Guide to Avoid Common Construction Errors

Building construction is a very old industrial activity. Ever since the search for an alternative means of shelter, (different from caves, trees and other natural shelter which they share with animals), man has been involved in the construction of various kinds of building. Naturally, as knowledge increased the methods of construction, the materials used for construction, the strength and the stability of the buildings constructed continued to evolve. As a result building process has become quite complex.

Some common errors occur in the construction of a typical home. Even an experienced site supervisor cannot be too used to the routine procedures on site. From time to time errors and omissions occur; those that could be avoided. Foreknowledge of these mistakes and tips on how to avoid them can be very helpful especially for the greenhorn site supervisor or the owner-builder.

This write up will take a look at some of the common possible mistakes in the construction of a building in the tropics at each stage of the construction process and provide a list of tips intended to serve as a ready reference or practical checklist to avoid omissions and errors on site for the new as well as the experienced site supervisor and other site workers.

PRE-CONSTRUCTION STAGE

POSSIBLE ERRORS

1. Omission of tasks may occur in drawing out schedules.

2. Estimated time for some task in the schedules may be wrong (insufficient).

3. There could be errors in the forged contracts e.g. ambiguous statements.

4. Omission of details and other oversights in the final drawings.

TIPS & OTHER CONSIDERATIONS

1. Contracts are better simply written instead of a verbal agreement.

2. A good contract should include the following specific items.

i) Total cost of the contract.

ii) Breakdown of cost per phase of work if work is in phases.

iii) Break down of cost of various aspects of the contract that make up the total price like labour cost, material cost, transport cost, etc.

iv) Type of material to be used or supplied, brand and model of equipment or fixtures to be installed and events for special installation (general description of work).

v) Payment schedules.

vi) Cost for change orders.

vii) General responsibility of each party; this might include clearing and cleaning up after work, safety precautions on site, etc.

viii) Completion date of the project.

3. Notification to contractors/sub-contractors who handles critical events should always be a priority.

4. The traffic flow of workers and materials on site should be put into consideration when locating the site store/shed/office.

5. Safety on site will be largely guaranteed by clearing the site regularly of rubble and by insisting on other safety measures.

CONSTRUCTION TO FOUNDATION FLOOR LEVEL STAGE

POSSIBLE ERRORS

1. Without proper supervision checking and crosschecking, setting out errors can easily be committed resulting in unaligned building to reference points and incorrect building perimeter.

2. Mix ratio of concrete could be assumed in error. Specifications must be followed for different concrete mix. The mix ratio specified for the foundation beams can be different from that for the floor.

3. Errors can easily be committed in the construction of different foundation levels where topography is undulating especially if this was not noted in the construction drawings.

4. Errors in assuming standard measurement instead of the specified. Specified measurement is not always standard measurements; it is wiser to follow specified measurement rather than standard measurement especially if the specified measurement is for extra precautions. Standard measurement is usually for minimum precaution.

5. Omission or wrong application of DPM and anti-termite.

TIPS & OTHER CONSIDERATIONS

1. The site supervisor should ensure that the right quantity of materials needed for any stage of work is available (supplied) on site before work is commenced, this is to avoid shortage of materials, which will result to delay, and likely flawed concrete structures.

2. Quality of materials also can delay or lead to failure of structures. The site supervisor should be able to differentiate between sharp sand and filling sand, various types and sizes of iron rods and any other details of materials as specified in the construction documents.

3. Precision instruments like leveling instruments should be used for precision in measurements, instead of guesstimating or using simple manual means.

4. Proper means of obtaining the level of the concrete in casting the foundation or floor is essential to avoid waste of material and for a perfect leveled spread. Usually iron rods are cut to size of the depth required and attached vertically to reinforcement rods or form work around and within the perimeter of the area to be cast. The tip of the rods serve as level for the concrete poured during casting.

CONSTRUCTION OF SUPER STRUCTURE STAGE

POSSIBLE ERRORS

1. The partitions can be marked out in error during setting out.

2. Block setting errors are always imminent, these bothers mainly on the perpendicularity, levelness and straightness of the walls.

3. Errors that arise from corrections made to the original plan, not promptly related to the site Engineer/Supervisor.

4. Windows and door frames not properly embedded and set in position.

5. Erectness of columns, straightness of beams, and lintels and right curvature of arcs. This may result from displaced formwork during casting or inaccurate formwork setting.

6. Positions, numbers, and levels of switches, sockets as well as plumbing joints can be erroneous.

TIPS & OTHER CONSIDERATIONS

1. A change in the house plans means a change in the roof design especially if the change affects the external perimeter. This calls for an immediate redesign of a new roof that will fit on the new house, to avoid waste of time and resources.

2. Correction to the plan drawings can be made (if necessary) after the first course of blocks is laid to avoid waste of materials. At this stage the sizes of the rooms and various partitions can be seen at the actual size by the client, who may call for adjustments.

3. Cement blocks are easily broken in transit, and in storage on site and during block setting. Ordering for too many to site at particular times will increase loss from broken blocks. Also wet blocks should not be accepted when supplied because there are easily broken.

4. Soft wood used for formwork if detached properly can serve same purpose again and for scaffolding. This will reduce total cost of the project.

5. Mortar for bonding the blocks together is made from the mixture of cement and sharp sand. For the mortar to bond well, the ratio of cement to sharp sand is usually high. If cutting cost is paramount, adding clay to the mixture will reduce the amount of cement needed without necessarily affecting its quality.

6. Since the treatment of the wood materials for the roof carcass is so important for the durability of the roof, the site supervisor should personally ensure that the woods are properly treated with the right preservatives.

7. The mechanical and electrical (M&E) drawings should be comprehensive enough for the plumber and electrician to follow in laying their pipes and positioning the various service junctions.

FINISHES, FIXTURES & FITTINGS STAGE

POSSIBLE ERRORS

Possible errors that may occur at this stage include;

1. The plastering work may not be perfectly done to cover up errors in the block work.

2. Installed windows could present many workmanship errors, which included; gaps between partitions, poor rubber boundary work, derailing sliders etc.

3. Installed doors could presented many workmanship errors, which may include; irregular and rough leaping, colour variations of wood/plywood material used, un-plumbed architrave and frames, etc.

4. Poor quality materials may be used before detection for any of the finishes, e.g. plastic T & G, roofing cover, plywood.

5. Colour variation of plastic and wooden material used at finishes stage is a common error.

6. The finish of wood materials used may not shine as required and needs to be re-polished.

7. Slope in the flooring.

TIPS & OTHER CONSIDERATIONS

1. Other alternatives to using a plastic T&G for the eaves of the building includes, the wooden T&G, the plywood/particle board ceiling, asbestos or aluminum roofing sheets.

2. Plywood of the same veneer type as well as same kind of wood like Acala comes in different shades. Care should be taken to select same kinds of shade when purchasing.

3. Also most wood/plywood work does not come out good because the materials used were substandard from the start. Care should be taken in selecting standard materials when purchasing.