Cracks in brick work/plastering

We build walls with thickness 225 mm and 112.5 mm thick using bricks. The windows and doors are made of Padak wood.
The building is 3 storey with framed structure.

Within four months plenty of cracks are seen on the walls.
Also on the parapet walls in the terrace.

Mostly in 112.5 mm thick walls.

What could be the reason for the crack? What is the remedy.

Regards

B.Suresh Babhu

 

[dik]

What type of soil is the home founded on? and can you describe the type of cracking? at window and door openings? If you look at a wall, can you describe the pattern of cracking?

 

[Sureshbabhu]

Dear Sir,

Sandy soil. 750 m from the sea shore.

1) Verically upward after a few inches from the top centre of the door.

2) Corner of window w5 deg downward from downward corner. Upward from upward corner.

3) No relation ship to window corners. just like that at 90 deg down ward from roof in 112.5 mm walls.

4) At Every 6 /7 ft distance in parapat wall on both sides continuing downward on the outer side of the parapet wall.

I hope I have explained.

 

[ishvaaag]

It is a matter of seeing how your building stands in rigidity. The general impression reading your description is being something related to dishing of the foundation, maybe being as well related to too flexible beams and/or floors. You say it is a framed building, for it I take there being columns and beams.

Now that we are FEM we can model entire buildings including partitions ans look how the deformations fare.

For spans over 5 m you may expect cracks in partitions if you have end to center distortions of L/500 under the total service load, live included. Masonry cracking starts even at L/1500 distortion, and is more noticeable if the parts are big since they have less binding per unit area.

A common rule here is not allowing for total service load, live included over L/400 or L/500 if only partitions not bearing loads and L/1000 if bearing.

The reinforced concrete code asks the damaging deflection (coming from superimposed dead load such floor tiles plus live loads after creep not exceeding L/400 if only partitions. If bearing loads the total deflection of the same loads after creep must not exceed 1 cm.
Furthermore, the longterm after creep total service load deflection must not cause at any part deflection over L/250.

You check then in FEM and for modest modulus of elasticity where you stand respect defelection and dishing of the foundation. Under dishing action the building sinks (usually) more at center than at corners. For moderate size buildings one can gain some control over it by designing continuous beam foundations able to effectively coopt deflections to deformations under those specified.

For modulus of elasticity of the masonries you can take about 500 times the squashing stress value.

Some creep and dishing effects surely are involved since you mark cracking becoming noticeable 4 months afeteer construction.

Also look if you exceed dimensions between joints common for trhe kind of building.

Solution? Make the deformation analyisis first. If you see this is something is not very grave case, and safety is properly established, dishing and deflection under creep eventually come to so slow progression that is tantamount to stop. The bad news is that if too flexible cracks could reopen upon use. You can track progression by measuring widths, do so, you will chart them and will know if divergent towards failure or convergent to a final deflection or width of cracks.

If sable and safe but still not rigid enough to oppose further unwanted deflection, you may think in reinforcing your foundation by lateral attached continuous beams to diminish the dishing action; if your building is too long this may be won't be effective. Setting your new added beams in the shorter direction will help more. And furhter action may be needed at the fllor levels if something has gone wrong with the stiffness of the beams and floors.

Respect repair cosmetically is not much difficult once the progression of the cracks has stopped. You ensure adherence sometimes breaking a bit more, and gypsum plaster plus some elastic repair wands are enought to satisfy most except the more exactings owners.

 

[Ron]

The cracking you have described is not load related, but related to shrinkage. It is likely that the bricks were wet when placed and/or the mortar was overly wet.

Masonry should be placed as dry as practicable so that further shrinkage is minimized. This also enhances the bond of the mortar to the masonry units, as absorption at time of placement increases the bond potential.

 

[ishvaaag]

What Ron says being shrinkage can be, there being parallel so close cracks. In any case, setting the units dry cause problems of adherence, since capillarly robs water to the setting mortar, and this lack of adherence could show as well as cracks in the joints both horizontally and vertically. Other possibility of the shrinkage kind is having used a too rich in binding agents (cement) mortar. That will make the masonry the stiffer it can become and then 1st) will have more shrinkage since the mix is too rich and 2) it will be fragile for any concomitant deformation or restraint.