Posted: Fri Jun 17, 2005 10:08 am
I'm building a raised patio and adjoining paths using Bradstone random carpetstones and need some advice -- I've scanned your excellent website, but found little specific advice for carpetstones. I assume the same basic techniques described for flags apply, but I thought I'd check with the experts.
The raised patio is constructed of a square slab of concrete 80mm thick upon which a low coping-topped perimeter wall approximately 215mm high has been built. I then filled the square void with a further 125mm of concrete using a thin section of specialist fibreboard between the concrete and the wall to absorb any expansion. This then left 90mm for the bedding mix and the carpetstones such that the carpetstones would finish flush with the coping.
I made a screeding bar with notches cut out at each end to sit on the coping such that the bedding mix would sit about 5mm higher than necessary on the assumption that the stones would bed in this distance. However, after I'd laid the semi-dry bedding mix (to Bradstone's recommended 6:1 sharp sand to cement ratio), I found that many of the larger stones (300mm x 200mm) refused to bed in properly using a rubber mallet (they're a little thin for anything more heavy-duty and I even managed to break one). A few days later and hey presto, over half the stones sound hollow when tapped and quite a few have a noticeable rock.
So here are my questions:
a) Did I add too much or too little water to the bedding mix? I know you're not supposed to add any, but the sharp sand was bone dry, the weather was quite hot and I was concerned that laying the mix onto a concrete slab wouldn't allow any moisture to be absorbed from the ground.
b) If I added too much water, could the bedding mix have started to set before I had chance to get the stones into position? It took a good 2-3 hours to get the mix in place and properly levelled before we started laying stones. Would I have been better adding no water at all? Would the mix have still set properly?
c) Could the bedding mix have been compacted too much? I doubt this is the case, since all we did was lay and level it. It would have been partially compacted during the process, but we didn't perform any additional compacting.
d) Would I have been better using a wet mortar mix? I know you don't generally recommend this, but would I have had more luck bedding the stones in? If making a wet mortar mix for bedding do you use sharp sand or soft sand and is the correct ratio 4:1 sand to cement?
I'm now worried about the best way to lay the adjoining paths (using a single line of carpetstones). Unlike the patio which at least has coping to constrain the edges, the paths will simply be bordered by a lawn on one side and a flower bed on the other. I don't intend using any edging since I want a flush finish on both sides.
To help me get the levels right, I'm building temporary shuttering to contain the concrete sub-base, bedding mix and carpetstones and arranging it so that the carpetstones will finish flush with the top of the shuttering (I know a sub-base isn't strictly necessary, but it will help me correct the slope of the garden). Since there won't be any permanent lateral support for the carpetstones (other than the lawn and flower bed), should I persevere with the semi-dry mix method (taking on board any responses to my earlier questions) or adopt the wet mortar method?
Apologies for the long description -- any help would be very much appreciated.
Jon.
The raised patio is constructed of a square slab of concrete 80mm thick upon which a low coping-topped perimeter wall approximately 215mm high has been built. I then filled the square void with a further 125mm of concrete using a thin section of specialist fibreboard between the concrete and the wall to absorb any expansion. This then left 90mm for the bedding mix and the carpetstones such that the carpetstones would finish flush with the coping.
I made a screeding bar with notches cut out at each end to sit on the coping such that the bedding mix would sit about 5mm higher than necessary on the assumption that the stones would bed in this distance. However, after I'd laid the semi-dry bedding mix (to Bradstone's recommended 6:1 sharp sand to cement ratio), I found that many of the larger stones (300mm x 200mm) refused to bed in properly using a rubber mallet (they're a little thin for anything more heavy-duty and I even managed to break one). A few days later and hey presto, over half the stones sound hollow when tapped and quite a few have a noticeable rock.
So here are my questions:
a) Did I add too much or too little water to the bedding mix? I know you're not supposed to add any, but the sharp sand was bone dry, the weather was quite hot and I was concerned that laying the mix onto a concrete slab wouldn't allow any moisture to be absorbed from the ground.
b) If I added too much water, could the bedding mix have started to set before I had chance to get the stones into position? It took a good 2-3 hours to get the mix in place and properly levelled before we started laying stones. Would I have been better adding no water at all? Would the mix have still set properly?
c) Could the bedding mix have been compacted too much? I doubt this is the case, since all we did was lay and level it. It would have been partially compacted during the process, but we didn't perform any additional compacting.
d) Would I have been better using a wet mortar mix? I know you don't generally recommend this, but would I have had more luck bedding the stones in? If making a wet mortar mix for bedding do you use sharp sand or soft sand and is the correct ratio 4:1 sand to cement?
I'm now worried about the best way to lay the adjoining paths (using a single line of carpetstones). Unlike the patio which at least has coping to constrain the edges, the paths will simply be bordered by a lawn on one side and a flower bed on the other. I don't intend using any edging since I want a flush finish on both sides.
To help me get the levels right, I'm building temporary shuttering to contain the concrete sub-base, bedding mix and carpetstones and arranging it so that the carpetstones will finish flush with the top of the shuttering (I know a sub-base isn't strictly necessary, but it will help me correct the slope of the garden). Since there won't be any permanent lateral support for the carpetstones (other than the lawn and flower bed), should I persevere with the semi-dry mix method (taking on board any responses to my earlier questions) or adopt the wet mortar method?
Apologies for the long description -- any help would be very much appreciated.
Jon.
