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How to repair rendered wall?

Hi guys!

I have a damaged render on my window sill. When I tap on certain areas, it sounds hollow. As you can see, I’ve peeled off some of the render, which shows that it isn’t bonded to the surface. I’d like to repair it and then paint it.

I’ve received advice from different people, and here’s a summary of my two options:

Option 1: Use something like Liquid Nail to glue the render back, then apply a filler product to cover the remaining gaps. Materials: Liquid Nail. Filler options: Parfix 500g Ready To Use Multipurpose Filler or Polyfilla 500g Exterior Brick and Render Masonry. Which filler should I use?
Option 2: Re-render the affected areas.

And should I apply a primer layer before starting anything?

a large patch of render peeledI suspect water runs under this and will make the timber rot.deep trackunder the timberanother crack

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Comments

EricL

Hello @handyfrog

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your render.

It appears that the render near your window has started to deteriorate. Looking at your photos, it appears that large sections are starting to break away. If you are currently not prepared to do a full repair, then option one would be the suggested course of action as you'll be able to quickly patch the surface just in case any bad weather comes your way. But from a long-term repair point of view, I recommend option two as you'll be removing all the weak spots on the render and refresh your window area at the same time.

I recommend using Polyfilla 500g Exterior Brick and Render Masonry as it provides a rendered finish and is weather resistant as well.

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you need further assistance, please let us know.

Eric

Nailbag

Hi @handyfrog

I agree with @EricL and go with option 2 and definitely re-render. The damage in some of the photos indicate the cracks are originating from the base brick wall, which maybe signs of more structural issues.

Before rendering, I would address the window frames which there are obvious signs of rotted timbers being held together by paint. Further investigation is required to determine the extent of the damage for repair or replacement. Once the window/s are rectified then fixing g the render can commence. It doesn't stop you though in researching render repairers.

Regards Nailbag

Screenshot 2025-04-14 at 6.31.37 am.png

handyfrog

https://www.workshop.bunnings.com.au/discussion/comment/51110#Comment_51110

Thank you, EricL and Nailbag, for your recommendations. I completely agree with your advice to fix the window frames first and then re-render this area.

This issue is located on the window sill of my bay window. Therefore, I’m not too concerned about structural integrity (or should I be?). It seems that water has managed to penetrate both the timber and the render, leading to these problems. My main concerns are the condition of the render and the timber, and what remains of them. I’m leaning toward option two: re-rendering as a long-term solution..

I have some follow-up questions based on your recommendations:

Timber frames: What type of timber should I purchase to replace the rotten sections? Should I treat the timber to prevent water penetration in the future?

Re-rendering: Could you recommend any DIY render products? I don’t have any experience with rendering, but I’ve watched some Bunnings videos on the topic. I found this product—Davco 20kg Off White Render—is it suitable for this job?

EricL

https://www.workshop.bunnings.com.au/discussion/comment/87698#Comment_87698

Hello @handyfrog

If you do decide to revamp your window frame, I suggest making sure that the timber you use has a rating of H3. This means that it is rated for outdoor use and is protected from insect and termite attacks. However, if you find that removing the window frame is quite involved, it is possible to patch it with a combination of Earl's 250ml Wood Hardener and Turbo 500ml Builder's Bog. My best advice is to make sure not to add too much activator so that you have adequate time to mould the bog into shape.

In regards to rendering, using the Davco 20kg Off White Render should be adequate to cover up the damaged sections. Another option would be to use Dunlop 20kg Multipurpose Acrylic Render in conjunction with Dunlop 4L Multipurpose Primer.

My best advice is to rewatch the How To Render guide and familiarize yourself with the tools and techniques before you begin your project.

If you need further assistance, please let us know.

Eric

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/109407#Comment_109407

Evening @handyfrog

I would go for option two and re-render after removing all the old render. At the same time you can asses the state of the base of the windows. Earls wood harderner I have seen a lot of how to's and it looks amazing. I havnt had a chance to trial it yet but was looking at it on the weekend 🙂

If the timber is perished more then just the base it may be worthwhile to seek a professional timber window installer. A bay window should be used and focussed on 🙂

Dave

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