Cultured Stone On A Fire Place
|Cultured stone is a manufactured product
designed to look like real stone, but with a flat back for
easy installation. It may be installed over cement block,
plywood, rigid backwall, stucco or metal. This instruction
will detail installing cultured stone for a fireplace with a
¾” plywood frame.
Tools: Hammer or staple gun, wheelbarrow and hoe,
trowel, masonry cement, circular table saw with carborundum
or diamond blade, wide mouth nippers or hatchet, safety
glasses, level, metal jointing tool or wood stick, grout
bag, whisk broom, stencil brush sold in craft stores.
Materials: Mortar mix, mortar color, weather
resistant barrier (water proof paper or asphalt saturated
rag felt or ASTM D226, Type 1 No 15 felt) Note: Weather
resistant barrier must be used on all exterior and interior
mortar applications except those over masonry, concrete, or
Metal diamond mesh lath (minimum 2.5Lb), galvanized nails or
staples, concrete nails.
Build your frame to support your fireplace and stone
according to the fireplace manufacturer’s instructions. If
you are installing a gas fireplace, it may be best to have
the dealer install it if you are unfamiliar or uncomfortable
with gas lines. When building your frame, be sure to take
into account the width of the stone (2 to 3”) and also add
¼” to 3/8” for mortar.
Cover your plywood frame with a breather type weather
resistant barrier, overlapping the joints 4”. You may use a
staple gun to install the barrier.
Next install the metal lath over the entire surface using
galvanized nails 6” on center vertically. Studs must be
penetrated a minimum of 1”
Lay out your stone on a template of your fireplace front.
You can use newspaper as a template. Keep in mind this will
just be preliminary plan. No matter how exact you think you
are, the rocks will never fit exactly like they do on the
template. Be sure and vary size, color, and texture of the
stone. You may have to cut or chip some stones to fit. Leave
your joints evenly spaced and place them fairly close
together. (1/2”) You may think you are placing the stones
close together, but will find they are farther apart than
you imagined they would be, so be very aware of spacing as
you go. You can break up one stone into small pieces to use
as fillers for tight spots. Keep an open mind while you are
installing the stone. If a piece doesn’t fit like you
thought it would, you may have to change your plan.
Mix your mortar to a consistency that is like cake batter.
Too thick will dry and crumble and too thin will be a mess.
You may have to experiment a little to find the right
consistency. When mixing your mortar, use the same recipe
for all batches. It may be one pail of water to 3 scoops of
mortar and 1 cup of mortar color. Whatever amount you decide
on, do the same for all batches, especially if you are using
a mortar color. Mix the mortar thoroughly so there are no
Using a mason’s trowel, apply ½” mortar to a small section
of lathe. (enough for 2 to 3 stones) We suggest starting at
the top and working down because this is a messy job and
mortar will fall on your previously applied stone. Be very
careful not to get mortar on the stone, as it discolors it.
Butter the flat back of the stone with a thin layer of
mortar and apply it to the mortared lath. Apply pressure
firmly enough to squeeze some mortar out around the stones
edges. Make sure pressure is applied to the entire surface
of the stone to ensure a good bond. Hold the stone in place
for several minutes. We used 3” screws screwed in with a
power drill at the bottom of each stone to help hold it in
place. We used one or two screws for each piece, and that
really helped to keep the holding time down to a few minutes
for each stone. The screws were removed after the mortar
dried and before the grout was put in. Continue to apply
mortar to the lath a few feet at a time and install the
stones. We set corner pieces in first and worked from the
ends in. Use nippers to cut small pieces between joints, or
just use a hammer to break one stone into several pieces of
varying size and shape for fillers. When using cut stone,
try to position the cut edges up when they are above eye
level and down when they are below eye level.
This is a big job and you will probably want to do it in
several sections over a few days. If you start making
mistakes, you are getting too tired and it is time to quit
for the day. After you are certain the mortar is dry and the
stones are all set, remove the support screws.
Now it is time for the grout. Mix your grout as you did the
mortar, using the same materials. (mortar and mortar color
with water) You may have to mix this a little thinner, or it
will plug up the grout bag. A grout bag is a bag with a
large opening on one end and a very small one on the other.
It is similar to a baker’s icing bag for decorating cakes.
Fill the grout bag with mortar and start filling all the
gaps between the stones. It is OK if it is a little thin, as
long as it does not drip onto the applied stone. Be very
careful not to get any mortar on the stone. If you do,
remove the grout only after is has become crumbly with a
whisk broom or dry bristle brush. Never use a wet brush or a
When the mortar has become firm or thumb print dry, the
joints should be pointed up with a wood stick or metal
jointing tool. Rake out the excess mortar with the tool,
maintaining even surfaces. Compact and seal the edges around
the stone, avoiding any cracks or open areas. A stencil
brush does a good job of compacting the grout. This is just
a circular stiff bristle brush about 1” in diameter sold at
most craft stores.
Cleanup is done with a whisk broom, lightly brushing over
the joints after they have sufficiently set up. This will
remove any loose mortar. Never use a wet brush to clean the
mortar joints. Never use acid or acid based products to
clean the stone or mortar joints.
Home Tips &