Overview
1, Chemin St Roch, 46140 Castelfranc used to look out on the river from both ground and second floors until they built a railroad on this side of the river to bring coal from Decazeville in the eastern Lot Department to the steel mills in Fumel, west of Castelfranc. To prevent steep inclines which locomotives cannot climb, they evened out the grade by building up an embankment at the back of our house which blocked the entire first floor. They left, however, a space
of about 2 meters between the exterior wall of the house and the wall of the embankment.
The long-time former owners of the house, the Miran family, headed by a fine furniture maker, covered over the space between the exterior wall of the house and the embankment wall, installed slanted wire-reinforced glass, like in a factory, to bring in light and keep out rain, and built a bathroom in the newly-created living space. My project is to remove this glass for half the width of the house and replace it with a concrete slab for a terrasse.
Step one, cut a channel in the house wall
Cut a channel in the stone wall of the house to receive and support one side of the concrete slab. The channel is about 6" thick by about 6" deep.
Robert was worried that the channel would compromise the floor joists in the main bedroom cut into and supported by the other side of the wall. We used his infinitely groovy 2-piece, radar-based tool
to see through the wall and tell us where the bottom of beams were in relation to the channel. It also read out the thickness of the wall: 56 to 59 cm = about 2 feet thick! The top of the channel on the bathroom side of this wall was exactly at the level of the bottom of the joists on the bedroom side. We therefore put in an oak beam supported by two steel columns to support the floor joists and thus prevent the tile floor upstairs from cracking.
(The oak beam used to be a floor joist in the spare bedroom where you now walk on click-clack flooring on a concrete slab.)
The channel
To cut a channel in a stone wall, you make two straight sawcuts marking the top and bottom of the channel and then jackhammer out the material between. I anchored a wood band the proper distance below a chalk line marking the bottom cut
and used Robert's brand new gasoline powered grinder
with a diamond blade, running its rollers along the wood band. It was a lot like using a very large chainsaw that shoots a blast of lime mortar, calcaire stone, and brick dust into your face. Every foot or so the dust in the air became so thick I couldn't see my line and had to retreat to the street to watch out for Chat Charmant wait for the dust to settle. The jackhammering took most of the day.
The composition of these stone walls is called "tout va" (anything that comes). There are solid calcaire stones at the corners as well as a few salted in in the middle. Otherwise, the stones are small with lots of soft limestone mortar filling in the gaps. As you progress toward the middle of the wall, you run into brick, gravel, crud, lunchbags from the 1700s (not really). The real stones went deep, some of them, so I was glad we had supported the other side of the wall by shoring up the joists.
Next, I set a cleat on the outside wall position the form plywood accurately and then cut this plywood to serve as the bottom of the form. Cutting in anything large, like plywood, in this house requires checking diagonals and a little forelock pulling because no two walls are parallel or perpendicular to one another. I would give a lot to know why. It just didn't seem to matter to anyone. Well, stone walls aren't built with plywood so when you build an interior wall, I guess you just sneak up to each side with relatively small stones and the wonders of mortar, bricks, and lunchbags for filler.
When we demolish the glass windows tomorrow, I will slather hydrofuge on the plywood in hopes that it won't be impregnated with concrete and rendered unusable for anything else.
Finally the oak floor joists support and level the plywood form. I like these French jacks very much-- practical and so ingenious their inventor deserves an article in wikipedia.
Stay tuned for Step Two: demolish the glass; form and pour the concrete.
