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Posted: Mon Mar 31, 2014 10:28 am
by Adrwilliams
Good morning....
I'm at an advanced (but very slow!!) stage with my DIY patio:
3 low level retaing walls in random stone in place / limestone infill well wacked and solid....All looks sound to me.
(mortar: 6 building sand / 1 cement / 1 limbux trulime (I've mixed the lime with water to a runny paste before adding....)
To top the walls (to be part of the paved surface) I've bought yorkshire sandstone, freshly sawn and tumbled 300mm x 100mm x 50mm to be laid in a 'side by side soldier formation'.... (then plan to fill the area between possibly with indian sandstone...
I layed a dozen of these topping stones late summer (no frost risk etc...)
Same mortar mix as above.
Left undisturbed for several weeks.
HELP!!! I've gone to them just now to find the stone hasnt bonded and they've lifted cleanly off leaving the mortar bonded to the wall tops.
I've obvioiusly done something wrong.... but I dont know what 
Is my mortar mix wrong? (although the stonework to the walls looks good and solid...)
1) Any advice?
2) Is lime essential? can I do without it? I know it 'softens' the mix but is that a good thing for the stone paving and the 'edgings' in particular if theyre being walked on etc?
3) Grit sand? should I use grit sand instead of normal builders sand - will it bond better?
4) Does it make sense to 'wet' the yorkshire stone before laying it, or should I use it dry? (I was advised to wet it to stop it pulling the water from the mortar, which I did....)
Any advice very greatly received
Many thanks!!
Adrian
Posted: Mon Mar 31, 2014 11:26 am
by Tony McC
Not sure why it hasn't bonded. The lime should make no difference, and as long as the stone wasn't dripping but just 'damp' when placed, it should have stuck in place.
Was the tumbled stone dusty? It's always a good idea to wash tumbled stone if using it with mortar bedding to get rid of any loose material which would impair bonding.
If all else fails, then re-seat them all using a sbr slurry and/or a sbr mortar.
Posted: Mon Mar 31, 2014 11:35 am
by Adrwilliams
Tony McC wrote:Was the tumbled stone dusty? It's always a good idea to wash tumbled stone if using it with mortar bedding to get rid of any loose material which would impair bonding.
If all else fails, then re-seat them all using a sbr slurry and/or a sbr mortar.
Aaah.... good point.... yes - the stone may be dusty, but I hadnt realised this might be an issue...
Out with the jet wash!
Would you recommend using an SBR admix in any case? along with the trulime? to improve adhesion?
Thank you!
Posted: Sun Apr 06, 2014 10:26 am
by Tony McC
Sorry for the delayed response - not been one of my best weeks, healthwise.
Given the problems to date, I'd be almost definitely using SBR to ensure the stones stay put!
Posted: Sun Apr 06, 2014 2:29 pm
by Adrwilliams
Tony McC wrote:Sorry for the delayed response - not been one of my best weeks, healthwise.
Given the problems to date, I'd be almost definitely using SBR to ensure the stones stay put!
Thanks Tony - thats great. Would you opt for the SBR slurry approach or add SBR to the mortar?
I expect to use a 6:1 grit/sharp sand : cement
Would there be any great disadvantage in leaving the lime out altogether?
Posted: Sun Apr 06, 2014 3:48 pm
by lutonlagerlout
adrian you need to make an SBR slurry and paint the stones on both faces to be fixed
(mix neat SBR with cement to a wallpaper paste consistency)
also I would add 150mm of sbr to the mortar its self
if the mortar is seen grit sand may leave too rough a finish
Building sand should be OK on a wall
any paving needs to be laid with grit sand
hope this clarifies things
cheers LLL 
Posted: Sun Apr 06, 2014 5:22 pm
by Adrwilliams
lutonlagerlout wrote:adrian you need to make an SBR slurry and paint the stones on both faces to be fixed
(mix neat SBR with cement to a wallpaper paste consistency)
also I would add 150mm of sbr to the mortar its self
if the mortar is seen grit sand may leave too rough a finish
Building sand should be OK on a wall
any paving needs to be laid with grit sand
hope this clarifies things
cheers LLL
Thanks LLL.
I've used building sand so far for the retaining walls and its been fine.
However, the topping stones that I've had a problem with here will actually form part of the paving and will be walked on as they'll be level with the indian stone paving.....
Should I deal with these in the same way as the stone paving which I'll be 'filling inbetween' with and use grit sand rather than building sand?
And - as regards the SBR mortar - you say add 150mm (ml?) would you say that a mix of 6 sand : 1 Cement : 0.2 SBR sounds reasonable?
Thanks again for your advice everyone.
Adrian
Posted: Sun Apr 06, 2014 5:26 pm
by Adrwilliams
Oh - and how essential is the lime?
I was told a short while ago that:
'mixing lime powder with water to a paste and adding it to the mortar is a waste of time as the lime has insufficient time to have an effect on the mortar'.
Im not sure of the science behind it, but several builders Ive spoken to recently say they would never bother adding lime when working with stone....???
Seems a bit contrary to the official line....
Posted: Sun Apr 06, 2014 5:30 pm
by lutonlagerlout
hydraulic lime has its uses,but chances are you are using hydrated lime which really just acts as a plasticiser and colour lightener
if you use any cement at all you are kind of defeating the object of using lime
i wouldnt bother with lime as it adds nothing strengthwise
cheers LLL
Posted: Sun Apr 06, 2014 9:19 pm
by Adrwilliams
Thanks LLL. In that case - I shall use no further lime.
Yes - you're right - its hydrated lime I've used so far...
One less thing to think about!
Thanks again!
Posted: Tue Apr 08, 2014 11:58 am
by Tony McC
There was a time when lime mortars were being heavily promoted for paving beds, but that seems to have all but faded away now with the obsession over rigid beds.
We only ever used lime mortar on a large scale on one job in the 80s. I go past that area a couple or three times a year and each time it strikes me how well the paving has stood up to the tests of time and illegal vehicle overrun.
Are we missing a trick for pavement bedding just because the lime mortar sector has such a weak voice in the face of bellowing from the cement giants?
Posted: Tue Apr 08, 2014 4:59 pm
by lutonlagerlout
yes boss but most just mix a shovel of hydrated with the cement mix which is pointless
if you use lime it must be lime and sand alone and it should be hydraulic
it can crack and reseal itself
to my mind its too soft for paving works and it takes at least 3 days to go off which is unrealistic the way folk work today
LLL
Posted: Tue Apr 08, 2014 9:26 pm
by Adrwilliams
OK then - as final confirmation - this is how I'm heading
1) 6 sharp sand : 1 cement : 0.2 SBR (for good measure)
2) No hydrated lime
3) SBR slurry: 1SBR : 1 Cement : 1 water
Hopefully - all of the above is now considered OK?
Many thanks for all your advice
Adrian
Posted: Tue Apr 08, 2014 10:19 pm
by lutonlagerlout
its the way we do it!
LLL
Posted: Tue Apr 08, 2014 10:47 pm
by Adrwilliams
Sounds good to me! Many thanks!