﻿What Happens When You Use Concrete as a Render?

What Happens When You Use Concrete as a Render?

25/1/2017

There you have it. That's what happens.

If you take a closer look at the photo though, we get some clues about the issues with Portland cement.

1. Portland cement is too hard. Your mortar or render should always be softer than the brick or stone it's used on. Why? If the mortar/render is too cementitious the stonework/brickwork takes all the weathering.

2. Portland cement doesn't 'breathe'. This means moisture and humidity seep into the wall and can't escape which is a killer in old buildings. Eventually your walls start to rot from the inside.

3. Portland cement is too rigid. It can't flex. If the material beneath the cement is clay based, it will expand and contract. Your cement won't. So it cracks instead.

4. Weirdly, despite not being vapour permeable, Portland cement manages to hold onto moisture. Notice how the concrete render is cracking in a grid. Those cracks are occurring at the joins between bricks which are filled with concrete mortar. The mortar has retained the moisture, while the bricks (which are porous) are letting go of it faster (evaporation).

This knowledge is crucial if you're thinking of repairing an old stone wall, rendering a traditional building, or maintaining a natural home. As Period Living says, "Sadly, the wrong techniques and materials are all too frequently used for repairs so moisture is sealed in, resulting in damage and decay, often with disastrous consequences to walls and floors."

So what should you use instead? Lime plaster and cretes, clay plasters and mud mortars are the way to go. Here's a useful article on the subject.

Have you restored an old natural home? Do share your tales and your tips.

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11 Comments

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Kate Welling link

3/10/2018 02:26:45 am

I appreciate your article talking about using concrete as a render. I see everything that you're pointing out in that picture. The thing that stands out to me is how its cracking everywhere. I need to get my home re-rendered, so I think I am going to seek out a rendering service to help me.

Atulya

3/10/2018 12:01:23 pm

Yes, the myth that concrete is 'strong' is slowly disintegrating. It cracks because it's rigid. Lime and clay based mortars and renders are not just breathable, but much more flexible too.

cement render link

4/10/2021 12:39:19 pm

Before you start you need to guarantee that the surface you are delivering is liberated from soil, dust, oil, oil, paint, silicone or friable material. Smooth thick surfaces with low retention rates like concrete or metal window casings ought to be ready with a "run coat" preceding utilization of the render. A scramble coat is basically an extremely amazing blend of concrete and water which is flicked over the divider or metal window outlines making a surface for the render to hold to. Permit the scramble coat to dry for something like 24 hours before you begin to apply the render.

Jason Erickson link

5/10/2023 04:25:56 am

I agree, adding too much Portland to your render will cause package because it cannot give. Specially, on the final coat using Lessi Portland is good

Ashley Lonergan link

2/2/2024 10:52:31 am

Nice Article...Very interesting to read this article. I have learned some new information. Thanks for sharing.

Cooper Edkins link

4/3/2024 08:52:04 am

Thanks for having this article, it helps a lot. It’s a well-written blog and it is very informative. Keep on blogging, looking forward to see more of your posts!

concrete resurfacing repair link

2/5/2024 08:50:47 am

When you use concrete as a render, it provides a durable and robust surface that can withstand weathering and impacts. It offers excellent fire resistance and can be applied to various substrates, enhancing structural integrity. Additionally, concrete renders can be customized with different textures and finishes, making them versatile for architectural and construction purposes.

7/6/2024 12:26:20 pm

Milla Tietkens link

7/6/2024 01:46:44 pm

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7/6/2024 01:54:35 pm

Great post indeed, I loved to read it as it provides all the necessary details of what I was searching for. Thanks for great information you write it very clean. I am very lucky to get these tips from you.

Joe Doe link

3/10/2024 12:21:44 pm

Great insights on the challenges of using concrete as a render! Concrete rendering can trap moisture, leading to cracking and decay, especially in traditional buildings. Instead, consider using breathable alternatives like lime plaster and clay mortars, which allow for moisture control. If you’re restoring an old home, ensure proper drainage and ventilation to minimize moisture buildup. Always test materials on a small area first to see how they interact with existing structures. Sharing experiences with others can provide valuable tips for successful restoration projects. What techniques have worked best for you in maintaining the integrity of your walls?

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