When you are designing cinder block projects, the actual size of the block needs to be factored in the planning. Standard unit measurements are 8 inch, but the actual size is 7 5/8, as manufacturers take the masonry used to fix cinder blocks in place into consideration. There are some half blocks on the market, but for most projects, they are unnecessary and end up as waste.
Corner finishing is not really something that needs to be focused on, as both single- and double-corner units have a smooth finish. If you are using cinder blocks around doorways or windows, there are jamb joists, header blocks, and sash units to help provide support or to allow space for surrounding construction with wood materials.
Concrete Footings for Blocks
Placing blocks directly on the ground is not recommended, and all cinder block projects should have a poured concrete base as a footing. If you live in a frost-free zone, you are providing a padding and support for the blocks, but if your project is going to be built in an area where cold is a factor, the concrete base needs to be set below the frost line.
The footing should be at least 8 inches deep and twice as wide as the blocks you are going to use. The general rule of thumb is that your concrete base should be twice as deep as the wall thickness of your cinder blocks and twice as wide as the units.
For 8 inch blocks, this means the footing needs to be 8 inches deep and 16 inches wide to be an effective base. Two by fours are fine for making a mold for the concrete, and if the slab you have to lay down is a large one and will need more than one pouring, you can section things off.
Take electrical wiring, drainage and piping into consideration when you lay your base. You will need to lay a drain line or create a drop to allow run-off to escape, or you may need to create a hole in the concrete base to pass the wiring involved in cinder block projects.
Before mixing up concrete and laying out the tools you will need for the masonry side of things, it is a good idea to do a test run of cinder block projects by building them up dry. The last thing you want is to slap on concrete, finish your project and realize that it is too high, too wide, or in a bad spot.
A dry run will let you see your finished project before it is even started and you can make corrections to the design or change your plans completely. You will also be able to see if you have enough blocks for the project or need to get more. When you do your dry run, allow 3/8 between blocks, as that is the space you will need for masonry.
While You Are Working
Once you have gotten started on your project, here are some quick tips to make sure the job turns out right. Always use a level while you are working on cinder block projects, and use a string and a weight for plumb vertical lines. Spread the mortar at a thickness of about an inch, and extend it enough to work with three to four blocks at a time, but no more. Make a furrow of mortar down the middle of this layer, so that when you place your block, the mortar will squeeze out to the sides and provide a firm hold.
Lay down the foundation row of cinder block projects, and then build the corners up a block or two higher than the base row. Always stagger blocks as you build and check the level of the structure often.
Masonry and Mortar
While you are working, if you need to make corrections, tap your blocks into the right position while the mortar is wet and before it starts to set. Only mix enough mortar that you can use in less than two hours, and if it is a dry day, put a sheet of plastic over the mortar to keep it wet.
Use a trowel to cut away excess mortar from joints as you lay the blocks into place to keep cinderblock projects nice and neat. Once you have built up your structure to the desired height, you can fill in the holes of the exposed cinder blocks with leftover mortar.