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Posted: Mon Jul 06, 2020 8:10 pm
by thistimenextyear
My patio has been down for 3 days and several flags are moving and the pointing is cracking in the corners of these slabs. The installer has already lifted a few and relaid but more have done the same since he finished on Friday. I'm wondering if this is normal? He told me it is normal with indian sandstone as it's so soft. They are laid on a full mortar bed (he started off ring beading but I asked him to change to full bed). After they were laid a few were moving, so I asked him to re-do before pointing. He advised that pointing would hold it all together but re-did them anyway on my insistence. They put down a type 2 sub layer, although it didn't look as compact as I've seen on the internet. I mentioned about putting an SBR slurry mix on the back of the slabs but he said he's never done it. Am I being unrealistic in my expectations? Is a bit of movement & cracking of the pointing normal?
Posted: Wed Jul 08, 2020 8:59 am
by Winnywood
Although a proprietary sbr product is not needed on sandstone a primer of either sbr mixed with cement or even just a cement slurry should have been used. Even just water on the sandstone will provide a better bonding than being laid dry. Unfortunately if some are already coming loose then they all probably will. The pointing will not hold the slabs in place. You need to insist that they are all lifted and re-laid. If the sub base is not adequate then the slabs will inevitably move and may subside but if a primer slurry was used they would still be bonded to the base bed. What pointing product was used.sand and cement or a resin type brush in product. As the resin type need a laying bed that is porous i.e a 6-1 mix. If the laying mix was stronger then water can permeate through the pointing and get under the slabs.
Posted: Wed Jul 08, 2020 9:11 am
by Winnywood
If when lifted the base mix is solid flat and level and in good condition then you may be able to apply a sbr product to the back of the slabs and also apply to the bed and re-lay. Then repoint using a 3-1 mix of soft sand and cement.
Can you attach some photies of the area as i suppect the laying pattern is probably not to standard either. I.e cross joints.
Posted: Thu Jul 09, 2020 11:11 am
by Tony McC
There was a long, long thread a few months back about re-seating loose flags onto an existing bed, and while I wouldn't recommend every strategy used, there were some valid suggestions that might be of interest.
On a wider note, I suspect you have a clown installer. *You* had to tell them not to use spot/ring beding? Any genuinely competent installer would know that. They are suggesting that pointing will prevent/correct rocking or loose flags? FFS! Again, any competent installer knows that flags are bed-dependent paving so cannot rely on the pointing to fix them in place. And they'd never used a slurry promer bond bridge previously? What have they been doing for the past 10 years (apart from bolling other paving works)?
No movement. No cracking of jointing. These are the basic requirements of any flagged area, not an unrealistic expectation!