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First, the old slab needs to be removed, and the floor further excavated to accept the new thicknesses. We discovered that the original contractor actually poured foundations (!) to support the window wall. The slab was carefully cut around the exterior supports to maintain bearing.
The soil base was compacted to 95% relative compaction and 2 inches of rigid board insulation was placed on the subgrade. Rigid board was also placed on the perimeter of the room (the majority of heat loss is at the edge of the slab). The board was chamfered at the top so that no gap would exist between the wall and the floor.
Next, 2 inches of sand was placed on the rigid board. This is an extremely important component of the system, as it allows water from the concrete to be absorbed by the sand during the pour. If the concrete is poured directly on the rigid board the water has no where to go other than up, making the shake-on process very "soupy" and difficult.
Steel reinforcing is placed on the sand, and the heating pipes tied to the steel. Use a FLAT mesh, not the rolled up variety, as its important to keep the steel and piping flat.
The concrete is laid in sections, using forms. This allows the concrete contractor to properly broadcast the shake on material, and "float" the moisture to the surface (twice) applying the material after each float. Also note that the forms are kept about one inch off the sand to allow the steel to be pulled up into the concrete immediately after the pour.
During the curing process, the concrete will appear slightly mottled. Some of this will disappear as the concrete dries, and the rest will even out after the application of the sealer. We have found that L.M. Scofield's Dark Red is the best match for the original A.C. Horn Product. The wax-based sealer is a special order in that color. After the concrete has set and sealer dried we have always recommended a red wax, rather than an acrylic finish, for the final coat. Both serve as "sacrificial finishes", i.e., they protect the colored concrete from wear, but the wax results in a much more attractive finish.
Any notable post mortem findings with respect to the original piping?
The plumbers (commercial plumbers with experience of installing hydronic heating systems) layered down some sort of insulating blanket just below the steel mesh and PEX tubing. The concrete contractor (who has a concrete floor over a hydronic system at his own home) has said this is how his was done as well.
DRN, before we started the excavation we visited the Weltzheimer Johnson House which had a failed hydronic system and used electric registers. Although slightly north of our property, they do not use the house during the winter because of the cold. This was unacceptable for our situation. So much stone and concrete would not be livable, in my opinion, without heated floors.
Also, a reflective barrier helps, but is not as effective as rigid insulation. Again, the highest heat loss is at the vertical edges of the concrete, so you will save a great deal of money over time properly insulating the edge with at least 2 inches of rigid board.
At this point we will not re evaluate the type of pour. We are in a race with winter to get the foods in before the usual winter weather hits. Also, the samples are vivid enough for us although the untreated product, (seen in the far right of the photo) do appear rather bland. the low gloss coating provides depth to the colored concrete.
Can't wait to feel the heat underneath my feet! Everyone who has lived with it loves it. Once the floor is cured we can move forward on finishing work for a late spring early summer move-in date. I appreciate you posting this information.
I toured this house when it was on the market and it's a fantastic solar-hemicycle. Can't wait to see the completed work.
- Wright would have preferred that the block remain unpainted, but the quality of masonry was low, so a cementitious paint was used to achieve greater uniformity. The interior colors have changed over time, so the colors are test samples over the years painted behind the bench seating.
- Existing conditions are always documented by both drawings and photos prior to initiating work. In this case it was discovered that the control joint on the curves (unit lines) were never executed per Wright's plan. The only joints used were the radial lines (originating from the centerpoint). Large expanses of concrete cracked without control joints. We introduced the curved lines as part of the work.
- I believe the wax sealer can be applied 48 hours after pouring - but you may want to check the Scofield product literature.
There are some architects that advocate using Tinturra Stain, but this product is generally used with an acrylic finish, which is basically a plastic that we avoid. We have had great success with the following sealer:(copied from the Scofield Website):
LITHOCHROME Colorwax in the matching color should be
used to cure exterior flatwork that will be allowed to weather
naturally or that will only receive occasional maintenance
and recoating. Exterior flatwork that will receive regular
maintenance and resealing and all interior floors should be
cured with COLORCURE Concrete Sealer in the matching color
or with clear SCOFIELD Cureseal-W or SCOFIELD Cureseal-S.
Scofield recommends that a thin coat be applied within 48 hours during the hot summer months to seal the concrete and prevent it from drying too fast, which sometimes causes cracking. The second coat is applied 28 days after, when the concrete is properly cured. The real beauty of the floor is created by applying Kemiko colored wax, as the red floor has greater depth and subtle color variations. It also serves as the "sacrificial finish" that takes the beating of normal use rather than the tinted top of the concrete. No acrylic/polymers needed.