Staining Stucco
with Iron Sulphate*

*Iron sulphate is a common compound used with plants to make their leaves go greener. The only warning on the label is :CAUTION: Will Stain Concrete.

We try to apply FeS while the stucco is still green--within days of the final coat. There is still unreacted cement in the mix, and it's damp, which allows the mixture to penetrate deeper into the surface. FeS on old concrete or stucco often will have pale patches where the stain couldn't work.

We begin by wetting the wall thoroughly, and try to keep it wet while we're working. Again, the idea is to help the solution penetrate, and it probably promotes a more even finish.

We use the powdered FeS from nurseries, and mix it up in a 5-gal bucket. It's kind of like mixing salt in water. We keep mixing it in until the FeS starts falling out of solution (crystals start to show up on the bottom). We stir the mix as we're working to keep everything in suspension.

You can apply it with most anything--sprayer, brush, roller, foam brush. Sprayers tend to get clogged pretty easily, and we usually use a roller and a big floppy brush for small areas. We apply very generously, and saturate an area before moving down the wall. If you don't saturate an area, you'll leave roller marks.

One of the great thrills is watching the owner's face when their house turns slimey green--the first thing that happens. It takes an hour or two before the rust color starts to appear.

We usually repeat the process two or three times a day apart--until additional coats have little noticable effect. The color will continue to deepen for weeks and months after the application. Extra FeS crystals will be left on the surface, and the first rainy season sometimes works that into the wall with some deepening. Some will leach out with rains, and deep areas of color will show up where there's lots of runoff--on the sides of window sills, for instance. This creates a very natural aging appearance for the building, something which plasterers and painters try hard to duplicate in faux finishes. FeS is the 'real faux'!

The final color will be influenced by the base coat of stucco. A white or tinted stucco base will show through and add a particular cast to the stain color. As always, experiment first. Nothing takes light quite like a natural stain, and a FeS stained building glows brilliantly in afternoon sun.

One caution. The stuff leaves a slight hazy film on windows which we've only been able to remove with lots and lots of elbow grease. We coat the windows with Rain-X, which is sold in auto stores for windshields, and have no problem. And FeS will turn wood grey, just as it stains concrete. Little splashes you don't notice will show up as grey spots in a few hours. We've used this to our advantage, and treated wood to give it an old appearance (and to match new wood with recycled timbers). At Shenoa, we've frequently had people come and ask us where was the new straw-bale house! The stone-washed jeans of the construction industry....



Some examples:
Octagonal Barn
Cottage at Shenoa
Round Meditation Space (ferrous nitrate)

John Swearingen



Skillful Means
PO Box 207
Junction City, CA 96048