Vertical rebar was inserted immediately after each section of the slab was screeded.
These wooden forms keep the rebar in the precise locations necessary to align with
openings in the 12" concrete blocks which will be used to build underground walls.
The complete slab as it appeared on the day after the pour. 1" deep control joints
were cut every 10 to 12 feet to help prevent cracks in the 4" thick slab.
Concrete was only screeded using two precisely level 22-foot 2x6 boards screwed together. (LEFT)
The concrete was not finished using a bull float, trowels or any other customary tools. Instead, the
slab surface was left quite rough (RIGHT) as suggested by underground architect Malcolm Wells.
Following is an excerpt from pages 50-52 of "How to Build an Underground House" by Malcolm Wells:
“Now a few words about the slab finish. Every cement finisher, every contractor,
every architect - everybody - puts a smooth (“steel trowel”) finish on concrete.
The smooth finish is not only slippery and expensive and easily marred, it looks
just like what we think of when we picture a concrete floor: ugh.
A far better finish, is one I’ve used with great success in many buildings. It is
not only the least expensive floor in town, it is also the toughest, the best for
solar energy absorption, and the least slippery of all finishes. The final product
looks for all the world like antique Italian leather, and we’ve fooled many people
into believing that’s exactly what it is when they rave about it. Here’s how it’s done:
1. Pour concrete into form, rake to a rough level.
2. Moving a straightedge from side to side, “screed” the surface. It can be left quite rough.
3. After curing concrete properly, remove forms. Clean for re-use.
4. After building construction is complete, and concrete is swept clean, use a cheap sealer
on the cleaned slab. Watery-milky looking phenolic sealers for concrete floors will do.
It hardly matters what sealer you use, it’s not there to resist wear but only to keep much
of the expensive stain and urethane mixture from disappearing into the porous surface of the slab.
5. Mix 3 parts Urethane Floor Sealer with 1 part Wood Stain. Use 2 coats. At first the concrete
looks too rough ever to use as a residential floor. Some of its ridges would be uncomfortable
under bare feet. But that’s before all the weeks of construction work take place on its surface.
Lumber gets dragged, heavy pails scrape across it, and man-hours of foot traffic erode the edges.
When everything else is done and the slab has been swept and thoroughly vacuumed, the finish is
applied, using a long-handled roller. The liquid mixture is, of course, deepest in the little
valleys between the tiny ridges, so it remains darkest there. The overall color is a dark,
antique brown. The best color to use, so the slab doesn’t look reddish-brown is a stain of
Minwax's called Jacobean. Here at the gallery, the slab has been under fairly heavy foot traffic
for a year and a half, and it looks like new.”