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Posted: Sun Mar 12, 2006 5:15 pm
by cwight
I've started laying my Indian flags. I'm using the semi-dry mix as suggested in the site (10 coarse sand+1 cement - no water). I was just wondering about the logic behind this method as opposed to adding some water to the mix. I understand the logic behind the criticism of spot bedding, but I was just wondering about how the semi-dry mix should finish. Is the intention that the semi-dry mix actually absorbs water from the ground, and what is already in the sand, and eventually 'sets', or is the intention that the flags never bond to the mix so that they are essentially sitting loose, but firmly bedded on the bed. I've seen some sites that suggest using a wet mix (not sloppy) to cover the the whole underside if the flag, so that the flagf 'bonds' to the motar - a bit like laying floor tiles. Is the logic behind the semi-dry mix something to do with being able to easily take the flags up and adjust, or is this nothing to do with it?
Thnaks in advance...
Posted: Mon Mar 13, 2006 1:29 pm
by Tony McC
Other than at free edges, flags don't really need to be bonded to the bedding. With "regular" flags, that is, flags with a smooth base, there is some risk that they could slip laterally, but many riven stone flags have riven undersides, and wet-casts have a 'stippled-effect' underside, both of which provide a 'key' that helps lock-in the flag onto the bedding and so minimise any risk of lateral movement.
So - no real need to bond: all we need is a firm and stable bedding layer that will support the flags without moving or being mined by invertebrates, and the 10:1 mix provides just that. There's ample cement to harden the mixture, without it ever becoming exceptionally strong. But, of more importance, a low cement content in a dry-ish mix means a much reduced risk of 'picture-framing', the effect where cement is carried through the flags and deposited at the edges as a sort of "frame of stain".
And, as a contractor mentioned to me last week, if it turns out that the flags have to be re-laid because some gormless so-called engineer has given you the wrong levels, the flags come up clean, with no resistance and no need for time-consuming tidying-up with hammer and bolster in an attempt to remove hardened mortar from the base. Not just that, the 10:1 bed breaks up with a few taps from the pick - no need for the jack-hammer or to be swing the sledgehammer until your arms ache.
Posted: Tue Apr 17, 2007 1:23 pm
by SamLumb
Hello Tony,
I have read your response to the above and would like to take one of your points further. I recently pointed my Indian sandstone paving with a dry/wet mix and by in large its a good job. However, a few of the slabs have been 'framed' with a faint cement boarder. I am unsure how this happened as I thought I has swept off all residue and the mix was not wet. Regardless, I would be grateful for some help on how to remove this cement. I gather from your website that acid is a big NO, and mechanical action is the answer. If I use a wire brush as advised, are there any precautions I should take, for example, if I scrub too hard will I leave pernament scratches? For all I know these might 'heal' over time but thought I should check.
Much Obliged,
Sam
p.s. I really am very impressed with this website. It provides access to professional and balanced opinion to all of us novies that are out there trying not to make a bodge of things!
Posted: Tue Apr 17, 2007 6:23 pm
by KevB
Colin.
I've just finished laying about 25m2 with Limestone and i had to take up one of my slabs today.
The bed which was semi dry was as Tony says, so dont hesitate in just going with the flow and the advice and guidance given. I've personally found it invaluble.
KevB
Posted: Wed Apr 18, 2007 2:35 am
by lutonlagerlout
just my 2p worth,i tried the dry method many times and didnt get on with it,i find it ok with 3 by 2 pressed but other than that i find it hard work===> rockers
i have used the wet method now for at least 10 years and although like the MAN says you can take your flags up easier with the dry method,i dont want any of my slabs to come up easy
had no comebacks in 10 years (apart from geo-fich) so will continue with wet bedding, both ways are acceptable its down to the individual
cheers LLL 