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Root Cellar Part 3: Walls

Updated: Oct 19, 2023

Welcome to our third installment on “How to Build a Root Cellar”. We are now moving on to building the walls and are getting a true feel for the space this building will give us for our family’s food storage. While cinderblocks may look like Legos there is far more involved in placing them than you would think.

Root Cellar Walls

First, we placed our cinderblocks (bricks) where we wanted our walls to go.

position blocks

Then, we drilled a 2-inch hole in every other cell space and any wall ends or corners. These holes made it so we could connect the walls to the floor with rebar which will give our building greater stability. After drilling the holes, blew them out and then used a shop vac to clear any debris.

drill holes

We waited to put the rebar in until after our third row of bricks but we had it all prepared for them.

third row

The first row of bricks is very important to get straight and level as all the above rows will be impacted by it. We used a level and a line to help with this. We actually had a level that hung on the line as well to let us know if that was level.

line level

The entire wall project was about measuring, leveling, and adjusting. We found it was best to place the corner bricks first and then run the line between them. If we placed a second brick next to it before running the line the corner brick was less likely to move when we pulled the line taut.

We picked up these great little blocks that we just wrapped with the line and they went on the bricks well.

corner line holder

We also regularly measured the distance/levelness of our walls, the distance/levelness wall to wall.

measure regularly

Mixing the type “S” mortar was a little more difficult than we thought it would be. Primarily because it was such a weird texture. We had to do a lot of research to find out how it should look. Eventually, we were able to get it figured out but it really does look more like kinetic sand than any kind of an adhesive.

mix mortar

When mortaring in the bricks we would place mortar under the perimeter of where the brick was going to be placed. We placed mortar not only under the bricks but between them as well. This required that we stand the brick up on its end and put a strip at the front and back edge before placing it. We had to be careful when we placed it as it was easy to knock off the side mortar unintentionally. If that happened we would have to work mortar into the crack and that is much more difficult.

apply mortar to where brick will be and the side of the brick

We would usually work one side at a time. By the time we were done with a side, the mortar was dry enough for me to knock down any excess and shape it in the seams with a small indent. I liked to use my gloved fingers for this. There are tools for it but I found I had more control with just the gloves. (Note: I did go through 3 right-hand leather gloves this way.) Some people come back and knock down the mortar after it is all dry but I liked working with it better when it was still a little wet.

For each row of bricks, we staggered them which of course reduces weak points. I did want to point out that cinderblocks have an up/downside. The “top” has a thicker middle section. For the ends near the doorway, we used some half bricks every other row to accommodate the staggering. We found it was better to just buy these than to cut the ones we had because the cut ones were pretty fragile and we wanted to have it as sound as possible in the doorway area.

After completing our first 3 rows, we used epoxy to glue #3 rebar (cut to 5 feet long) into our predrilled holes. With the rebar glued in place, it was now time to fill the cells with concrete. We mixed it slightly wetter than normal and filled the cells to the top.

use cement mixer

After each batch of concrete, we used a concrete vibrator to shift the bubbles out and fill in all the cracks and crevices with the still-wet concrete. After the vibrating, it usually settled around halfway down the cell which is where we wanted it so the bricks would tie in well with the next application of concrete. We used a lot of different delivery methods for the concrete. When the walls were low my favorite was to use an old rain gutter and direct it in the cells but as it got higher I preferred to use small buckets. We tried to keep the edge clean of concrete so it didn’t get in the way of the mortar later. Sometimes, when we used the vibrator, we would get a small leak through thin sections of mortar. We found that a little bit of back pressure helped with that and it dried quickly so we would watch for any leaks and knock it down quickly.

use cement vibrator

With the bottom three rows cemented in, we felt much more comfortable with the stability of our walls. Our next step was to add a horizontal layer of rebar and tie it into the vertical bars with rebar ties. Anything that helps distribute weight more evenly across the structure increases the strength of it.

connect horizontal rebar

Because of the horizontal bar, this next layer of brick needs to be tunneled.

tunneled layer

We ended up buying some and making others. Either worked fine. They were the same price but we had extra of the regular bricks so we used them sometimes to avoid a trip to the store. The only tricky pieces were the corners because you had to keep straight where all the holes were needed.

The tunneled level was considered row one of this set and then we did two more regular rows. We repeated this all the way up to row 12. So we ended up with tunneled bricks on rows 4, 7, and 10. The other nice thing about the tunneled rows is that it allowed the concrete to flow through horizontally as well.

cut for tunneling

When the rows got near the end of the vertical rebar we used the ties to attach another piece of 5-foot rebar to it. Usually, there was about a foot of overlap.

Root Cellar Walls – connect vertical rebar

After our walls were constructed, we painted the outside with black tar paint and the inside with white waterproof cement paint. Both required two coats but that wasn’t unexpected. The hardest part about this was painting the outside below the ground portion, as we made it so close to the dirt wall.

tar paint

White waterproof concrete paint for the interior

After painting, we were able to backfill the dirt around the wall. We used gravel for the layer directly against the wall to increase drainage. We are in an arid area but if we had to worry about too much water we would have put in a french drain around the bottom of the walls.

back fill

The last step for this stage was installing the door frame. We knew the opening that we needed and it allowed for about 9 inches on each side of the door. This made it much easier to install lighting later. We just made sure we used good insulation to maintain our temperature.

interior view

It was a little harder working with concrete because all the tools are a little different than working with wood. When we attached the door frame to the building, first we had to drill a hole with a masonry bit and then use a screw anchor specific for concrete. It worked amazingly well though.

drill holes

hammer screw into hole

use wrench to open inside hole

The last step was to add the plywood and we now had a four-sided structure that just wanted a roof.

add plywood

We were really nervous about doing the roof and did all kinds of research but I’ll have to tell you about that in our next post.

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