STAINING LIME PLASTER
WITH FERROUS (IRON) SULFATE
Ferrous Sulfate comes in 50 pound bags (for about $16 each) and is available from most stores which sell fertilizer -- get the water soluable kind in powdered form. It is the main ingredient in "Ironite" (as ferrous sulfite), used frequently by gardeners to increase the iron levels in their soil, but this comes in a granular form which is not readily soluable in water. On the bag are the words "Caution - stains concrete", and as it turns out it makes a lovely stain for both concrete and lime stucco after it has been applied. But don't panic when it turns DARK GREEN for awhile when it is first brushed on the plaster surface.
Ferrous Sulfate also adds a light tan color to the otherwise white/grey plaster when added directly to the stucco mix. In the picture to the right the left side of the bale has been plastered with Ferrous Sulfate added directly to the stucco mix; the right side has been stained with a Ferrous Sulfate solution after the plaster was applied and had started to cure (but was not completely dry).
Here Mindy is measuring out some Ferrous Sulfate to add to a sample formula before applying it to a test bale at the left. Keep lots of notes and keep testing till you get what you like...
We have hand applied lime stucco to our interior wall partitions. Ferrous sulfate powder was added to plaster mix itself. Check below to see how this turned out and compare it to ferrous sulfate liquid staining applied to actual wall surface as it was curing...
Surrounding the door: lime plastering with ferrous sulfate powder added to the plaster mix itself
Walls inside the room: lime plastering with ferrous sulfate solution brushed on while the plaster is curing
Above the door: small area with straw/clay plaster
Bottle decoration area: motared in with "tufa stone" mix (portland cement, sand, peat moss, and some burnt umber and sienna earthen pigments added)
Wall to the far right of door: the original base coat of lime plaster which was shot on professionally
LIME-CEMENT STUCCO FORMULAS
White Portland (or Universal) Cement: 1/2 bag
Type-S Lime: 2 1/2 bags
Masonary Sand: 90 shovels
Chopped Strand Fiberglass Fiber: lare handful
White Portland (or Universal) Cement: one shovel
Type-S Lime: 2 bags
Masonary Sand: 65 shovels
Ferrous Sulfate Powder (water soluable type): 16 cups
NOTE: The Portland Cement was added to basic lime stucco plaster mix in order to decrease drying/curing time. Lime plaster takes a minimum of two to three weeks to cure otherwise. Since we were under time constraints and had to shoot the walls within a two day weekend, adding approximately 20%cement (one to five ratio of cement to lime) produced sufficient drying/curing that the second finish coat could be applied within 24 hours.
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