Based on drying method bricks are classified into two groups:
- 1. Sun-dried bricks: These bricks are dried using sun heat directly after moulding. This type of brick is used in construction of temporary or simple structure like pizza oven. If there is a heavy rain, this brick should be used.
- 2. Brunt bricks: Normally, this brick is burnt in mechanical burner.
Bricks are also classified into four groups as follows:
- 1. First class brick: This type of brick is table moulded with uniform shape. Normally, these bricks are burnt in kilns. Edge and surface of this bricks are sharp, smooth, square and straight as well. It contains all composition in right proportion and for this right amount of silica, sand, water makes it first class brick. It doesn’t contain any salt as composition. You can use this bricks to build dome wall, foundation and hearth of pizza oven.
- 2. Second class brick: This type of brick is also ground moulded and burnt in kilns. But its surface, edge is not smooth, sharp like first class bricks. Surface is comparatively rough. Hair cracks may be in this type of bricks and size is also not uniform. This brick is less recommended for making pizza oven. Normally, it is used where brickwork with plaster is needed. But you can use this only for making foundation of pizza oven.
- 3. Third class brick: This brick is also table moulded and usually burnt in clams. This brick is not so hard like first class and second class bricks. Rough surface with burnt and irregular edge is seen on this bricks. If two third class bricks are struck together, it will produce dull sound and one brick may be broken. It’s use only for temporary structure and unimportant works. It is not recommended to use this type brick in making pizza oven.
- 4. Fourth class brick: Over burnt bricks with dark color and irregular shape is known as fourth class bricks. Fourth class bricks are used as aggregate in making foundation, surkhi, brick floor and the like. As this type brick is over burnt, it gives compact structure and higher strength. Sometime, it gives more strength than first class bricks. But it is not recommend for pizza oven construction. Only it can be used as aggregate under foundation of pizza oven.
How to test good quality bricks!
Brick is one of the important materials in making pizza oven. There are various types of bricks but all types are not good or suitable for making pizza oven. Even bricks are classified depending on their composition and quality. It is better to use first class brick for making your pizza oven. If you use first class bricks, it will mean better longevity of your pizza oven. Now, it is a question how to test quality of bricks or how to find out first class bricks! It is not very difficult to test bricks quality. If you subject a brick to some tests as follow, you will able to check quality of bricks that it is first class or second class.
At first weight of a dried brick is measured and recorded the data. Then brick is immersed completely in tape water for sixteen hours. After 16 hours weight of that brick is measured and difference in weight is calculated. Difference in weight means water absorbed by that brick. This amount should not be more than 20% of the original weight of dry brick if it first class brick. This test is simple and you should test your brick following the method.
Compressive or crushing strength
There are several local institutes which test compressive or crushing strength of brick by using compression testing machine. If there is any place where it is done, you can check your bricks. First class bricks will show crushing strength 14 Pa. Second class and third class bricks will show this value 7 to 13 Pa.
Hardness test is very simple and you don’t need to go outside for it. Just you have to hold a brick by your one hand and then try to mark on the surface of brick using your finger nail. If there is no remarkable scratch, brick is definitely of high grade. If there is mark on surface, it means damp brick and you should avoid this brick in making pizza oven.
Amount of soluble salt
Sometimes, bricks contain salt as a component of soil. If brick contains salt, it will cause efflorescence on the brick surface. If you use bricks contain salt, effloresce may be results on wall of pizza oven. So you have to check the salt content in bricks before using for pizza oven.
At first, you have to immerse a brick in water for a period of 24 hours. Then it dried in shade. If there is any white or grey deposit on surface, it will indicate the presence of soluble salt. If grey or white deposit covers 10% of the surface, brick is second class. Again, this deposit more than 10% to 50% indicates low quality of the bricks. First class brick does not contain any salt. So if there is no grey or white deposit on brick surface, it is definitely first class brick.
It is another simple test to check brick quality. For this test, you have to struck one brick by another one. Brick will be first class if it creates metallic sound without breaking down. Second class or third class bricks will not produce clear sound and may be broken. ok
Size and shape
There is a definite specification of brick. Quality bricks mean appropriate size and shape. Brick should be inspected closely for this test and brick will be rectangular with its sharp edge. Standard size of brick will be 190 mm × 90 mm × 90 mm (length × width × height).
By breaking a brick structure is examined. First class brick will be compact, homogeneous and free from defect like lumps, holes and the like.