Casting the ground floor slab

Ground Floor Construction

Now the plinth beams were cast and had gone off, preparations were made to cast the ground floor slab. This involved bringing the ground level up to the edge of all the ground floor beams and then casting the concrete which would form the ground floor.

In between that process, the ground floor plumbing would be placed (see the plumbing section) and also the termite control pipework (see termites post)

With the plumbing for waste water and toilet waste in place, the next task was to raise up the ground level and compact the ground. This had to be done in layers – a thin layer of soils placed in between the beams and then that soil layer passed over with the plate compactor.

K.Pot started backfilling to a plan, and one of the workers immediately started levelling what was barrowed in. Once the layer was spread out evenly, the plate operator moved his vibrating plate over the loose soils and started to compact it. The next layer was then placed and the process repeated.

Even this compaction was not hap-hazard – the operator had a recognised plan, so many passes over all parts and in each direction. Without this plan it was possible to have soft spots where the soils were not adequately compacted

Going along in tandem with this was preparation to cast the ground floor columns. The steel cages were already in place and attached to the ring beam. See the section on casting the columns for more detail on this.

Finally the compacted soils were brought up to parallel with the top of the plinth and support beams. During the final part of the process, those termite control chemical lines were fitted all around the beams, to periodically deliver the chemicals under the house (see Termites).

Next the building team started to lay out the steel re-enforcing into a mesh, tying the rods together with binding wire, covering the whole ground floor area. This mesh would be set into the concrete once it was poured, to give added strength to the floor slab.

 The steel re-enforcing was lifted up off the ground so that it was completely encased in the concrete. This was achieved using the concrete chairs that were made earlier, before the ground floor work had started. The build team went around the finished mesh, attaching sufficient chairs underneath it to lift it all up off the compacted soil and beams.

Once that was completed and checked, the team went around the perimeter of the floor slab, fitting the shuttering to contain the concrete pour. Although the slab was not deep, there was a large mass of wet concrete in place when poured so it was essential that those shutters were adequately braced to prevent shutter collapse and wet concrete going everywhere.

On the day of the slab pour, the team were on hand to carry out all the tasks associated with casting the slab. Making sure the shutter remained strong and in place with no leaks. Directing the wet concrete into position over the steel mesh. Making sure that the mesh did not sag sown against the soil when the weight of the concrete was on it. Vibrating the concrete. Pushing the concrete into the corners. Levelling the poured concrete.

The pour commenced when the first delivery was made. The total volume was worked out, and translated into cubic meters of concrete. The order was placed and the mixer trucks started to arrive. Each load was poured into the slab area and the build team got to work spreading it out.

The vibrator was used to make sure the concrete flowed around the steel mesh and there were no air pockets trapped in the concrete.

The mixer trucks were scheduled to come at regular intervals until all the concrete had been placed and the slab was completed, so that there were no dry joints in the slab.

The final part of the process involved shunting a straight edged board back and forth over the top of the pour to level it. This was a judgement of eye, not equipment but the foreman had several years’ experience of this important part of the slab pour and it went well.

Once the slab was poured, vibrated and levelled, the team covered the concrete over with plastic sheeting and the curing process began. Periodically, the slab was lightly sprayed with water to prolong the hardening process of the concrete.

First floor column shuttering and pouring

Ground Floor Construction

Once the ring beam ‘foundations’ were finished it was time to turn to the uprights – those RC columns that would hold up the first floor (and the rest of the house)

Thai building methods use the tried and tested RC frame for construction. A linked re-enforced concrete network formed the frame of the building, and all the external and internal walls are non-load-bearing. It’s the same method as used in skyscrapers, but obviously on a much, much smaller scale!

The steel cages for the Thai House Build were already in place. They had been previously tied to the ring beam and foundation plan before that foundation was cast. Now the builder needed to shutter up those vertical cages and cast concrete to form a series of re-enforced concrete uprights, or columns.

The column cage shutters were purpose built, and were different to the arrangements for the ring beam. Of course, our builder had those column shutters so there was no need for a trip to the builders’ merchants.

The column shuttering was put into place, and bolted together, around those vertical RC cages. The builders then used the concrete chairs the position the cage in the middle of the shutting, so that it would end up central to the column once poured.

After that, of course there was a final check to make sure the shutters were secure and no leaks. Just imagine if the shuttering was not fully secured, and the concrete was poured in. and the shutter popped open? Even if the shutter is not 100% secure, the concrete can ‘run out’. Either case will result in a mess all over the build, wasted concrete and wasted time while it is cleaned up.

A little later, and the concrete was made ready for the column pour. Although K.Pot had all the gear, for this job, it was placed into the shuttering by hand. Plastic buckets tipped into the top! This is fairly standard practice in Thailand.

The larger columns, at the end of each zone were also poured this way.

To ensure the concrete had flowed around that rebar ‘core’ and that correct settlement had occurred. K.Pot had the use of a vibrator. This powered device agitated the shutter, causing a more fluid consistency of for the concrete that had just been poured, encouraging it to get into every area. There is an important reason for this. Any air pockets, or voids in the concrete would weaken the structure.

As you can see, at the same time, the ground floor was being backfilled with fine aggregate ready to company and pour the floor slab too. This will be covered in another post, even though the two activities overlap.

You can also see that the plumbing is in place and this too will be the subject of another post.