Lack Of Concrete Rendering Causes Thai Builder To Be Sacked From The Thailand Retirement House Build

Photos Taken In Thailand April 2011, Posted Tuesday 24th May, 2011

Kanyah Wants To Sack Our Thai Builder

A few minutes ago Kanyah phoned me from the construction site in Pakchong (Pak Chong), Thailand, where we are having a house built for our retirement to Thailand and told me that she is so fed up with our builder that she wants to sack* him and continue the build with her nephew, Jalan.

(* For American readers the term “to sack” in English means “to fire” in American English, i.e. to kick somebody out of their job)

At last it seems that Kanyah is getting the message about this builder and starting to show an interest in the house build and quality of the work.

I’m not convinced yet how firmly Kanyah will deal with the builder – I would have sacked him ages ago.

Anyway let’s look at the quality issue that she is referring to that has finally made an impact on her. There’s no doubt that she is feeling under a lot of pressure to sort this builder out.

Problems Rendering The Columns And Fixing The External Wooden Walls

The message from Kanyah was a bit garbled and she hasn’t sent me any photos so most of what follows is my interpretation of events, but since Kanyah mentioned this issue more than a week ago it I think I’m pretty well on target.

Typically, the finish on cast-in-situ concrete in Thailand is so appalling that it’s customary to ‘render’ the concrete after casting to achieve a smooth finish. ‘Rendering’ is like plastering except that a mixture of cement is used instead of plaster. It is labor intensive and very slow.

This is how how a concrete column or beam would be rendered:-

Image Showing How They Render Concrete Columns In Thailand

How They Render Concrete Columns In Thailand

And below are some photos and a movie showing the progress with rendering on our retirement house in Pakchong (Pak Chong), Thailand.

Image of Pakchong House Rendering Concrete Beams 04

Pakchong House Rendering Concrete Beams 04

Above, the first stage of rendering beams (or columns) is to do the corners.

Image of Pakchong House Rendering Concrete Beams 05

Pakchong House Rendering Concrete Beams 05

Above a close-up of rendering the corners. You can see a string line used to get the corner dead straight and even. Also you can see the straight edge used to make sure that the cement is nice and straight.

Image of Pakchong House Rendering Concrete Beams 03

Pakchong House Rendering Concrete Beams 03

Above, can you see the sharp corners awaiting rendering of the flat infill?

Image of Pakchong House Rendering Concrete Beams 01

Pakchong House Rendering Concrete Beams 01

Above, it is not only cast concrete that is rendered, the blockwork walls are also similarly treated and there is a very good finish.

Image of Pakchong House Rendering Concrete Beams 00

Pakchong House Rendering Concrete Beams 00(Alan's comments)

Above, the beam is not yet rendered, but the column is.

Below is a movie showing the rendering on the beams and columns of our house in Pakchong (Pak Chong).

The Problem Of Fixing The Wooden Walls

The extract from the Thai Architect’s construction drawings for our house shown below has been slightly modified by myself the illustrate the concrete column and the rendering. The wooden wall is shown butting up to the rendering i.e. the finished column.

Image of Wooden Walls And Concrete Columns Interface

Wooden Walls And Concrete Columns Interface(Alan's comments)

Above, the design intention – the wooden wall butts up neatly to the finished (i.e. rendered) concrete column.

The next image is a close-up:-

Image of Wooden Walls Butting Up to The Rendering On The Concrete Columns

The Wooden Walls Butting Up to The Rendering On The Concrete Columns

But Kanyah is telling me that the builder has not yest completed the rendering but is installing the wooden walls, as shown below:-

Image of The Wooden Walls Butt Up Directly To The Concrete Columns

The Wooden Walls Butt Up Directly To The Concrete Columns

Above, the wooden walls butt up to the concrete column which has not been rendered.

How, then, is the column to be rendered to give a neat finish.

My guess is that what is visible will be rendered but it is not clear how the rendering around the wood wall will be dealt with. The inner-most layer of the wall construction is to be bamboo mat and it’s not at all clear how/when this will be installed with respect to the rendering.

I’m sorry that I don’t have any photos from site to confirm all this, I have asked Kanyah to send me some, but she is (understandably) preoccupied with getting the builder to do his work correctly.

That’s all for now, I’m awaiting an update from Kanyah.

PS Rendering Crack Control

This is a photo of a neighbours house and you can see a vertical line in the rendering just to the right of the doorway. This is intentional and is a shallow grove in the render about 10 mm wide and 10 mm deep, called a ‘crack relief channel’.

Image of Neighbours House - Crack In Rendering 01

Neighbours House - Crack In Rendering 01

The idea is that as the rendering dries and contracts any cracks forming will tend to be formed withing this man-made channel instead of forming randomly and uncontrollably across the wall. Our house has these channels and at first I thought they were for decoration, but no, they have a practical purpose – to control crack formation.

The picture below is a close-up of the ‘crack relief channel’ and indeed you can see that a crack has formed.

Image of Neighbours House - Crack In Rendering 02

Neighbours House - Crack In Rendering 02

PPS Shockingly Poor Concrete

The photos below are of the underside of a second floor concrete beam on our house. The defects are plain to see. The concrete has not penetrated to the bottom of the formwork, there are holes in the concrete and the steel reinforcement is exposed.

This is very poor but I suspect typical of concrete pours in Thailand if not done and supervised properly. Where was our inspector when the concrete was poured? Well, maybe he didn’t know about the importance of getting the concrete to the bottom of the formwork. This is often achieved using a concrete vibrator or ‘poker’ which I’ll explain later down the page.

Image of Pakchong House Poor Concrete 01

Pakchong House Poor Concrete 01

Above, this concrete beam has both air pockets and exposed steel reinforing bar.

The Dangers of Air Bubbles And Exposed Rebar In Cast Concrete

Air Bubbles In Cast Concrete

Clearly air has no strength.

Therefore concrete with air bubbles is weaker than concrete without air bubbles. Another danger of air bubbles is that the cavity is a stree uinducer. Like a crack it concentrates the stress in the beam and can lead to premature failure.

I just hope that the beams have been oversized compared to the stress they are expected to carry. They certinly look big enough for a two storey house. I’ll may get a structural engineer colleague of mine to lookat the pictures and the structural calculations and let me have his opinion.

Exposed Steel Reinforcing Bar (Called ‘Rebar’)

In addition to the fact that the concrete/steel composite material cannot be so strong if there is no concrete around the reinforcing steel, there is another danger and that is corrosion – commonly termed rust.

If steel reinforcement is left exposed it will corrode or rust. This corrosion expands the steel and the concrete bursts away. So not only is the beam (or column) weaker because the steel has turned to rust whch has no strength, the concrete will fall away.

In the cases you see in the photos here, this is not such a danger because the steel will be rendered and when the rendering is complete will not be exposed.

The danger is in the foundations of the house and the underground columns and beams. Being underground, anay exposed steel will be sitting in water for a large part of the year.

Based on my observations of the beams as seen on this page, the general lack of care by the builder and the inefective monitoring by Jalan, our ‘inspector’ and not using the concrete vibrator I would say that there’s probably a 100% chance that some of the steel reinforcemnt in the underground concrete is exposed.

Image of Pakchong House Poor Concrete 02

Pakchong House Poor Concrete 02

Above, air pockets have weakened this concerete beam.

Image of Pakchong House Poor Concrete 03

Pakchong House Poor Concrete 03

Above, exposed steel reinforcement in the concrete beam.

Using A Concrete Vibrator or ‘Poker’ To Consolidate Concrete

Below is shown a petrol-powered handheld concrete internal vibrator (oftern referred to as a ‘poker’) used to compact concrete and ensure that air bubbles are removed.

Image of a Concrete Vibrator or 'Poker'

Concrete Vibrator or 'Poker'

The concrete vibrator shown in the picture is alled the ‘insertion’ type because the vibrating head is inserted ito the concrete like a poker is used to poke into a fire.

Handheld concrete vibrators are used to consolidate concrete, make sure that it travels to all parts of the formwork and to remove air bubbles and air pockets that would weaken the concrete if left in.

To use the concrete vibrator it is simply pushed into the concrete at intervals of approx 500 mm apart for 5 to 10 seconds or a few seconds longer.

Although this is a simple and cheap device, not many small builders in Thailand use it. Clearly it was not used on my house. I should have explained this to Jalan.

Below is a movie of a concrete vibrator in use.

In the movie notice how the concrete ‘slumps’ as soon as the concrete vibrator (‘poker’)  is pushed into the concrete. that means the concrete is ‘falling down’ to the bottom of the formwork. This proves that there exist air pockets under the concrete that will remain there unless the poker is used.


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