Finally starting - The Slab

After waiting 7 months for the registration of the property ownership to be done, a lady at the municipality, feeling sorry for me, made a few phone calls, and arranged for the building permit to be issued. She told me in December that she received it. I haven't seen it yet, but, she says she has it - and I am choosing to trust her word (written in WhatsApp).

So we started the building process now in March - before the dry season ends.

Last year in June already we had prepared the ground by flattening the space where the house is going to be, and adding a 20 to 30 cm (8 to 12") layer of crushed stones. The concept is the same as used for train-tracks: The crushed stone interlocks so much, that it can carry a tremendous load.

On top of the we're putting a 15 cm (6") concrete slab. Enforced with 1/8" (3mm) rebar-mesh and by glass fibre added to the concrete mix.

I am thinking, that in case of an earthquake, the forces will be spread across the whole slab, which kind of floats on top of this layer of stones. Thus, less cracks in walls. I'm also anticipating less sinking foundations due to water.

This space has been sitting like this for more than 1/2 a year. The rain and weather has compacted it even more. On one side it sank a little into the ground, while on the other it stayed pretty stable. So we needed to add some more rocks to get the whole area to be level again.

Instead of building a frame with wooden boards for the slab, I decided to build a frame of concrete blocks - similar to a typical foundation: a ditch, and on the bottom a 10 - 15 cm concrete bed, on top of which one or one and a half layers of blocks.

Once this circumferencing mini wall had cured,  we placed 10 cm high 1/2 blocks all over the area, about 1 m (1 yard) from each other to support the rebar mesh that came on top of them. That way, the mesh will be inside of the concrete slab, supporting it's strength, and not on the bottom rusting away and serving no purpose.

Once the mesh was laid, we tried to place the rebar structures that form the center of the columns on the corners and at those places of the wall that carry the columns for the roof. Also, every so often we placed rebars to support the strength of the walls between the doors and columns. 

I decided to build frames for the doors and windows using cariolas. These door frames were placed, too. 

Once all that was in place, we pored the slab. There where three masons, and 8 helpers, 2 concrete mixers and 6 wheelbarrows. Yet, it took us two days to get the whole 200 m2 (2200 sqft) slab completed.

The lessons I learned:

The rebar structures for the columns and the door frames where very hard to keep vertical and in place, because the mesh would bend and shift as the concrete was pored. We had already filled the holes of the blocks that support the mesh with concrete beforehand. Now I know, that i need to put such supporting blocks for the door frames and columns first, maybe even building little foundations ensuring there's plenty of iron sticking out of them to bind well with the slab later. That way, it should be much easier to keep these things stable and secure.

Secondly: don't believe the local masons when they say something is possible. Think for myself, and go with my gut feeling! I should have had 4 concrete mixers 10 wheelbarrows, 6 masons and 14 helpers. Then we might have been able to do it in one day...

Thirdly, I have to stay at the concrete mixers and ensure that they are not mixing soup! Kindergarten! Grrr! 

Finally: I need to come up with a way to reduce the waste of sand, polvillos, and crushed stones. simply poring them on top of the gravel road ensures that a lot of it turns into the road, instead of being usable for the concrete.

What worked well where the strips of plywood I had prepared. With those we built caminos (paths) for the wheelbarrows to bring the concrete to all the spots necessary.

It is amazing how much strength and energy the local workers have!!! They worked tirelessly all day, with these very heavy loads! The guys at the concrete mixers appeared to be in a competition of who can shovel the sand and polvillos faster into the mixer. The folks with the wheelbarrows filled the to the very top - they appeared to be in a competition of who can lug more mix faster from the mixers to the location of the slab.

I noticed the amazing functioning of the fibre we added to the mix when washing the wheelbarrows, and cleaning up some concrete that was splashed here and there. Totally fascinating! The what seemed like VERY little amount of fibre added created a fine but very strong mesh inside of the concrete. I am curious to see if the large slab is getting some of the typical shrinkage cracks or not, and if so, how severe. So far, after about a week, there are no cracks - so I am hopeful...