Causes and How to avoid cracks when laying blocks.

Laying blocks without cracking requires some basic steps to watch out for. If you are careless the probability of having cracked walls will be high.
These amongst others are the causes and how to avoid them-
(1)Wrong block moulding mixture-Cement and sand mixture for sand needs to be properly checked which is usually between 1:6 to 1:8 depends on types of constituents.
Very good mixture for a 9” block will produce 30 pieces worst it should not exceed 50 on any account.
Stone dust are also added in a proportion to give a stronger block, trying to save cost by using inadequate cement, sand ratio will weaken your walls and can lead to cracks.
(2)Wrong cement mortar mixture-Mortar is what you use as the bond between one block and the other, the blocks are expected to be adequately bonded by the mortar, if this is weak it can also affect the block and can lead to cracking.
(3)Wrong laying pattern-Blocks should be set on each other in herringbone manner see diagram——


Laying the edge of one block on another causes cracking along the mortar line when is not broken by locking it up with other blocks, The vertical mortar line is the weakest point and should be broken by walls, straight line from top to bottom will cause cracking.
(4)Weak Foundation- Weak foundation causes unusual settlements and movements on foundation that will ultimately affects the blockwalls ontop, this surely will cause cracks from foundation through the walls . Cracks could be horizontal or vertical, the horizontal requires serious structural remedy because that may be due to uneven settlements.
(5)Plumbness or straightness when laying your blocks can also adversely affect the blockwork especially when is terribly done.
(6)Boring holes indiscriminately-Electricians and plumbers are major culprits on site when it involves creating holes on blockwalls. Caution needs to be taking when creating these holes which are used as scaffolding else you will have crack walls or you can go for total free standing scaffolds.
(7)Long, successive horizontal and vertical blockworks without concrete breaks- laying blocks on each other with any height beyond 3.6m without a corresponding concrete break will create pressure on blockwalls which can also cause cracking especially when the blocks are not strong and loadbearing.
(8)Wet blocks-Blocks are supposed to be left to dry and strong before usage, usually it takes minimum of 48 hours to cure, using blocks under 24 hours is not advisable and it leads to cracking.
(9)Mishandling of blocks-Proper care should be taken when blocks are in use.
(10)Impurities in mixture-When there are dirts in constituents ,expect a weak block which will surely leads to cracking.
(11)Improper or wrong materials will not help save money but will create problems, for instance using sand gathered from drainage gutter.
(12)Loosely compacted blocks during moulding will also affect the block which will lead to cracking of blockwalls.
(13)Inadequate concrete support incase of load.
(14)Shrinkage-When you build on a clayey soil which contract and expand. Clay causes movement in foundation and when the foundation is shallow it will affect the blockwall.
(15)Using fresh blocks
(16)Using unclean sand with clay just as stated in ‘14’,clay contracts when is dried and expand when it is wet, these movements causes cracking.
(17)Flooding-Areas susceptible to longterm flooding will also experience walls cracking, water can go underneath foundation, weaken the foundation and cause movements which will affect the blockwalls and leads to cracking.
(18)Differential settlements in foundation-Please check to make sure where you are building, the problems of differential settlements does not arise.
(19)unevenly compacted fill. When you fill the foundation with laterite but you didn’t ‘rammer’ or compact very well the areas with loose soil will affect the blockwall on top of it and cause cracks.
(20)When one side settles on rock which can’t have any further settlement with a corresponding soil area that is required to settle, expect cracking of walls especially when the block spans across.
(21)Poorly designed structure without adequate planning of walls joining each other.
(22)When you have extremely rich mortar mix, this will also affect block and make it to crack, especially when you want to remove and place elsewhere. It causes wall stiffness, there should be room for the wall to breathe.
(23)Rapid loading of blockworks-When you have a deadline and you put too many blocks on each other you are most likely to have cracks.
(24)Removing props or construction supports too early will create tension on the blockwall which can lead to cracks
(25)When you have deciduous trees with roots growing underneath the foundation.
(26)Natural disasters like earthquakes,winds,tremor,volcanoes etc
(27)Free standing walls-This is caused by bad designs when you have too many walls not locking with other walls. The isolated walls are likely to crack
(28)Rising damp around building.
(29)Poor drainage will make water gather around building which will ultimately affect the walls.
(30)Mining activities around building will cause vibration and affects the wall which can cause cracking especially when it involves blasting of rocks etc with explosives.
(31)Very short lintel (concrete) ontop of windows, doors and other openings will affect the surrounding blocks and cause cracks.
(32) No oversite concrete or german floor.

An architect with decades of experience

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