Tom Ramcigam (magicmarmot) wrote,
Tom Ramcigam
magicmarmot

Masonry blather


So yesterday I got some concrete block at Menards. Just a few, as I'm starting off with doing the side walls on the front of the house, which are something like 21 inches wide each. And I'm doing these with the 4-inch thick blocks instead of the normal 8-inch blocks that will go on the rest of the porch.
The first thing that I have to do is to repair the footings. That is what the 80-lb bags of cement are for. Despite being well underground, the old footings managed to absorb some water and go through some freeze-thaw cycles so they are spalling (flaking off concrete in chunks). I got lumber to create the forms for what I need, which should be fairly easy (if a bit tedious).
The other pain in the ass is that I have to cut concrete in a couple of places. First, the location that the blocks will be placed butts up against some of the old undamaged foundation brick. Since all that was removed was the damaged stuff, there is a really jagged edge that neads to be cut off and cleaned up. It doesn't have to be perfectly plumb, but the closer the better.
Second, the blocks themselves will have to be cut. You see, a sixteen-inch concrete block is just under 16" long-- the extra is designed to be taken up in the seam-- and I have a 21-inch space to fill. Two blocks are too long, one block isn't enough. And as you might suspect, you don't cut concrete with a hand saw. In this case, I splurged and bought a cut-off saw and some masonry blades.
Honestly, I already have a cut-off saw with a metal blade installed, but since I'll also be cutting rebar, it's a mondo time-saver to not have to keep swapping blades on one saw. Besides, the masonry saw needs to cut wet and the metal saw dry.
I don't know how long it will take to cut through a 4" solid concrete block. I guess I'll find out.

Something that ocurred to me as I was doing some reading on concrete block construction is alternative ways of laying the brickwork and building the walls.

For instance, here is a picture of a pretty standard concrete block:


You notice the holes in it. Aside from issues of weight, when you build a wall and stagger the blocks like so



The holes line up. This is of course intentional, but it is also comes in handy for filling the holes with things like gravel, perlite (for insulation), rebar, or other stuff like mortar.

Normally you lay down a course of the block on a bed of mortar, then do the next course on mortar and so on and so on until you have built up your wall. The downside of this is that you can't make any mistakes, and you have to make sure that your walls are level and plumb as you go.
The other concept is to dry-stack the blocks, and use a fiber cement on the outside to hold the whole structure together. This isn't really good for foundation walls because it lacks lateral strength, but it's easy, and you can line up the blocks ahead of time.

My thought was to do the same dry-stacking technique, but after the outer parging coat was on, to add rebar and pour cement into the cavities of the blocks. That would then make a series of reinforced "posts" in a monolithic wall, which should then be incredibly solid.

Interestingly enough, after investigating a bit further, it turns out that there is a company (DAC-ART) that makes buildings with specially-formed concrete blocks in exactly this way-- everything is dry-stacked, rebar is added, and cement is poured. Their blocks are specially engineered, but the idea is the same.

I are smart.

The other thing to consider is whether to get a cement mixer. While I can rent a small one, I can actually buy one for about two days worth of rental, and considering how much concrete work I need to do around the house what with the porch and sidewalks and garage/deck, it might be a worthwhile investment.
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