A Guide to Building with SIMS by Mannok
The solution comprises of two key component parts: on the inside, we have the masonry substrate, which is built using Mannok aircrete thermal blocks; and on the outside, we have an external insulation and render system.
Single Leaf Masonry Substrate
Beginning with the masonry substrate, in the example shown, the solid wall is built using Mannok Aircrete Seven blocks (7.5N). Building the masonry substrate using a Mannok aircrete block has a number of advantages:
- Construction / labour costs: the aircrete block used is 9 inches wide by 9 inches high, built in a single solid wall structure. Typically, a 9-inch wall built using dense blocks would see two 4-inch blocks built on the flat, and likewise, traditional cavity wall construction would be built using two 4-inch dense blocks. With SIMS, the double masonry wall is replaced by one single leaf masonry structure, built with the nine inch Mannok aircrete block, essentially cutting the number of blocks to be built on site in half, giving a significant time and cost saving.
- Another key advantage of the Mannok aircrete block is it is a low thermal conductivity block; it’s thermal performance is almost 10 times better than a dense concrete block. So by using a Mannok aircrete block as the masonry substrate, you’re automatically improving the thermal performance or u-value of your wall. Given that heat loss through walls accounts for up to 35% of a building’s heat loss, this helps to greatly reduce heat loss and results in a much more energy efficient building.
- And the third key benefit is the impact on thermal bridging, another significant source of a building’s heat loss. Again, using a low thermal conductivity block as your masonry substrate, you are dealing with your thermal bridges in the junctions throughout your house almost by default.
The resulting cost, time and thermal performance benefits of using Mannok aircrete blocks as the masonry substrate are some of the key advantages of our SIMS by Mannok solution.
SIMS by Mannok can be built using either traditional sand and cement mortar, as shown in the example, or thin joint mortar. Sand and cement mortar is a good system to use with SIMS in Ireland, largely due to the fact that it is a traditional method that blocklayers are familiar with and happy to use.
Alternatively, thin joint mortar can be used with the Mannok aircrete blocks to give a stronger bond. Thin joint mortar is a 10N mortar, and with the strong bond, makes the overall wall construction much stronger, so much so that a 9-inch Mannok aircrete block built with thin joint mortar is almost 3 times stronger than a 350mm wide traditional dense block construction. If the block layer is familiar with building with thin joint mortar it can also add speed to the construction, but the key benefit here is the added strength due to the increased bond strength. When using thin joint mortar, it may be a possibility to reduce the thickness of the wall from a 9-inch block back to 6-inches, which can again save construction costs.
External Insulation System
The second key component part of Sims by Mannok is the external insulation system. There are currently 20 NSAI approved external insulation systems in Ireland, and any of those can be used in conjunction with the Mannok aircrete masonry substrate. Quite simply, the external insulation system includes the insulation layer and then it has a build up of layers on the outside of that to provide your water tightness and render finish.
Traditionally, blockwork in Ireland was cavity wall construction, but with advancements in material and technology, waterproof renders were developed which basically replaces your outer leaf of blockwork, so we have done away with our cavity wall. The insulation is fixed to the Mannok aircrete block and the waterproof layer is installed on the outside of that.
In the example shown, the insulation is 140mm Mannok EPS insulation, which gives you a u-value of 0.18W/m2K through this wall construction. Another key advantage of this solution is that the thickness of insulation is not limited. With cavity wall construction, you are restricted to the amount of insulation you can install based on the size of the cavity. Here, we can increase the depth of insulation to the desired thickness, for example, we can go from 140mm to 200mm to achieve the target u-value desired.
Once the masonry substrate, the Mannok aircrete block, is completed by the block layer, the roof is installed and the windows are installed. The fact that the masonry structure can be completed much quicker than traditional cavity walls means the building is ready for follow on trades earlier, again helping increase speed of build.
The location of the windows in relation to the Mannok aircrete blocks and the insulation is quite important: the further the window sits outside the aircrete block, the better the thermal performance of the junction. In the example shown, we have chosen to have the window sitting about 40mm on the Mannok aircrete block and about 30mm external to that. That means that the window is supported by the blockwork. It’s also an option to have the window supported completely external to the aircrete block and supported on brackets.
Starter TrackMechanical fixings to install external insulation
Once the windows are installed, it’s time to start the external insulation system. The first process is to put on the starter track, which is positioned at the bottom of the wall, usually at plinth level. The starter track is basically fixed into your Mannok aircrete blocks and kept level so it gives you a platform to start your insulation on.
The insulation can be fixed using mechanical fixings, such as thermally broken mechanical fixings shown. The mechanical fixing goes through the insulation and into the aircrete block. Another option to fix insulation is adhesive, which comes in a bag and is mixed up with water. The adhesive is fixed to the back of the insulation and is then plumbed to the Mannok aircrete block to give a good strong bond and fix the insulation. Sometimes, mechanical fixings are not required.
Once the insulation has been fitted up to window level, window sills are installed. In the example, we have chosen to use a Passive Sill, which is manufactured in Cork. This is essentially a high density polystyrene insulation coated in a strong resin for aesthetics and durability purposes. The upstand of the sill sits nicely behind the drip on the window which weatherproofs the junction well. A seal tape is also required, which expands when wet to prevent water ingress at the junction. The Passive Sill gives very good thermal performance through the junction, essentially eliminating thermal bridging. Alternatively, an aluminium sill can be used.
Once the insulation has all been put in place, it is time to start putting on the beads. On the starter track, beading clips onto the track, giving a bead to start rendering up. Around all your openings, you have what we call a seal bead, and this prevents water ingress around all the windows. Basically, it’s got an adhesive strip on the back of it and it sticks against your window frame and seals that junction, giving a bead for plastering to. Once that’s installed, you put on your corner beading, which sits on at the corner and overlaps your seal beading ready for plastering.
Once all the beading is in place, it’s time to render the main part of the wall. The render system comprises of three components: reinforced mesh, a base coat and a waterproof render finish.
The reinforced mesh comes in rolls and is rolled out across the entire insulation. As you roll it out, a base coat is trowelled on, which will hold the mesh in place and also gives a base coat or key coat for the final render solution to be adhered to. At some of the high stress points, e.g. corners of window sills and lintels, a second patch of the reinforcing mesh is put on at an angle. Some systems will use a fine second coat of base material across the surface, which needs a very smooth finish to give a perfect substrate for the final render coat to go onto.
There are a number of options for the render coat: in the example shown, we have used a highly waterproof acrylic render, which is also available with a coarser finish; you can also have a silicone type or monocouche type render; or some installers also offer a dry dash option. Once the base coat and mesh is in place, the plasterer will either spray on or trowel on the final render finish, and essentially that is your external insulation system complete.