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## Block-Laying Basics

Estimating Masonry Materials

I begin each project by carefully estimating the square footage that will be built and adding in a factor of about 12 percent for cuts and waste. Next, I calculate the number of units needed based on the padded square-footage calculation, then determine the amount of mortar needed based on the number of units. Finally, I calculate the amount of sand I need based on the number of bags of mortar. I use the following formulas for my calculations.

## Units

• 1.125 8x16 concrete blocks are needed for each square foot of wall area

• 6.75 standard modular bricks are needed for each square foot of wall area

## Mortar

• One 80-pound bag of masonry cement, mixed 1-3 with mason’s sand, lays 35 8x16 blocks

• One 80-pound bag of masonry cement, mixed 1-3 with mason’s sand, lays 135 standard mod- ular bricks

## Sand

• 3 cubic feet of sand are needed for each bag of masonry cement

• 1 cubic yard of sand is needed for every nine bags of masonry cement

• 4.5 5-gallon buckets of sand = 3 cubic feet, the amount needed for each bag of masonry cement

word “masonry”). The letters indicate each type’s tested com- pressive strength, which is achieved by adding or reducing the percentage of portland cement in the mix. Type M mortar, for example, has the highest percentage of portland cement and the highest compressive strength, but for many applications it’s not the best choice.

Masonry cement mortar is the best overall choice for begin- ner masons. It’s inexpensive, easy to use, and the first choice for most residential masonry contractors. While cement-lime mortar and mortar cement mortar are frequently specified for large commercial projects, they are rarely necessary for residential work.

Generally speaking, Types M and S are used for foundations, for work under and in contact with the ground, and for flat work. Type N is a general-purpose mortar that can be used for loadbearing walls and exterior surfaces. It is usually recom- mended for vertical work above grade, such as brick veneer and chimneys. Type O is usually reserved for nonbearing walls not subjected to freezing temperatures. Because of local dif- ferences in climates, soils, and so forth, local codes concern- ing mortar requirements differ.

For the foundation shown here, I used Type S masonry cement mortar for both the block and the brick. This kind of mortar is required in my area for foundations and any work below grade.

## Mixing Mortar

Because premixed mortars are expensive, somewhat hard to work with, and sometimes of suspect qualit , I recommend buying mason’s sand and mixing it with masonry cement on site, even for very small jobs. You can get mason’s sand at just about any masonry supply house and most building supply stores. It’s usually sold in very small quantities; my supplier sells it by the shovelful, the 5-gallon bucket, and the cubic yard (see “Estimating Masonry Materials,” left).

While some masonry crews mix mortar by the bag (a com- mon recipe is to add 18 shovelfuls of sand for each 80-pound bag of masonry cement), I think that this method is inexact and makes too much mortar. A better way of mixing perfect mortar in manageable batches is to measure the sand and the masonry cement in buckets.

The recommended proportions are 1 part masonry cement to 212 to 3 parts sand. To make a fairly large batch of Type S mortar, therefore, I just fill up one 5-gallon bucket with Type S masonry cement and three equal-sized buckets with sand. I mix these together and add water until the proper consis- tency is reached to make correctly proportioned mortar that

NOVEMBER 2006 I JLC I 4

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