hi boo-semi-retired!

thanks for this post and it really helps a lot.
i want to make a calculation on my own since i felt i was being ripped off by our foreman with the materials before since i was not on the site most of the time.So on our next project i want to be there.lesson learned.

So based on the formula you provide i came up with this and correct me if i'm wrong pls.

1 cu. mtr of sand could be divided into 8 parts based on 0.0120 sand per sq mtr of wall.

0.0708 bag of cement multiply by 8 is 5.6 bag of cement or round it to 6 bags.

with a ratio of 1:6:0 for mortar
1 cubic mtr of sand + 6 bags of cement can fill 8 sq. mtrs of CHB wall.

is my computation right?and please bear with me on this.

thanks in advance

yes, your computation is right if you want to get an estimate base on a cubic meter of sand. don't forget to allocate some percentage for wastage and other factors. in my case, in our house construction, i use a 10% variance for wastage ... cheers

Boo!

thank you so much.i'm working on my calculation bit by bit.i also used your formula for plastering.
at least in 2 mnths time i could gather all the info needed and my foreman would be surprised that a woman like me knows a little bit of this and that and i won't be ripped off again!

Mind if I interrupt cause I don't want to just sit and do nothing about this wrong information, this might lead to others to follow wrong computation and might fired from their job by following this very tedious and lenghtly process of estimation and ending with wrong output.

First, the computation of 10.5 cavities of 0.008cu.m. is for the first layer of chb only, it must be multiplied by 5 layer the same thing you did in the horizontal mortar in between layers. Thus the correct volume of all cavities for the 1m x 1m area of chb is 0.008*5 + 0.006(5 horizontal)=0.046cu.m. ,then the rest of ratio can be now computed correctly.

Secondly, the idea of Ms. idp of dividing the sand by parts is OK, but you already fall in wrong factor of 0.0708 bags of cement per sq.m. of chb. And one more, Ms. idp computation of 0.0708×8=5.6, really!!! my gosh, this is a complete defeat of all your math subject since elementary, compute again it's 0.566 not 5.6...

i just found a bug in the mortar (cement and sand) computation of my estimate for a 1 sqm of wall using 4" CHB while i was reviewing the formula last night. the 0.0532 cubic meter of sand and 0.3133 bag of cement from my previous posting replies was WRONG. the 12.5 4" CHB for 1 sqm of wall is still CORRECT ...

below is the correct computation for the estimate i did, after checking all my old notes from our house construction ... apologize for the wrong info before ...

4" CHB dimension ... L=400mm x H=200mm x W=100mm (approx 16" x 8" x 4")

dimension of 1 cavity in a 4" CHB ... 50mm x 90mm x 170mm

i have remove the plastering and rebar (2 pcs of 1m lenght 9mm deformed rebar for 1 sqm of wall) in the estimation of a 1 sqm of wall as it makes more sense to compute the estimate of these items separately on a per wall basis based on the house/bldg plan.

to get the amount of mortar required for a 1 sqm wall, first we need to estimate the area/volume in which the mortar will be put. these are:
- a 4" CHB normally has 3 cavities each measuring an area of approx 90mm x 50mm x 170mm.
- at the sides of a 4" CHB, you can also see a half-circle (or half-square) grove. if you set 2 CHB in a line with a 1/2" clearance between the 2 CHB, the area for the mortar can also be computed as approximately 1 cavity too. since each 1m (1000mm) length of wall will require about 2.5 CHB, this means another 3 cavities for the 2.5 CHBs in a row.
- so total cavities (vertical area) per row will be 6 (for the 2 CHB) + 1.5 (for the 1/2 CHB) + 3 (for the 2.5 CHB per row) = 10.5 cavities.
- the height of a CHB is approx 200mm, add the 1/2" (12mm) mortar height between rows, you have approx a 212mm height. in a 1m high wall, you will then need approx 5 rows (1000mm / 212mm = 4.72) of CHB.
- the area for the mortar in between rows (horizontal area) of CHB will be about 1/2" (12mm) high with a lenght of 1000mm (1m) and a width of 100mm (4")

using the same formula for computing concrete with a mix ratio of 1:6:0 (cement:sand:gravel) for mortar, you can then compute the total volume of concrete needed for the area of 1 sqm wall of 4" CHB ...
- for each cavity (vertical area), the area/volume is ... {[(90*50*170) / 100000] / 10000} = 0.0008 cubic meter * 10.5 (number of cavities in a row) = 0.0080 cubic meter of concrete
- for each row (horizontal area), the area/volume is ... {[(1000*100*12) / 100000] / 10000} = 0.0012 cubic meter * 5 (number of rows) = 0.0060 cubic meter of concrete
- total volume = 0.0080 + 0.0060 = 0.0140 cubic meter of concrete for a 1 sqm wall

having the concrete volume, we can then compute for the cement and sand using a mix ratio of 1:6:0 - gravel or aggregate is not needed for mortar ...

so, to get the amount of cement needed for a 0.0140 cubic meters of concrete the formula is ... (volume * ratio of cement) / mixture total ratio ... (0.0140 * 1) / 7 = 0.0140/7 = 0.0020 cubic meter of cement ...

so, to get the amount of sand needed for a 0.0140 cubic meters of concrete the formula is ... (volume * ratio of sand) / mixture total ratio ... (0.0140 * 6) / 7 = 0.084/7 = 0.012 cubic meter of sand ...

in summary ... 0.0140 cubic meters of concrete with a ratio of 1:6:0 will require ...
0.0020 of cement
0.0120 of sand
--------
0.0140 cubic meters of concrete (total) ...

to convert the amount of cement into bags of cement ... just multiply the cement in cubic meters by 35.31 ... 0.0020 * 35.31 = 0.0708 bags of cement ...

cheers ...

Boo!

pls correct your computation, all cavities for 5 layers of chb or 4.75 layers to be exact because of horizontal mortar in between layers total volume should be 0.008*4.75 (or 5) layers= 0.038 + 0.0012*5layer = 0.044 cu.m. for 1sqm of chb

Hello po, how about 1 sqm Wall of 6"

Let me check my old notes, i know i made some calculations using a 6" CHB ... cheers ... Boo!

You have a good point here!I totally agree with what you have said!!Thanks for sharing your views...hope more people will read this article!!!