Our Philippine house project: layout, footers and columns

Our Philippine house project: layout, footers and columns

Building our house in the Philippines. January 15, 2010.  After months of planning and many changes we finally have our house plans completed, we have a foreman and crew and are ready to start construction next week.

This is the design we’ve settled on.  More detail on how we chose this design at /our-house-project-design-devolution/

Beginning to layout the house foundation

The first glitch occurred when the foreman doing the layout assumed that the front of the house faced the road to the south. The house actually faces north toward the mountains. As a result, much of the layout was reversed and had to be redone. Fortunately, no concrete had been poured and the corners were correct.

Rebar cutter in action

Our first load of rebar was delivered — 450 six meter long pieces.  All of these need to be cut and formed.  We bought a rebar cutter to speed the process, being shown here snipping 16mm rebar.  On our wall construction project we cut all the rebar with hacksaws. The rebar cutter really speeds the work.

Foreman Tatoy fabricating rebar cage to reinforce our corner columns

This photo shows foreman Tatoy performing part of the big job of fabricating rebar cages.  This one is for a house corner column.  It six meters long.  The long vertical bars are 12mm and the stirrups are 10mm.  The rebar seems to have been made at Qian’an Jiujiang Wire Rod Co., Ltd. in China.  They claim to make 16 millions tons of steel products per year.  We paid (Jan 2010) P288 for 16mm rebar, P163 for 12mm and P113 for 10mm.  We are paying P209 for a bag of cement, P300 per cubic meter of sand and P420 for stone.  Sorted, washed 3/4″ stone is much more, P700 per cubic meter.

Digging

Column footer

This is a good overview shot showing how most construction is done in the Philippines.  This shows a column footer excavation which is 1.2 meters (about 4′) below natural grade.  The footer is one meter square.  A 8X8 mesh of 16mm rebar is at the bottom.  The column rebar core rises almost six meters (about 20′) above the bottom of the footer.  This rebar core will be encased in a plywood form into which concrete will be poured and then vibrated in an effort to ensure that there are no voids.   Easier said than done!   This is what greeted us when we removed the form from our first column.

bad_column

The complicated rebar framework devised by our engineer is much more demanding than the usual square column with a vertical rebar in each corner.  Getting the wet concrete to flow through the multiple rebars is a challenge, especially when trying to avoid over wet concrete.  It’s a perpetual struggle to keep the workers from making the concrete too wet.   Another factor,  we were using 3/4″ gravel rather than the sandier gravel which is typical here.  The gravel “hung” in the rebar framework leaving big voids.  We demolished this column.  You can be sure that this kind of a problem wold be quickly hidden away if you are not on-site supervising.

Editorial comment. If we had it to do over again,  we’d use plain square columns rather than the complex design devised by our engineers. While there may be advantages to the design our engineers provided, the practical problems of building them correctly in the provincial Philippines are several.  Our good, experienced workers had no experience with such columns, or generally such complex rebar configurations.  The aggregate generally available in our rural area contains larger stone which tend to hang up in the small openings.  We had the advantage of a good crew who wanted to good work. a concrete vibrator and screened gravel.  Still we had continuing problems and wasted lots of time trying make good columns using the design we were supplied with. In a situation where supervision was lax the situation would be worse.  Trying to fill the complex framework, the workers would use soupy concrete.  Any voids and defects would be plastered over.  The real world end result could easily be a significantly weaker column than employing the usual simple  square column with four vertical rebar.

An almost perfect column

The rebar at the top of the columns will be tied into the reinforced concrete beams which top the walls of the house.  These elements make a strong, well-anchored frame which is filled in with weak hollow cement blocks which are also filled with rebar and concrete and then parged with a thick coat of stucco-like concrete.  Metal roof trusses are also anchored into the concrete room beams.  The trusses will support long span steel roofing.  We decided to use 6″ hollow block for the exterior walls and four inch block for the interior partitions.  We are purchasing our block from Damasco in Pavia, Iloilo.  We used Damasco block for our perimeter wall.  In our view Damasco is the gold standard for block in Iloilo.  One does pay a premium. Local four inch hollow block costs P9, delivered.  Damasco 6″ block costs P13 delivered, 4″ Damasco block costs P12.   Using better block is a minor extravagance as the cost of block is a surprisingly small part of total construction cost.  More on hollow block shopping at /our-house-project-cement-blocks/

At the end of our first week of construction the first concrete is poured

2″ X 2″ lumber is a staple of construction in the Philippines, used for layout as seen above and with 1/2″ marine plywood for building forms.  Typically the 2X2 is “coco” lumber – lumber from the coconut tree.  My foreman insisted that we buy mahogany instead, saying the coco is dangerously weak.  I reluctantly agreed – coco is P55 for a 2x2x8′, mahogany is about P75 and we needed a few hundred pieces.  Now I’m a convert.  The mahogany is stronger and more durable.  Coco lumber in forms under under pressure from wet concrete does give way more easily.  I do feel guilt.  Much of the mahogany is beautiful furniture grade material.

A ponke in action

This photos shows the workers adding material to the mixer using a “ponke”.  The ponke is a wooden box with handles.   The ponke is sized to hold one sack of concrete, 30cm x 30cm x 30cm (one foot square).  I asked that the ponkes be built and used as a means of controlling the concrete mixture.  We decided on a mixture of one part cement, two parts sand and three parts gravel – a 1-2-3 mix. The use of the ponkes makes it easy to get the mixture right.  Ponkes are rarely used in the Philippines now, but used to be common.  Now materials are more commonly measured using empty cement sacks refilled with sand or gravel.  I wanted the ponkes and my ever patient crew accommodated another whim of the kano.  (Anyone with information on the correct spelling and etymology of “ponke” please leave a comment.   It sounds like it may have a Chinese origin.  This makes special sense as Chinese workers were prominent in the Philippine construction trades.)

One of the crucial advantages of being you own contrator is that YOU control the quality and quantity of concrete and reinforcing bar.  If you don’t think this is important, study the photos of the Haiti earthquake.  While there was widespread destruction, many building survived with little or no damage.

Our 1-2-3 mix is almost considered to be an extravagance.  The house you buy already built probably won’t have such strong concrete.  1-3-5 is in common use.  I have seen deliveries of substandard reinforcing bar.  A poorly built house may be built with a “class B” or “class C” concrete mix and not enough rebar.  You’ll never know what’s in your house unless you build it yourself.  It might never matter, but here’s a photo of the church in nearby Oton, Iloilo which was destroyed in the January 28, 1948 Panay Island earthquake.  You can still see damage from this earthquake at the Alimodian church, only a few KM from our Tigbauan site. Also see http://earthquake.phivolcs.dost.gov.ph/update_SOEPD/Earthquake/1990PanayEQ/index-panay.html regarding the 1990 7.1 Panay earthquake which collapsed buildings in Culasi and elsewhere.

The plan of our house was designed by a structural engineer.  We’re trying to be quite strict in following the plans.  We see quite a bit of good engineering in the plans as we build.  Lots of reinforcing steel is used in critical areas, but much less in columns not carrying much load.  Sometimes Filipino builders use traditional rules of thumb not based on engineering basics.  This can mean too much steel in places which really don’t need it and not enough in others.

Magnificent Oton Church, destroyed by 1948 earthquake

Concrete vibrator in action

Look closely and you’ll see the worker using a length of rebar as a probe.  They’ve learned that large pieces of gravel can become lodged in the rebar preventing the flow of concrete down the column.  The internal concrete vibrator (more info at /our-house-project-equipment-shopping/) makes the concrete flow better but can’t be depended on to dislodge stuck gravel.

Our latest response was to screen our gravel exclude larger stone that could hang up in the columns or beams.  We built a simple screen for our gravel using hardware cloth with a 1″ x 1″ mesh.  About one-half of our supposed 3/4″ gravel makes it through this mesh. We will use the smaller material for critical uses such as columns and beams, the larger stone is used in footers and fill for the hollow block.

Our conclusion is that the concrete vibrator caused more problems than it solved.  Most this is because most of our workers had never used a vibrator before and over used it.  In the case of columns, over vibration caused a slurry of water and cement to drain out of the bottoms and sides of the forms.  Left behind were the aggregate but not enough cement to hold it together.  This is shown in the photos below.  Probably with trained workers and larger projects, concrete vibration results in higher quality concrete but for us that was not the case.

The effects of over vibration at the bottom of a column pour.

A column error corrected.

Here’s another worker error caught by our engineer.  Generally the column rebar goes up first, then footers for the hollow block walls.  Then the walls go up around the column rebar. The pouring of the column is the last step.

Here the workers put the hollow block almost against the rebar cage for the column, leaving no room for the concrete forming the column.  This would have resulted in a much weaker column because the block has little strength.  The solution was quite time consuming, chipping or cuting back the block to give one inch of clearance between the hollow block and the column rebar.  With hollow block filled with concrete, this took quite a bit of time.  My foremen, who have built many houses, allowed this to happen, suggesting that it was their usual practice.

Read all about our Philippine House building Project at /building-our-philippine-house-index/