Progress Report

This week I worked pretty much exclusively on stacking blocks for the tornado shelter walls. I had a couple of hurdles to overcome; such as how to best join two walls when they meet at a “T” as shown in the first pic. At first I thought I would embed full-sized blocks in the exterior wall on every other course. Every time you do that you have to use a half block to fill the remaining void. Using half block isn’t a problem, but every time you do you create three butt joints adjacent to each other, and I definitely didn’t like that. To me all those butt joints just represent weak points in the wall, so as far as I am concerned, the fewer butt joints the better. With all my thinking and cogitating during the design phase of the block walls, this is something I didn’t realize would happen.

So, here’s where we are. The exterior wall (north wall) will be built normally with no half blocks used in it. That makes the interior wall a free-standing wall, not connected directly (with overlapping block) into the north wall. There needs to be a good, strong way to connect these two walls at the T-joint. Rebar comes to the rescue, especially since I have lots of rebar scraps sitting around. I decided to make rebar “hooks” (pic 2) which fit into notches cut in the tops of blocks (pic 3). These hooks extend down into those block 5” on each side, giving lots of surface area for concrete to grab on too. There will be five rebar hooks used in the T-joint, one every other course of block.

Even though the joint is pretty much built, and half-way concreted I'd still be interested in your other ideas and suggestions.

Bond Beam Basics

Last week I also got started cutting the block for my bond beam. You can buy “bond beam block” already cut to roughly this shape, but those block have solid bottoms, so there would be no way for the vertical rebar to enter the bond beam. So, I had to make my own.

These modified block are pretty easy to make. It just takes two cuts with the diamond blade, a hammer, a chisel (known as a “brick set”) and a little elbow grease. So far I have 16 of them cut (and about 80 more to go). In pic 1, the two yellow lines represent where the horizontal rebar will lay (though I may only use one piece of rebar).

There is one little problem to solve with this home-made block design. See pic 2. I want all of the bond beam block to be filled with concrete. I also want concrete in all the cells that contain the vertical rebar. but no concrete in the adjacent cells that don’t have vertical rebar. So, I have to put something in to block the concrete from falling through and going down into the cells where I don’t want it. I have read about stuffing the tops of those cells with newspaper to block the concrete, but I don’t like that idea. I have also heard about putting window screen material in between the block to act as a dam. I don’t think the screen would be strong enough to hold the concrete while it cured, but I suppose I could make up a test piece and concrete up a test block to see how it works.

I am also considering using thin metal sheets made out of the metal found in “trim rolls” that some siding people use to make metal trim for soffits and around windows and doors. The material has to be thin so it won’t raise the top of the block above my desired elevation. I’m not locked in to this trim roll approach; I’m still open to suggestion. Anybody got any ideas?

The window screen material would probably be a lot cheaper than the metal pieces, as well as being lots easier to cut and handle.

Tornado Shelter Block Layout

I mentioned last post that I had gotten started laying out the block for the tornado shelter. Here is a closeup of that layout. The left side wall I will call the interior wall, the right side the exterior wall. You will notice all the blocks on the interior wall have been cut down to 3.5” height. Add the 4” slab thickness to that and you’re back to the height of the full-sized blocks on the right side (exterior wall).

Cutting down concrete blocks isn’t all that blog-worthy by itself, but how I got them all leveled and to the same elevation is. There is a stringline over the exterior wall that is used to set the correct elevation and location of everything (footers, block walls, floors, etc). I don’t have a stringline over the left side blocks and didn’t want to take the time or effort to rig one up. So, I just took a long, straight piece of galvanized fence pipe (leftover from another project) and put my level on it. It was long enough to reach all the way across from one wall to the other. I figured I would prop up the end of the pipe with wood blocks until it was level, then use that block height to measure and cut my blocks. I had a 2x4 piece close by, so I tried that first. When I put the pipe and level on top of the 2x4, low and behold, it was perfectly level. I am never this lucky on the first attempt, so something has to be wrong. So, to be sure, I took it all apart and put it back together again. Checking it again yielded the same result. So I cut the concrete block to 3.5” height and moved on to the next one. In the end, all five blocks were cut to this height.

These block I didn’t actually mortar to the floor because, 1.) they were already level (on top) and to the exact height desired and 2.) each block has a piece of vertical rebar in it. When concreted in place, the rebar won’t let them move. In the first block in the pic I stuffed some mortar to kind of hold it in place.

It was only after getting them all layed down that I finally realized why the 2x4 worked as the exact height needed. At first I reasoned that the 4” slab thickness plus the 3.5” block height added up to 7.5”. But full sized concrete blocks are 7-5/8” tall, so somewhere I’m off by 1/8”. But, then I realized none of the full sized blocks on the exterior wall were in fact full sized. They had all had at least an inch cut off them because of irregularities in the surface of the concrete footer. So now, mathematically nothing adds up right or makes any sense. But, in the end, the tops of the blocks are level and to the desired elevation so I’m going to stop worrying about it and leave it up to you, the reader to figure out. As before, you got any ideas, I’m all ears.

P.S. The first diamond blade is about used up. I probably made a hundred cuts with it, but I’m not believing the 200x printed on the side of the blade means it will last 200 times longer than a regular masonry blade. I bought a new Skil brand diamond blade at Walmart for $14. It only says 50x, so we will see how long it lasts.

P.S.2. The two cut down block in the front of the pic haven’t been leveled yet, but that’s where they will go eventually. There are no blocks placed yet which will make up the back wall. That’s next.