Construction 52: Cobblestone floor

26/02/15 | ۩ |

The cobblestones ("rissêu" in genoese dialect) it's an old paving technique used to decorate outer floors with colored cobbles.
It's commonly used in Liguria since XIV-XV century, mainly in the parvis of churches or religious buildings, but also in public and private architecture. Prevalent colors are black and white, but there are many examples chromatically more varied. Take a look here and feast your eyes with some pictures.

As it is quite a rich flooring, it could be placed before the main entrance to characterize the noble area of the house with a purely decorative touch, separating it from the commercial zone.
Of course I'm talking about "my" Domus. The real medieval houses  were probably not equipped with such elements. The use of "rissêu" spread mainly in the following centuries. However, it could be an explicit and unordinary request of the customer. If he has the cash and he's determined to spend some more genovinos...
As I said previously, in the building of the Domus we will not spare expense.

Once decided for this technique to floor the small loggia, I must select the design of the decoration I'm going to compose. It could be merely decorative or it may represent something especial, as a sort of signature for the entire work.
This second chance lures me more: I could draw my monogram with cobbles (made crossing W and M) and maybe also the date (2011).
In the picture on the left you can see two modern examples of these compositions.

After these observations, I realize a series of rough sketches to think things through and set the amount of black and white cobbles I'm going to use.
Actually, I have to sift through the little stones picked up on the beach, selecting the appropriate ones.
The challenge is harder than expected, because there are a few fully black or white stones. Furthermore, the size is varied and especially the white pieces presents different shades of white: from pure white to gray-white or slightly yellow...

Anyway, in a few hours of selection with tweezers and magnifying glass, I manage to collect two little piles of cobbles for my mosaic.

The third sketched subject is my favourite, the one with the date in roman numbers and the initials on white background. The white square is placed inside a bigger one, at first thought to be formed by slate sheets but now converted to cobblestones (the black stones outnumber the white ones).

Now I need to develop a different method from the real making of cobblestone floors that will allow me to compose the mosaic off-site and place it once finished.
The original method illustrated in the picture would force me to work inside the narrow space of the Domus. In addition to this, the small cobbles would hardly grip to the concrete base.
I start making a temporary base with clay, drawing the guidelines for the laying of cobbles. The bigger stones will be inserted deeper down the clay, obtaining a regular planking level..

In mosaic art this technique would take the name of "double indirect method". The tiles are placed to form the desired shape over a temporary medium (clay, adhesive paper...) to be covered afterward with gauzes and a water-soluble glue. Then the clay is removed and the mosaic can be placed in its final position. When the mortar is dry, the gauzes can be carefully removed using lukewarm water and the joints are filled with cement.

In my case the temporary medium is colored modelling clay. It has the advantage to keep moldable for a long time (it doesn't dry like natural clay).
A simple layer of gauze is placed over the clay, and the stones are glued one by one to form the mosaic.
The gauze will remain glued to every single stone, avoiding the risk of losing parts of the floor.

I start the laying from the corners, marking this way the inner square. As the cobbles present very different shapes, it results impossible to me to obtain a regular composition like in the real cobblestone floors. Some are flat and placed vertically, some others are rounded... I take care that none of the stones will result too visible breaking the homogeinity of the surface.

Once this sort of frame is finished I start composing the date. The initials (W & M) are made with yellow cobbles, also found on the beach, but in a limited number.

Now it's time to fill in the inner square with white stones. Once again the shapes are varied, but the final effect seems not so bad.

When the glue is dry I can finally remove the modelling clay, finding this task easier than i thought, and cut away the surplus of gauze along the border.

The first stage of the floor-making is done. Now I need to prepare the ground where it will be layed.
I cover the filling of the vault with a thin layer of cement, also partially spread on the back side of the mosaic, and proceed with the placing.

These are critical moments: It's necessary to work quickly but without soiling the rest of the structures and avoiding the wire leaning out from the walls. Actually it already had the opportunity to taste my flesh...
Moreover, the floor must result perfectly horizontal and at the same level of the stone step.
It has not been caught on pictures, but after this operation I can test that the grip is still not adequate and I fix the issue with another layer of glue. Then I press gently with my putty knife and leave to dry.

The day after, the resistance of the floor can be test (not walking on it, obviously) and a final layer of cement is used to fill the joints.

The cobblestone mosaic is now finished. The last touch is a slight polishing with Dremel and sandpaper to give the floor a "consumed" effect, making it even more regular.

Some blade of grass would be the final touch now, but maybe I'm pretending too much...

beach gravel, gauze, modelling clay, cement, vinyl glue, paper sheets, ruler

tweezers, punch, putty knife, brush, Dremel, sandpaper

SIZES (in cm):
perimeter 5,7 x 5,7 - cobbles ± 0,2


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