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Stonemasonry

Removing concrete from stone steps what lime mix to fill large gaps with?

Anonymous user 1 March 2024 - 2.59 PM

I own a large Grade II listed Methodist chapel dating from 1876. I am currently restoring the front of the building. In the 90's the huge stone entrance steps were covered in concrete. This was probably a health and safety project but also an effort to stop water ingress into the large basement space underneath - the huge stone slabs form parts of the ceiling below. The concrete is now cracking and broken in parts, not to mention really ugly and comes off easily, but I mainly want to reveal the original stone steps for aesthetic reasons (though I have no idea what state they are in). I can see there are large deep gaps between the steps, so my main question is what lime mix should be used to fill? It looks to have nothing between but loose rubble, nothing solid. This will need to form a good water barrier as the rain hits the steps hard - and they currently leak into the space below. I've used NHL inside the building with great results. Wonder if I should use NHL5 or if 3.5 will be fine and what sand mix and ratio would you all recommend. I'm hoping not to be opening a can of worms with this project! Expert lime and stone advice much appreciated.

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3 Answers

Crescent property Services (SW) ltd
Rating: 5 out of 5552 reviews
Exeter
Hi that sounds like a tricky problem you have, most likely you're going to find something in rather poor condition as once concrete is involved in an area of stonework that would usually make matter worse. So, I suggest you try NHL 5 with a gritty sand (not coarse sand) something like a rendering sand with some fine and some grit, expose a small area and judge how bad it is, if the cracks are really deep or wide you can mix a liquid grout solution of say 2.5 to 1 and pour into the voids allowing a gap of at least 25mm of over pointing, look up grouting for stonework on the net you'll find what you need, be peppered for a bit of a mess and some cleaning up after, and think to yourself less is more until you have stopped the grout going all the way though to your basement, once you have stopped the ingress you can go at it with a bit more vigour, you can drill and pin stone in place with s/steel pins and epoxy resin if it's all on the move, and the colour of your sand dictates the colour of your mortar, reds produce pinks and reds, and yellows are buff or brown.
Answered25 October 2022
19
Restoration Sussex Stonemasons
Rating: 5 out of 5554 reviews
Bexhill On Sea
Hi its hard to give a 100% correct answer without seeing the steps in need of restoration. The mortar mix depends on the depth of repair required, any holes deeper than 50mm will need a stronger mortar to fill voids and prevent cracking. 3 part washed sharp sand. 2 part silica or plastering sand. 2 part NHL 3.5. You can also add fibres if required. This will normally give a good base coat and should be left to dry and shrink back to prevent cracking before adding colour matched topcoat. My only concern with mortar repairs to steps is they don't tend to last on areas of high traffic as lime will damage easy and weather away faster. Ive been a stonemason on historical buildings for over 30yrs and would recommend either replacing any major stone that's damaged or if possible cladding over with new 50mm stone tread and risers would be my recommendation.
Answered28 October 2022
1
Aris stone Restoration
Rating: 5 out of 55518 reviews
Ware
I would need to see the job. See how bad the condition of steps are, and what the problem is. Lime joints won't deal with this problem alone
Answered17 November 2022
0