The exterior of the church is not painted but mostly consists of Gunite, which is like stucco except that it contains larger stones. It also likely had some tan (and possibly white) dye added to it. This gives the building a tanish appearance and thus supposedly eliminates the need to ever paint the building. When the church was built it was claimed that its rough and rugged texture (and color) resembled the stone of a genuine ancient Gothic church built of stone.
The exterior has been defaced in past years by patching it in several places, some of which were painted with a gray paint (making it look like gray putty). Painting these tan (or better yet applying a thin coat of tan-dyed stucco) would improve the appearance. Removing them and repatching is another possibility.
Washing the stains off the exterior walls is difficult. The stains are mostly found where the surface is protected from rain such as below window sills and below roof gutters. The N. side is the worst, possibly since the wind during storms is seldom from the N. Also the sun hits the S. side more. Sun may result in more weathering.
Thompsons cleaner containing bleach and detergent makes some (say 25%) improvement. Acid does better but tends to lighten the surface so that the spot stands out as lighter than the rest of the wall. If one gets acid on the surrounding area beyond the edge of the stain, a light border is created. The Jason concrete cleaner contains both phosphoric acid and hydrochloric acid. The phosphoric acid is said to lighten the surface lighter than the original. It says on the label not to use on surfaces such as our which has been colored (dyed) by adding dye to the Gunite. However, it seems to be the only fast and simple way to remove the stain. Orchard sells a hydrochloric acid cleaner (no phosphoric acid) but we haven't tried it yet (Mar. 2003).
To make much progress on bad stains (even with acid), wire brushing is required. High pressure sand blasting has not been tried. Much of the wall surface easily exfoliates, but the stained spots don't do this. That may be why they remain stained. Thus using these abrasive methods on the entire wall will remove some of the surface, and could even expose more of the metal lath which will then create a rust stain.
There are many cracks in the exterior Gunite, some of which have leaked water into the building in the past. The crack locations are mostly high up on the tower and on the W. facade. I have put clear caulk in most of them, but never finished the N. part of the W facade. One reason for not finishing it was that in doing the S. part my hand became temporarily paralyzed due to the stress of holding a caulk gun in one hand (with the other hand on the rope for balance and/or braking). The S. part of the W. facade still leaks some water down the S-facing butress and into the upper choir loft ceiling. Plastic sheets in the attic have temporarily prevented ceiling damage (which has happened in the past). Also, the capstone on the W. facade broke loose a little after the last earthquake (1993 ?) and has a wide crack along the bottom of it that needs repairing.
Throop's are Gunite. Notre-Dame-du-Haut in Ronchamp France used Gunite. Built 1950-4 ??