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I have a bay window that needs some love.

I think its sandstone and has had several coats of paint over the years. I've scraped all the paint off. Here's where I'm at:

Sandstone bay window paint removed

As you can see, it has a few cracks here and there, and the surface isn't particularly smooth after removing the paint.

Sandstone bay window bumpy surface Sandstone bay window cracks

A property on the same street looks like its had a similar issue, and there they've skimmed the stone with what looks like regular cement.

Sandstone bay window skimmed

I was thinking that I'd need to do something similar, but cement doesn't seem like too great an idea as it wouldn't allow the stone to breath.

I'll be painting the stonework again so that it ties in with neighbouring properties. What's the best process for this after I've tidied up the surface?

  • Skim coating with mortar won't seal the stone work mortar breathes similar to stone unless sealing binders like addmix's are added.paint can seal the stone so I would believe you have that part backwards. I have seen both methods used where stone work has been painted and other jobs where it has been coated with mortar. Both have advantages and disadvantages. Depending on the final finished look you want a combination may be the best long term solution. – Ed Beal Feb 21 '18 at 14:05
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I have seen stonemasons apply a repairing paste where the mortar is mixed with powdered stone of the same type and color, possibly adding a drop universal tinting pigment to match the stone color exactly after testing it in patches. This is applied as a last finishing layer on top of normal mortar (max thickness 1/4 inch).

If you are going to paint the stone, then you should use a silicate-based paint, but you need to protect your eyes and skin from exposure to the paint because it is toxic.

  • We ended up getting some stonemasons to do the job. This is what they did. – ghr Mar 17 '18 at 10:32
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I'm getting something similar done. Either get a stone mason out to do the job or to give you a quote/some advice. Like you said not a good idea to use cement as it will trap damp and degrade the stone quicker. Use a diamond grinder to get the sandstone smooth and fill in any cracks with lime mortar. Then only use limewash or a good quality mineral paint to finish so it allows the stone to breathe.

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