Monolithic Concrete Foundation Footing Floors
How To Do a Concrete Monolithic Floor and Foundation
“Build your castle in the air . . .
but put a good foundation under it first.”
Monolithic Definition: “Having a massive uniform structure that does not permit individual variations”, according to, Funk & Wagnall’s Standard Dictionary.
With proper reinforcement this is my foundation of choice for cost, speed and structure. It is also the easiest to convey. When the concrete is poured all together and backed up with enough steel so as not to separate, it is by far the best choice. There are no seams or cold joints unless there is joint reinforcement. There is no use of precast footings.
This is the type shown in the animations under weight bearing styles listed above. The steps are as follows:
- Forms are set and braced to an elevation established during layout (8″ minimum above highest corner) and straight to the string lines on the batter boards plus the width of perimeter insulation. All set for footing foundations.
- Dirt or fill (highly compactable ‘AB’ is recommended for depths greater than 3″) is brought in to be spread and compacted to 4 to 3 1/2″ below the finished floor grade. (Get Groovy Concrete for better concrete details). Any sub-floor plumbing and electric is installed.
- Floor reinforcement or concrete mesh is set. Plus, slab on grade reinforcement must be installed. This should be structure reinforcement calculated for building reinforcement of the upper structure and any column reinforcement. Allow for any seismic reinforcement as necessary or per code for reinforcement walls.
- Rebar is set and braced into trenches and another is set 3″ below floor line by top of slab (see Reinforcement).
- County or City Inspection is made.
- Bolt or embed marks are made on the forms.
- Insulation is placed along the inside perimeter of the forms.
- Termite treatment is done if required or desired.
- Slab and footing are poured from a concrete truck all together – no cold joints.
- Toe up is installed into the wet concrete – for adobe or straw bale constructed walls.
- Bolts and embeds are placed into the wet concrete.
In the animation below, the steps are much clearer and more easily absorbed, study it for a few moments before going on:
Now things begin to get crucial, if I have done my job well, you will get through this next section, no sweat! Let me reassure you here: some of the techniques you find here, I invented, some were passed down to me – there is only one rule: Make a beautiful project! If you come up with an idea as you go and it seems like it will save you time or effort and it looks as though it will still keep your work flat and draining: GO FOR IT! Just don’t sacrifice on the structure i.e. the mixes , the reinforcement or the depth of the concrete.
Your lines are in place and marked. Your sub-grade is compacted and/or excavated. The form setting and grading are the back bone of nice flat work. I am tempted to skip a couple of steps so you can see right now how important the next couple of steps are – but instead of confusing you by giving you all of that too early, I am going to ask instead, that you trust me! I mean, hey I did get your money up front and I did come through, so don’t get all scared on me now!
The forms not only enable you to get your concrete at the right height and shape, they are your guide for fine grading and you are going to depend upon your fine grade to keep your concrete from cracking randomly. I have a couple of really cool tricks in store for you! Worth all you came to me for, but first let’s set some forms.
“There is more to life than increasing speed.”
A Straight 2×4 Is A Straight Form:
That’s it, basically! If your 2×4 form is straight and you set it up to and straight with the line, you will have done it all right! To get your 2×4 shopping list, measure your perimeter, divide by 10 (the size board I recommend), round up and add 3 to that number – you need extra for grading, screeding, cutting and closing off a pour. While you are shopping for your forms, hold those puppies up to your eye and sight down them as though you were selecting a pool cue for a world championship tournament – watch out for twisting! I will be talking 2×4 as we go and that is the size for grading and screeding, but if your perimeter is over 31/2″ you will need to get a 2×6 and if it is over 51/2″ a 2×8 and over 71/2″ a 2×10.
You spent a good deal of time setting those lines, so be sure to check that your dogs, cats, kids neighbor kids etc. did not move your lines or stakes – check your dimensions and put your level on to see that all is how you left it. If you quit for the day or take a break, when you return check your string lines!
Lay out your forms so you can see the best way to fit them together with the least possible effort. Place your cut forms last so you can go by the infamous construction axiom: Measure twice – cut once! Set the form up against the line and brace it to the correct height with some stakes or small pieces of scraps – leave a playing cards width between the line and your board, do not let your form touch it for it will slowly creep out on you.
Note: Save your straightest 2×4 for the grading and screeding!
Stand on the inside of the form (the stakes go on the opposite side of the concrete) brace the 2 lbs sledge against the form and hold it steady with your toe while you nail, and the stake won’t wobble loose!
Continue in this fashion, placing your stakes at 3-4′ intervals and no farther than 2′ from splices. Use a wooden stake to firm up your board joints – brace with sledge again.
Splices help keep your forms straight while you are grading, filling and pouring.
Splices are a must for nice straight edges!
“Success is the result of spontaneous combustion.
You must set yourself on fire.”
Fine Grade – The Word “Fine” Is No Accident:
Now, if you did your excavating and filling with care and patience this part is a snap. Now that you’ve come this far – finding muscles you forgot you had – I must say GOOD JOB!
Take the 2×4 that you set aside for grading and nail a stake on the end as shown in the illustration.
Place one of these on each end of your grade board for smoothing out your fine grade!
Be sure your fill is nice and tight up to the bottom of grade board.
For fill you can use the concrete aggregate mix – or if the quantity is more than a yard, you can haul in some AB, it is an architectural mix made to compact and spread easily.
If your area is too large (or the grade board too small) for the board to reach from side to side – allowing each scab to ride on the form – you will need to hook up some grade lines.
Nail a 1×2 stake (ear) on the top of the grade board as shown. If the grade board will not reach from one form to the other, stretch a taut line across the top of the forms 6″ from the end of the grade board.
Let the ear rest on the form on the one side and keep it up to the line on the other side.
With a little practice this method saves hours of labor and gets a perfect grade.
Grade – Compact – Grade
Measure from the grade line to the existing ground in several places to average the depth (e.g. measure 10 places, add those dimensions and divide by ten (number of measurements) to average). Enter the average depth under Depth Inches. Measure from the inside edges of the footing, wide and long and enter those in the calculator accordingly.
All techniques are as lined out above, but the steps change. This is easier if you have a little help.
Conventional Foundation Footing
(in frost zone application, ALL footings are below frost line):
Inspections will follow any plumbing, electrical or reinforcement called out on the prints, only the steps themselves change.
- A footing grade is established from the batter boards. Floor minus to 4″” below ground (or below frost line where applicable).
- Rebar is placed and inspected.
- Footing is poured.
- Stem walls are laid out of block or formed and poured of concrete 3-4″ above the established floor height.
- Either option requires rebar reinforcement to be placed at 3″ below floor height.
- Bolts and embeds are placed into wet cement in the stem wall.
- Perimeter insulation is placed along the inside of the retaining wall.
Filling and grading and compacting as in monolithic version.
Plumbing and electric set.
- Floor is poured and finished.
Old School Footing
If you had to do this enormous task alone and/or wanted to stay with in the realm of earthy styles this is a great system.
Old School Footing and Hand Mixed Floor
This style requires more labor. If your lot is in a rocky region, you can probably get all the stones necessary out of your excavation for the footings. As a kid I hated this kind of footing, now I love this type of work; it is more labor intensive, in terms of start to finish, but it doesn’t have the fire drills and rushed feel you get when tailgating with a concrete truck that can charge you as much as $4.00 per minute standby time for any time over 5 minutes per yard. In addition to that there is a feel I get (now in middle age) knowing this is the type of successful footing that was done all over the planet almost from the advent of concrete up until the 1940′s when concrete trucks began to make their appearance in all parts of the country. This footing will stand the tests of time, there are structures over three hundred years old still resting on foundations like the one described below. I have one modern difference to save you some mass, I reduced the volume by 25% and added rebar to pick up the weight. If you are into that sort of thing, leave out the rebar and add 25% to the dimensions and you will have the original old word footing.
- Trenches will be 1.5 times deeper and wider than for concrete.
- Stone rubble no smaller than your fist are fit together, slushing with a rich mixture of cement and concrete sand filling all voids as you lay the stones.
- 8″ below ground level lay three #4 rebar horizontally into the cement and surround with a minimum of 3″ of cement mixed with gravel.
- The stem wall starts 3″ below ground level, narrow to the width of your bale and continue to 3-4 inches above finished floor elevation. At 4″ below the top of the stem wall lay 2 more rebar horizontal and surround as before. Batter board lines are used to keep the wall vertically plumb and level to the finished height.
- Bolts and embeds are placed as the last 6″ of wall is built.
- The sub grade and compaction is addressed as above.
- Plumbing electric is set and inspected.
- The floor is poured in sections small enough to be mixed in 1/2 half a day and big enough to keep you busy – typical one labor one technician is 3-4 yards mixed in a work day. By pouring in sections you can do some elaborate designs in the concrete that will give you the look and feel of real expensive tile – only it will never wear out or need replaced. ((Get Groovy Concrete)).
In order to give you the volume of concrete that you will need you will have to give me the following dimensions (round up all of your fractions: