We’re building a house in the Philippines. This account will show how we’ve constructed our floors; filling, compacting, reinforcing bars, and pouring concrete.
Generally, lots are not filled before the house is built. It’s generally a bad idea to build on fill, especially in earthquake country. We did do some filling of the lot before we built the house, but all footer depths were measured based on undisturbed soil — the footers are set in undisturbed soil, not fill. If we had one foot of fill and needed to install a footer 1.2 meters below grade, the excavation was 1.2M + 1 foot.
The height of the fill contained within the perimeter walls of the house and supporting the floor is adjustable based on local conditions. It can be as much as several feet. Our house is located on level agricultural land on Panay Island. We want the have our finished floors about one meter above the surrounding terrain because we wanted to avoid any possibility of storm water entering the finished house. We already owned our property when Typhoon Frank hit Iloilo. We were able to see that there was lots of rain water in the surrounding rice fields but not deep, and no flooding such as from overflowing rivers.
Still, we had to consider that the surrounding land is open to development and that our future neighbors will fill their lots. This filling is sort of an “arms race” with the loser receiving the storm water from higher filled neighbors. This requires serious consideration. There are hundreds or thousand of structures in Iloilo City which routinely flood because the lands and roads around them were raised. It’s easy and relatively cheap to add extra fill before building but a near impossible problem to remedy once the building is built. With our high ceilings, I suppose we could add fill and pour a new floor over the top of the old one, but what a discouraging prospect!
We trucked in sand and gravel fill to raise the entire lot and the house location even more. The height of the finished floor was raised even further by filling the area within building walls. This sandy fill was put in in layers with lots of water to settle it. The final layer of fill was gravel. Initial compaction was done manually using the medieval device shown below.
Then we were able to rent a gas powered compactor for P450 per day including the operator. Three days of compacting produced a very, very firm surface. The next step was installing the plumbing pipes and electrical conduit which will be embedded in the concrete floor.
All electrical circuits embedded in each floor are tested with a continuity tester before the floor is poured. While all electrical circuits are in conduit and theoretically could be rewired, some wires in this room go outside the house to lighting at the front gate, so they could be a little difficult to repair.
Next the reinforcing bar was installed. We used 10mm rebar on a 60cm x 60cm grid. Philippine workers are not always careful about positioning the rebar up from the ground in the concrete. We had the same problem with our footers. Workers would let rebar lay in the bottom of the footer excavation rather than raise it up into the concrete. Plastic rebar “chairs” are used to position rebar in the U.S. but I have never seen them for sale in the Philippines.
Fellow blogger Yannic made his own cement “chairs”. See his excellent house building blog at http://www.pattayaforum.net/forum/showthread.php?7365-Hausbau-in-Bohol-Philippinen
I showed a photo to my foreman and said that’s how I wanted things done. I suspect that if he was left to his own devices no rebar supports would be used. Anyway, my foremen supported the rebar grid using scraps of “L” or “J” shaped rebar scrap driven into the compacted fill and wired the the rebar grid. At first I was dubious, but in fact the fill is so heavily compacted that these supports are probably stronger than the plastic chairs. My foreman drilled holes in the finished walls into which he inserted the rebar ends. This provided good support for the rebar at the edge of the room.
We did not use a vapor barrier under the concrete. My reasoning was that such barriers are essential in sealed, heated houses in the north to try to keep interior moisture levels under control. Since we are aiming toward an all windows open, maximum ventilation approach, I could not see the function of a vapor barrier in the floor. Others disagree. See comments below. Now that the house is done and we are living in it we see no problem with moisture coming from below.
Our concrete floors are about 5″ in thickness. We are using a 1-2-4 mix (one part cement, two parts sand, four parts gravel). I do not allow any concrete to be poured except under my supervision. My crew had no problem accepting my mix — generally 1-2-3, but I had many fights with them over how wet the fix should be. Over the months they have gotten much better about that. Another problem was not allowing enough time in the mixer. When mixing and pouring concrete my crew gets into a hyper-macho mood, wanting to go really fast. Concrete should be in the mixer at least 2 1/2 minutes. Unsupervised, they would dump the mix too quickly. I have insisted that they slow the pace and do careful rather than fast work. They really would rather work hard rather than deliberately. After these months of working together, we generally produce good concrete without much fuss, as long as I am there supervising.
This photo shows how my crew goes about floor cement work. Chalk lines (faintly visible on the right) show the desired floor level on the walls. As a first step, a narrow band of concrete at the proper level is laid down the middle of the room. Then similar bands are laid at the room edges. These two start to set. Then the areas between these bands are filled in, starting at the far corner of the room and progressing toward the door. Tools being used are a bamboo pole to “vibrate” the wet cement into all areas, a simple wooden float and an 5′ aluminum bar.
Since the rooms are to be tiled, an ultra smooth surface on the concrete floor is not desired. While we have our roof on and the concrete is not exposed to the sun, we still keep the floor wet for at least three days.
These electrical conduit will soon be buried in the concrete floor. The genius of this system is that wires can be replaced (if necessary) by pulling them through the conduit embedded in the floors. For this to work, there can be no shortcuts. The wide arc elbows must be used. There are no electrical conduit tees. The blue water system fittings can be used with the electrical conduit but such use may well defeat the ability to pull new wires as the bends are too sharp to pull through. We used one tee and I regret it!
The kitchen/living room pour used 41.5 bags of cement 160 bags of gravel and 80 bags of sand – 42 loads mixed in our one-bagger mixer. This took a very full day for our seven workers. They were really tired afterwards. We bought them three pizzas and three liters of Coke.
Note the concrete on the right. The workers are now consistently making concrete with a decent slump — not soup. The mix is 1-2-4.