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Best way to install K1 Silicone K-Rend scratch render

K-Rend is a household brand name associated with the application of scratch or monocouche render to a property. This product has a scraped texture or finish and should strictly be applied directly to a masonry wall including brick, block or an existing rendered surface. When installing the K-Rend scratch render, there is no better solution that choosing the K1 Silicone scraped texture.

In this blog we look at different ways that the K-Rend K1 Silicone scraped texture can be installed to different masonry substrates.

How to install the K1 Silicone K-Rend to brickwork?

An existing brick wall is probably the most common type of masonry structure in the UK. It is still the most popular way to finish an external wall by using decorative brickwork to finish off the construction. Now some brick walls in the UK are well over 100 years old and over time some brickwork tends to weaken and lets in penetrating water. The water coming through the wall can cause issues to internal plasterwork and other problems to the property.

To avoid these problems, the K-Rend K1 Silicone scraped finish is enhanced with “silicone”, which creates a barrier to rainwater – helping prevent further damage to the brick.

The first step of the K1 Silicone K-Rend installation process is to get a good sense of the wall that is going to be worked on. Using the beading, namely 14mm-16mm beading profiles for stops, corners and drips – install them onto the walls that are due to be rendered. Do not use spray foam to hold the beads in place as this may cause product performance issues further down the line – we recommend using a small amount of the cementitious product to hold the beads in place.

The substrate may then require further preparation, including a fungicidal wash and a substrate primer. Substrate primers typically work in two ways – firstly they help aid adhesion between the substrate (in this case brick) and the render being applied. They also help regulate the moisture absorption by the brickwork, giving time for the render / basecoat to cure correctly. When applying K1 Silicone K-rend to a brick surface we would recommend using the K-Rend R7 Acrylic Primer. This can be applied mechanically with a spray machine or using a roller/ brush.

When the R7 Acrylic Primer has dried, we would then apply the K-Rend HP12 Base Coat with the alkali resistant fibreglass mesh. The HP12 is probably K-Rend’s most well known polymer modified basecoat product, that is robust enough to use on a number or preparation or undercoat application processes.

The HP12 Base Coat should be mixed water, using the appropriate water content on the back of the bag. It can then be applied with the rendering tools. If you are using a spray machine, then use the water pressure settings as recommended. In this installation the HP12 should be applied 6-8mm thick in one pass. You then cut the fibreglass mesh and place it into position on top of the spread-out basecoat.

Before putting on the scraped coat you must ensure that this HP12 Base Coat layer is fully dry. The fibreglass mesh needs to sit close to the surface of the base coat build-up. When embedding the mesh, ensure each strip overlaps at least 100mm on the edges. If you come across any openings like the windows, door or even surface boxes, then use additional fibreglass mesh in each corner to act as reinforcement patches. These need to be applied in every corner and should sit at 45 degrees to the opening, and remember these are on top of the strips of overlapping mesh!

You may ask what the purpose of the mesh is at this point? Well – it helps with the render’s structural integrity and also ensures the final K1 Silicone scratch coat has a solid surface to bind to.

When the mesh is in position, use a scarifier tool to make scratches in the surface of the HP12 basecoat, which would ensure the substrate would provide a nice key.

Having waited a good 24-48hours for the HP12 to set, you are now ready to apply the final K1 Silicone scratch render.

Mix the K-Rend K1 Silicone scratch powder in a bucket with the appropriate amount of water if you are looking for a hand-application. For machine use, follow the instructions on the bag and ensure you have set the machine to the correct settings. The product is then ready for the application.

Apply the K1 Silicone scratch render onto the substrate liberally trying to achieve a thickness of 10-12mm on the wall. Using an I-bar or a speed skim level off the surface so that the lines have been flattened out. The K1 Silicone scratch render needs to be firm, but not completely dry before the next stage can be completed, so we normally recommend going back to site the next day to produce the final finish.

Using the scratch pad or the scraped trowel take off approximately 2mm off the surface of the K1 Silicone render to leave a nice scraped finish. Take off any dust residue with a brush.

Obviously use your judgement and in the colder months you many need to wait a little bit longer for the product to set properly for it to be scraped off.

How to install the K1 Silicone K-Rend to dense blockwork?

Building new construction like extensions requires the use of dense blockwork (7N or above) rather than brickwork, which tends to be quite expensive. It is very popular to the finish the external layer of this blockwork with the K1 Silicone render, taking costs out of the construction process.

The initial preparation of the K1 Silicone K-Rend installation process is very similar to when installing the product onto brickwork. Using the stop bead, corner bead and bellcast bead pin them to the walls in the appropriate sections. You can use 14mm, 15mm or 16mm beading profiles for this job. Do not use pink grip or spray foam, rather try and use some of the product, namely the HP12 basecoat or the K1 Silicone scratch render to stick them off. If you are doing this, you need to make sure you leave the product to set a bit prior to the application of any other layers.

If you are worried about substrate suction given the new blockwork in place then use K-Rend R7 Acrylic Primer. This will help with the product work time and allow the applicator to properly skim it. The primer can be applied mechanically with a spray machine or using a roller/ brush. Allow this to dry.

Then use the K1 Silicone render bag and mix it with the correct water content – use a paddle mixer. If you are using a spray machine, then follow the correct machine settings according to bags. The first pass of the K1 Silicone render should be 8mm thick. In this layer you will need to cut up the alkali resistant fibreglass mesh and install it into the product. Make sure that when installing the mesh, it is overlapped at least 100mm on each edge and additional reinforcement is installed around openings.

You do not need to fully push the mesh through as another layer of K1 Silicone render will be applied on top as the finishing coat. You may choose to notch or scratch the surface with a scarifier to provide a better key for the next part of the install process.

Remix the K1 Silicone render or set the machine again to the same settings. When the product is ready to apply or spray you ensure that approximately 10mm of product applied in this second pass. Do not allow the first layer to dry out or fully set – this step should be performed “wet-on-wet”.

When the 10mm thickness has been achieved, then level off the surface. You can use a range of tools to do this. We recommend using a spatula trowel, an I-bar or a speed skim leveller. You should then wait up to 24 hours for the product to set before attempting to scrape this off the wall.

Using a scrape tool or scratch pad, take off the 2mm of skin formed on the surface of the product taking back to the beading profile. If you have used 16mm beads then this will be taken back to the 16mm depth. When scratching off the surface try to use your judgement and in the warmer months you many need to work quicker, because if the product hardens off too much, it maybe tricky to work with the following day.

How to install the K1 Silicone K-Rend to lightweight blockwork?

You may also render onto lightweight blockwork or clay blocks, but you may need to use a slightly different basecoat to help with this installation process. We recommend using the K-Rend HPX basecoat product but be aware that this is not always in stock, so check with us instore or on the phones to that we may suggest any alternatives.

However, the installation process would be very similar if installing to common brickwork.




4 thoughts on “Best way to install K1 Silicone K-Rend scratch render

  1. existing sand and cement render on thermalite 7n blocks cracked and hollow , hacked off blockwork has cracks, want to apply k- rend, what is recommended in this situation?

    1. Hi Andre, you’d probably need to get the blocks checked by a structural engineer first. We’d then recommend a thin coat render system like Silicone Render; much less likely to crack and it offers great weather resistance. You can use a levelling mortar for very minor cracks but anything larger could impact structural integrity.

  2. Hi.. i have a job with 3 substrates..
    1. Hardie backer cement board
    2. 7n block work
    3. Brickwork.
    Customer wants a colour top coat and all to be scratch finish.

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