Build point foundation yourself – instructions for concreting

Sure, a foundation in points, but if you want to put a horticultural work on such a foundation, you would want to be more precisely defined:

• A point foundation is so called because here concrete is poured into a single, more or less large “point”.
• Or several points if it is not just about a stable stand for a flagpole, but also about three-dimensional structures.
• The point foundations consist of a certain volume of solid concrete in which the posts of the structure are attached.
• The load of the structure is concentrated on the point foundation and is diverted into the surrounding soil.
• For structures with walls, a point foundation at every corner is the minimum requirement.
• With more load there are more, e.g. B. In addition, a point foundation in the middle of each side.
• Your building stands on a series of fixed points that stabilize it and keep it away from moisture.

When is a point foundation enough?

As you can already guess after this description, the point foundation is nothing for the subsoil of the six-story villa. This type of foundation can of course only be used for lighter structures, but there are many ideas for lighter structures in gardens.

How light a building can be so that a point foundation is sufficient tells you a little bit how easy it is: you would hardly think of putting a 10-meter-high play tower with a swing on a point foundation, rather beams torn from the earth and genes emerge Horizon vanishing swings with kids on your mind’s eye. Which is very correct in this case, especially for structures that are exposed to constant vibration / movement, point foundations are not the best form of foundation. How light or difficult a building on a point foundation can be, however, is a matter of more precise planning.

The planning

Once it has been clarified in principle that point foundations can be used, more detailed planning can begin:

• The number of point foundations must be calculated depending on the weight and load of a structure.
• A structural engineer should actually calculate that, but with many horticultural works you can get the necessary data free of charge.
• If you buy a children’s swing, a play tower or the like as a kit, you will receive all the necessary information with the assembly instructions.
• If this is not the case, that would probably be an indication to keep your hands off this kit.
• Because if the important information for the structural stability of the structure is not included, not much can be expected from the rest …
• In any case, to be on the safe side, you should ask the municipality whether you need a building permit for any horticultural work
• Even with very small ones, here design specifications often also play a role
• You can take advantage of this fact, the employees in the building authorities are often very helpful (if they are addressed nicely)
• They can often give you tips as to which point foundations are definitely sufficient for your building
• If this is not possible due to legal liability reasons, they can often tell you how you can obtain certainty inexpensively.

The construction

Before you start pouring the point foundations, you need to make some preparations:

• The subsurface must be leveled, the area on whose corners / sides the point foundation is to be poured.
• Hills are dug up, roots removed, and the ground pounded.
• You can determine whether the bottom is level by creating a batter board and measuring it with a spirit level.
• Now the position of the point foundations is determined and marked.
• At these points, pits are now being dug for the point foundations.
• In the previously calculated size, 40 x 40 cm is z. B. a common measure for smaller buildings.
• How deep you dig also depends on the load.
• For a frost-proof point foundation you have to go at least 80 cm deep into the earth.
• This is also recommended for structures with very little stress.
• Otherwise water can collect under the floor of the foundation.
• When this water freezes, it can lift up all of your beautiful structures.
• If the ground is solid, there is no need for formwork in the earth.
• If it is rather crumbly and sandy, it will need support before watering.
• In other words, a formwork, whereby you do not necessarily have to use the prescribed formwork boards for point foundations.
• Rather, you can build your own formwork from materials that can remain in the ground after the concrete has been poured.
• For example, old concrete blocks that you stack on the edges of the pit and that simply stay in.
• If a certain high load-bearing capacity is important, you should use formwork that complies with the regulations.
• If wooden structures are to be placed on top, it is advisable to let the point foundations protrude slightly from the ground.
• Then the beams will never stay wet any longer, a form of so-called “constructive wood protection”.
• Of course, if you don’t need formwork, it is more convenient to pour down to the surface of the earth.
• Then you can do good to wooden beams by putting them in metal joist hangers.

Before that happens, your point foundations need to be filled with concrete:

Instructions for concreting

The instructions for concreting are actually instructions for mixing concrete, because it depends on the mixture whether the concrete holds up well. Often not the client’s problem because the concrete plant takes care of it. But especially with point foundations, it is typically not worthwhile to let a concrete truck drive up, so mixing yourself is the order of the day, and this is how it works:

Step 1 First,
the most pleasant news: Mixing concrete yourself is pretty cheap, you don’t need more than cement, gravel and water.

• 25 kg of cement in a sack cost around 3 euros
• Sifted and washed gravel sand (here grain size 0 / 16a) around 30 euros per cubic meter.
• One cubic meter is 1.6 tons, i.e. 1,600 kg, which is about that much you need for our sample calculation.
• In addition, there are around 10 liters of water for every 25 kg of cement, which is a few cents even in regions with high water prices.

Step 2
Our example calculation is based on a point foundation that will be sufficient for most horticultural works, namely 50 x 50 cm with a depth of 1 m. With four point foundations results in exactly one cubic meter of concrete, therefore such a nice example calculation. One cubic meter of concrete weighs around 2,200 kg and is mixed as follows:
In a mixing ratio of 3 to 1 you need 20 bags of cement (500 kg) and 20 x 75 kg of sand (1,500 kg) and 20 x 10 l of water (200 kg) = 2,200 kg , costs around 90 euros together.

Just for comparison: If you buy ready-mixed dry mortar, you save yourself mixing cement and gravel and only have to add water. On the other hand, this dry mortar does not cost 12, but up to 50 cents per kg, i.e. four to five times as much. For this it is worthwhile to mix cement and gravel yourself.

Step 3
Cement in 25 kg bags is printed with mysterious numbers, 32.5, 42.5 or 52.5. These are the strength classes, 32.5 cement initially hardens much more slowly than 52.5 cement. Important, if you are concreting at low temperatures, you need a fast-setting 52.5 cement to avoid possible frost damage. But since you are more likely to tinker around in the garden at friendly temperatures, the normal 32.5 cement, standard offer in the hardware store, is probably enough for you.

Step 4
For the gravel sand, 0/16 was specified above, a standard for all common purposes. 0/16 means that the grains contained in the gravel-sand mixture have a size between 0 and 16 mm. You could use a larger grain size such as 0/22 or 0/32, then the hardened concrete would have a slightly higher strength, but all fine work is more difficult in such a mixture.

5th step
The cement-gravel-sand mixture is mixed with water to become concrete. So you put your three parts of concrete gravel with one part of cement in a mixing vessel and add about 10 liters of water to each cement sack, little by little. You should definitely wear rubber gloves to do this, cement irritates the skin. The mixing itself is a matter of feeling:

• Of course, everything has to be mixed really well.
• Basically, what matters is that cement and water combine to form a thick paste.
• Which in turn should cover every single grain of gravel sand.
• When this is achieved, all three parts join and cure in exactly this structure.
• By the way, hardening is not drying, but a chemical reaction; concrete also hardens under water.
• The right amount of water in the concrete itself is important for optimal hardening.
• Too much water later evaporates and leaves rough pores, too little water leaves dry cement in the mixture that does not harden.
• But none of this should scare you, 10 liters of water on a cement sack is a tried and tested mixture.
• All in all, a nice, thick mush should be created, not too runny, rather (felt) a little too thick.

Step 6 – How to mix:

• Fill the concrete mixer in the following order: two thirds of a 10 liter bucket of water, 75 kg of gravel sand, a bag of cement, the rest of the water.
• Only half of the above mixture fits into very smaller mixing machines.
• The mixer is now run for three to four minutes, then the concrete is ready.
• When mixing in the mortar bucket, you should work with helpers, one of whom operates the whisk, the others pour in previously measured amounts of gravel sand / cement / water.

7th step
Now it is poured and compacted (poke around in the concrete with long break-proof rods and stir a little), then the concrete is allowed to harden in peace. At rest, even below average temperatures, if you want to pour concrete in extreme heat or cold, you need to find out what special treatment the concrete then needs when it hardens.

If you create a lot of point foundations for a really large structure, so that mixing is almost impossible, you can use ready-mixed concrete. It is more expensive, starting at 140 euros per cubic meter (often plus a hefty surcharge for small quantities), but it also has advantages. You get exactly the quality you want, you can have all sorts of useful aggregates mixed in, and get your concrete right into the pit in one fell swoop.

The quick alternative – point foundation light

There are some building ideas for the garden where you can use a kind of point foundation for stabilization, but the effort involved in creating proper point foundations, with formwork, etc., seems to be excessive. Perhaps only one mast (anniversary flag, maypole) should stand straight, or four posts for a light woven roof should be stabilized … Then you can make your work a little easier, there are several options:

• They knock in metal sleeves into which the stands are placed.
• You use such ground sockets, but also concret them in by placing them in a hole and pouring concrete around them.
• They dig in concrete plant stones, several on top of each other, depending on the desired depth, and insert a sheet of panicle tape into them.
• Bars can later be screwed to this panicle band (band made of sheet steel with holes), the plant stones are simply poured over with concrete.

Conclusion
A point foundation is usually sufficient if it is only a question of stabilizing a light horticultural structure a little or protecting it from moisture from below. Then it is usually worthwhile to concern yourself with instructions for concrete mixing and concreting, especially if you want to place even more structures on point foundations – even mixed concrete is really unbeatable inexpensive compared to the alternatives.