How to render internal wall?

[pavlo1]

Hi guys

i have been highly recommended to render walls with cement, lime and fine sand 6:1:1 

I have removed old sand/lime render however still have bits and pieces of old render on the bricks and want to render brickwork to make it level with white render/set plaster to tile the walls. 

need some guidance on how prep walls for cement render. Is it ok to go with new render over old bits and pieces of render ? Or do I need it all removed completely? Do I need to prime the  walls ? How many layers of cement render do I need to make ? How long does it take for it to dry ? 

[JacobZ]

Hi @pavlo1,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

To prepare your walls for cement rendering, begin by removing as much of the old render as possible. While small and firmly attached remnants can remain, it's best to clean the surface thoroughly to ensure a strong bond with the new render. You can use a Trojan 5x15 Row Brass Wire Brush or  Craftright 2 Piece Cold Chisel Set to knock off any loose bits and debris.

Additionally, it's advisable to prime the wall with a bonding agent. Consider using Dunlop 4L Multipurpose Primer, which will improve adhesion between the old surface and the new render, especially if you're working with mixed surfaces like bricks and leftover render patches.

When applying the render with your 6:1:1 mix (fine sand, cement, and lime), two layers are typically required. For the first coat, you can use fine sand, general-purpose cement and builder's lime. 

Start with a scratch coat, applying the first layer at a thickness of around 10mm. Once this coat is on, scratch it up with a notched trowel to create a texture that will help the next layer adhere better. Allow this first coat to dry for about 24 hours before applying the finish coat. The second coat should be applied at about 5-7mm thickness, creating a level surface for painting.

Cement render generally needs 24-48 hours to dry between layers. The full curing process can take a week or more, depending on weather conditions. In cooler or more humid environments, drying times may be slower. Properly drying the render will ensure durability and a smooth, even finish for your project.

Let me know if you have any further questions.

Jacob

[pavlo1]

Hi Jacob, thank you very much for assistance 

The thickness I need to achieve to make it level with the existing render is about 10 cm

should I increase the number of coats and potentially put a bar mesh for a second or third coat to reinforce the render so it doesn’t come off eventually ? 

Also what product would you recommend to patch up holes (they are about 1-2 cm deep) in existing white plaster which is above the brick wall  (please refer to the photo) ? 

[pavlo1]

How much of a primer would I need to use ? Does the primer need to dry before I’m to apply scratch coat ? 

[JacobZ]

Hi @pavlo1,

Thanks for the further questions.

To go that thick with your render, I'd say it's necessary to include mesh and increase your number of coats considerably. A single coat of 6:1:1 render should only be around 10-20mm thick, so you may need to do this in a number of stages.

Focus on getting the render on first, then use Hardwall Plaster over the new and old render. This can be ordered through your local store's Special Orders or Trade Desks.

The primer will cover approximately 6 square metres per litre. It should be allowed to fully dry before rendering over the top.

Let me know if you have any further questions.

Jacob

[Pavlo]

Hi Jacob

Thank you very much for you contribution.

Just a quick update - I ended up using Coharo Level Coating which I sourced from other shop. It is a cement based lightweight polymer which can be built up to 5 cm at a time and can be sanded.  Saves lots of time and efforts as there is no need to mix cement, lime & sand, etc.

Over the Coharo base coat I have applied Gyprock Cornice Cement - worked really well. 

[EricL]

Hello @Pavlo 

Thank you very much for the update. Please make sure to post a photo of the finished project so that our members can see the results of your rendering.

If you need further assistance, please let us know.

Eric