8 x 8 = 64 SF x 2 (sides)= 128 SF Total = 448 SF 448SF ÷ .89 SF/CMU = 503.4 or 504 total FB block Or, you can multiply the square footage of the building times  the  number  of  block  per  square  foot  (1.125 CMU/SF). 448 SF x 1.125 CMU/SF = 504 CMU If  you  were  planning  a  modular  building,  you would   use   the   square   foot   method   for   quicker estimating, but now there is another step you need to know—the   DUPLICATING   FACTOR.   This   means that every course will have a half block at each corner. For example, you estimated 504 FB for this building. To estimate the FB accurately, you would deduct two FB/course or multiply 12 courses x .5 (half block HB) x four corners = 24 FB. Then deduct the 24 FB from the total FB as shown in the following formula: 12 courses x .5 x 4 corners =  24 FB 504 FB -24 FB = 480 FB ESTIMATING DOOR AND WINDOW  OPENINGS When  you  estimate  CMUs,  usually  the  window and door openings are designed to be modular and the window and doorframes are of the same mode. If the design is NOT modular, you can expect a lot of cutting time. When you estimate for openings, just calculate the area of the opening, then subtract the area of the opening(s) from the overall area of the wall or building to get the net area. Then multiply the number of CMU per square foot by the net area. ESTIMATING  MORTAR Builders  have  found  that  it  takes  about  38  cubic feet of raw materials to make 1 cubic yard of mortar. Therefore, you can use  “rule 38”  for  calculating  the raw  material  needed  to  mix  1  cubic  yard  of  mortar without  having  to  do  a  great  deal  of  paper  work. However,  this  rule  does  not  accurately  calculate  the required raw materials for large masonry construction jobs.   For   larger   jobs,   use   the   absolute   volume   or weight   formula.   In   most   cases,   though,   and particularly  in  advanced  base  construction,  you  may use   “rule   38”   to   make   a   quick   estimate   of   the quantities of raw materials required. Here  is  how  you  use  “rule  38”  for  calculating mortar: take the rule number and divide it by the sum of   the   quantity   figures   specified   in   the   mix.   For example,  let’s  assume  that  the  building  specification calls for a 1:3 mix for mortar, 1 + 3 = 4. Since 38 ÷ 4 = 9 1/2, you need 9 1/2 sacks, or 9 1/2 cubic feet, of cement.  To  calculate  the  amount  of  fine  aggregate (sand), you multiply 9 1/2 by 3. The product (28 1/2 cubic feet) is the amount of sand you need to mix 1 cubic yard of mortar using a 1:3 mix. The sum of the two required quantities should always equal 38. This is how you can check whether you are using the correct amounts.  In  the  previous  example,  9  1/2  sacks  of cement plus 28 1/2 cubic feet of sand equal 38. In table 4-3, it takes 8.5 cubic feet (CF) of mortar to lay 100 SF of 8" x 8" x 16" block. In the previous example, you estimated the building at 480 SF of wall area.  To  calculate  the  amount  of  mortar  to  lay  the CMU,   first   convert   the   480   SF   to   units.   See   the following formula: 480 sf ÷ 100 sf = 4.8 units then multiply the units by the number of cubic feet of mortar; 4.8 units x 8.5 cf = 40.8 cf of mortar To calculate the ingredients needed to make 40.80 CF of mortar with a 1:1/4:3 mix, the 1/4 being hydrated lime, first calculate the amount of cement using rule 38. Remember the formula: 9 1/2 sacks of cement (94 lb/sk) per cubic yard. Use  the  following  formula:  First,  convert  cubic feet of mortar to cubic yards, 40.8 cf ÷ 27 cf/cd = 1.51 cubic yard. ESTIMATING MIXING TIME Let’s briefly cover the mixing time it will take to mix mortar. A typical mortar mixer has a capacity of mixing 4 to 7 cubic feet per batch, and each batch must be  mixed  for  a  minimum  of  3  minutes.  In  the  most recent example, we calculated a total of 61 cubic feet of  raw  materials  needed  to  construct  this  building. Now just divide the number of cubic feet per batch by the  total  number  of  cubic  feet  of  raw  materials,  then 4-4