Jump to content

sanding bits for limestone?


Will Dikel

Recommended Posts

I am making an art-nouveau style dragonfly birdbath out of Indiana Limestone (see "New Work" section). I am having a lot of problems sanding and polishing the crevices on the piece- if I don't get them fully polished, they show up as ugly white lines. I have plenty of carving bits, but what I am looking for are sanding bits, preferably thin and pointed and able to get into narrow areas to polish. I tried some of the dremel bits that are impregnated rubber, but the limestone's hardness wore them down almost immediately. I have been sanding the old fashioned way, bending sandpaper over a thin hard rubber holder that I got at a woodcarving store, but it is taking forever and not very satisfactory. Does anyone know of hard, durable sanding bits that I can use on a Fordham or Dremel?

 

post-2-1194274750.jpg

Link to comment
Share on other sites

Hi Will,

 

I sometimes use this method for wood, ivory and antler, chucked in my Foredom. I have no idea how it will work for limestone, but what the heck - it's not expensive so maybe try it and report back?

 

post-11-1194198817.jpgpost-11-1194198826.jpg

 

The picture shows an exploded diagram of a mandrel with sandpaper squares (about two inches by two inches) between small washers. The washers are necessary to increase the gripping surface, or the mandrel will just tear a round hole in the center of the sandpaper. On something as abrasive as limestone, I suggest using four squares, two facing (out) one way, and the other two facing (inwards) the other way, so you have grit exposed on both sides (I just use one piece of sandpaper for wood, antler or ivory). Stagger the squares. Be sure to tighten the mandrel screw down for actual use. While the sandpaper disk starts out square, it will soon become round with use. The sandpaper won’t last long, but is cheap and effective. At high speeds, the rotational force is so great that the screen or sandpaper disk acts as if it is quite stiff. Try using it at various speeds.

 

If it works, it will make lots of dust and sling it everywhere. You know not to breathe the dust and use eye protection, right? Good luck...

Link to comment
Share on other sites

Hi Will,

 

Speaking as someone who makes a living as stone sculptor, working in Indiana limestone and Tyndal limestone, I would offer a few suggestions.

 

Indiana limestone is one of the best materials there is for carving, but it is not really conducive to taking a polish. I carve primarily with steel tools, mostly made by Auriou, and a mallet. Occasionally I will use a pneumatic hand piece with tungsten carbide chisels for roughing out. On rare occasions, mostly for delicate roughing out of undercutting I will use a foredom tool with a tungsten carbide bit. These will hold an edge in Indiana limestone very well. For abrading or sanding of hard-to-reach areas, I have a selection of Kutzall bits that also work very well, and come in a variety of shapes and coarseness that will serve your purpose very well.

 

Phil

Link to comment
Share on other sites

Hi Will

 

Just like Tom I tried this on metal but never on stone, but who knows.

 

Take a worn out carving bit and wrap a little piece of cotton around it. Let it take up a polish compound and see what it will do.

Works great with little dril bits on precious metals. Maybe its more for the final stage.

 

Succes, its looking great already!

 

Leon

Link to comment
Share on other sites

Hi Will,

 

I use many different methods to remove the white lines on my stone carvings. The hand-sanding method allows the greatest degree of control, and is what I have used the most often in the 34 years I have been carving stone. You do use silicon carbide paper, correct? And wet-sanding is much more efficient than dry. Though I use Foredom and Dremel tools for many things, this ain't one of them. Those little abbrasive-impregnated rubber wheels work great on metals and non-pourous materials, but a not much use on stone. The 'flap-sanding' method will work, but it is not any faster than hand sanding on limestone and just not worth the trouble 90% of the time (IMO). And I'd avoid using buffing compounds on the limestone -- you'll never get the residue out of the pores -- though it does work on less-porous marble. One hand sanding method you might try is to use flexible rubber forms to wrap your sandpaper around rather than something rigid -- a ceramicist's rubber rib works great.

However, if you are just trying to get rid of the "ugly white lines" on limestone (or true calcium carbonate marbles) you need not sand them at all -- especially if the loss of a little bit of control over the surface is worth the time you save by not doing all the tedious handwork. Try a little bit of muriatic acid with a small (cheap) artist's brush. This needs to be done outdoors or under a ventilation hood (be hard to breathe if not). I do it in the driveway with a water-hose handy, but not when it is raining -- the acid fumes don't disperse when the humidity is really high and you'll spend most of the time coughing and trying to breathe.

 

The acid will etch the surface of the limestone, leaving the stone the same color as the polished (well, sanded smooth because Indiana limestone doesn't really polish, does it?) areas. The acid-etched areas will be rougher feeling than the sanded areas, so it is best to do the acid work before the final sanding stages, and then final sanding can be done to blend the surface smooth right up to the crevice proper. No one will notice the roughness if you do it this way because the crevice is too small for their fingers to touch and the visual clues will not show except in very strong light (crevices will usually be in shadow, right?).

 

Wet the limestone with water beforehand so the acid won't make a hard/sharp etch-line on the surface of your stone (hard to remove later). Make note of the areas that need work before wetting it, as wetting it will hide the telltale whiteness. Brush the acid on over the areas needing work -- it will fizz as it etches, when it stops fizzing apply more. If the surface of your piece is wet-down then even if you splash some acid on areas where you don't want it you can rinse-off before the surface is etched too much. Rinse the entire piece periodically and dry it off to see if the white is gone -- a blower-nozzle on a air compressor line works great for this, but towels and a heat-gun will too.

 

If you want to take your time and be less-likely to damage surrounding surfaces on the carving then dilute the acid further with water before applying. I sometimes use a little bit of acid when wet-sanding by hand on surfaces that are hard-to-get-to.

 

Muriatic acid is 20% solution of hydrochloric acid -- the same kind that's in your belly. You can purchase it by the gallon at building suppliers or local big box for $5 or less -- it is used for cleaning mortar work on bricks, concrete walks, pools, etc. I usually don't wear rubber gloves unless I have a cut on my hand (stings like salt!), but I always have running water to rinse off while working. Safety glasses will help the odd splash from burning your eyes (that stings too!). Keep an open box of baking soda handy to neutralize acid spills quickly, but limestone dust also will . . . <grin>

 

Now all that has been said, I have one more observation to make. If the birdbath is going to be used, the white lines (inside) will disappear in a few weeks, and (assuming it will be placed outdoors) the white lines and your 'polish' will disappear in a few months with acid rain.

 

Good carving to you,

Don

www.dondougan.com

Link to comment
Share on other sites

Thanks to everyone who took the time to answer my question. I may make a mold of the finished carving and cast the bird bath in concrete- that way I can preserve the original and protect it from the ravages of acid rain, bird droppings, etc. I would then have a mold that could be re-used for casting.

 

I will post a better picture of the project when it is finished.

 

It's great to be part of a forum of artists who are so generous with their knowledge!

 

Regards,

 

Will

Link to comment
Share on other sites

Hi Will,

 

I neglected to say in my more technical reply that I enjoyed seeing your design -- nice work!

 

You don't think the patina nature gives to your work will only add to it?

 

I sometimes leave pieces outside next to my studio for years (seriously) just to achieve the patina that only nature can provide. Of course (according to me?) I always work the piece some afterwards too -- so as to contrast the patina with polished or tooled areas. And then I usually bring the piece inside and stop letting nature have her way . . . you know, give her an inch and she'll take a mile . . .

 

But employing the molding/casting method does allow one to have one's cake and eat it too, doesn't it?

 

Enjoy your cake (eat a bite for me),

Don

 

www.dondougan.com

Link to comment
Share on other sites

  • 2 weeks later...

Don's comment about limestone patina makes me curious. This is my first limestone carving, and I have no idea what would happen if it sat outside, exposed to rain, snow and of course, bird droppings. Some folks have recommended that I finish the piece with tin oxide, others say that is not a good idea because of the color change, etc. I left some rough limestone outside and it eventually got covered with greenish blackish algae-type stuff. (crud).

 

So, if I decide to not cast the piece, should I just be prepared to have a stained (or lovely patina, depending how you look at it) piece, should I think about periodically sanding it down (but I imagine that the stain would penetrate fairly deeply) or should I even consider an impenetrable (e.g., polyurethane) finish (heresy?).

 

Thanks for any ideas.

 

Will

Link to comment
Share on other sites

Hi will,

 

Being in charge of an architectural carving program that has been ongoing for the last 90 years or so, I am very fond of the patina that limestone takes on with time. The attached website shows the natural patina that limestone and/or sandstone will take on over the years, although none of these sculptures or carvings were designed to hold water. HOC heritage spaces

 

If I were you, I would avoid polyurethane like the plague. Sound's like a recipe for disaster and regret to me.

 

Phil

Link to comment
Share on other sites

Hi Will,

 

The building that I work on has approx 3,000 exterior carvings as well, that have been done over the last 90 years. The adjacent buildings have approximately 7,000 exterior carvings that date to the 1860s. There are essentially two very important things to keep in mind when dealing with exterior stone, and a well preserved surface. The stone HAS to be able to "breath", or absorb and give off moisture easily (this means no coatings), and it must be well drained. There are consolidants that can be applied to degrading stone, but they are designed to let the stone breath as well. Unfortunately, you can't avoid the water-holding aspect. Another contributing factor is the build up of bird droppings, which will contribute greatly to the degredation of the stone surface, and the build up of the brown/green slimy layer that you are trying to avoid.

 

Unfortunately, the benefit of many years of experience in the conservation field, and the many volumes of well-documented observations of the progress 30 some odd years of degredation that I have inherited, and also contributed to, tell me that you have created the perfect environment for just the sort of thin that you are trying to avoid.

 

My best suggestion to you would be to cast your piece in a material that will hold water, and can be easily cleaned, on a regular basis.

 

Phil

Link to comment
Share on other sites

  • 3 weeks later...
muriatic acid ------

you'll spend most of the time coughing and trying to breathe.

 

howdy all :rolleyes:

 

at the forge we employ muriatic acid (hydrochloric acid) to pickle steel and in various steel patina formulas

I would strongly urge anyone considering its application to review the MSDS and take full precautions.

(side note the white residue left after pickling steel is ferrous chloride- iron II chloride, it can be upgraded with additional chlorine to iron III chloride, the stuff you employ to etch copper plates, but Ive yet to find a good guide for small scale production)

 

Ive read about prehistoric alternatives as applied to stone carving and casting

Fabrication of stone objects, by geopolymeric synthesis, in the pre-incan Huanka civilization Joseph DAVIDOVITS, Geopolymer Institute - presented at the 22nd Symposium on Archaeometry

 

At the XXI Archaeometry Symposium we presented the hypothesis that the large stones in precolumbian monuments were artificial, having been agglomerated with a binder obtained by disaggregating certain rocks (in agreement with local legend and tradition). We present here the first results on plant extracts on the dissolution or disaggregation of calcium carbonate containing rocks (Bio-tooling action). The feasibility of chemically working calcium carbonate with various carboxylic acids found in plants (acetic, oxalic and citric acid) has been studied. Maximum bio-tooling action is obtained with a solution containing:

 

* vinegar (1 M) (acetic acid)

* oxalic acid (0.9 M)

* citric acid (0.78 M)

common calcium carbonate bearing rocks being Travertine, Marble, Limestone, Chalk,

its worth downloading the full pdf

 

as well as looking into Geopolymers in general ( for casting as opposed to bio tooling)

http://www.geopolymer.org/

inorganic polymers are a green alternative to cement (CO2 footprint)

limestone based cements with alkali cation (alkali-activation of aluminosilicates) being nigh on indistinguishable from natural limestone

NATURE: report on pyramid limestone concrete

Cutting-Edge analysis proves Davidovits’ Pyramid theory

Geopolymer Archaeology Articles

 

Davidovitis employs the term Geopolymer, Dr Waltraud Kriven Alkali-bonded ceramic, Dr Kluchovsky Geocement

incase you want more leads :unsure:

 

http://www.ceramics-silikaty.cz/2007/pdf/2007_03_173.pdf

Link to comment
Share on other sites

  • 2 weeks later...

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...