WetSet Method

Concrete Slab Floor - Footings and stem walls combine to form the perimeter foundations of buildings (see detail 7) When the planned floor for a given building is concrete slab, the stem wall acts both to support the exterior walls and to contain the concrete that is poured inside the stem. In most cases, the concrete slab is finished level with the top of the stem wall, and the stem acts as a perimeter screed support for finishing the slab.

Wood Floor Attachment - When the floor is wood, the traditional stem wall acts as a rim joist or ledger support for the floor joists (see detail 8) With Tech Block stem walls, the ledger is bolted to the inside face of the stem at a height that will hold the floor above grade to that dimension required for the crawl space. Basement ceilings are supported the same way, in fact, basement walls can be seen as tall stem walls in this regard. (If your project requires a wood floor, the installation manual you receive will cover that procedure; the following information details the construction for slab floor only).

The WetSet Method - Our procedure for using Tech Blocks for stem walls is a tremendous time and money saver over conventional methods of building stems. Using our WetSet Method allows us to install the stem and footing for an average home in just a few hours, rather than the several days a concrete or block stem wall usually takes. The stem wall at right, for instance, is for a 5,300 square feet home and we installed the footing and stem in 3 hours and fifteen minutes! We don't even have to do a vertical rebar layout - we just stab a vertical into every grout channel while the footing concrete is still wet. The WetSet Method is not only a huge time and money saver over the other procedures, but the result is an insulated slab (or crawl space if your floor is wood). Essentially, we have R-35 right down into the ground which will also allow us to stucco the finished wall right down to the footing - an added barrier against termites and moisture.

Stem Walls for Concrete Floors - Our local requirements dictate that we must install concrete floors 8" above grade, and that our footings are 10" thick and in a trench that is 16" wide by 18" deep. This works out pretty well for our blocks -- if we have a trench 18" deep, and we pour 10" of concrete in the bottom, the top of our footing will be 8" below grade. If we then place our 16" block on the footing, it will stick out of the ground 8", which is exactly what we need. Since we want to bed our blocks a little bit into the footing, we actually pour our footings 10-1/2" thick by measuring down 15-1/2" from our batter board string, rather than 16". This adds an extra 1/2" of concrete to the footing, and allows us to nestle our blocks 1/2" into the wet concrete (see Detail 7). When the concrete sets, the blocks are held rigid. (Measuring down from the string, by the way, precludes having to set grade stakes.) The actual step-by-step procedure follows.

1. After excavation of the perimeter trenches, install one #5 continuous horizontal rebar about 3 inches above the bottom of the trench. (Building site is assumed to be level, flat, and compacted.)

2. Set up and shoot batter boards and string with the string set 8" above grade. The area enclosed by the string will define the perimeter of the building.

3. On the top of every batter board, measure 10-1/4" towards the inside of the building, and move the strings to the new mark. Doing this moves the string out of the way of the concrete chute. It also allows you to later set the inside top edge of the blocks to the string, rather than the outside edge -- this edge is sharper and more exact than the exterior edge of the blocks, which are made rougher in order to be a better bonding surface for stucco.

4. Wrap 20' of a 30' length of #4 bare copper ground wire to the rebar in the trench at the service entrance location, leaving 10' for grounding the electrical service.

5. Call for footing inspection.

6. Pour footing concrete by measuring down from the string 15-1/2". If your footing trench is the same size as described above, you will need about one yard of concrete for every 23' of trench. The PSI should be 3,000 and the slump should be about 4.

7. Starting with a corner block, set Tech Block stem blocks on the wet footing with their top inside edges even with the string. We usually set the blocks in their approximate locations on the wet footing, and then continually readjust them closer and closer to their exact locations until they become bonded with the footing and won't move anymore. Don't worry too much about the blocks being plumb -- the inside face will be under the slab, only 8" of the outside will be exposed, and it will eventually be stuccoed or covered in some way, and the top surface of the blocks can be rasped down to level if needed. You can eyeball them for plumb.

8. Before the footing gets hard, remember to stab the vertical rebar into each vertical grout channel. We're required to use 3" x 30" L-shaped #4 rebar that are meant to hook under the #5 that's installed in the trench, and it's easiest to do this as soon as the blocks are approximately in place.

9. After the blocks have hardened to the footing, locate the exterior doorways and cut the blocks out horizontally to a depth of 8" and about 6" wider than the door on each side. Then bend the vertical rebar in the doorway areas into the interior of the house so that they will later become imbedded in the slab. These doorway areas will get formed to the outside of the blocks and finished solid by the concrete finisher, and will provide a hard foundation for jambs and thresholds.

The project is now ready for ABC, rough plumbing, under slab electrical (if any), termite treatment, and slab floor. When these items are done, you can start building the walls. That process is described in the next chapter of this manual.

Note: If your building site is sloped, you can step the stem in 8" increments by cutting stem blocks in half lengthwise and using both pieces. The cut side is set downward into the footing so that the integrity of the grout channels is maintained. However, if you have the option, it is much easier to install a level, compacted pad before excavation than it is to deal with steps .

It should be noted that the requirements for footings and stem walls will vary from one area to another, and from building to building within an area. This is because specifics for foundational elements are dictated by local conditions (seismic zones, frost lines, soil composition, etc.) and design conditions (wall height, opening spans, etc.) The procedure above is typical, but may not meet the requirements of the local building department. Every Tech Block wall system should be engineered to meet local requirements.