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Posted: Sun Jan 17, 2010 4:44 pm
by dr benway
long time lurker, second time poster :laugh: :laugh:
after the ground being frozen solid here/under snow/ice for 3-4 weeks, sandstone flags laid in october on full mortar beds are now loose.
it doesnt appear that the beds have crumbled, just that they're now "unstuck".
whats the best way to reseat them please?
I was also thinking about repointing with rompox/romex, but please see my other post for questions about that.
any advice much appreciated
Thanks!
Posted: Sun Jan 17, 2010 10:35 pm
by lutonlagerlout
if they have "come loose" then all the bedding needs to be cut back to sub base and rebedded
sorry there is no easy fix
in all honesty the weather has been out of the ordinary ,but there has been talk of using bond bridging techniques when using sandstone
LLL
Posted: Sun Jan 17, 2010 10:45 pm
by DNgroundworks
I do like using a bondbridge, a cement slurry with a SBR mixed in is what i used on sandstone painted directly on the back of the flag.....just to be sure 
Posted: Mon Jan 18, 2010 9:46 am
by dr benway
thanks all, for the replies
Is their a preferred brand of SBR?
the flags were painted with PVA, and PVA was added to the mortar-- obviously to no avail -- but as you say, it has been very, very cold.
thanks
Posted: Mon Jan 18, 2010 4:57 pm
by lutonlagerlout
I have had good results with PVA in the past ,although apparently its not recommended
can you post a picture of the bedding under the flags?
if there was any void at all and water got there,it would freeze and expand ===> popping the flags up
LLL
Posted: Mon Jan 18, 2010 9:08 pm
by Craig2
I went back to work today for the first time since 4th Dec to find the frost has blown 60% of my 4" double cobble borders(about 300) gutted! the Flags seem ok and 40% of the cobbles are holding on.I laid them in November with PVA and Frostproofer in the mix and dipped the cobbles in 50/50 PVA before laying but it would seem the severity of the frost has caused the problem.
I laid the Flags pretty much the same, full bed and painted with a 50/50 PVA before being laid and touch wood they are ok.
I was looking at using something like this to refix them
http://www.rockbond.co.uk/datashe....r07.pdf
any thoughts?
I have real trouble if i have to take out all the mortar and relay the cobbles as the mortar is tight in with the Flags and I can't see it being done without causing further damage.
Posted: Mon Jan 18, 2010 10:39 pm
by GB_Groundworks
run a cut off saw along the flag edge cutting the mortar to stop any cracks spreading as you pull it up but i'd be tempted to relay them all now so your not having future problems lay them with sbr in the mix and on a stronger mix(more cement), did you use sharp sand or builders sand?
Posted: Tue Jan 19, 2010 7:55 am
by cookiewales
lads you should not use pva on any paving or in mortar for pointing at all its a big no no as it emullsifies on contact with water and then looks like you have poured milk over your job as for the best in my exp ronofix but all sbr should be to a standerd unibond is good but to pricey :p :;):
Posted: Tue Jan 19, 2010 3:39 pm
by Tony McC
Returning to the question asked by the OP, I'd leave the flags well alone until I was sure there was actually a problem. They may have de-bonded from the bed, but unless they are actively rocking and/or moving, lifting and re-laying could well be unnecessary additional work.
Posted: Tue Jan 19, 2010 4:54 pm
by lutonlagerlout
i thought unibond was PVA?
definitely wouldn't use any additives in the pointing,even the dyes leach out fast
LLL
Posted: Tue Jan 19, 2010 10:49 pm
by Craig2
I use Plastering sand which gives me an extra body to my mix, never had a problem with my Flagging.
I trialed a few cobbles today with an SBR Slurry bonding mix. 50/50 with OPC, I will report back my findings.
eyup Tony, its been a while :p you still on the Boddingtons?
Posted: Tue Jan 19, 2010 11:39 pm
by GB_Groundworks
plastering sand is this a southern name for sharp sand?
i always use sharp sand bigger grains give better interlock stronger mix.
or plastering sand as in what you use to make a sand cement render?
Posted: Wed Jan 20, 2010 12:10 am
by Craig2
Southern?? how very rude! :p I am more northern than most. 
Plastering sand is a mix of both building and fine sharp (not as rough as cardewmires?)giving the best of both worlds, the stickability of building sand with added strength from the sharp.
Posted: Wed Jan 20, 2010 6:43 am
by msh paving
in norfolk alot off people call it medium sharp, as it is not to sharp but not soft MSH 
Posted: Wed Jan 20, 2010 11:01 am
by cookiewales
lutonlagerlout wrote:i thought unibond was PVA?
definitely wouldn't use any additives in the pointing,even the dyes leach out fast
LLL
unibond is a sbr in most cases take a look on the tin :p ??? ???