Painting with Lime Wash

Once again, we’re arriving at lasts…this time the last exterior paint. This will be applied to the north and south bump-outs. This paint is a lime wash because we applied lime plaster to the bump-outs which have limited protection from precipitation. The questions arises – what color should we use?

On the south bump-out, we selected yellow ocher. We’ve used this color frequently throughout the interior of the house—we must really like it. We chose it for the south bump-out for a specific reason: the intensity of the southern sun. We have noticed that the dark frames of our windows become very hot in the midday sun and cool quickly at night. The thermal expansion and contraction of the frames have caused a small bit of plaster to slough off in several places. A large dark plaster wall would also be subject to increased thermally-induced movement. Therefore, we opted for a light color to minimize the expansion and contraction that occurs during the day and night  and across the seasons. Plus, the dark window frames in the pale yellow wall look fantastic.

Scott repaired the plaster with a commercial concrete patch mix with polymer additive to make it more elastic. He made an expansion joint at each problem area around the frames. Then we covered the south bump-out wall with a paint created from pigments we purchased from Capital Ceramics in Salt Lake City - a mixture of yellow ocher, ceramic brown and raw sienna. In addition to the pigments, the lime wash consisted of one part Type-S lime and three parts water.

 We were uncertain about the color for the north bump-out, so Scott mixed several colors and applied test patches.

We contemplated these for several days and decided upon eggplant (or aubergine in the world of color design). Aubergine is the darkest color in the set.

Two friends – Jean and Catherine - arrived just in time to help with all of the painting. After completing the south wall, they jumped right in on the north wall with three coats of aubergine.

Yikes! It wasn't the ugliest thing we had ever seen, but it wasn't working here. Scott said this color might be nice somewhere...but somewhere far from here. The coats seemed much lighter than the test patch, and, despite all our efforts to smooth things out, we could see every brush stroke. This wouldn’t do at all.  Scott declared that we were going to revert to our tried and true color – yellow ocher.

He mixed the same pigments as before – yellow ocher, ceramic brown and raw sienna with a slightly greater proportion of ceramic brown – and we did the entire wall over again with much better results.

With patience, stick-to-it-iveness and friends, you can do anything.

We're Almost Home

I’ve always had lofty goals. For this, our fourth building season, I hoped to have the plaster work totally completed - the entire house as well as the garage. We are close.

Here you can see Scott and Jerry working on exterior plaster.

Next summer, the fifth and, one can only hope, last building season, we will put the final coats of plaster on the exterior of the house and all of the garage. That means finish work and landscaping are all that remain.

It’s almost time to call Torrey home.

It A Matter of Lime

Water and straw do not go well together...at least not when that water is precipitation and the straw is your wall. Therefore, it is extremely important to design a straw bale house with features that keep rain and snow away from the straw walls.

Our house, with its eight-foot porch, demonstrates one way to do this. However, on two sections of the house, the north kitchen bumpout and the south sunroom bumpout, there is no porch. There is only an eighteen-inch eave overhang. This is perfect for passive solar design but not so good for shedding weather.

In order to protect these two vulnerable walls, we will use lime plaster rather than the earthen plaster used under the porch. Earthen plaster will erode when precipitation hits it. In contrast, lime plaster chemically sets up in such a way that the plaster becomes hard enough to shed water without eroding.

We actually have two such scenarios to deal with. On the south sunroom bumpout, where we have three, nine-foot by five-foot windows, we decided against using any straw at all. You might ask why. Of course, straw bales have excellent insulative value, but, as mentioned above, you must protect the bales from moisture. There is only room for one bale of straw beneath these huge windows. To us, it seemed that one bale would provide minimal insulation and, as an extra bonus, would present all of the challenges of moisture exposure. So, no bales there.

Instead, we framed this section with 2X6s and our timber frame. We covered the exterior and interior with oriented strand board (OSB) then insulated the air space between the OSB walls and the ceiling with icynene foam (see June 23, 2011 - More Insulation post). We stapled expanded metal lath to the OSB to provide a tooth for the plaster. Now we have great insulation, no moisture issues and an opportunity to use lime plaster on the inside and the outside of the south sunroom bumpout.

Scott made our exterior plaster with Type S lime purchased in bags from our local building supplier, Loa Builders. He added water, sand, polypropylene fibers, pumice (purchased  from Hess Pumice in Malad, Idaho), kaolin clay and soda ash.

There are two main challenges to using lime. One, it is extremely caustic so we needed to wear  rubber gloves, dust masks and eye protection. Two, lime plaster does not like wind or direct sun, so we needed to wait for a calm day. When two such days were in the forecast we set to work. The 18-inch eave overhang was enough to shadow the wall for nearly the entire day, so the wall was shaded as we worked. Once we finished the first lime plaster coat, we protected the lime from sun and wind by leaning boards against the lower part of the wall. The upper part was shaded by the eaves. For the next two days, Scott misted the lime periodically to prevent it from drying out too quickly. The result was perfect...no cracks and the first of two lime coats finished!

Scott applying plaster under the eaves

A section of wall with the first lime coat

Pete helping

The entire wall with the first lime coat finished