| Self - Help construction of 1-story buildings |
|Directions for construction|
|Construction of the foundation walls|
|Block foundation walls|
When the footing has been poured and has cured for about a-week, and the blocks have been made, construction of the foundation wall can begin. All block foundation walls, whether concrete, sand-cement, or stabilized earth, are laid the same way.
First, stack a number of blocks at intervals along each wall line so that a supply is always at hand.
Next, lay out the planned number of blocks for the first row (course) on or alongside the footing and check to see how well they fit the length of the wall. Very small adjustments in the length of a wall (under 7.5cm over the length of the whole wall) may be made by increasing the size of mortar joints between every 5th or 6th block. For example, if 8 joints are made 1cm instead of ½cm the wall length will be increased 4cm without cutting any blocks.
To give the wall strength, the courses (rows of blocks) must be staggered so that the bond between any two blocks rests over the middle of the block beneath them.
To stagger the courses, turn one corner block on the first course so its "head" faces out. Then, on the next course, turn the block at the opposite corner head out. Continue alternating between courses in this way.
To ensure that the blocks are laid in a straight line, run a string from corner to corner along each wall. For outside walls, attach the string to the batter boards; for inside walls, attach it to a nail hammered between two courses of blocks.
If the string sags, as it is likely to do over a distance, support it with a piece of paper that is weighted with a small rock.
Use the string as a guide, laying each block up to but not touching the line. The string can be moved up later for each new course of blocks.
Once the string is in place for the first course, you are ready to prepare the mortar.
The recommended mix for mortar to lay blocks is 1:3, 1 part cement to 3 parts sand. Mix these ingredients with each other and with water as concrete is mixed (see page 132).
During the dry season, it helps to sprinkle the blocks with water before they are laid in mortar. This prevents them from absorbing too much water from the mortar.
To lay the first course of blocks, use a trowel to spread out a full bed of mortar about 1.25cm thick on the footing. To prevent the mortar from drying out before blocks are laid in it, spread only enough for 4 or 5 blocks at a time.
Using the batter board lines as guides, position the first block the corner block - very carefully: an error here will cause problems that are hard to correct.
When the corner block is positioned, tap it down firmly - do not pound until it is solidly bedded in the mortar.
Butter the ends of each new block to bond the vertical joints between blocks. Press each new block against the previous one until a solid mortar joint about 15cm wide is formed.
Keep trowelling of the bed to a minimum: it will draw water out of the mortar mix, weakening the bonds.
Any excess mortar that squeezes out between blocks should be scraped off. It can be re-used if it has not dried out. Once mortar dries out it must be discarded.
After every 3 or 4 blocks are laid, check the course with a level. If it is not level, remove the blocks, add mortar, and lay them again.
Once the entire first course of blocks is down, build up the corners at least 4 or 5 courses up, or all the way to the top. This will give you something to attach the guide string to for the upper courses.
Use a story pole to check the height of each course, and to check that all corners are going up evenly.