Checking a Builder's Square on a Construction Site
On most construction sites you will come across building squares which are lying about, don’t assume that they are accurate and true.
Generally, after their initial use, they are mistreated so you need to check the building square for accuracy.
There are two ways I am going to show you how to check your build square is accurate and true, one method is using a mortar screed and the other is measuring the building square using the 3-4-5 method.
Tools and Equipment Needed
Pencils
Spirit Level
Builder's Square
Brick Trowel
Tape Measure
Find an area on the construction site which is clean and level and nobody is working on, lay a small bed of mortar in the shape of a upside down T
T shape band of mortar needs to be slightly larger than your building square, remember to allow enough mortar screed when you need to reverse the building square on the perpendicular line.
With the back of the trowel spread the mortar out into a thin layer of screed
Place your spirit level onto the mortar screed and strike a line with the point of your trowel, this is your baseline.
Your building square needs to be placed onto the baseline so that the corner of the square is more or less in the centre of your baseline.
Using your point of the trowel strike a line with the point of your trowel, this is your perpendicular line.
To check the building square is accurate simply lift carefully and placed the building squarely on the opposite side of the perpendicular line and the baseline, if both lines are in line with your building square then your square is accurate and true.
3:4:5 Method
You can check a building square by using the 3:4:5 method, all you need is a tape measure and a pencil.
Place the building squarely on the flat surface, using the hook of the tape measure to place it on the end of one of the sidearms of the building square and using a pencil mark out 300mm.
Repeat the above process on the opposite arm, but this time do a pencil mark at 400mm.
To check to make sure that the building square is accurate, you need to place the hook of the tape measure on one of the marks and extend the tape measure so it crosses the opposite pencil mark.
The building square is accurate if the measurement between the two pencil marks is 500mm.
When using the 3:4:5 rule works the same if you’re using metres, centimetres or even feet and inches providing that you use the same units for all three sides.
Issues with Inadequate Buildings Square
Setting out a building with an inadequate building square will send your ranging lines out of square.
For example in fig 10, the arm of the building square is out by 2mm doesn’t look a lot but over 5m this will increase the inaccuracy to 10mm.
So you must check your building square for adequacy before setting out any square or rectangle shapes in your construction project.
