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I have seen numerous construction drawings of individual Usonian houses on which there have been clear specifications printed on exactly how it was desired that the work on the floor slab should be carried out, but nothing on how the work should be protected thruâ€™out the remaining building operations.
If a brick fell from staging, a carpenter dropped a hammer, or some other accident occurred during the major period of construction, the surface of the floor was at peril unless some form of protection was afforded it.
What measures were taken in this regard?
This photo taken by Bob Beharka during the construction of the Llewellen Wright house suggests the slab was after the CMU? (Photo from FLlW Foundation archives)
Regarding the grid, were any usonian slab joints saw-cut? I thought they were all tooled. I think I remember Bob telling me he covered his own house slab with Masonite to protect it, so perhaps that was used elsewhere.
My understanding is that during the 1950â€˜s some of the grids were saw cut. My preference is for the tooled joints: the rounder edges are more appropriate.
The problem with pouring the slab after the masonry is laid up is that it is difficult to get the grooving tool hard against the wall, especially if the grid is not rectilinear.
Unless the slab is poured at the end of the construction process, the need to protect it still arises. Moreover, in that circumstance the masonry walls require masking, to protect them from splashes of concrete.
I have always specified for the slab to be poured before the masonry is laid up. For protection, I have used on occasion, thick sawdust, 6 mm plywood, or carpet underlay, but the best results have been using layers of discarded carpet. It provides protection from the base plates of the staging, not least when the masons decide to drag the latter over the floor!
Regardless, it is a perennial problem, but one it is necessary to live with thru the period of construction.
My experience with screeds is that they have to be either very thin - 19 mm, or comparatively thick - 75 mm. For some inexplicable reason 50 mm screeds always develop cracks.
It is difficult to bond a screed to an existing slab, given the 28 day curing period for the latter. As a consequence, measures have to be taken to allow the slab and screed to move independently, necessitating the laying of a membrane to separate the two.
Furthermore, there is the cost of the additional labor, concrete, and mesh reinforcement to be accounted for if screeds are employed.
Given their edge condition, I have found that all slabs in the Sweeton house were poured prior to wall CMU being laid up. I assumed Wright favored this detail because it eliminated an unsightly joint in the floor with the wall that would be prone to chipping or opening, and it eliminated the chance of concrete splatter on the wall masonry. While digging at the exterior of the house when we ran the gas line, I found that the slab meets the exterior face of the wall with a thickness of about 1" or less, as if the top course of foundation block may have been cut or hollowed to allow the outer shell to form a pourstop of sorts....so much for thermal bridge prevention.
In the correspondence, I found mention of "lay slab plank" in some notes between the Sweetons and the builder. This seemed puzzling to me until I read this thread. Possibly, wood "planks" were placed at the slab edges to protect them from the masons?
Not really relevent to this thread, I might start a new one reporting on a product I used on my red concrete floors to wax them, with unexpected beautiful results....and no back breaking polishing on hands and knees like with the paste wax I tried before.
The photo is not conclusive, I guess. I had never heard of using sawdust as a protective barrier while in construction, so there very well could be something there. Unfortunately all the other photos I have are from the exterior.
Nevertheless, I seem to recall that the beautiful stone walls of the Shavin house were constructed before the slab was poured. Perhaps this approach would work okay with square-grid designs? Of course, one would have to account for splatter issues and running the grid lines hard against the walls.
During the construction of our own home (unfortunately many years before we "discovered" FLLW), we utilized sawdust from the family lumber mill as well as discarded carpet and carpet pads to protect our basement slab with very good results.
I always specify that no work is to take place on, or around the slab for 28 days after it is poured. This not only allows the concrete to attain its maximum strength, but also ensures that the sawdust does not adhere to it.
Check Michael Maguire's gallery for photos - especially July & August 2011. http://www.buildingtheusonianhouse.com/galleries.html
If I could add a few comments: Here at Dobkins, Wright used a masonry/retaining base to level out the first floor elevation by projecting the structure out from the subtle sloping terrain.
Some of you are familiar with this feature which many describe like the "prow" of a ship.
Notable examples would be the Hagan, Walker, Reisley, Dobkins and others.
Masonry went up first, the pour of the concrete mat second. We have evidence of that with cement splashed on masonry walls that were not wiped in areas of closets and built in base cabinets. There are areas where the dry shake pigment can still be found in masonry bed joints.
Also the hand tooling of module joints are just short of the exterior masonry walls.
In many areas one can slip a fingernail between the masonry and the concrete mat.
In areas where the backfilled soil and or stone subsequently sunk the concrete mat sunk as well, and one can see that the pour came after the masonry.
An interesting side to all of this is every now and then we discover paw prints impressed in the floor concrete mat. It is always a pleasant surprise when we discover one. A cat, a raccoon? Perhaps a squirrel that appeared after the cement contractors left for the day? We know curious neighbors liked visiting the job site when they got wind of a home designed by Wright was being built. I guess critters were also curious.
We visited the house some years ago but never noticed anything odd about the floor, perhaps not aware of its unusual construction at the time.