Selecting
a stone for use requires that many questions
are asked. "Who is doing the selection?" is
one main question. When an architect/designer
selects a stone he should be aware of the criterion
for color, finish, application, quality, installation,
and aesthetics for the job. When a contractor,
owner, or individual selects a stone he will
normally do it for price considerations and
color only. For this article let us assume that
we are selecting a stone for a commercial job.
Let
us define dimension stone or building stone
for commercial purposes as any decorative stone
such as marble, limestone, travertine, slate,
quartzite, and granites which has been cut to
size for specific applications. These probably
are most of the stones used in such jobs. More
and more people are looking at shellstone, sandstone,
and other natural fossil type stones that have
a rustic look. People are always introducing
other stones in hopes of finding a niche in
the market for the rustic look that so many
people are requiring.
Most
often consideration should be given whether
the stone is for the exterior or interior, or
for vertical or horizontal surfaces (walls vs.
floors or table tops-countertops vs. bathrooms).
Do not forget to know whether stone in cubical
form for columns, arches, or other applications
is required. This may cause a different selection
to be done due to price and structural strength
of the stone which at this moment we are not
considering. We will consider the selection
as it applies to tile, or standard 3/4" (2cm)
or 1-3/16" (3cm) thickness as this accounts
for 95% of all stone purchased.
In
considering a stone there are always lots of
questions to ask about the job before looking
at any stone. It is imperative to know whether
the stone is to be used in freeze-thaw climate,
wet conditions like around spas or in bathrooms,
heavy traffic areas like shopping mall floors,
or exterior cladding. Know what size panels
will be required or how much quantity is estimated
to be needed and when will it be required?
To
select a stone we need to understand how stone
is quarried and fabricated. Some stone comes
from mountains, others from underground, and
others from river beds. Slate is usually found
in river beds or underground mines.
Slate and Quartzite will have size
limitations and finish limitations. Usually
these can be used on the exterior and interior.
Slate is derived from shale and is usually clad
together as layers, thus allowing it to be split
with irregular facing. Normally slate can be
supplied in tiles of 1/4" or thicker and is
normally supplied with cleft faces or honed
faces. The sizes are usually limited to tiles
of no more than 18" x 18" x 1/4" or slabs cut
to size of no more than 28" x 50".
There are always exceptions and some kinds of
slates can be quarried in larger slabs of 4'
x 8'. Slate is good for flooring due to its
natural cleft face which gives more slip resistance.
It is also good for exterior and roofing applications
in most cases. It comes in an abundance of colors
from many countries.
Limestone
or Travertine (sandstone, coquina, dolomites,
fossil or shellstone) is usually quarried underground.
It often has size restrictions and usually will
not take a polish finish. Sometimes you will
need to specify whether you are needing a dolomitic
or oolithic limestone.
Normally buyers are selecting this stone with
honed or rustic finishes for its texture and
grain. This material may be used for exterior
applications if it passes certain tests. You
must be careful to question the absorption of
the stone for its application. Normally limestone
will have a high absorption rate and are not
suitable for wet climates unless treated with
sealers.
Also many limestone's are soft and thus wear
easily on flooring applications. Some limestone's
are very hard and can be flamed. However, there
are not as many of these available as those
that do not take a flamed finish. There may
also be size restrictions when selecting this
stone. Many times you will find holes in this
material which may be kept as natural or filled
with synthetics such as epoxy or cement.
Marble
(greenstone, onyx, serpentine, some limestone's)
is defined two ways: as a stone which has been
re-crystallized (the geological definition)
or as any limestone that will take a polish
(the commercial definition). As we are all finding
out today, most marbles coming from Spain, for
example, are really limestone's and customs
is charging a higher duty. Usually marbles will
be found in mountainous areas.
Therefore, the factors that apply to limestone's
apply here. In addition to the comments about
limestone's, consider that many colorful marbles
have quantity restrictions as they are only
a selection within the same quarry.
Many marbles have tremendous color variation
and could require 20 samples to show the full
variation in the stone. However, due to the
colors available you will usually have a much
larger selection from which to choose. Some
of these marbles may have holes or cracks and
require reinforcement with fiberglass net backing
or filling.
Most marbles are used decoratively on interiors
and very few are acceptable for exterior use
unless you have special conditions. Most buyers
want this material to be polished even though
it is recommended to be honed, especially on
flooring applications.
Granite
(gneiss, gabbro, diorite, basalt), an igneous
rock, is probably one of the most used commercial
stones, especially in exteriors. It is very
hard and durable, as are quartzite's, and very
suitable in most cases for severe weather conditions.
Usually granites are found in mountainous areas
and are monolithic in design. The size of the
grains may vary from fine to large. The color
may vary but is usually homogeneous. In some
cases you can find granites with a lot of character,
veining, and color variation. The granites are
usually found in large deposits and large sizes.
Many granites are being used on interiors, especially
as flooring since it will hold a polished finish
longer than marble and wears less than marble
or limestone. Being one of the most dense stones
and very good for abrasion resistance it lends
itself to many textured finishes such as flaming,
bushammering, sandblasting, acid, chiseling,
etc.
The
problem most buyers have in selecting a stone
is that they only see a very small sample or
only what the salesman shows them. The name
is usually changed to confuse the buyers and
maintain a lock on who can supply the stone.
Usually the buyers do not get enough information
on the stone to make a proper judgement.
They select the stone simply for its color,
only to find out later that the color varies
more than they can accept or it is not suitable
for the application intended, or there is not
enough time to obtain the quantity they require.
Therefore, it is wise to ask the following questions
about the stone before making a final selection:
1)
What color and texture do you want? There may
be many stones that fulfill your requirements
after much investigation. Once you have chosen
several stones that fit your needs, then proceed
to the next step in narrowing down whether the
stone will fit your qualifications and standards.
2)
What is the actual quarry name of the stone?
Where is it quarried and is there more than
one quarry? If you do go to bid with a fictitious
named stone, you may have lots of problems getting
competitive bids and others will offer alternate
stones in lieu of what you want. Further, if
you ever had to get more material at a later
date, you may not be able to obtain it. What
type of quarry is it? Are blocks available in
large sizes? If so, what is the maximum size?
How much quantity per month is available? In
some cases, you may even wish to specify the
layer in the quarry where the stone is located
that meets your requirements, so ask if this
is possible? Further, if the job is large enough
ask for contiguous blocks from the same wall
in the quarry. In random slabs, you may ask
or specify alternating facing be polished to
give book-matched slabs, and have them numbered
sequentially.
3)
What color variation can be expected in the
stone? Are there veins, and if so, how do they
change in size and color? Obtain enough samples
of the stone to show the variation and understand
what the problems are in selecting the color
range acceptable to you. You may have to pay
a little extra to get what you want but at least
you will not be surprised at what you get. If
the job is large enough, demand that the contractors,
architects, owner etc. visit the quarry and
factories and see other jobs where the stone
has been supplied similar to the intent you
are planning.
Be
cautious, because what is variation to you may
be nothing to a stone person. Once selection
is made, have several sets of control samples
prepared, signed off on, and kept by all parties
concerned for control.
4)
Find out about the integrity of the stone. Does
the stone show holes which require filling,
cracks or seams which require gluing, or other
faults which require extra labor or care such
as backing the stone for strength? These features
may add to the cost or be a problem when it
is time to grout the stone, seal the stone,
or cause problems with failure later on, such
as cracking, pitting or spalling. Some stones,
such as Negro Marquina, spall. Other stones,
such as green marbles commonly known as serpentines,
warp when wet. Some stone effloresce, or lime
powder, comes to the surface, and it looks milky.
5)
Find out about the stone's standards and require
A.S.T.M. testing on the stone to make sure it
passes the requirements the architect has set
forth. Make sure the finish you have selected
will wear well and that it will pass all codes
and standards required for slip resistance.
Make sure the absorption will satisfy your needs.
Make sure the stone does not change color or
fade in sunlight or have metallic contents or
other minerals that will cause it to rust. Each
type of stone may require different testing
for the application intended. Get these tests
done by qualified labs as it is your protection
that it meet certain standards. In some cases,
test the stones several times in production
to make sure that it maintains these standards,
as it can change in the quarry and from quarry
to quarry.
6)
Set standards of the finish you want and be
specific. Not all polish stones have the same
mirror reflection. Not all honed stones allow
for the disappearance of cutting and honing
marks on the face. Test each stone and see what
is suitable and will satisfy your requirements
and find out the type of finish and grit that
is being used to accomplish this. Even today
flamed finishes are accomplished by several
methods and one may suit you over another.
Also,
find out how the stone should be maintained
and demand information on maintenance. Should
the stone be sealed? If so, get recommendations
of sealers or try some samples out with labs
to determine the best sealers and how they may
affect the color or look of the stone? Most
sealers require a more porous finish such as
honed to start with, so know this in the beginning.
7)
Find out about the suppliers and have them qualified
before bid date. (The same applies to contractors.)
Give suppliers a questionnaire and ask them
about job references where they have supplied
similar jobs and quantities? Ask them for warranties
or guarantees about their service, their quality
control, and their delivery times. Ask how they
will correct and take care of problems should
any occur.
8)
Get references of projects that either you can
visit or you can call and check out the stone
or the suppliers. Get pictures of the jobs showing
the stone to see what a large quantity looks
like.
9)
Ask for recommendations of installation methods
and thickness of stone for the application you
are considering. Some stones require certain
white portland cement, or epoxy to set. Other
stones will stain easily with colored epoxy
grouts. Part of the cost of selecting the stone
is getting it installed properly and economically.
The overall budget will be approved based on
the stones delivered cost installed. Sometimes
the installation method can cost more than the
stone.
By
finding out about the quarrier, the supplier,
and the stone you will avoid problems down the
road. You will alleviate the problems of surprise
that so many buyers have when they open their
containers.
Finally
demand everything verified in writing. Find
out how the stone is to be paid for, whether
open account or with letters of credit. What
will the supplier accept as a hold out for final
payment until the stone is approved at the job
site or warehouse? This will usually indicate
to you whether you are working with reputable
companies or those on a shoestring budget.
Once
you have checked out all the variables on the
stone, the contractor, the costs, and other
details, than stay with your specification and
make sure no one bids an alternate stone which
has not been checked out and approved.
Offering alternates is very common. In some
states or jobs, the architect has no control.
Once the job is turned over for bidding, the
general contractor takes out the names of the
specified sources of supply and in turn states
"and/or equal or alternates allowed". As soon
as this is done, everyone takes risk to get
the quality, price, and assurance of the supply
of stone in question. Selecting stone requires
that all parties concerned, the general contractor,
the owner, the architect/designer, the contractor,
and the supplier work as one to do a job that
all will be satisfied with and that will last
a long time.
Cooperation and communication are important
in any project if it is to work well and smoothly.
