Hi! We have an 1860s sandstone property. When we moved in, the gable end sandstone wall (poorer quality stone than the front!) Was crumbling quite impressively. It had been pointed with cement, and we had it dug out and redone with lime. This has improved the problem markedly, but it is still dissolving in places. We have been advised to get it coated with a 'breathable' sandstone sealant. Struggling to find any information on this. Is it a good idea? Any alternative advice?
- Thread starter lizBiz
- Start date
A picture tells a thousand words.
I personally wouldn’t trust any kind of sealant product on a soft crumbly stone wall. I see the cement as a sealant in the first place which you rightfully removed, and I wouldn’t want to then backtrack with adding another sealant back in.
As an alternative, if I was very worried about the wall continuing to erode away, I would render the entire wall with a soft Lime-rich render (NHL 2 at the hardest, but probably ideally a non-hydraulic lime based render).
What type of lime was used in the repointing out of curiosity? Normally I don’t think this is hyper important, but with a very soft sandstone the choice of lime probably becomes more critical.
I personally wouldn’t trust any kind of sealant product on a soft crumbly stone wall. I see the cement as a sealant in the first place which you rightfully removed, and I wouldn’t want to then backtrack with adding another sealant back in.
As an alternative, if I was very worried about the wall continuing to erode away, I would render the entire wall with a soft Lime-rich render (NHL 2 at the hardest, but probably ideally a non-hydraulic lime based render).
What type of lime was used in the repointing out of curiosity? Normally I don’t think this is hyper important, but with a very soft sandstone the choice of lime probably becomes more critical.
Cubist
Member
- Messages
- 2,302
- Location
- Shropshire/Herefordshire Border
The best advice I can offer would be to look down at the foot of the wall to see whether there is anything that may be limiting the ability of rainwater to drain away from the walls face. Then check to the right, left and behind you to see if there are obstructions to air movement across the face of the wall or heavy shade that blocks sunlight.
There are stone stabilisers on the market but I would be deeply reluctant to use one of these. Most include a water repellant component to resist rain BUT these in effect also trap moisture exuded from indoors which then leads to spalling. I don't know if theres any way to check if such a material has already been used on that wall but if it has, then its the likely to be a major contributor to the erosion you are seeing.
There are stone stabilisers on the market but I would be deeply reluctant to use one of these. Most include a water repellant component to resist rain BUT these in effect also trap moisture exuded from indoors which then leads to spalling. I don't know if theres any way to check if such a material has already been used on that wall but if it has, then its the likely to be a major contributor to the erosion you are seeing.
Stevers
Member
- Messages
- 576
- Location
- Mendip Hills
No personal experience of crumbly Sandstone to draw on as I'm in limestone country, and the old red sandstone cap up on the Mendip ridge is a) not red, and b) much harder than nails!
I did a liitle bit of digging for another thead back in August and came across this little nugget.
"Sandstones are quite variable in that the 'cement' that binds the grains can be silicate, or non-silicate such as calcite - worth a mention as it might dictate the correct solution. The Wiki article on Sandstone (https://en.wikipedia.org/wiki/Sandstone) made specific reference to an expensive and hazardous chemical that might help stabilise sandstones - presumably the silicate ones:"
"Sandstone that becomes depleted of its cement binder through weathering gradually becomes friable and unstable. This process can be somewhat reversed by the application of tetraethyl orthosilicate (Si(OC2H5)4) which will deposit amorphous silicon dioxide between the sand grains. The reaction is as follows. Si(OC2H5)4 (l) + 2 H2O (l) → SiO2 (s) + 4 C2H5OH (g)".
I did a liitle bit of digging for another thead back in August and came across this little nugget.
"Sandstones are quite variable in that the 'cement' that binds the grains can be silicate, or non-silicate such as calcite - worth a mention as it might dictate the correct solution. The Wiki article on Sandstone (https://en.wikipedia.org/wiki/Sandstone) made specific reference to an expensive and hazardous chemical that might help stabilise sandstones - presumably the silicate ones:"
"Sandstone that becomes depleted of its cement binder through weathering gradually becomes friable and unstable. This process can be somewhat reversed by the application of tetraethyl orthosilicate (Si(OC2H5)4) which will deposit amorphous silicon dioxide between the sand grains. The reaction is as follows. Si(OC2H5)4 (l) + 2 H2O (l) → SiO2 (s) + 4 C2H5OH (g)".
Itchinfilth
Member
- Messages
- 23
- Location
- Bingley
Beek Fixative which can be purchased from Celtic Sustainable has worked on our extremely delicate sandstone damaged from cement. Water down 1 part fixative to 5 parts water and flow coat it many many many times. No change to appearance of the stone when dry and it's now no longer dusting / crumbling if rubbed.