I am just relaxing after mixing 400 lbs of lime putty. I have chosen to use high calcite lime, type "N", from the Chemical Lime kiln here in Vancouver. They are using a limestone deposit from Texada Island which is very pure - the magnesium is less than one percent. The magnesium should be no more than 5 to 10% for fresco. There are high calcite klins all over North America. The price is $6 for a 55lb bag here.
There are three ways to mix the lime. The first is "manually" using a box similar to a big wheelbarrow, and a hoe. The lime must be sieved into the water already in the tank, 14 quarts per 50 lbs of lime. This is similar to when you add plaster to water. The next day the putty has to be seived through a fine mesh wire screen to catch any small lumps. The next way, which I am using, is to get one of those 55 gallon plastic drums, cut the top off, and use this as your mixing and storage container. The second technique adds the lime to water but then you mix it with a 3/4" drill, at least nine amps, and a large "jiffy" mixer - ask at a concrete supply store. These drills are expensive to buy new $600 - $700 in Canada, and the paddle is about $75. (Of course true to my style, I bought a used drill made in 1945 from the pawnshop for $175, cleaned it up, changed the plug/wire, and it should last another 50 years;-) )In this technique, you will not have to seive the lime before or after mixing - but the mixing is very hard physical work. It took me about two hours to mix 400 lbs. to a nice creamy putty with no lumps. I will use the same technique and drill to make my intonaco mortar, mixing the lime putty with white marble sand. I also use the drill to mix concrete for my panels. The third way is to rent a proper mortar/plaster mixer from the rental yard, at a cost of $55 to $75 a day. This is a big paddle mixer, vertical or horizontal, gas or electric - make sure you understand that this is not a "cement" mixer - our stuff is too stiff for that. It can handle a minimum of three cubic yards a load, so that is a lot of lime putty. Measure out the water into the mixer, add the lime and mix it for about five minutes, tip it out into the barrels/pails, clean up the machine - it really is that simple. They cost over $2000 to buy. If you have a group of artists, you could collaborate to make a batch of putty and intonaco mortar all in one day.
So - I do not sell lime putty at this time, it costs me too much sweat to make it. Some day, when I have a mechanical mixer, I may offer five gallon pails.
Is this putty different than European putty made from marble? As far as I can tell, going by the chemical analysis, my lime is even more pure! I notice the German putty from Kremer is 95% pure, 5% magnesium. Also the modern kilns are highly accurate for slaking and purity. The high calcite lime, other than the potential magnesium problem, also holds water tighter than impure limes. This water retention is what we need for good fresco (and good lime mortar). I would not discourage anyone from making their own putty from quicklime (as long as it is high calcite quicklime), they will soon realize how much hard, dangerous work it was to make putty in the old days, and you would tend to appreciate the material and your artwork much higher. For me, I already have an appreciation, I need to spend my time painting, developing technique, and selling the finished product.
(if you want to purchase aged Italian Lime Putty go here:
see it on http://www.youtube.com/FrescoSchool Channel:
Making of Practice Lime Putty: