Seismic area
It is an active seismic area, which significantly impacts local building regulations. This article will hopefully help you save yourself from many troubles, disappointments, and doubts that we have gone through.
Do you think that for the foundations of a non-basement house, it is necessary to excavate foundation trenches in the ground, possibly reinforce them with steel rods, pour concrete, and then place a concrete foundation slab on them, on which the house itself is then founded? Forget this simple and efficient process if you want to build in Crete!
From "clearing" to foundation trenches
Here, it starts with a layer called “clearing,” which is the plane below the foundation trenches. Yes, it begins by excavating the soil down to the surface below the foundation trenches, onto which about 10 to 15 cm of plain concrete is poured without any reinforcement or border. No one could explain to me the practical significance of this layer. The only logical reason that local professionals confirmed is that it makes it easier for workers to walk on the construction site afterward. 😊 I don’t see any static benefit. If anyone can correct me and there is another reason for this process, please write in the comments!
On this basic layer, formwork is built for the foundation trenches. And these are truly massive in Crete. Look at the photos of the reinforcing of a ground-floor house. I repeatedly asked why placing such strong irons to such a massive extent into the foundation was necessary. In Central Europe, such massive foundations are only used for high-rise buildings. The only explanation is the threat of potential earthquakes.
In our case, the architect and the concrete company also agreed during the project that placing one complete load-bearing layer of concrete under the foundation trenches would be better. That is, on the clearing, a two-story reinforcement, 30 cm of concrete, and then 60 cm high foundation trenches. Tens of thousands of euros are flying week by week… But neither the architect nor the workers care. I am the last one to find out about such changes, by the way. I think such a founded house has to withstand even 8.0 on the Richter Scale, which hopefully will never happen.
From foundation trenches to foundation slab
After the foundation trenches have matured, the formwork is removed, and the space between the trenches is backfilled with the soil removed from there. Especially when you build on a rock, like us, it seems like a lot of unnecessary and absurd work, but that’s the local regulations and the practice. I was frustrated when I saw how many days a special excavator broke the rock to get 90 cm lower, knowing that this mass would be returned in a fluffed-up form.
Then comes the foundation slab as we know it, but instead of reinforcement with the usual grid of several mm thick steel rods, expect a grid made of wires with a diameter of 1 cm and more. And if you have a basement, the reinforcement is double level.
Protection of foundations
Alright. You have successfully poured the foundations. You have come to terms with the amount of concrete used for the foundations of your small house and how many months it took to lay the foundation strips and the foundation slab in this way. And how should you now treat the foundations? Heavy asphalt cardboard is practically not used here, although it can be purchased. However, it is one of the most expensive insulation materials. Due to its insulating capabilities, it prevents water evaporation from the concrete foundations, which is a problem due to the reinforcement. The water then stays in the foundations, which can cause iron corrosion and thus reduce the statics of the foundations.
All concrete that comes into contact with the ground is treated with a special cementitious mixture coating. Asphalt coating is also used. Spraying or a putty knife is possible, but the most common is a brush coating, which ensures good material penetration into all the concrete pores. This coating is applied in two to three layers. This prevents water from penetrating the foundations, and the reinforcement is protected from rust, significantly extending the structure’s life. Before applying the coating, removing any remaining metal used to secure the formwork is necessary.
Since the coatings are not abrasion-resistant, it is reasonable to protect this insulation layer with bubble wrap. It’s no longer such a high expense, so considering the foundation investment, this investment is worth it. Bubble wrap is attached to the foundations using special nail guns. We circumvented this by gradually lining the wrap with stones and gradually filling in the gaps. The situation where the wrap, which has tons of soil on it, would subsequently shift and the foundations would lose this protection is very unlikely, even in a seismic area. However, if an expert with the appropriate equipment does this part, nail guns are a more reliable choice.
High school of patience
I must admit that although we had a detailed project, including a structural study, the subsequent concrete practice was a great test for me. Combined with the Cretan style of work, which does not use any planning, it was a high school of patience and absorption of local culture and the Cretan way of life. That is why we moved here. 😊 To learn this experience.
Cracks in concrete
We were convinced that so solid work was not purposeless a few weeks after the workers finished their work and left the construction site. After a minor earthquake (3.2 Richter), significant cracks appeared in one place in the load-bearing wall. There is no danger of collapsing the structure, but it needs to be treated. There are special materials based on epoxy or polyurethane, one-component or two-component. Due to the high temperatures prevailing here, a two-component polyurethane adhesive is the safest choice. However, it is also the most expensive material, so in practice, only a limited number of investors use it, and an ordinary Greek will fill the gap with regular concrete. 😊 And they may have to do this every year when the wall keeps cracking… But thanks to the strong reinforcement, the structure will endure.
Otherwise, minor cracks caused by drying concrete, even if you diligently water the concrete continuously, and larger ones caused by improper laying of reinforcement are not addressed. The following layer will cover them.
All's well that ends well.
We have half a year of foundation construction behind us, and now we can entirely focus on the next stage, which will be much simpler!
