The stucco finish on Underhill House has turned into quite a testing ground. The prep work and first coats began in July (See my post Underhill House Gets Plastered part one ).
Finally in October is the end in sight.
It usually doesn’t take so long to stucco a house. Part of the delay came from the fact that the straw bale walls were late in going up. Part of the delay came from a very steep learning curve in lime plastering. Almost all stucco walls in the past hundred years have been made of Portland cement, but we chose to work with lime for some very good reasons. (See my post Why We Chose Lime Plaster instead of Portland Cement .
Part of the purpose of Underhill House is to demonstrate alternative building materials and techniques. We wanted to use lime stucco, a natural material, and we wanted to use local lime. It had to set up very slowly and that involved misting each of the four coats to slow the drying process. During the record heat of July, Doug and I were clambering about on the scaffolding while dragging heavy hoses – sometimes more than once and hour – trying to slow down the drying and cracking that was occurring as the plaster dried.
Still, it was cracking, and when the final coat was mixed and applied, and we misted it — the plaster started to fall off the wall in glops. It was all pretty horrifying. Perhaps most horrifying to Krome Burke-Scoll, who runs Artisan Exteriors, and had agreed to step away from the Portland cement mortar with which he is vastly experienced to try lime plaster with us.
We worked with the local lime and used a product to make it set up faster, but it just didn’t work. PowerPozz turns out to be used as a lubricant in the gun line for spraying Portland cement. As Krome says, “They need something slippery to reduce viscosity when they need to gun up truck after truck after truck of ready mix.
It was locally produced, and it was low cost, but it was not working on our walls.
Back to the drawing board!
After a lot of consultation with East Coast plasterers who have a lot of experience in restoration work, Krome has settled on a different lime plaster.
It seems there is a form of lime that does set up without misting in a reasonable amount of time. It is hard and durable. It comes from France. Sigh.
When balancing all the variables that make a building material sustainable, one that we weight highly is durability. Living in a very cozy little house in the Netherlands that had been providing shelter for over 300 years made me want to build a house of materials that will last, and in this case, that means lime from France.
Krome is dealing with an American supplier, and he asked them not to ship until they had a full truck coming this way. He was told there was a truck of stone coming our way that they could add it to. So I take some consolation in that. We are still using local sand.
Now that the new plaster is in use, things are moving forward again. One of the carpenters told me yesterday that he heard laughter coming from outside on the scaffolding. That’s a good sign. For a while, things were pretty glum out there.
Now we are coming to the fun part – picking the tint. At first we were planning to go with the natural plaster and add no tint. But it goes up very light and then dries lighter, and it just seemed to be jarringly bright.
I would like the whole building to blend into the hill and for the stucco to have a “dialog” with the tans and grays of the stone foundation, and so we are going for adding a little buff tint. The buff tint is also local – mined just south of Galena IL.
Krome tinted the scratch coat so we could get a sense of what kind of color we were talking about. In part of the wall he used a bag of tint. In another part only half a bag and in the next stretch just a quarter bag, and in the next section no tint at all.
Della and I came out Tuesday morning, and Krome and Steve pulled up the plastic tarp so we could all study the effect. We have decided on half a bag. It will warm up the plaster a bit, but leave it light enough to reflect heat in the summer.
After the brutal heat we have just survived this July, I think keeping the house cool in summer will be more of a challenge than keeping it warm in winter.