Mortar
Mixes
Here are seven common
and uncommon mortar mixes. They are types N, M, S and O. There is also
mortar for glass block, straight lime mortar and type K. Type K is used
solely in historic preservation. Each one has a certain proportion of
Portland cement, hydrated lime and sand. Mortar proportions are always
expressed in that order. Plus, these proportions always refer to volumes,
not to weight or a combination of volumes and weights. But then, the components
of these mixes are usually purchased by weight but that's not how the
mixes are measured.
A mix designated as 3/1/12 has 3 parts of Portland cement, 1 part hydrated
lime and 12 parts sand. Now let's say that you want to compute mortar
by the cubic yard. So how much of each mortar component is in a cubic
yard? Let's go through all seven of the mixes and see.
Be aware that the proportions of lime, cement and sand in each mix type
can vary a bit by geographic regions or by contractors within a region.
However, we are showing you the commonly used proportions and if you are
used to something a little different, then you are simply using a regional
or personal variation on the standard.
Also, these amounts are designed to add up to exactly one cuyd of material.
Field amounts can show other quantities of components due to the realities
of outdoor mortar mixing. Much of the literature on mortar proportions
and mixes show greater or different quantities due to the great amount
of waste in the actual preparation, transportation within the job site
and handling during the use of a batch of mortar. The numbers shown here
reflect computed amounts. These are exact mathematical measurements down
to the spoonful (though we give you final amounts of sand in tons and
the other parts in bags). The tons and bags are finely measured. The terms
hydrated lime and lime
putty mean the same thing since lime putty is simply wet hydrated
lime (you added some water to it and stirred it up) whereas in hydrated
lime all of the water molecules are stoichiometrically bonded to the calcium
and magnesium in the lime and the lime remains a dry powder. Lime putty
is just wet hydrated lime.
The mix calculations use densities set out by the ASTM.
These are:
Portland cement 94
lbs/cuft
Hydrated lime 40
lbs/cuft
Sand 80
lbs/cuft
The purchased items are by these:
Portland cement 94
lb bags
Hydrated lime 50
lb bags
Sand by
the ton
Component amounts
Type N mortar
This uses a 1 / 1 / 6 mix and results in a mortar with a 750 psi compressive
strength. Type N is the normal, general purpose mortar mix and can be
used in above grade work in both exterior and interior load-bearing installations.
To get 1 cuyd of N mortar, you need 27 cubic feet of the components in
a 1 to 1 to 6 proportion.
Portland cement 3.375
cuft
Hydrated lime 3.375
cuft
Sand
20.25 cuft
Total 27
cuft
Based on the ASTM densities, this gives you 317.25 lbs of Portland cement,
135 lbs of hydrated lime and 1,620 lbs of sand.
To put together a single cubic yard of type N mortar, you need to buy
and mix together:
3.375 bags of Portland cement (94 lb bags)
2.7 bags of hydrated lime (50 lb bags)
0.81 tons of sand
Type M mortar
This uses a 3 / 1 / 12 mix and results in a mortar with a 2,500 psi compressive
strength. Type M is used for below grade load-bearing masonry work and
for chimneys and brick manholes.
To get 1 cuyd of M mortar, you need 27 cubic feet of the components in
a 3 to 1 to 12 proportion.
Portland cement 5.0625
cuft
Hydrated lime 1.6875
cuft
Sand 20.25
cuft
Total 27
cuft
Based on the ASTM densities, this gives you 475.875 lbs of Portland cement,
67.5 lbs of hydrated lime and 1,620 lbs of sand.
To put together a single cubic yard of type M mortar, you need to buy
and mix:
5.0625 bags of Portland cement (94 lb bags)
1.35 bags of hydrated lime (50 lb bags)
0.81 tons of sand
Type S mortar
This uses a 2 / 1 / 9 mix and results in a mortar with a 1,800 psi compressive
strength. Type S is used for below grade work and in such areas as masonry
foundation walls, brick manholes, retaining walls, sewers, brick walkways,
brick pavement and brick patios.
To get 1 cuyd of S mortar, you need 27 cubic feet of the components in
a 2 to 1 to 9 proportion.
Portland cement 4.5
cuft
Hydrated lime 2.25
cuft
Sand 20.25
cuft
Total 27
cuft
Based on the ASTM densities, this gives you 423 lbs of Portland cement,
90 lbs of hydrated lime and 1,620 lbs of sand.
To put together a single cubic yard of type S mortar, you need to buy
and mix:
4.5 bags of Portland cement (94 lb bags)
1.8 bags of hydrated lime (50 lb bags)
0.81 tons of sand
Type O mortar
This uses a 1 / 2 / 9 mix and results in a mortar with a 350 psi compressive
strength. Type O is a lime rich mortar and is also referred to as "pointing"
mortar. It is used in above grade,
non-load bearing situations in both
interior and exterior environments.
To get 1 cuyd of O mortar, you need 27 cubic feet of the components in
a 1 to 2 to 9 proportion.
Portland cement 2.25
cuft
Hydrated lime 4.5
cuft
Sand 20.25
cuft
Total 27
cuft
Based on the ASTM densities, this gives you 211.5 lbs of Portland cement,
180 lbs of hydrated lime and 1,620 lbs of sand.
To put together a single cubic yard of type O mortar, you need to buy
and mix together:
2.25 bags of Portland cement (94 lb bags)
3.6 bags of hydrated lime (50 lb bags)
0.81 tons of sand
Type K mortar
This uses a 1 / 3 / 10 mix and results in a mortar with but a 75 psi compressive
strength. Type K is useful only in historic preservation situations where
load bearing strength is not of importance and the porous qualities of
this mortar allows very little movement due to temperature and moisture
fluctuations. This aids in prolonging the integrity of the old or even
ancient bricks in historic structures.
To get 1 cuyd of K mortar, you need 27 cubic feet of the components in
a 1 to 3 to 10 proportion.
Portland cement 1.93
cuft
Hydrated lime 5.79
cuft
Sand 19.29
cuft
Total 27
cuft
Based on the ASTM densities, this gives you 181.42 lbs of Portland cement,
231.6 lbs of hydrated lime and 1,543.2 lbs of sand.
To put together a single cubic yard of type K mortar, you need to buy:
1.93 bags of Portland cement
4.632 bags of hydrated lime
0.7716 tons of sand
Straight lime mortar
This uses a 0 / 1 / 3 mix and is used now only to recreate the construction
and review the methods of times past or maybe for purely visual purposes.
This mortar was made before Portland cement was available in many areas
and so this is what was used. Sometimes you'll see straight lime mortar
called "L" mortar (for lime)
but this is not designating it as "type L" mortar as in the
MSNOK types. There is no "type L" mortar.
To get 1 cuyd of lime mortar, you need 27 cubic feet of the components
in a 0 to 1 to 3 proportion.
Portland cement none
Hydrated lime 6.75
cuft
Sand 20.25
cuft
Total 27
cuft
Based on the ASTM densities, this gives you no Portland cement, 270 lbs
of hydrated lime and 1,620 lbs of sand.
To put together a single cubic yard of lime mortar, you need to buy:
No bags of Portland cement
5.4 bags of hydrated lime (50 lb bags)
0.81 tons of sand
Glass block mortar
This uses a 1 / 1 / 4 mix and is used with as little water as possible.
This is a mix designed specifically for glass block. Also, note that it
uses waterproof Portland cement in
place of "regular" Portland cement.
To get 1 cuyd of glass block mortar, you need 27 cubic feet of the components
in a 1 to 1 to 4 proportion.
Waterproof Portland cement 4.5 cuft
Hydrated lime 4.5
cuft
Sand 18
cuft
Total 27
cuft
Based on the ASTM densities, this gives you 423 lbs of waterproof Portland
cement, 180 lbs of hydrated lime and 1,440 lbs of sand.
To put together a single cubic yard of glass block mortar, you need to
buy and mix:
4.5 bags of Portland cement (94 lb bags)
3.6 bags of hydrated lime (50 lb bags)
0.72 tons of sand
Note
Lime types versus Mortar mix designations
Limestone formed by nature contains varying proportions of calcium to
magnesium. No large scientist with a giant beaker and a set of stoppered
test tubes measured out the things that make up rocks beforehand. Some
of it has more magnesium while other limestone rock has more calcium.
For making mortar, it is desirable to have from a third to a half of the
rock from which the mortar lime is derived composed of magnesium carbonate.
The remainder then would be from one half to two thirds calcium carbonate.
A limestone whose composition falls within these percentages is dolomitic
limestone and from it is made Type
S lime hydrate. Masonry lime made from limestone that is composed
of less than 5% magnesium carbonate (called high
calcium limestone since it is 95% to 99% calcium carbonate)
is labeled Type N lime hydrate. Type S lime is used to make masonry mortar.
Type N lime can be used only if it
is tested and proven on a batch by batch basis. The type S
lime designation stands for Special
and the type N stands for Normal.
The special lime hydrate is the one normally used and the normal lime
hydrate is used only with special testing. These lime "types"
have absolutely nothing to with mortar mixes type N and type S. You must
never, ever confuse these lime hydrate types with mortar mixes. They have
nothing to do with one another. Why "they" should label them
with the same designations, we have no idea.
Mason Work
The five typical mortar mixes designated types M,S,N,O
and K are labeled so because each
is an alternate letter in the term MASON WORK
in descending psi strength. These designations were assigned in 1954 and
replaced the mortar designations A-1, A-2, B and C.
M 2,500 psi
A
S 1,800 psi
O
N 750 psi
W
O 350 psi
R
K 75 psi
Know that a weaker psi mortar is not a "bad" or inferior mortar
to one with a higher psi. A lower psi mortar has much better adhesive
and sealing powers than a higher one. Mortars are selected on the balance
between these attributes as to what is required for the building situation
on a particular spot in the job. A type M mortar with its high strength
yet poor adhesion and sealing can be a bad choice for one area of the
job and just what is needed in another.