2 questions of granite driveways: Sealing before or after & what to do about weeds?

[Adsibob]

We are laying a patio out of rough edge granite setts (or cobblestones). One supplier, London Stone, is quite expensive and has also recommended their pre-sealing service where they seal all faces of the granite sett with Dry Treat Stain Proof so that they are delivered ready sealed. Their marketing blurb says: "Sealing stone prior to installation will help to protect against efflorescence (a white ‘bloom’ which appears on the surface of the stone after installation as a result of salts from the
bedding layer travelling through the stone to the surface). Sealing prior to installation will not completely eradicate the possibility of efflorescence occurring, however it will reduce the risk significantly in comparison to unsealed stone."

 

Another supplier, has said that they don't pre-seal and that sealing all faces is also not required. Instead, they recommend installing the setts and then sealing just the exposed face with a product called "Wet and Forget". This is significantly cheaper than Dry Treat Stain Proof, and the supplier is also quite a bit cheaper.

 

What have people on the forum who have laid granite outdoors done about sealing? Do you do it before or after installation?

 

And how do you stop weed growth? Is it simply a case of laying a geotextile membrane between the hardcore and the sand and cement bed for the granite?

[SteamyTea]

Do you know how slippery when wet granite is.

I am nimble and lithe, with cat like reaction. Stepped on one, slipped, broke my pelvis.

Would have been worse but my Pentax DSLR broke my fall.

[Adsibob]

hmmm... what kind of granite was it? The one we're looking at is either this expensive one which has the following on its data sheet: 

 

Slip Resistance	89 Dry / 79 Wet

 

Or this one which has a cropped surface but no data sheet. 

 

Obviously don't want to slip in the rain, but the impression I got from both suppliers is that the rough edge ensures they are not slippery. Am i mistaken?

 

Sorry to hear about your hip and Pentax. Did the pentax sustain any damage? As K-5 owner, I have been surprised how hardy they are. I dropped a wide angle lens on a hard airport floor once and nothing (discernible) happened to it.

[SteamyTea]

11 minutes ago, Adsibob said:

what kind of granite was it

The best, Cornish.

 

  

11 minutes ago, Adsibob said:

Slip Resistance	89 Dry / 79 Wet

Does that actually tell us anything?

 

Edited March 28, 2022 by SteamyTea

[Adsibob]

1 minute ago, SteamyTea said:

The best, Cornish.

 

okay, but was it a smooth surfaced granite you slipped on or a tumbled / riven surface?

[SteamyTea]

3 minutes ago, Adsibob said:

okay, but was it a smooth surfaced granite you slipped on or a tumbled / riven surface?

Once I picked myself up, I was not too interested, was as much as I could do to get back to the car.

 

https://en.wikipedia.org/wiki/Floor_slip_resistance_testing

[AliG]

The old roads in Edinburgh are made of granite setts. We have three rows under our gate.

 

They are slippery to cars but I have never had an issue walking on them, even when wet. Looks like a high number is better slip resistance. Our riven sandstone paving slabs are more slippery when wet.

 

I wouldn't think granite needs sealing it is a lot less porous than other stones.

 

I don't believe the ones under the gate are sealed, I have never seen efflorescence on them. On the other hand, we do get it on our sandstone which we should have sealed.

 

That Londonstone place seems absurdly expensive. What's the difference between their granite and everyone else's which is half their price?

[Adsibob]

9 minutes ago, AliG said:

The old roads in Edinburgh are made of granite setts. We have three rows under our gate.

 

They are slippery to cars but I have never had an issue walking on them, even when wet. Looks like a high number is better slip resistance. Our riven sandstone paving slabs are more slippery when wet.

Yeah, issue is that my setts will be laid on a 10 deg slope. We will have a separate stone staircase, probably made of sandstone, for accessing main door of house from street, but to get to and from the car will require traversing the inclined gravel. Interestingly, the attached document from Westminister council says they have "excellent" slip resistance.

9 minutes ago, AliG said:

I wouldn't think granite needs sealing it is a lot less porous than other stones.

 

I don't believe the ones under the gate are sealed, I have never seen efflorescence on them. On the other hand, we do get it on our sandstone which we should have sealed.

 

That Londonstone place seems absurdly expensive. What's the difference between their granite and everyone else's which is half their price?

It is absurd. We get a 16% discount through a friend, but it still works out crazy expensive. I will look elsewhere!

[AliG]

I would be wary of a sandstone staircase. Our sandstone paving is very slippery when wet. OK for occasional use, but not for your main entrance. I think it is the way that dust settles on it and then gets wet. I sometimes wonder if it would help if we scrubbed it clean.

 

I am a little confused, is the driveway gravel, with a granite path? Here, you would not be allowed to lay a granite driveway as it is non permeable.

 

1/10 is a steepish slope. Looking at them they have quite a rough surface so I think you are OK. The granite setts in Edinburgh are smooth and lethal in frost. The ones you are looking at are much rougher than the ones under my gate.

 

Weeds should be OK. We are now getting some weeds/grass in our resin bound driveway. The issue is not stuff growing through it, it is stuff settling on top and growing into it. I need to go out and pressure wash it. As granite setts sit on a mortar bed, weed coming through are less likely than on most surfaces and there are not may areas for them to take hold. You might get some moss on the joins but it will scrub off.

 

 

 

 

[Adsibob]

33 minutes ago, AliG said:

I would be wary of a sandstone staircase. Our sandstone paving is very slippery when wet. OK for occasional use, but not for your main entrance. I think it is the way that dust settles on it and then gets wet. I sometimes wonder if it would help if we scrubbed it clean.

What stone do you recommend for the steps then? I need something fairly light coloured, a light grey or off white, that isn't too expensive and has good slip resistance. 

33 minutes ago, AliG said:

I am a little confused, is the driveway gravel, with a granite path? Here, you would not be allowed to lay a granite driveway as it is non permeable.

No, the driveway is completely granite and completely impermeable. I was also confused by this, but having looked up the local requirements it seems my council only "recommends" that it is permeable. The reason for this, i suspect, is that the entire borough sits on London clay which is notoriously impermeable to water, so if I were to have a permeable driveway, all that would happen is the water would drain down through the cobblestones and then sit somewhere on top of the hardcore underneath, as below that is dense clay which just does not let water through. I consulted a RICS surveyor about this and he recommended making sure I have sufficient drainage channels both at the top of the driveway and at the bottom, so we've gone for an aco drain channel top and bottom as well as a french drain at the bottom.

 

33 minutes ago, AliG said:

1/10 is a steepish slope. Looking at them they have quite a rough surface so I think you are OK. The granite setts in Edinburgh are smooth and lethal in frost. The ones you are looking at are much rougher than the ones under my gate.

Actually, it's worse than a 1/10 slope. A 1/10 slope, if I understand you correctly is that for every run of 10m there is a fall of 1m. The inverse tangent of 0.1 is about 5.7° and my slope is closer to 10°. Not much I can do about that.

33 minutes ago, AliG said:

Weeds should be OK. We are now getting some weeds/grass in our resin bound driveway. The issue is not stuff growing through it, it is stuff settling on top and growing into it. I need to go out and pressure wash it. As granite setts sit on a mortar bed, weed coming through are less likely than on most surfaces and there are not may areas for them to take hold. You might get some moss on the joins but it will scrub off.

 

 

 

 

Nice entrance!

 

[AliG]

I misread it as a 10% slope, which I think is similar to ours.

 

10 degrees is pretty darn steep. Our driveway is scary if covered in a little snow. That natural granite finish looks to be quite rough and about as good as you will get for wet grip.

 

I would be worried about ice forming on a non permeable surface, but water should run off the surface due to the slope. Snow will be your biggest issue, but the surface doesn't make any difference once there is a few cm of snow on it.

 

As to the steps, that London Stone website is pretty useful. I would want something that is over 65 for wet grip. TBF I am probably ultra cautious. There are sandstone and granite steps that meet this requirement. The range for different kinds of sandstone is pretty wide. It is amazing how sensitive it is to the shoes you are wearing. We have rough granite paving on three sides of the house and a resin drive in front. We sometimes do laps of the house when we are exercising. None of us want to do them if it is wet, as we have all found we slip on the wet granite in trainers. But this is when jogging.

[Gone West]

As a point of interest we had honed sandstone paving pathways at our last house which weren't slippery when wet. We found out the hard way that sandstone is badly affected by salt (NaCl), when I put some salt on some weeds growing near the edge of the sandstone. It isn't therefore a good idea to put salt on icy sandstone paving.

[Adsibob]

14 hours ago, Gone West said:

As a point of interest we had honed sandstone paving pathways at our last house which weren't slippery when wet. We found out the hard way that sandstone is badly affected by salt (NaCl), when I put some salt on some weeds growing near the edge of the sandstone. It isn't therefore a good idea to put salt on icy sandstone paving.

Why, what did the salt do?

[Gone West]

8 hours ago, Adsibob said:

Why, what did the salt do?

It somehow chemically affected the surface of the sandstone making it shiney and smooth.

 

[Adsibob]

So my search for a non-slip stone sett continues. Rock Unique (which is often mentioned on this forum) don't have enough stock but then we found a supplier in Northern Ireland who we were going to go with until they said they wouldn't accept credit card on "an order as big as this one" which made me run for the hills, given their website does say the accept credit card.

I've now found a supplier that has offered Basalt setts instead. Quite a bit cheaper than granite, but not quite as anti slip. The supplier has said it is considered a "non-slip" stone, but he accepted granite would be slightly less slippery. The basalt does look very nice otherwise.

Anyone have any experience of basalt setts? Slippery?

[markc]

‘Slippery ness’ of stone depends more on how it’s used, what lands on it and how often it is cleaned (assuming it’s isn’t polished to start with.

granite has a very course jagged surface when broken making it ideal for non slip areas, basalt is finer grained but still much harder than many rocks so will keep the roughness longer.

Foot and vehicle traffic will polish any surface over time.

biggest cause of slippery is moss and general dirt filling the surface causing it to become slippery.