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Posted: Wed Sep 20, 2006 4:30 pm
by Wildfang
after my last posting re laying on sand only, I checked again the main website.
Instructions start off by discussing mortar beeding techniques and advising against spot bedding (fair enough), but then go on to advise laying on a dry bed of sharp sand (as per my original question!), perhaps stiffened 10:1 with cement.
The instructions also say no sub-bed needed for patios! ..just the 10:1 sharp sand/cement 35-50 mm bed (just crushed hardcore to fill hollows)
Please any commemts/advice/clarification
Thanks again
Posted: Wed Sep 20, 2006 9:52 pm
by cwight
Wildfang, trust me it's easy. I'm a novice and have done over 100m2 of random indian stone. If it's just pedestrian traffic just make sure you have a level site (don't even need to worry about a subbase of hardcore) and lay your slabs on a full bed (meaning every bit of the slab should be on this bed, not just spots/dabs) of a 10:1 dry mix. This means dry, do not add any water as the mix draws up sufficient water from the ground. Don't walk on the slabs for 24 hours to allow the mix to set. It won't set really hard since it's a very weak mix, but it will do the job and makes it easier to correct mistakes than a wet mix.
Posted: Wed Sep 20, 2006 9:52 pm
by cwight
Wildfang, trust me it's easy. I'm a novice and have done over 100m2 of random indian stone. If it's just pedestrian traffic just make sure you have a level site (don't even need to worry about a subbase of hardcore) and lay your slabs on a full bed (meaning every bit of the slab should be on this bed, not just spots/dabs) of a 10:1 dry mix. This means dry, do not add any water as the mix draws up sufficient water from the ground. Don't walk on the slabs for 24 hours to allow the mix to set. It won't set really hard since it's a very weak mix, but it will do the job and makes it easier to correct mistakes than a wet mix.
Posted: Wed Sep 20, 2006 11:23 pm
by Stuarty
I always lay a subbase, even on solid ground. I always lay Indian Sandstone and other riven slabs. If the slabs have a flat base, eg BS slabs, Marshalls Saxon etc etc, ill usually lay them on a dry mix.
Posted: Wed Sep 20, 2006 11:23 pm
by lutonlagerlout
im seeing double :p
lol LLL 
Posted: Wed Sep 20, 2006 11:25 pm
by lutonlagerlout
ye stuarty is right,sub base never did any harm and a lot of times does the business
i will take a picture of the paving where we are working tomorrow to show you what no sub base does
cheers LLL
nearly there stuarty for the ton club
Posted: Thu Sep 21, 2006 7:31 am
by cwight
Well a subbase will never go amiss, but it's a question of whether you actually need one. I did on my project. Just check out the main site it has good info on when whether you do, or do not, need a subbase.... Sorry for the double posting earlier. Computer seemed to lock, I hit the reload key and reposted, but it had obviously sent it already...
Posted: Thu Sep 21, 2006 10:48 am
by Wildfang
Dear Colin, LLL and Stuarty
I feel like I'm getting somewhere now, although I still can't believe the variation in guidance on this website, in books and in replies on this message board as to the right thing to do!
As a novice, I'm beggining to think laying my riven slabs on a dry bed is the right thing to do (recognising LLL's usual advice to use wet mortar) - easier to rectify slope issues, etc as I go along.
Is 10 sharp sand : 1 cement the right mix? Better to add more cement - say 8:2? Does this really "set" in any meaningful way simply by drawing up water from the ground ? Would it set at all if I added a sub-base between the 10:1 dry bedding and the clay soil beneath (i.e. wouldn't the sub-bed act as a barrier to water uptake)? What if there has been a prolonged dry spell - will I still get sufficient water uptake - especially knowing how dry clay soil gets
If I go the dry bed way, I assume I just mortar the joints 24 hours after laying
Questions, questions!
WF
Posted: Thu Sep 21, 2006 12:03 pm
by bobhughes
The point is that there is no absolutely correct way of doing it. It depends on the underlying ground. Also a contractor will go for the higher spec to "be on the safe side" where a DIYer can settle for the easy way.
In my garden I can take off 3 inches of topsoil and find virgin clay that needs a pick axe to shift it. No way would I bother with anything other than a screed bed for levelling.
When I did the drive, that had been partly a flower bed and partly dug up by the original builders, so that went on top of the full monty as per this site.
Whatever you put under the flags the mix will get damp enough to set.
Posted: Thu Sep 21, 2006 1:54 pm
by cwight
yes my situation is a bit similar to Bob's. It's a new build in W. Yorkshire and the ground after the excavation is almost like solid rock. In which case I just used a bit of sub-base to get the levels I needed. The 10:1 will set fine and if you are using riven flags just lay the bed for each flag at time to allow you to adjust for differing thicknesses etc. To be honest I'd never done it before, and was really nervous, but using the full bed dry mix there is less pressure because you can always try the slab, take it up and adjust as you go along.
I don't find the info on this site confusing, it's just trying to be comprehensive. You need to make a judgement on your particular circumstances. I laid over 100m2 of Indian Stone in a random pattern (and I had to do the pattern myself as well) and even my builder says it looks professionally done. Just give it a try and see how you get on. With the dry bed system, it's no big deal, even if the stuff sets, to lift everything and start again. The only thing I would change on mine is the width of the mortar joints. Thinking that this would be my weak spot I kept them quite tight, but I've since seen some that are quite wide with the black mortar and they look great. Also, following the mortar advice on this site makes it much easier than I thought. Again, the trick is to keep the mortar much drier than you might think so as not to stain the slabs....
Posted: Thu Sep 21, 2006 3:46 pm
by Wildfang
Thanks Bob and Colin
No criticism of this site intended!
I also have clay soil, although not sure how firm it will be once I get to below 5 cm (I can certainly dig to below that depth in my boarders - maybe to 35cm).
Assuming then I allow for a 5 cm dry bed of 10:1 sharp sand:cement and just use a "screed bed/a bit of sub-bed" for levelling (as per your posts), how deep do you recommend this layer be and (excuse my ignorance) but what is "screed" - i.e. what material should the sub-bed consist of.
thanks muchly again
Posted: Thu Sep 21, 2006 4:25 pm
by cwight
I think by 'screed bed' Bob means the actual 10:1 dry mix. If your ground is good enough you don't need anything above or below this for pedestrain areas, but it does very much depend on your ground. If you need sub-base just order some 'crusher run' from your local building yard, or just tell them what you want to use it for. It's dirt cheap to buy by the ton bag. To determine the depth you need to dig out just work back from the finished level. So if you are using 50mm slabs with say a 50mm bed you would need to dig out 100mm. If you need 150mm subbase as well however, you'd need to dig out to 250mm.
Posted: Thu Sep 21, 2006 4:51 pm
by lutonlagerlout
i suppose that half the craic is ,that doing it professionally we cannot cut corners,your only as good as your last job as they say
i used to use dry mix but got fed up with service calls for rockers 3 years later,wet mix sets really firm
dry mix works ok if the area is well retained by edgings say or walls
like i say i used it for a few years but had too many comebacks
and we dont like complaints even years later,it make you look bad
cheers tony LLL
Posted: Thu Sep 21, 2006 8:03 pm
by Wildfang
Brilliant replies - Thanks
LLL - on edging, I was planning on using cobble sets (not completely decided). If I use sub-bed+dy mix method as above, at what point do I put in my sets? After the sub-bed, but before the dry mix? I assume I just use wet mortar to bed the sets direct onto the sub-bed?
Perhaps I should point out I'm only talking about a very smal patio (perhaps 10 m2)
WF
Posted: Thu Sep 21, 2006 8:07 pm
by Wildfang
Brilliant replies - Thanks
LLL - on edging, I was planning on using cobble sets (not completely decided). If I use sub-bed+dy mix method as above, at what point do I put in my sets? After the sub-bed, but before the dry mix? I assume I just use wet mortar to bed the sets direct onto the sub-bed?
Perhaps I should point out I'm only talking about a very smal patio (perhaps 10 m2)
WF