Sand Void Percentage Calculation
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| Sand Void Test |
Sand
Void Percentage Test: sand is nothing
more than irregular rocks that come are found in various sizes and shapes. Due to the irregular shapes and sizes in
grains of sand, there is a fair amount of empty space that must be filled in
order to create a high quality binder, such as lime plaster. It is important to note that this is a volume
test. The procedures for the Sand
Void Percentage Test are as follow:
Dry
sand as much as possible. Ideally, the
sand used at a job site will be dry, but since sand is generally sold by the
cubic yard, it is often delivered in bulk and is exposed to the elements.
Place
an arbitrary volume of sand in a quantified measuring container. The larger the sample, the more accurate the
results. 64 oz. of sand was used for our
project.
Add
water to the sand from a measuring container until the water just begins to
pool on top of the sand. It is essential
to note how much water it took to saturate the sand. 20 oz. of water was required to saturate the
sand used for our project.
Apply
the formula: Water Volume / Sand Volume x 100% (For our test: 20 oz.
water / 64 oz. sand x 100% = 31.25 % or approximately a 1 : 3 of void : sand)
Bulked Sand Test
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| Bulked Sand Test |
When
sand is damp or even slightly wet, it tends to swell in volume, but returns to
its true volume when completely saturated.
It is important to test the bulked volume of sand before developing a
mortar mix as it will indicate the true amount of sand on hand and possibly
alter production costs. It is important
to note that this is a Volume test.
The procedures for this test are as follow:
Take
an arbitrary amount of sand in a quantified measuring container. Larger samples will produce more accurate
results. 64 oz. of sand was used for our
test.
Add water to the sand until it is completely saturated and pools at the
surface of the sand. It is not important
to note the amount of water used.
Measure
the new decreased volume of the sand.
Apply
the formula: Original Volume of Sand - New Volume of Sand / New Volume of
Sand x 100 % (for our test: 64 oz. sand - 48 oz. sand / 48 oz. sand x 100 %
= 33%. This shows that the dampness has
caused the sand to bulk, increasing its natural volume by a third).
Preparing a Test Mix
When designing a mortar, it is more
convenient to prepare small samples. Dry
binders swell even more than sand, so the data gathered in the Sand Void
Percentage Test will be used for this procedure. Unlike the Sand Void Percentage Test and
Bulking Test, this is a Weight test as it will yield more accurate
results for a test mix. The procedures
are as follow:
Take
an arbitrary, measured amount of dry sand.
48 oz. was used for our test.
Weigh the sand on a scale. For our test, 48 oz. of sand weighed 5.40 lbs
.
Recall
the sand void percentage from the earlier test.
( void : sand 1 : 3 in our test)
Apply
the formula: void: sand x sand weight = binder weight (1 /3 x 5.4 lbs =
1.8 lbs in our test)
Make
a mortar mix of binder weight: sand weight and apply (for our test: 1.8 lbs NHL
to 5.40 lbs sand)
Compare Binder Volume to Sand Volume
This
is a important step to take after the test mix is made as it will save time
when preparing the production mix. This
is a Volume test. The procedure
is as follows:
Make
note of the binder volume when weighing in the test mix process. (in our test,
1.8 lbs NHL took up 40 oz.)
To
find the percentage of binder volume to sand volume apply the formula:
Binder
volume / Sand volume x 100% = Binder % (in
our test, 40 oz. NHL divided by 48 oz. sand x 100% = 83% binder)
Calculating the Production Mix
The
production mix will be using much larger quantities than the test mix, and for
our test, the bulking of the sand from the outdoor pile will be taken into
account. The results from the Bulked
Sand Test and Sand/Binder Comparison will be used for this procedure. It is important to note that this is a Volume
test. The procedures are as follow:
Determine
a convenient volume measure of sand (1 ft3)
Convert
this to an even more convenient volume (1 ft3 = 7.5 gallons)
Bulking
is accounted for by the applying the formula: Bulked sand volume + Bulked
sand volume x Bulked sand % = volume of bulk sand needed (for our mix 7.5
gal + 7.5 gal x 33% = 10 gal bulk sand)
Remember
that once bulked sand is saturated, it shrinks back to its true volume (this
means that in our project, it took 10 gal. of bulked sand to obtain 7.5 gal of
saturated sand, its true volume).
Determine
the volume of binder as a % of the volume of sand. The true volume of sand is used not the
bulked volume. Apply the formula: Sand
volume x Binder % = Binder volume (in our test: 7.5 gal. sand x 83% = 6.25
gal. NHL). These results showed us that
10 gal. bulk sand to 6.25 gal. NHL would give us a 1 : 3 ratio of sand : binder
by weight.
Estimating Binder and Sand for a Project
In
traditional three –coat plastering, the scratch and brown coats serve to fill
voids and provide keys therefore; there is a minimal amount of binder in the
mix. As a result these two coats do not
increase the sand volume which means that it can be assumed that the sand
volume is the equal to the volume of the material on the wall. Estimating is a Volume test and will
use the arbitrary sand volume and determined binder volume from the Production
Mix Calculations (1 ft3) in our estimate.
Sand is typically delivered by the cubic yard which is equal to 27 ft3. The procedure used for estimating our project
is as follows:
1/8”
is the thinnest coat typically applied in plastering, so based on this we can
figure that 1 ft3 of plaster cut into
1/8” slices yields 96 slices (8 x 12 = 96).
This means that at 1/8” thickness 1 ft3 of plaster will cover 96
ft2. Each slice is 1 ft2 and 1/8”
thick.
This
information can be used to calculate the following:
@
1/4” = 48 ft2
@
3/8” = 32 ft2
@
1/2” = 24 ft2
@
3/4” = 16 ft2
@
1” = 12 ft2
To
estimate the volume of sand needed apply the formula: total ft2 / average
thickness yield = # of batches (for our project we estimated that at an
average thickness of 1” and a total of 600 ft2 = 50 batches or 50 ft3 of sand).
The
amount of binder is estimated by applying the formula:
#
of Batches x binder volume per batch = total binder volume
(for
our mix we estimated that 50 batches x 6.25 gal NHL = 312.25 gal NHL)
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