How To Fix an Undulating Wall Foundation




How to fix the problem?

From the beginning, it was clear the concrete blocks forming the perimeter foundation of our do it yourself earthbag wall home…were anything but level. When you’re starting from scratch with nothing but a contractor’s front end loader for a homesite leveling device on land like that in the above photo, you make allowances. You especially make allowances when the trenches containing septic and water piping have yet to be filled in with a number two shovel.

However, I figured it wouldn’t be all that difficult to even things out at the proper time by rigging a level wall atop an anything-but-level line of blocks. Today turned out to be the “proper time”. I was right. The task was pretty straightforward.

Though it did require several hours to rig the first twenty-foot two-by-four sill board properly. Thankfully, this first section is by far the worst; the rest of the perimeter should be a piece of cake, a portion of pastry, a….

Well, it will if I can keep Murphy distracted. (For the confused reader, that’s a reference to Murphy’s Law.)

The front (eastern) half of the house had all of the roof trusses but one installed. The back (western) half would require that sill board to be in place for a number of reasons.

The front (east side) of the house under construction.

The front (east side) of the house under construction.

Masonry Nails And A Twelve Inch Spike

The first step after putting a long (20 foot) two-by-four where it needed to be along the tops of the concrete blocks (as the first portion of a wall that will later receive R-11 insulation) was to tack it firmly in place at the two spots where it actually touched the blocks. Every other spot had a gap between block and board. These gaps were then filled here and there–so that the sill board had plenty of support points–using a combination of short board pieces (horizontal) and super-short board pieces (vertical).

Although a tad time-consuming, this procedure worked extremely well…except where the gap went beyond reason to “humongous”. Now we had a problem:

1. Where the gap was widest, the longest masonry nail I had…couldn’t even reach the block, let alone sink into the concrete far enough to provide significant resistance to lateral movement.

2. Naturally (assuming Murphy’s Law to be natural), that was exactly where several feet of earthbag wall bulged inward due to an error I’d made one night while finishing a shift by flashlight. More than anywhere else on the entire perimeter, that precise location had to be firmly anchored.


After pondering the best laid plans of mice and men for a while, I decided to drill a 3/8″ hole down through the wood…and as far as possible through the concrete block itself. A twelve inch spike would then be tapped down through the hole and into the underlying earth. This would have been an absolutely brilliant solution…except….

The drilling went really well as far as it went, but it did not go far enough. Could not go far enough. Even with the masonry bit barely held by the drill chuck at all, reaching for every possible millimeter of length, the bit was still not long enough to reach down through all that wood and all that concrete at the same time. It came up short by about half an inch.

Okay. Nothing for it. I wasn’t about to lose the better part of a day by running to town in a likely futile attempt to find a longer masonry bit. It could only be hoped that when that bottom half inch of masonry broke to the pressure of the spike, it would break a chunk downward, leaving the outside edges of the block intact and all that.

Yeah, right.

However, the obviously cracked-open portion held position fairly well. Tugging firmly on the sill board didn’t produce any movement. Murphy or no Murphy, this was a result we could live with.

Although it did take three hours of steady work to install just one board. If every chunk of lumber required that sort of attention, the house would be ready for occupancy in or around the year 3032….

Note: Several years after the home was initially constructed–in fact, during the construction of a front porch addition in 2013–I finally learned how best to deal with nailing wood to concrete. There’s no need to use either masonry nails or oversized spikes. Instead, you drill a hole that will take two regular nails at one time and hammer them down in there, side by side. I used a 5/16″ bit and 10d nails. As it turns out, this is an old contractor’s trick. There’s very little stress on the concrete this way, yet the resulting bond (wood to concrete) is powerful. You won’t separate the two with anything short of a crowbar.

I used spikes that were far larger than needed; a 16d would have reached down into the concrete block just fine.

I used spikes that were far larger than needed; a 16d would have reached down into the concrete block just fine.

It took 3 hours to get this worst "dip" securely level--but it was worth it.  The house is now 3 1/2 years old with no discernible sag.

It took 3 hours to get this worst “dip” securely level–but it was worth it. The house is now 3 1/2 years old with no discernible sag.

Question: Now that we’ve lived in the completed building for several years, would I do it the same way the next time?

Answer: Yes, except of course we’d put in somewhat smaller spikes and do it the easier way as described in the above Note. This place is really solid. It’s shifted a bit, settled some, as all new homes do–but within acceptable limits, and no complaints.

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