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Posted: Tue Jul 21, 2015 2:14 pm
by London Stone Paving
Opinions are opinions but when you have seen something with your own eyes happen with alarming frequency and in 90% of case the common denominator is the fact that the paving has been laid on a concrete base, you start to put 2 & 2 together.
I have seen it happen with granite, sandstone, limestone. The 2 most common products where I have seen it happen are with sawn kandla grey and sawn raj green (two of the hardest natural stones available on our market). Its not correct to blame it on the stone type. The common denominator is the concrete base.
If you ever want to carry out some tests Tony I would be happy to provide a range of stone materials to test on
Steve
Posted: Tue Jul 21, 2015 5:38 pm
by lutonlagerlout
from a contractors view i would rather lay stone on type 1 than concrete
2 reasons
1 if you lay on concrete the water in the bed cannot get through the concrete
it tends to rise up between the joints and spoil the paving ,it takes ages to set and it causes picture framing
obviously you could use a dry mix but then you run the risk of the paving not adhering to the bedding layer
2 when you lay On type 1 (which is fairly permeable) the water in the mix is generally sucked into the type 1 within the hour
its much less messy and to date has worked every time
I do believe sawn paving is on the whole softer than riven (cuts a lot easier) but you can make a great job if you are careful with it
I would err towards presealing as with british weather you may not get the chance to seal
Not sure on the installation of pavetuf specifically But I have always been told never seal new paving till it has been down for at least 6 weeks
LLL
Posted: Tue Jul 21, 2015 7:09 pm
by PavingSuperstore
The Pavetuf is specifically designed to be used straight after laying - wouldn't recommend it with anything else.
Posted: Tue Jul 21, 2015 7:29 pm
by sy76uk
I've only ever laid sandstone with a full mortar bed on a concrete sub base one.
The stone was reclaimed York stone and was uncalibrated 50 - 100mm thick.
We were using a stiff mix of crushed glass and cement for bedding (commercial project specifying recycled materials) with a neat cement slurry for bonding.
We had no issues.
Posted: Tue Jul 21, 2015 9:14 pm
by London Stone Paving
PavingSuperstore wrote:The Pavetuf is specifically designed to be used straight after laying - wouldn't recommend it with anything else.
But George, that's the same for all impregnators, it's not specific to Pavetuff.
While you can theoretically use any impregnator immediately after installation the circumstances don't always allow it.
As already mentioned the British weather can get in the way, the stone can and usually does get grubby during installation which means it needs cleaning with water and you have to let it dry again. You could get the stone clean and dry and then a fox might a walk muddy footprints all over it. It then needs cleaning and drying again. These are the kind of things that can and do happen to contractors.
I have known for clients to hold back large stage payments on projects because it's rained for 2 weeks and the contractor hasn't had chance to seal the paving.
That's why I always say pre-seal if you can
Posted: Tue Jul 21, 2015 9:26 pm
by sy76uk
I also see a problem with pre sealing.
stone fresh out of the crate is usually covered in quarry dust and be quite difficult to remove.
I wouldn't want to seal that in.
I personally won't seal paving but advise customers on the pro's and cons then if they want to they can do it themselves.
Posted: Tue Jul 21, 2015 9:47 pm
by lutonlagerlout
sy if they want it sealed its better to buy it presealed as steves mob do
the stone is cleaned then put in a drying container till it is bone dry
then sealed twice with dry treat
by doing this the client is getting it sealed and you/me are not getting the headaches
LLL
Posted: Tue Jul 21, 2015 9:47 pm
by sy76uk
Good idea.
Posted: Wed Jul 22, 2015 8:55 am
by London Stone Paving
sy76uk wrote:I also see a problem with pre sealing.
stone fresh out of the crate is usually covered in quarry dust and be quite difficult to remove.
I wouldn't want to seal that in.
I personally won't seal paving but advise customers on the pro's and cons then if they want to they can do it themselves.
Your right, that is a potential problem with natural stone. We started to put the onus on our suppliers to clean the stone properly prior to packing which reduced this down. Anything left can be brushed off or at the worst wiped with a cloth. There are always a few that need a proper clean but its only a small amount and they would need to be cleaned properly.
The drying container is akin to a sauna. 
Posted: Wed Jul 22, 2015 5:29 pm
by lutonlagerlout
I can confirm that it is as dry as a nuns in there :;):
LLL
Posted: Thu Jul 23, 2015 10:58 am
by London Stone Paving
Kandla Grey and Raj Green are the two hardest sandstone products you can buy in the UK.
The following is an image of Kandla grey that was laid on a concrete sub base
When this occurs there is no cleaning or maintenance solution that will get rid of this marking. You have two choices, either rip and relay or live with it and watch the marks slowly fade over a period of time. Neither choice is very palatable when you have just made a serious financial and emotional investment in a garden that you hoped you would be able to enjoy for the next 10-20 years.
I have seen this happen on many occasions when stone is laid on a concrete sub base. This is why I am SO against stone getting laid on a concrete base. Enough things can go wrong on a job anyway without creating problems for yourself. Why even take the chance of this happening?
Steve
Posted: Fri Jul 24, 2015 9:29 am
by Tony McC
I'll see if I can get some Kandla Grey and try to replkicate this. I can't fathom a mechanism that would implicate the concrete base when the stone itself is laid on a full mortar bed.
There's more going on in that image than just the bedding!
Posted: Fri Jul 24, 2015 10:10 am
by London Stone Paving
I agree Tony, I think the fact that the paving is closed in by rendered walls is amplifying the problem
Posted: Fri Jul 24, 2015 10:41 am
by lutonlagerlout
I kinda wonder where the water drains to?
but still do not like concrete bases for paving
have done it and its a pain
LLL
Posted: Sat Jul 25, 2015 8:12 pm
by split59
Cheers for the advice. Have decided not to use Sawn. And our first choice after sawn was mint but if we are taking staining and weakness into account we are thinking along the lines of Raj Green Or Jewsons are doing a fantastic deal on Marshal and natural stone Sand stone ranges and the Lakeland or buff look like good deals.