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Posted: Mon May 07, 2007 5:21 pm
by SparksMayFly
Hello All ,
New to this so forgive me for any errors or lack of important detail..
This saturday I laid a trustone radius 2.8m circle with corner kits . The postion is a slightly lowered patio area , for the base I have 75mm mot 1 and for a mix I have used 5:1 slightly wet . Each stone was pasted with a mix of neat wet cemet and a tiny amount of pva to help adhesion . All this is as set out by stonemarket instructions apart from the hard core.
Sunday afternoon I decided to check for any rocking slabs before using geo-fix ( ok its pricey but would save me from messing up my hard graft) . To my suprise even after using a large piece of timber and lump hammer I have 5 rockers. " Ok not too serious " I hear you say "just lift them and try again". After a second attempt by lifting around 20mm of mortar out I still have 2 of them rocking and now find an additional 2 ..... so back to square one .
The only thing I can think of is an error in my definition of the term "slightly wet" .
Has anyone any ideas before my dummy is thrown out of the pram ( so much hard work to be disappointed) ?
Martin , Notts UK
Posted: Mon May 07, 2007 6:03 pm
by Stuarty
Are you making sure they dont rock when you lay them? rather than only checking once the mix has gone off?
Posted: Mon May 07, 2007 6:16 pm
by SparksMayFly
Yeah , strange thing is the first 2 I redid are rocking again , seems like they rock once they've gone off and not before. Other thing is I cant even blame kids or anybody for walking on it because they haven't . I'm wondering if its some kind of shrinkage when the bed layer is going off . To be honest I'm not bothered if they dont actually stick to the bed as long as they dont rock .
Martin
Posted: Mon May 07, 2007 6:43 pm
by TheVictorianCobbleCo
I've just laid 140 off 600 x 600 slabs and experienced the same prob, I've a suspicion it being a hot day the contraction of the "pug" from a corner as moisture is sucked into the slab/ground is the culprit. AND I'M VERY careful about a full underlay, with grooves for sideways movement of the"PUG" when settling the slab. My partner swears its the large lump of timber and lump hammer that causes it and that one has to gently tapp the slab into place. Out of frustration for the one or two that I could not re-lift, I mixed a very wet slurry of kiln dried sand and cement (OK, I know its frowned upon) and poured it into the hollow sounding section. Let it go off,checked and found it remedied it and only then moved onto the grouting.
Posted: Mon May 07, 2007 7:21 pm
by lutonlagerlout
first things first
DO NOT ATTEMPT TO USE GEO-SH!T
it is one of the worst products ever invented for paving,it will fail in no time
use romex terrace or rompox easy
secondly why are you using a bit of wood and a club hammer?
a rubber mallet costs £2.99 in wickes and makes slabbing 10 times easier
thirdly
i use a wet mix for slabs/flags and if its a hot day the mortar can go off too quickly leaving little adhesion,but they still should not rock
strange???
regards LLL
Posted: Mon May 07, 2007 8:12 pm
by SparksMayFly
Cheers ,
Both my local wickes and B&Q had no large mallets in stock , maybe because its the season for diy paving and have run out . The softwood and hammer seemed the next best solution and you'll obviously be suprised to hear that is what was recommeded by stonemarket in their brochure. (if only my camping mallet was a bit bigger lol)
As for the geo fix i'll take your advice.
Thanks
Martin
Posted: Mon May 07, 2007 8:57 pm
by seanandruby
Using hefty blows with a lump hammer on a timber seems to be the wrong approach. a lump hammer used that way you have less control of the weight. tapping down lightly with the shaft of the hammer in the corners and centre gives you more control. with a wet mix the weight has to go somewhere so if it cant spread, then obviously its got to rise. if it raises a couple of mil on one end then that's enough to rock it. bulbs of pressure etc; Try a slightly drier mix and tap rather than wack. ???
Posted: Tue May 08, 2007 6:42 pm
by Rich H
Dry sub-base + dry slab + dry day = sandstone not bonding. What happens is that all the moisture is sucked out of the mix before the cement cures.
Feather the mix well so that you just have to tap the slab into place. (I can't imagine using timber and a lump hammer and I've done dozens of the bleeding things.) TP/Jewsons/Builder Centre etc will deffo have rubber mallets.
One tip is to give the MOT a good wetting before you lay, and give the each section of laid paving a good wetting before you move on or finish for the day.
Remember that despite your mix going 'hard', the cement takes several weeks to reach 100% cure and while it is still 'green' like this the slabs will be prone to losing their bond.
If you use Geofix or Pavefix you can expect the problem to never go away. If you can't find Romex (who can!?) point with semi-dry sand and cement as explained in these pages.
Posted: Tue May 08, 2007 8:33 pm
by SparksMayFly
Thanks Rich
Your equation makes perfect sense , and the feathering is something I never did intially thinking it wouldn't make a solid base but with the weight of the slab and use of lump hammer I can't honestly see it not setting in properly.
Hats off to you guys I thought this was goinmg to be a piece of cake , mind you trust me to pick a natural stone circle as my first project .
Martin
Posted: Wed May 09, 2007 5:24 pm
by Tony McC
Further: wet mortar that is parched by excessively dry flags, excessively dry sub-base and/or excessively dry weather will shrink. It's the shrinkage that leads to rocking, which, for me, is yet another reson to be very wary about using wet mortars for bedding.
As for GeoFix! Why not just hand all your dosh over to me and I'll sell you a few tins of mushy peas that will do a far better job of jointing the flags than does Geo-bloody-fix. 