Rescuing a Block Foundation, continued

Securing the Brackets

When all the posts are in the ground, we leave the hydraulic cylinder connected to the final post installed and attach smaller hydraulic cylinders to the posts installed earlier (Figure 7). This important step equalizes the loading on both piers. These smaller cylinders have just about 4 inches of travel, so we use them only for equalizing the bearing pressure between all the posts.

Figure 7. After both piers are in place, a second small hydraulic ram is attached to the hydraulic pump and attached to the first post (top left). With both rams connected, pressure is applied to equalize the loading on the two posts (top left). Once the bolts are tightened with a pair of adjustable wrenches, the hydraulic cylinders are removed (bottom right).

On larger jobs, we can connect up to 16 cylinders at a time, allowing us to work on foundation walls as long as 40 feet. On the job shown here, there were only two piers, so the process went quickly. With the pump connected to both cylinders, we again brought the pressure to 4,000 psi. With both piers under equal pressure, we bolted the caps that lock the piers in their final position. We then moved on to the second part of the job, the bulging foundation wall.

Installing Wall Ties

Grip-Tite's wall ties consist of two 24-inch steel plates connected by a section of 3/4-inch galvanized rod. One wall plate is placed in the center of the bulge inside the building and the other goes in a hole outside, buried about 9 feet away from the foundation in virgin soil (Figure 8). Tightening the nut on the threaded rod draws the two plates together and straightens the wall. In this case, the outside earth anchor was located about 36 inches below grade in a 2-foot-diameter hole, which we dug with an auger, saving the sod so we could replant it later.

Figure 8. To bring the bulging wall back into line, the author uses a wall plate and an earth anchor connected by a threaded rod — the wall plate goes against the inside face of the wall; the earth anchor goes in a hole in the ground outside (bottom). A hardened point screwed on to the end protects against thread damage as the rod is driven (top right).

Wall ties go in pretty easily. The only difficulty is lining up the threaded rod so that it hits in the center of the hole outside. We look for pipes and wires running to the outside and use them as landmarks, but if there's nothing close to the hole, we measure off a house corner. We drill through the block with a 7/8-inch bit on our rotary hammer. The proprietary rods are 9 feet long, and the manufacturer offers 4 1/2-foot extensions that connect with a coupling. The extensions are handy when we have to locate the holes outside around obstacles such as sidewalks, trees, and decks.

Grip-Tite recommends a pneumatic demolition hammer for driving the rods; we have one, but sometimes it's easier just to use a sledgehammer, which is fine for most soils. A pair of hex nuts on the threaded rod prevents thread damage while driving it, and a hardened conical tip on the other end breaks through most obstructions without a problem. It's usually just a matter of driving the rod until it appears in the hole outside. Having a second person steady the rod makes it easier to hit, and a spotter on the outside watching the hole prevents us from driving the rod too far — it's tough pulling it back toward the house.

Before installing the washer and nut, we slip a plastic sleeve over the threaded rod (Figure 9). Once all of the ties are in position and hand-tightened, I use a torque wrench to tighten the bolts in 10-pound increments until the wall is back in place or we reach 80 foot-pounds.

Figure 9. A plastic sleeve over the end of the rod (top) prevents the threads from catching on the block instead of transferring the force to the wall anchor. The three bolts are tightened incrementally with a torque wrench (middle) to gradually move the wall back in line without breaking the block. After the bolts are tightened, the soil in the hole outside is compacted (bottom) to prevent water from collecting there and causing frost movement.

We can often bring bulging block walls back in line without any excavation, but it's obviously easier when there's no soil pushing back. So when we have a hole already dug, as on this job, we tighten the wall ties before backfilling. In this case, we were able to almost eliminate the 3-inch bulge in the center of the wall.

Once all the wall ties are tight, we backfill the holes in 6-inch lifts, using a hand tamper to compact the soil.

Cost

One advantage of a Grip-Tite repair is that it generally costs less than other methods. The foundation work on this house cost about $3,000 and was completed over three days. The next-door neighbors, whose home was built at the same time and had a similar problem, spent more than $15,000 having their bulging foundation wall completely rebuilt. Steve Shackett is project foreman and Scott Anderson is president of Tri-State Basement Systems in Berlin, Vt.