ST. THOMAS CHURCH
Fort Washington, PA

 

GRANITE RESIN INSTALLATION

This beautiful 40-acre campus is more than 300 years old. We made the labyrinth by hiring local people found through the Labyrinth Society membership.

Zak, Christy, Connie, Mary, our labyrinth crew. We were joined by Diane, another Connie, Sarah, and other volunteers, including those who took these photos. Our thanks. Since we had six workers and perfect weather, things moved along at a good pace.

 

The concrete is completed a month before we come to install the labyrinth pattern so that it cures to its final density. The first thing we do it to power wash the concrete to make sure it is clean. If it is existing concrete rather than new concrete, we acid etch it to gain a favorable profile on the surface to which the granite resin adheres. This photo was taken after the pattern was completed, for reasons shown below.

 

Drainage is an issue on this site. The mud was washing onto the labyrinth because the surrounding ground was filled in above the level of the concrete. The concrete should be a few inches above the surrounding terrain, and slanted or crowned to encourage proper drainage. We spent a hard several hours digging around the labyrinth to protect it from the coming rains, pending re-grading of the area. I power washed this slab a record four times before we solved the drainage and the concrete dried out.

Once the concrete is clean, we mask off the pattern. In this case, it is a full-size Chartres design (exactly 42' 3 3/8" just like the original -- with an error of no more than 1/8 inch) with a slight variation to the pattern (wider labryses -- the back-to-back turns). We used to cover the paths with plastic, but our technique for hand-applying the granite resin doesn't splatter, so the tape alone offers sufficient protection.

Our material is real pulverized granite in an acrylic resin. There is no pigment to fade in the sun, just the natural color of the granite. When it is first applied (as Zak is doing) it looks cloudy until the acrylic dries, at which time it becomes clear and the true color comes out. Once it reaches its final color, it is dry enough to remove the masking tape.

If we wait too long to remove the tape, the granite becomes too hard and the tape isn't strong enough to pull up. In the decorative concrete world they use strapping tape, as it is much stronger. But it leaves residue. We use an expensive tape that sticks firmly, survives rain, and leaves no residue. We used about $400 worth of tape, putting it down only to pull it back up days later. Then we sweep up the little crumbles left behind.

We're done now, right? Not yet. We spend a full day detailing. If there are any thin spots, we add more material. If it is too thick, we scrape it down. We trim the edges of the lines of any irregularities caused when pulling up the tape. We use pumice blocks and diamond-bladed grout knives (photo).

Then, the labyrinth received two coats of sealer. Here's the final result, which has a very nice rapport with the church. With a bit of delay due to rain, I was on site for 10 days.

 

 

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