Thanks Nollie. The stone has not been sealed, so that's one thing. I will contact the sites you mentioned and see what they say. I am fully expecting an argument, but I'm not going to let it go - we paid over 4k for the slabs to be fitted and a gazebo to be set up (gazebo not included in price). There's 70 slavs and he charged £780 for those, but looking online, that seems to be over the odds, especially for a low-end product (which is not what we asked for).
Ouch, Craig! If you want chapter and verse on how to redo it property and what materials to use let me know - there are pics somewhere on this forum that I posted on a previous query.
Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
Ouch, Craig! If you want chapter and verse on how to redo it property and what materials to use let me know - there are pics somewhere on this forum that I posted on a previous query.
Yes please! That will arm me with info for my argument!
If you could also tell me how to spot good quality stone vs the flaky type we have, that would be great too. I get the feeling I'm going to have to get some sort of partial refund out of the builder.
Just spoke to the builder. He says he has been doing it like that for 20 years and has never had a problem, thinks it will just dry out. He reckons the full covering for the base is only for driveways where it has to take more weight. That's not the case is it?
Hi, in answer to your last two queries - will do the how to redo it shortly but you need to get your builder to agree to it first so...
Well that was the predictable, indeed predicted response from the builder! There are a number of reasons, not just the staining which may or may not ‘dry out’ (explained in my earlier posts) why spot fixing should never be used with natural stone, so no it’s not correct to say you only need to do that for driveways. Sandstone, especially much of the Indian stuff, is a soft porous material. I would be interested to know what materials he used to fix it (a cement mortar, presumably, but what was the stuff he mixed with the mortar to ‘aid drying’??
How to spot good quality- a reputable stone supplier - and it’s worth visiting one in your area - will provide upon request technical data sheets showing test results for density, flex and compression strength, porosity etc. Visually, are the slabs of an even depth (a stronger, denser stone will be capable of finer tolerances), are there what looks like raised shapes or puddles of stone on the surface (like the bit near your foot on your photo), is the edge crumbling, can you break off bits off with a bit of pressure... a weaker stone will be fine for light traffic areas if it’s bedded, jointed and sealed properly so it’s not always essential to go for the very best, but I would go for the lowest porousity for outdoor use otherwise it might go green quickly, be frost damaged very easily and start to spall and delaminate. Time and a winter will tell. Have a look at https://www.marshalls.co.uk/homeowners/stone-standard which will give you some idea. There are also lots of sites that say ‘never spot fix sandstone!!’ So a bit of googling will unearth you plenty of ammunition.
As you have chosen a grey stone, tbh if you redo it, slate is stronger, much less porous and will give you a much more durable product with a similar look. Just a thought!
Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
and I would still use this cheaper method if the slabs were chunky, +30cm thick, but I would want to use flexible adhesive to create a cushioned, more shock-absorbent base for thinner slabs. The flexible adhesive does not react with the stone. A flexible grout, suitable for the wider grout lines often used with natural stone, is also recommended. My preferred method is also explained pretty well on Marshall’s site:
Grouting and Sealing - some sandstone suppliers (including Marshalls) claim their stone doesn’t need sealing, but I would always recommend several permeable or ‘impregnator’ sealant coats with sandstone. For my sandstone interiors and patio I cleaned, air-dried, impregnated and then air-dried the slabs before they were laid, including coating the edges of each slab. This gave some protection to the porous stone from adhesive and grout smears. The grouting method is like piping in the cracks, rather than spreading the grout over the surface of the stone and wiping off, because it doesn’t wipe off easily, especially if using a darker grout. After laying and grouting, once completely dry, another coat was applied.
I use Sika Starflex FA, Weber is also fine. Grout is proprietary flexible grout for stone floors/wider joints, Lithofin Impregnating sealer for natural stone. I’m sure there are other good brands. It is a skilled job to use this method. I had to teach the local builder how to do it when I had mine laid!
Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
Posts
Well that was the predictable, indeed predicted response from the builder! There are a number of reasons, not just the staining which may or may not ‘dry out’ (explained in my earlier posts) why spot fixing should never be used with natural stone, so no it’s not correct to say you only need to do that for driveways. Sandstone, especially much of the Indian stuff, is a soft porous material. I would be interested to know what materials he used to fix it (a cement mortar, presumably, but what was the stuff he mixed with the mortar to ‘aid drying’??
How to spot good quality- a reputable stone supplier - and it’s worth visiting one in your area - will provide upon request technical data sheets showing test results for density, flex and compression strength, porosity etc. Visually, are the slabs of an even depth (a stronger, denser stone will be capable of finer tolerances), are there what looks like raised shapes or puddles of stone on the surface (like the bit near your foot on your photo), is the edge crumbling, can you break off bits off with a bit of pressure... a weaker stone will be fine for light traffic areas if it’s bedded, jointed and sealed properly so it’s not always essential to go for the very best, but I would go for the lowest porousity for outdoor use otherwise it might go green quickly, be frost damaged very easily and start to spall and delaminate. Time and a winter will tell. Have a look at https://www.marshalls.co.uk/homeowners/stone-standard which will give you some idea. There are also lots of sites that say ‘never spot fix sandstone!!’ So a bit of googling will unearth you plenty of ammunition.
As you have chosen a grey stone, tbh if you redo it, slate is stronger, much less porous and will give you a much more durable product with a similar look. Just a thought!
The traditional, and still good, method is explained pretty well on:
https://www.marshalls.co.uk/homeowners/assets/pdfs/driveway-garden-installation-instructions/indian-sandstone-paving-installation-details.pdf
and I would still use this cheaper method if the slabs were chunky, +30cm thick, but I would want to use flexible adhesive to create a cushioned, more shock-absorbent base for thinner slabs. The flexible adhesive does not react with the stone. A flexible grout, suitable for the wider grout lines often used with natural stone, is also recommended. My preferred method is also explained pretty well on Marshall’s site:
https://www.marshalls.co.uk/tile-and-stone/advice/installing-natural-stone-floors
Grouting and Sealing - some sandstone suppliers (including Marshalls) claim their stone doesn’t need sealing, but I would always recommend several permeable or ‘impregnator’ sealant coats with sandstone. For my sandstone interiors and patio I cleaned, air-dried, impregnated and then air-dried the slabs before they were laid, including coating the edges of each slab. This gave some protection to the porous stone from adhesive and grout smears. The grouting method is like piping in the cracks, rather than spreading the grout over the surface of the stone and wiping off, because it doesn’t wipe off easily, especially if using a darker grout. After laying and grouting, once completely dry, another coat was applied.
I use Sika Starflex FA, Weber is also fine. Grout is proprietary flexible grout for stone floors/wider joints, Lithofin Impregnating sealer for natural stone. I’m sure there are other good brands. It is a skilled job to use this method. I had to teach the local builder how to do it when I had mine laid!