Excavation, Foundation and Good Concrete

If there is no basement, the excavation will be rather simple and not too difficult. If

you are in an area where there is no really cold, freezing weather, the foundation

may not need to go down more than a foot into the original undisturbed earth, of

a width sufficient to carry safely the weight of the building without settlement. The

width of the footing under the wall must never be less than 12". Local building

regulations, available upon request at the place where building permits are issued,

will usually give information as to the required width and depth of foundations.

In locations where the ground freezes the foundation must extend below the depth

to which frost penetrates; otherwise, the frost will lift the foundation unevenly,

destroying the usefulness of the building.

In some localities special foundation problems are encountered, in which case the

builder must get a person experienced in foundation work in that region to design

and help with the foundation. Don't take chances with a foundation; if you do

not have an adequate foundation, you will never have much of a house, no

matter how carefully you do the rest of the work. Much information can be

gained by seeing what others are doing in your neighborhood and talking the

problems over with them.

Photo owned by Kgwo

If you must build on earth that has been filled-in within the last twenty years, be

sure your foundation goes clear through the fill to the original undisturbed earth.

Excavation for footings can usually be done quickly by hand, but if there is a

great deal of digging to do, many people would rather see it done with a

bulldozer or some other mechanical equipment.

If you are building on a piece of land that is not level, the bottom of the

foundation must be kept level. Otherwise, it might slide down the hill when heavy

rains come and the ground gets slick. The excavation can be made with steps, so the

uphill end will not be too deep.

To indicate the top of the concrete when pouring in a trench as for a footing,

drive small stakes at intervals of three or four feet in the bottom of the trench and

let the top of the stake indicate the top of the concrete. Then fill the trench

until the concrete reaches the top of the stakes, after which you smooth it off.

Although the stakes should do no harm if left in place, if you wish, you can easily

pull them out if you do it while the concrete is still soft. These stakes need not be

larger than 3/4" in size to serve their purpose.

To smooth the top of the concrete a float can easily be made which is cheaper

than a trowel and often more effective and easier to use. Take a length of board

about 1/2" thick and 4" or 5" wide and 18" long; make a handle of a small

board 11/2" wide and 8" long and support it above the back of the board by

using two short blocks. Nail together. A more elaborate handle can be cut from

a piece of pine 2" x 4" as shown, if desired.

Foundations and Concrete Forms

Forms for footings are usually just dug into the earth. For a shallow foundation, you

can dig carefully and let the earth serve for the forms of the footing. You can then

Photo owned by Khaosaming

build your forms or a wall of blocks on the footing you have poured in the trench.

The forms for the foundation can be made of lumber that you will use later in the

building. Try to use lumber that you will not want to cut, as the cement clings to

the lumber and will dull your saw. Do not use the sub-floor lumber for forms; it is

too hard to get them clean enough for a satisfactory sub-floor. Use the studding for

uprights, the roof boards for the face of the forms, and the joists for strong-backs

and bracing, and possibly for the face of the forms for the outside of the wall.

If the wall is not more than 2' or so high, you can usually drive stakes to hold the

bottom of the forms in line, and you can tie across the top with wire, or you can nail

1" x 3" strips across the top above the concrete to hold the forms together.

If the forms are to be high, as for basement walls, you will need to make them

very strong and secure. The forms, which are built only to hold the concrete until

it has "set," should always be thought of as temporary in nature. They must be

accurate, as the concrete will take the shape the forms permit. They must be well

braced, and a person should think of the direction the pressure will take as the

concrete is poured into the forms and build them to withstand that pressure. The

pressure will depend largely on the height of concrete placed at one time. If you

pour a foot or so and let that "set" a half hour or more before more is placed on

top of it, the forms do not have to be nearly as strong as if several feet are poured at

one time in one place. Rapid pouring does make a better job, however, than having

too much time elapse between successive layers.

If the earth will stand without danger of caving, you can often use it for the outside

forms. If, however, you want to waterproof the outside of the basement after it is

poured, have the bulldozer excavate two or three feet larger all around than the

basement is to be. Then dig trenches for the footings. Pour the footings and use

them as a platform on which to build the forms for the walls. Build the outside

forms first, get them square and plumb, and well braced; then build the inside

forms. The two will be tied together with wire, or with special bolts, or ties which

you can often rent for the job and return after the job is finished.

The uprights for the forms will consist of 2"x4"s placed at not more than 2'

intervals; the lining of the forms can be heavy plywood, 5/8" thick or heavier, or it

can be 3/4" shiplap, or other common lumber. The horizontal pieces that are

placed back of the upright 2" x 4"s are called wales; they are composed of two

pieces of 2" x 4" or 2" x 6" with bolts between them, spaced at 2' intervals. These are

the pieces that hold the wall straight and to which the braces are often fastened.

Forms should be built with the idea of ease of removal in mind as well as for

sturdiness.

Piers under the house where there is no basement can be precast or they can easily

be made of concrete, right in place. Dig a hole down to solid earth about 2'

square; pour 8" of concrete in the hole; then place a form on this concrete and fill

it up to a point at least 8" above the ground. Then take a piece of redwood 6" x 8"

into which you have partially driven five or six I6d spikes, and place it on the top

of the pier with the heads of the spikes down in the concrete. When the concrete

has set, this piece will be permanently fastened in place, and you can place the sill

on it, or a short post under the sill if necessary to bring the sill to the right

height.

A quick way to make the form for the pier is to shape a cylinder 10" in diameter

from a piece of tough roofing felt, using two 8d nails to pin it together at the

seam. One man can hold this in place while another fills it by shoveling concrete

into it. When it is full and the redwood block placed on top of it, no further

attention is necessary, and the paper does not have to be removed, unless you

wish to do so.

Or you can get large hollow concrete blocks and place them on the 8" of poured

concrete with good results. Then fill the cells with concrete and fasten a wood

block on the concrete blocks with bolts or nails.

To indicate the level of the top of the concrete in the forms, it is a good idea to

make the forms come exactly to the top on the outside, whereas the inside forms

will be higher to avoid pouring the concrete over the wall. But if it is inconvenient

to make the top of the forms the right height, drive finish nails at four-foot

intervals, letting them project into the forms 3/4" or so along the line of the top of

the concrete. Then when you pour the concrete these nails will indicate how high

to fill the forms, and when you smooth the top of the wall, you can find these

nails and get the top exactly right.

Do not forget to put the 1/2" bolts at 6' intervals in the top of the wall,

projecting up enough to go through the mud sill.

After the concrete is placed and finished, wait a few hours and then sprinkle it

frequently and keep it wet for several days to be sure it will set properly.

Concrete must not be permitted to dry out before it has "set" thoroughly, which

is about two weeks after it is poured. Keep it wet for at least a week, anyway;

longer is better. It is theoretically not set for 28 days, but a shorter curing period

seems satisfactory for house floors, especially in warm or hot weather. Concrete sets

much faster in hot weather. In cool weather, when the temperature, is near freezing,

the set is very slow. Concrete must never be allowed to freeze, until it has been

cured for at least a week or two.

If you must pour your foundation or slab in freezing weather, you should heat

the gravel and sand, and perhaps the water before mixing. Then place it

immediately, covering with straw or earth, or other insulating material to prevent

freezing for several days. In large buildings they cover with canvas and heat the

space under the canvas to keep the building warm until the concrete has set. It is

simpler to do other work and let the concrete pouring wait for good weather.

Concrete does the best in the spring when the weather is cool and the humidity is

high, but can of course be poured any time of the year.

Foundation Walls

If the foundation is not to be more than two or three feet high, considerable time

and effort can be saved by making the walls of concrete blocks.

Pour the footing in the usual way in a trench, taking special care to see that it is

level. Stretch the strings again to find the corners of the building. Take the level

or a plumb bob and locate the exact corners of the building on the concrete

foundation. Then strike chalk lines showing the exact outlines of the building on the

footing.

To chalk a line, hold the chalk in the right hand, round side in the palm of the hand,

pass the line over the flat side of the chalk and hold it in contact with the chalk

with the right thumb. Fasten the line at one end. Hold the line with the left hand.

As you back up from the place where the line is fastened, draw the line over the

chalk, holding it in contact with the chalk with the right thumb. Rotate the chalk

with the fingers of the right hand so a groove will not be worn in the chalk by the

line. When you have reached the place where the chalk line is to end, hold the line

down on the surface with the left hand and stretch it tightly. Lift the line with the

right hand reaching out as far as you can from the place where the left hand is

holding the line in contact with the surface and drop the line suddenly. When the

line strikes the surface, it will make a uniform straight chalk line on the surface.

Do not try to strike the line more than once at any one place. Always put chalk

on the line again before attempting to strike another line.

If the footing was poured level, it will be much easier to start the block work. Place a

block at each corner of the building, bedding it in about 1/2" of mortar; then stretch

a line tightly between the two corners even with the top of the blocks. Lay the

blocks with 1/2" to 5/8" joints between them, and put them right up to the line,

taking care that the line is not pushed out of place. Keep the outside of the

blocks plumb and the tops of the blocks level.

For laying blocks use a mortar composed of one part cement to three parts sand,

plus a little lime or fire clay. Mix the mortar to an easy working consistency, wet the

blocks, and begin work. If the mortar is too thin, it will be easily squeezed out of

place, and if it is too thick, you will have difficulty in getting the blocks to bed down

properly into it. A little experimenting will indicate the proper consistency for the

mortar.

Take care to keep the wall plumb; laying up the corner plumb and stretching the

lines tightly should assure a plumb wall.

About two hours after the blocks have been laid the joints should be pointed up

with a small trowel or other tool to give them a neat appearance.

When the foundation has reached the desired height, place anchor bolts at 6'

centers along the foundation wall, filling the appropriate holes with concrete or

mortar to hold the bolts in place. These anchor bolts are 1/2" in diameter and

should be about 10" long. Be sure they extend up far enough to come through

the 2" x 6" plate and leave room enough for the nut, but not so far that the nut

will not tighten down.

Reinforcing is not usually considered necessary if the wall is less than 4' high.

Walls higher than this are better built of concrete, or the blocks can be reinforced

with 1/2" iron rods spaced at 2' intervals around the wall, with a bond beam at the

top reinforced with four 1/2" or two 5/8" reinforcing iron rods.

How to Make Good Concrete

Even if you live where ready-mix is available, you may wish to know how to make

good concrete, and if ready-mix is not available, you must learn how.

Select good clean gravel or crushed stone. If the largest stones are not much larger

than 1" in diameter and are well graded from fine to coarse, you have a fine start

toward good concrete. A few larger stones will do no harm. The most important

single ingredient that determines the quality of concrete is the sand. Sand must

be clean and free from organic matter. This is a must. The grains should be sharp,

not ocean sand that has been rolled until the grains are almost round.

Cement as you buy it from the dealers in the United States is almost certain to be

good, unless it has been on hand so long that it has become lumpy, or has been

wet and is partially hardened. If it is fine like flour and free from lumps, you can

use it with confidence.

The best proportions for good concrete are to use one part cement, two and one-

half parts sand, and three and one-half parts gravel. If you find natural river gravel

and sand already mixed by nature, and it is clean, use it with one part cement to

six parts sand and gravel.

Water for concrete work should be clean; the water that comes out of the faucet,

suitable for domestic use, should be all right.

The mixing and placing has an effect on the quality of any concrete job equal to

that of the quality of the ingredients.

Good concrete is not hard to make if you are willing to follow a few simple rules.

Select good clean gravel for the large aggregate. Ordinary river gravel is good if it

is clean; if it is not clean, wash it with a hose, letting the water strike the gravel with

considerable force. Arrange it so the water can run away from the rocks after they

are washed. Avoid rocks that are active chemically, and avoid ores, quartz, sandstone,

and mica-bearing rocks; just ordinary hard rocks are the best.

The quality of the sand has a much larger bearing on the quality of the concrete

than the gravel. Sand is more liable to carry dirt in varied forms. Avoid sand that

contains clay or organic matter. Sand should be well graded from fine to coarse and

should contain some very fine particles, but these must not be clay.

Here are two simple tests for sand.

Fill a clear glass bottle about half full of sand and add enough water to

almost fill the bottle. Shake it well, let it stand a few hours, and observe the

layers of sand. The coarse particles will be on the bottom with fine particles

above. The line at the top consisting of very fine particles should not be

much more than one-eighth inch thick. A little salt added to the water will

hasten the settling process and clear up the water much sooner. The water

should not look muddy after a few hours of standing.

Below the top layer there should be a gradual increase in the size of the

particles, until the large grains at the bottom are reached. It is important

that the sand should not nearly all be of the same sized grains, but it should

be well graded from fine to coarse.

To test for organic matter, fill a bottle two thirds full of sand, add a bit of

caustic soda, calcium hydroxide, or lye, and fill with water. Shake well and

let stand overnight; if the water is clear the next day the sand is free from

deleterious quantities of organic matter. If the water is dark brown or red,

do not use the sand. A slight tinge of pink will probably do no harm.

The amount of water put into concrete is a matter of importance. The less water

you use, if you still get a good workable mixture, the better. Concrete should not

be so thin that it will run like gruel, and it should not be so stiff that it stands up

dry. It must not be so dry that it cannot be spaded into place, but it should not be

so wet that it will run ten feet down the form when poured in at one place. Don't

make it too soupy. When first put into a wheelbarrow it should not flatten out

completely, but after you have wheeled it forty feet, it should be smooth on top. If

it will smooth out under a pat of your hand, it is about right.

For the very best concrete do not use more than seven and one-half gallons of

water to one sack of cement; a little less water is better, provided you can get a

workable mixture. The strongest concrete has been made with about five gallons

of water to the sack, but this requires mechanical vibrators and other means of

compacting the concrete, not available to the average builder.

If you can make a mix that you can get to fill the forms without leaving voids,

using only six gallons of water to the sack of cement, you will have better concrete.

Even if it takes more spading and working to get it into place, it will be stronger

and more waterproof. Perhaps seven gallons per sack is about the best that

most people can do. If the mixture is so dry that you can't get it properly into

place, you will get a poor job. It is a rather narrow channel that you have to

navigate: too much water, weak porous concrete; too little water, honeycombed and

porous concrete; just the right amount of water, the aggregates being good and in

the right proportion, perfect concrete.

A certain limited amount of water is necessary in the setting of concrete. This water

enters into chemical composition with the concrete, becoming a permanent part of

it. Since excess water, beyond that which is needed in the chemistry of the

concrete, must evaporate, leaving minute pores where it was, concrete that has

been mixed with too much water is inclined to be porous. Of course, this

porosity leaves the concrete less strong than it would be if more compact. Where

water has dried out, it can go back in if given the opportunity.

Photo owned by Sarang

Concrete must be mixed thoroughly, and although it can be done by hand in

emergencies, a machine will do the job a lot easier and generally much better. If

you have to mix it by hand, mix it thoroughly about three times dry. Then add

water and mix it through twice. It should then be in good condition. If you are

mixing by machine, let the machine run at least one full minute after all the in-

gredients are in the machine. Letting it run two or three minutes will result in

better and more workable concrete. The extra mixing will help you to get more

benefit out of the cement you use as well as resulting in a denser and more

waterproof concrete.

Photo owned by Hohum

After the concrete is in place in the forms, do not let it dry out for two weeks. It can

be kept wet by frequent sprinkling, or by covering it with wet sawdust or burlap.

There are also waterproof materials that can be sprayed on the fresh concrete to

form a membrane to keep the water from evaporating out of the fresh concrete. At

any rate, some means must be found for keeping it wet for several days, if you want

good concrete.

To make a good job, concrete should be encouraged into place in the forms, by

spading or working with some tool to get it to fill all the corners, leaving no void

places, and no places that look honeycombed when you remove the forms. A tool

made by straightening a hoe, so the blade is parallel with the handle, makes a

good tool for spading concrete into place. Spade next to the outsides of the wall

that is near the forms, and the center will take care of itself. Thorough spading is

important to a good job.

Do not try to pound concrete into place with a blunt stick, but rather slice or

spade near the forms on each side. Often tapping the outsides of the forms with a

sledge hammer, not too violently, just gently and firmly, will result in much better

compaction of the concrete. You can be proud of a good concrete job, as many

people have trouble with their concrete, and it is a relatively simple matter to get

a good job, if you are careful and observe these few precautions.

Do not forget to put the bolts in the top of the wall while the concrete is still soft.

They are usually spaced from four to six feet apart, and additional ones are

added at the corners and at the sides of doors or at other places where there

might be a loose end.

As far as possible, the concrete should all be poured in one day. If it is necessary to

join new concrete to that which has already set, or to join new concrete to old,

thoroughly clean the old concrete, and rough it up if possible, make a thin paste of

cement and water and brush it on the old concrete to make a thin coating over the

entire area; work this paste thoroughly into the surface with an old broom or

suitable brush, then immediately pour the new concrete while the paste is still

wet. This should bond the new concrete to the old.

Concrete is the universally accepted material for foundations. Formerly large stones

were used. If you have them on the property, they may still be used if you take care

to bed them properly into the ground; or they may be used in combination with

the concrete.

When ready-mixed concrete is available it is often much better than trying to mix

your own, and as cheap if labor is considered to be worth anything. By the time

you buy the cement, sand and gravel, and do the mixing you have had a lot of

trouble and mess for nothing. Use ready-mixed concrete if you can get it.

Ordinarily the grade known as 2,000 lb. concrete is good enough for ordinary work.

For floors that are to be troweled without an additional finish coat, it would be

better to get a mixture containing five sacks per cubic yard. This latter mixture

would also be preferred for reinforced concrete work.

The pressure on a container can easily be calculated by the following simple formula:

pressure per square foot at a distance h below the surface is equal to the

weight of the liquid per cubic foot, 150 lbs.

for concrete times the h distance below the surface. At 7 ft. this would be

1050 lbs. per square foot at the bottom of the wall.

To get the total pressure on a wall use this formula:

2

2LwhP

which for a wall 7 ft. high and 20 ft. long would give 150 x 7 x 7 x 20=

73,500 lbs.

pressure against the forms on a section of wall only 20 ft. long. This is

somewhat reduced by the fact that concrete is not exactly a liquid. That is

why it is almost impossible to brace a wall enough to hold it in line. You

must have some ties through the wall, either wires or bolts, or other metal

ties.

Of course if you do not pour more than a section a foot high at a time, going

around and around, letting the previous pour set slightly before you pour more

concrete on top of it, the pressure is greatly lessened. If your form starts to give a

bit, move on to another section and pour in other places until the concrete at the

weak place sets up a little. Then you can safely pour the rest of the concrete.

Build your forms as strong as you can. It is very embarrassing to have your forms

give and let the concrete bulge in the wrong places, or run out on the ground,

and it is hard to repair once things have given way.

Pouring the Slab for a House

The simplest way to build a house is to build it on a concrete slab. Dig a trench

around the outside of the house, making the overall dimensions of the trench

measuring from the outside the same as the house, and extend it at least one foot

into the solid undisturbed earth, and more if necessary. The trench must be at least

one foot wide. Set up forms of 2" lumber exactly on the lines of the outside walls

of the house, and to the exact level of the floor. These forms should coincide with

the outside wall of the trench just dug. Then stretch strings over the area of the

house and fill with sand to a point just 4" below the tops of the forms. This will

leave room for a 4" floor. Be sure the sand is well compacted by sprinkling with

water. Dig trenches 12" deep and 12" wide for the bearing partitions. Waterproof

the entire area with a large sheet of plastic waterproofing membrane, or with roofing

paper, or in some satisfactory manner, and then you are ready to pour the concrete

floor. You may need to put a straight 2" x 4" across the house to help in keeping

the floor level.

Pour the foundations up to a point about 4" from the top of the floor first, then

begin and pour the floor from one wall to your straight edge called a screed, and

rod off the top with a long straight 2" x 6", going over it several times with the

straight edge until it is level, and proceed over the entire area. Then you are

ready to start finishing.

Take the float you have made and rub hard on the surface to work it down.

Follow immediately with the steel trowel, trying to get it as smooth as you can.

Work rapidly, not letting the concrete get too hard, as it becomes more difficult to

work as it gets harder. You can do more with concrete during the first half-hour

after it is poured than you can ever do later. What you do not do within two or

three hours, you will never do. Don't forget the bolts for the outside walls.

The surface should be level and smooth for the application of floor coverings later.

If you plan to put ceramic tile on the floors in certain places, leave these places 2"

lower by surrounding them with 2" x 4"s laid flat. You do not need to finish or

worry about the level of the parts to be tiled later.

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