EXPANSION JOINTS DEFINITION AND CALCULATION
In the previous Fixcer Informa we talked about the reason for expansion joints, their advantages, regulations, types, etc.
In this new report, we will develop other no less important aspects.
The quality of the filler:
We differentiate between the quality of fillers by looking at speed at which they cure, their sag resistance, Shore hardness, elastic modulus, etc., but it is their Elongation until breakage and their Capacity for Movement which are the two most important data points. The problem is that these points are often confused.
Elongation until breakage is defined as the maximum elongation that a filler can reach until it yields by breaking. It is usually a spectacular value, as we are talking about 250%, 400% or even 500%, but its importance is relative as this value is only achieved on a very small number of occasions.
The really effective data is the filler’s capacity for movement. We conceive of this as the value of elasticity that is capable of developing for a practically unlimited number of times. The aim is to be able to “absorb” the movement of the facing as many times as the number of days the expansion joint has been in use.
Calculation of width “A” of a sealed expansion joint:
We will need to know the following data:
- T1 = maximum temperature to which the facing will be subjected (e.g.: +40ºC)
- T2 = minimum temperature to which the facing will be subjected to (e.g.: +10ºC)
- D = distance we are interested in having between expansion joints (e.g.: 15 ml.)
- C = coefficient of thermal expansion of the material the facing is made in (e.g.: 7×10-6)
- M = movement capacity of the filler we will use to seal the joint (e.g.: 25% => M = 0.25)
The minimum width of our sealed expansion joint will be:
A = D x (T1-T2) x C x 100 / M = 15 x (40 -10) x 7×10-6 x 100 / 0.25= 1.26 cm.
Correct execution of the expansion joint:
We already know that our expansion joint must have a minimum width of 1.26 cm. It will now be good to stick to a few basic tips for proper implementation:
- the depth of the joint shall never exceed the width of the joint.
- the filler must not stick to the bottom of the joint. Before applying the filler, fill the bottom with an elastic element such as polystyrene, rubber,…
- we can smooth out the filler using a similar tool and a little soapy water.
- use masking tapes to protect non-slip, rough ceramic tiles,…
- in swimming pools, the drying speed shall be taken into account before filling it with water.
