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Boral Cultured Stone® – Installation Tips

Tips by Chris Hines – Technical Manager, Boral Stone Products

The mockup used in this video is a wood framed construction. We have a wood base sheathing, studs 16” on centre, and we have a mock foundation, which would represent a block or concrete foundation.

The first step, in a system that is framed — be it wood framed or metal framed — is to protect the transition from foundation to the beginning of the framing section. And we do that with a part called a weep screed. That’s this component here. It’s comprised of a 3 1/2” flashing/flange on the back, a sloped surface. This is called the beak, and it has a drip edge on the bottom. And the purpose of this weep screed is to direct, and provide a means for drainage of any water — incidental water that gets into the system — and allow it to drop free from the foundation.

After the weep screed is installed, the next step is the installation of the water resistent barrier systems. There are two layers in an adhered veneer system, over wood or metal framing. Each has a different purpose. This first layer, here, of water resistent barrier, is called the primary WRB, or water resistent barrier, and its purpose is to drain water out of the sytem. All of your flashings should be integrated into this layer of the WRB, or all the way to the exterior of the system.

There are many types of water resistent barriers. And the building code defines what can be a water resistent barrier. There are liquid applied versions, which are applied via roller or spray. There are mechanically attached versions, like you see here. This particular one is a Grade D building paper. It’s probably the most common, so it’s what we’ll use in today’s demonstration.

The second layer, that we put on top of it, is called secondary — or sacrificial — WRB, and its purpose is to prevent the mortar products from sticking to the primary WRB, and affecting its performance. And what’s created then, between these two layers, is a small drainage plane, so that incidental water can work between these two layers, to the bottom of the system, and via the weep screed, escape the system. Again, with the sacrificial layer of WRB, there are many products that you can use. Mechanically fastened paper-like products are most often used for that application, because of ease of installation; and because it’s sacrificial.

Once the layers of WRB are installed, the next is the lath. And the lath is the most important, because this is what transfers the weight of the system into the frame. There are several types of lath available. What you see here is a 2.5lb./yard expanded metal lath. You may or may not be able to see some small dimples that are in this lath. That is the self furring feature on this lath. And its purpose is to space the lath 1/4” off of the wall. And the reason for that is to get good mortar encapsulation.

Lath is galvanized. However, it’s galvanized before it’s slit, and stretched, and turned into the shape you see here. So the area in the middle of these diamonds doesn’t have a zinc coating. So in order to gain it’s corrosion resistence, it must be completely encapsulated in mortar. That minimizes the amount of water and air that can get to the lath, and begin the corrosion process. By spacing it 1/4” off the wall, you enable mortar to get around to the back side, and the front side, and get a 1/2” scratch coat.

This particular scatch coat, you see here, has already been scored. This would be a separate step if this were a new installation. And you’re shooting for a total 1/2” total thickness of mortar here. After you’ve completed the scratch coat, you can go on to the second step. However, I’d like to go back and cover a concept called the soft joint.

When you have dissimilar materials, in an adhered veneer system, things are going to move at different rates, with temperature changes and moisture changes, and so on. And so, one of the strategies to accommodate that movement is with a soft joint. In an adhered veneer system, you have to think about this during the lath installation. It starts by the application of a casing bead. The casing bead is shown on both sides. Essentially, it is a metal “J” channel-shaped accessory. And it does nothing more than provide a nice clean straight edge to caulk against.

However, caulk does not function well when it’s adhered to 3 surfaces. And so you use a material called a backer rod. This is nothing more than foam rope, and it goes into this 3/8” space, between the casing bead and the dissimilar material. In this case, it’s a window, but the same thing would hold true if this was a trim board, a transition to a completely different siding; anything like that. So, backer rod goes in, fills the base of the space, a high quality sealant goes over top, and you’re left with a joint that can accommodate movement as the sytem changes temperature and moisture levels.

So now we’ve taken the system as far as the scratch coat. It’s a good time to break and talk about how this system would be different, if the substrate itself was different. For example, had this been a concrete wall, you would not have had to do any of this. You would already be to this point (scratch coat) and could install directly to the concrete wall. However, concrete walls often have form release agents, other bond inhibiting chemicals; and it’s important that it’s also rough enough to receive the mortar, and adhere the stone.

And so there may be a step, with a poured concrete wall, where you have to clean it. You’re generally cleaning off form release agents, and so on, to prepare the surface for bonding. You may have to powerwash, or even bead blast, to get an appropriate texture to bond to. Had it been CMU block or brick, those products typically already have enough texture for you to bond to, and you would go right to either a scratch coat, or in some cases you can go directly to your bond coat. And we’ll talk about that here in a minute. But the point being, masonry structures, whether it’s unit masonry, or poured concrete, do not require WRBs or lath. However, you can use both if you need to.

When would be an example where your might need to use both? Let’s say, for example, you’re going to apply stone to a painted block wall, and did not want to strip all the paint, you can install lath. If you had a concrete or block wall, that maybe had a tendency to leak a little water, you may want to install WRBs, and also lath.

So what I’d like to talk to you about now is requirements for clearance. All adhered veneer systems, be it Cultured Stone® or any other, require clearance from either grade or paved surface. The purpose for this clearance is to allow proper drainage of the system, to prevent staining from soil splashing up, to help minimize freeze/thaw damage; and in some juridictions, to even allow an area to inspect for termites.

The distance of clearance is measured from the beak of the weep screed. We use two distances to cover most of the situations we run into. So, for example, if this system was being installed where this was soil, we would require 4” of clearance from soil. If it were a paved surface, like poured a concrete, or even a paved patio, you can reduce that clearance to 2”. If you’re installing on something like a front wall that has a porch, and the porch is supported by the same foundation as the wall itself; in those cases you could drop that clearance all the way down to a 1/2”.

We have all of these installation instructions in the Cultured Stone® Printed Installation Instructions, and also in the MVMA — our trade association’s — Installation Guide.

So what I’d like to do now is take a moment and talk to you a moment about a water management technique. If you followed the description of the 2 layers of WRB, and how incidental water could find its way into that space, drain to the bottom, and out via the weep screed, it won’t be a stretch for you to understand that when I put a pentration in a wall system, that could interupt the flow of water down and out, we use a drip screed. The purpose of this accessory — very similar to the weep screed — is to allow an exit point, or a means for drainage, for water to exit, when it could have potentially been blocked by penetration, or dammed. The water could be dammed.

What I’d like to do now is give you a technique that gives you the best opportunity, for the best bond, when you’re sticking stones to the wall. Mortar is made with Portland cement. And Portland cement requires water for the purposes of hydration, to gain its strength. In adhered veneers there are strict building code requirements, that if the weather is too hot, you do X, Y and Z. If the weather is too cold, you do X, Y and Z. The steps I’m talking about are really outside of that. These are tricks that you can use to prevent you dryer scratch coat, and dryer stone, from extracting water out of your mortar, and preventing it from being as strong as it could be. So how do you do that?

You could use a garden hose. You could use a sprayer. You could use a brush and a bucket of water. What’s very handy is your typical garden sprayer. In this case, we’re able to wet the backs of the stones very easily. You want to allow that water an opportunity to soak into the stones. Those stones should look wet, but not glossy. You don’t want liquid water still on the stones, but you want a well-saturated stone. The same holds true of the scratch coat. This is especially important if it is very hot and dry. With all of Cultured Stone® and Prostones®, Component stones, these steps are actually required, regardless of weather.

While we continue on the best bond, I’m going to give you some tips that should help achieve good bonds. So, we’re looking at the back of a Cultured Stone® right now, and one of the things that you’ll notice is that there’s a texture to the back of the stone. Take a good look. Are there any loose particles on there; anything you should remove with a wire brush? In this case, it’s a pretty clean and well textured stone. Is there any overpour around the edge that might need to be broken off? In this case, very little.

There are two techniques for applying the setting bed of mortar. We call them Method A and Method B. These were developed at ASTM through a commitee that involved many manufacturers of stone. And I’m going to demonstrate them for you.

The first step, often referred to as a back butter step: You have your mortar material mixed to a consistency that’s easily workable. And I’m going to press some of that mortar into the stone texture. The description I like to use is, I’m applying it as if I have high cholesterol, and I’m applying butter to toast, and my wife is watching. That’s the first back butter step, and I would suggest that this is a good step on every single installation. And I know many viewers today are cringing, thinking about how their labour rates go up when you do this.

The second step in this application then would be to truly apply the mortar setting bed. This is a material thicknes, that once pressed on the wall, should end up with approximately 3/8” thickness. You can see there’s a fair amount of mortar on the stone. And when I press this into place, you should see squeeze out around all sides. Hold that for a moment. Allow the mortar to set. When you release, it should stay. This mortar here on top, that’s extruded out, you can remove. That stone is now good to go. So let’s talk about Method B.

Method B is probably best explained, if we contrast it with the stucco system, which our system evolved from. A stucco system would be built just like this. There would be 2 layers of WRB, there would be lath, there would be scratch coat. In the stucco system, your next layer would be the brown coat. And at this stage, you’re talking about a 3/8” brown coat. We’re trying to do the same thing with our mortar setting bed on the stone. So in Method B, you actually trowel the setting bed onto the wall, as if it were a stucco brown coat. You still back butter the back of the stone, as we showed you in the previous Method A. And then you press your stones into the mortar. You only cover about 5 square foot of space with mortar, so that can install your stones before the mortar skins over.

So we’ve talked about how to set a stone properly. Let’s talk about some improper methods. One that we run into fairly frequently is called the donut method; and it is also improper. As you can see, the mason installs a thin layer of mortar around the outside. They leave a void in the centre. The theory, in the field, is that this provides a suction. When you press it onto the wall, it gives you a better initial tack. And while that might give you the opportunity to leave the job faster that day, it does wreack havoc on the long term installation. Because this pocket can capture water. The water can then freeze, and expand, and attempt to break the bond. Or, it can work its way through the surface, and evaporate here, and cause efflorescence. So, a void anywhere in the setting bed system is bad.

Here are a couple other examples. The mason probably thinks that the mortar will squeeze out, once this is pressed on the wall, and provide a full setting bed. However, this just isn’t enough mortar. Again, leading to voids in the system, and the things that can go wrong with that.

So, let’s just review the proper method to install the stone. So, scratch coat is already wet, stone is already wet, that thin texture pressed deep, enough mortar to provide squeeze out around the entire perimeter of the stone. Again, at this stage, you can remove this excess mortar; and that’s known as set. And that should give you the best opportunity for a good bond.

So, as we set each of these stones, in order to get a decent amount of squeeze out around the outside of each stone, which you’ll likely need to add more mortar, and you can do so with a grout bag. It makes your mortar a bit thinner than you typically would, so it will flow out of the bag, and begin squeezing into the joints. You would allow that to become thumbprint hard, so that when you press your thumb into that mortar, your fingerprint almost shows up. And at that point, it’s time to tool it. A standard brick joining tool, a woodend stick, are appropriate to compress and compact this mortar, and remove any excess.

So what we just showed you was a grouted application, or a jointed application. We installed the mortar with a grout bag. And when it becomes thumbprint hard, we would tool it, allow it to become dry and crumbly; you would go back and clean the installation with a whisk broom. Had this been a tight-fit installation, you would have simply raked any excess mortar out, after you set the stone, and stopped there. These steps would not be necessary.

So let’s review what we covered today. A mason showed up at the site. There was a wood frame constructed wall, with sheething, studs 16” on centre. The window had already been installed and flashed properly. The primary, or the first, layer of WRB may, or may not, have been installed. The mason would install the second layer of WRB, lath, casing bead (to prepare the soft joints where necessary), a drip screed above any large penetration (to allow water drainage). We talked about the lath. We talked about the scratch coat, and the importance of the thickness of the scratch coat, and proper mortar embedment. The key to that is a self furred lath, properly mixed mortar, and the appropriate pressure to get that mortar encapsulating the lath. We talked about dampening the scratch coat and the back of each stone. We talked about Method A and Method B, for applying the mortar setting bed, and the importance of no voids in the mortar setting bed. We showed you how to add additional mortar with the grout bag, and if necessary, and described the tooling and cleaning steps that follow.

So that wraps up the basics of the stone installation, and we feel that if you follow these instructions, you’ll get the best performance, and long term longevity of your stone system. If we didn’t cover something here that you’re interested in, you can find that invormation on the Cultured Stone® website, in the Cultured Stone® installation instructions, or in the MVMA Installation Guide.


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