granite surface. This is a “Catch 22”, eliminating the possibility of using chemicals.
Plan “B” So, if this cannot be done chemically, the only other option is to remove the mineral scale mechanically. What I mean by mechanically is by using abrasives to grind thru the layers of mineral build-up to expose the polished granite surface. This polished surface will, in most cases, be in great shape once you remove the mineral film. But how is this done without scratching the polished granite finish?
This is how I do it. Using a variable speed hand machine, what is known as a Sander/Polisher, (800-2000 rpm.) and a five inch Velcro drive disk, and Velcro backed silicon-carbide paper sanding disks, simply sand trough the layers of mineral scale. The sanding to be done will be performed dry. If the mineral build up is thick you can start off at a 120 grit or even 80 grit pad to cut through the layers of minerals. Once you see that you are getting close to “breaking thru” to where you will be exposing the granite you want to stop with the 80 or 120 pads. Switch to 220 grit pads and finish up. The 220 silicon carbide will not be hard enough to scratch the polished granite and harm the finish, but it will be effective in removing the remaining minerals. The silicon-carbide is approximately 4x harder then the granite (not much, compared to diamond which is even 4x harder then carbide), but the polished surface of the granite tends to be too smooth for the 220 grit pads to get a “bite” and will not be scratched. Use about 1000 rpm. speed and apply light pressure. Be careful not to put the pad on edge. Do not sand over the exposed granite with a fresh pad, rather use one which is broken in, the same pad used to remove the mineral film would be a safe bet. Once you do see the polished surface appear, move on to the next area taking care to keep a light touch when passing over a finished area. This does take a measure of skill. Test it out in an inconspicuous area if at all possible. If you are good with your hands you will be fine. This is a great little trick for doing small monuments, benches, sills, garden features, anything with a flat surface. Best it all it is fast.
Of course there is one other way to remove mineral scale from granite, ceramic tile, stone, or almost anything. Glass Bead blasting or Soda Blasting (Armex). These are a better option if the job is a larger area or has a textured surface which will not lend itself to sanding with a flat sanding disc. The problems with this method are; Glass-Bead blasting will leave a powdery mess that can be very hard to clean up, and the Soda Blasting will kill vegetation. The system I use (to do swimming pool waterline tile) involves a Glass Bead blasting system which also vacuums at the same time, returning the beads back into the pot to be recycled- no mess at all. I only use this system on ceramic tile or textured surfaces which cannot be sanded with a rigid system.
To learn more about stone maintenance, please go to:
Professional Stone Restoration Secrets - Handbook for the Stone Restoration Trade
© 2005, Orbital Marketing Group, Permission granted to re-distribute article in it’s entirety including website link and credits.
Linear Mode
