External render repair

I’ve got two types of render on my house I recently bought. A really thick render (stone cast I think) on the original walls (1930s house) and a much thinner render on the extension done about 10 years ago. Both types have small patches which need repairing. A render specialist came and looked at the stone cast render and said the render was fine and it was just the paint which had peeled off and so needs repeating. He didn’t look at the thinner render. Is it OK to just paint over the stone cast render, should I use a filler first (render guy said no) although it looks like there is a grey/bluish layer first and then paint. On the thiner render it looks to me like the render has come away leaving a brown colour brick or maybe cement? How would I best repair this, do I need a filler first? Some of these patches have a bit of moss growing on it which I was planning on removing first.

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Answer:-

For the thick, stone cast render on the original 1930s walls:

1. If the render specialist confirmed that the render itself is in good condition and only the paint has peeled off, you can likely just repaint over it after proper surface preparation.

2. The grey/bluish layer you mentioned is likely a primer or sealer coat applied before the topcoat paint. This helps the topcoat adhere better to the render.

3. You don’t necessarily need to use a filler if the render surface is sound and not cracked or damaged, as advised by the professional.

4. However, you should thoroughly clean the surface, remove any loose paint, moss, or debris, and apply a suitable masonry primer before repainting.

For the thinner render on the extension:

1. If the render has come away in patches, exposing the brown brick or cement underneath, you’ll need to repair those areas before painting.

2. Remove any loose, crumbling render from the affected areas using a stiff brush or scraper.

3. Clean the exposed surfaces thoroughly to remove any moss, dirt, or debris.

4. For small patches, you can use a suitable exterior patching compound or rendering mortar to fill in the gaps and smooth over the surface.

5. For larger areas, you may need to apply a new scratch coat (thin base coat) of rendering mortar before applying the top coat to match the existing render texture.

6. Allow the patched areas to cure completely according to the manufacturer’s instructions before painting.

7. Apply a masonry primer or sealer over the repaired areas and any exposed render before applying the topcoat paint.

It’s always a good idea to follow the manufacturer’s instructions for any patching compounds, rendering mortars, primers, or paints you use for the best results.