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Cultured stone wallWe now launch into Part Four of my five-part series on walls; we have previously looked at natural rock, pressure-treated timbers, and engineered wall units. It's time to examine synthetic, or cultured, stone (a trade-marked product of Owens Corning. Unfortunately for them, all synthetic stone, at least in my neck of the woods, is generically termed "cultured.") I like it because it's easy to handle (rocks in a box), easy to put up, and looks good.

I call it "phony stone" because it is a man-made product -- consisting of light-weight aggregates, crushed rock, and cement, it is colored with oxides to provide a very natural look. The biggest advantage I see is that, owing to an approximate 3/4" stone thickness, the weight of the rock is sometimes as little as 1/3 that of a real face stone. In addition, the individual pieces range in size from that of a brick to that of a sheet of paper; with both these advantages, handling is a snap.

But first, a gallery to give you some idea of how the stone is installed on a wall.


Given that I have indicated what I like about cultured stone, it's incumbent on me to to mention the downsides:

  • The material costs for synthetic rock may be more expensive, per unit. If you reside in an area where natural stone is readily available, you still have to consider the labor costs of installing real rock, which can be steep. You should certainly look at the installed costs of both real and synthetic stone before you make a decision. If your project is fairly substantial in size, have a contractor bid the work to get an idea of the cost; if it all comes down to appearance, have the builder put up some test panels of real and synthetic rock; that will cost you several hundreds of dollars, but will be a huge help in your decision-making process.
  • If the rock is installed sloppily, and you end up with excessive gaps between the pieces, the project looks fake. This is because the veneer is so thin compared to natural rock, that there is no "visual depth" to it. The solution here is to be careful in the installation process.
  • Some manufacturers "top color" their product so when it's cut, the interior color is not consistent with the surface; this can be easily resolved by breaking a sample and taking a look for yourself.

The rock comes in flats (for the flat portions of the wall) and corners for (coincidentally enough) the corners. Also, there are a number of available accessories, e.g. wainscots, ledges, electrical cutouts, and wall caps. All of the rock is homeowner-friendly and was very suitable for our project -- to cover four small walls, each approximately 3' x 7'. You may want to consider a contractor, however, if you are contemplating something larger.

First off, safety - hearing, dust, and eye protection are all advisable. Gloves are not a bad idea, and if your hands tend to dry easily, rubber gloves.

Materials:

  • You have to buy the rock by the box; it generally comes in 10-12 square foot quantities, depending on the manufacturer. It's sold by the square foot, but get the usual extra 10% for cutting.
  • Corners; again sold by the box, but in lineal feet. Measure the corners, window and door openings, etc. and add the usual (you got it) 10%.
  • HINT: strongly consider using a colored mortar; given that most cultured stone comes in earth tones, something other than a gray mortar will blend nicely with the surface tones and will tend to visually "close" up the joints such that the work appears much more natural in appearance. We used a buff mortar for this project.
  • The "glue" - we used a mix of type N buff mortar, fine sand, and Portland cement in a 1: 2: 1/4 ratio ,which makes a nice sticky mix, but which tends to dry a little faster than other proportions. Preferred mix ratios are like noses, everybody has one; you should check with your stone vendor for the recommended mix for your area - it depends a bunch on temp, humidity, skill of the installer, etc. (Some areas of the country sell a "mason's mix" which has the mortar, sand, and Portland already combined.) For this project, we used about 3 bags of buff, 6 bags of sand, and 1 of Portland. Your stone vendor will help you noodle the approximate amounts for your project, but be warned that you will never be able to purchase, on your first trip, the exact amount of the ingredients needed - just won't happen; you'll either get too much or too little; that's the way it always is; sorry.
  • Prep for the wall. We used a house wrap over chip board sheathing; on top of the wrap, we screwed concrete board (rough side out). All are purchased by the square foot; assuming that this is not new construction you likely have only to attach the concrete board. (If you have other wall materials to work with, you will need sheathing, a weather barrier, and lath .)
  • Mesh lath. Not necessary if you are rocking on top of concrete board, but required in all other instances - sold by the piece, generally in a 2' x 10' size. You need enough to cover the required area. HINT: be sure that you install it with the "cups" up, to help hold the mortar mix -- you'll see what I mean when you buy it. Put it up with galvanized nails so that the fasteners don't fail over time, and the "walls come tumbling down."

Time: It took two young ladies (first-time volunteers) about one day to do each wall. Their work wasn't perfect, but it was well-performed and turned out looking quite nice.

Tools: Now is a good time to review the gallery, in particular the masonry tools:

  • wheelbarrow or mud box.
  • mason's hoe.
  • mason's trowels.
  • mason's rock hammer.
  • joint tool; we used a stick about the diameter of your pinky to do the joints.
  • small whisk broom for cleanup of the faces of the stones.
  • tape measure.
  • carpenters pencil
  • grout bag.; optional. We didn't need one as this project was limited in scope and our joints were kept fairly tight.

The process:

  1. First, screw the concrete backer board to the wall.
  2. Mix the appropriate components of mortar, sand, and Portland cement to a milkshake consistency and then apply a 1/2-3/4" thick base, or "scratch coat", to the wall so that the rock will more easily stick; allow it to dry.
  3. Lay the rock out on the ground, approximating your prospective project area, so as to mix the shapes, colors, thicknesses, and sizes and give you some idea of the general appearance of the finished work. This is an important step and one which many folks skip, to their ultimate chagrin, when one of the neighbors wanders by and says "how come the colors/ shapes/sizes/thicknesses are all the same, in the lower left corner?" Oops. Take your time for this step; as with most construction projects, prep is generally the most important part.
  4. If you have corners to install, do them first and follow with the flats. Alternate the long and short legs of the corners -- you'll see what I mean.
  5. 'Butter" the back of a rock (see the gallery photos) and, starting from the bottom row, push the stone firmly against the scratch coat such that the mortar squeezes out, wiggle it a bit to seat the mortar, then check the approximate level to ensure you don't end up eventually going up or downhill, thus subjecting you to muffled laughter from family and friends. (Not that anything like that ever happened to me.) HINT: don't let your joints line up vertically; looks unnatural and give the visual impression that the wall is about to keel over -- not good.
  6. Continue with the process, ensuring that you mix the rocks so you get a natural look. When you get to the end of a row, break the rock by scoring the back with the rock hammer, then crack it with the hammer or trowel. Given the variety of sizes and shapes, you'll occasionally encounter the need to solve the puzzle of how to make all the pieces fit; here's where your prep comes into play, but you'll still have to mix and match, no question about it.
  7. Breaking the rocks accurately is the key to TIGHT JOINTS. You'll waste some material, but that's why you bought extra, right?
  8. For the joints that just won't close up, use the mortar to coat the broken ends, and stuff it into the open spaces, smoothing it with the jointer or stick and trying not to get mortar on the face of the stone.
  9. As you approach the top, start thinking about how to mix the rocks such that you don't have all the skinny pieces stacked in the top couple rows. If you laid the material out at the beginning, this will be easier.
  10. clean up your work area and enjoy the adulation of those who came by to look at, but not help with, your project; you've now become the local expert - what a deal!

So, there you go; a very nice project that you can complete over a weekend, or stretch out as you like, so long as you keep your materials dry. You've improved the appearance of a wall, saved some money, and increased your stock of do it yourself satisfaction.



  • Mark

    Thank you for your thoughts on the 'cultured stone.' We have been looking at this type of product for a small landscaping project we have going. The issue we have run into regards the amount of 'stone' we want to purchase. We only need about 30 sq ft of coverage but all of the stores in my area require a minimum purchase that is much larger (usually around 400 sq ft). Does anyone have suggestions on where I may be able to purchase smaller amounts?

    Thank you!

    Reply
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