Hi,
I have a problem with the joints within my newly laid slab paved patio which I am unable to sort. The slabs are 450 x 450 x 38 mm pcc slabs from B&Q. They are the rivened style which when butted together at their base, create a joint at the top of up to 25mm between 2 slabs. The slabs are laid on sharp sand/cement. I have jointed twice now and in both cases, the joints have cracked and broken out. I appreciate that the joints are wide and the sand base may move a little but what can I do to address the cracking problem I now have. I’ve searched your site and looked at things like using polymeric sand or modified mortars. Is this overkill or can someone suggest a simpler solution??
They're upside down !!
Should have been laid on a proper base. You may have searched for polymerics, but sounds like you haven't read the main site? Laying flags
"Meet the new boss - same as the old boss - We all get fooled again"
The slabs are not upside down - the texture surface is on top. I appreciate the clever answer from the last guy but I wasn't aware of this site until the job was complete. That said, is there anything I can now do or is it really a matter of ripping the whole thing up and repacing the bedding?
thanks.
think suggers is thinking of indian stone where the slabs taper with the widest edge at the top, what mix did you use for bedding and pointing? Did you put a sub base down?
Also, a sub base was put down consisting of a thin layer of type 1. Subgrade is very stiff so not much sub base was laid. Pointing was 3/1 sharp sand/cement.
as long as the slabs aren't rocking or loose etc then i don't see any need to take it up and start again, the problem could be with the pointing, dried out to quick in the sun, mix to weak. you could always try geo fix or cementone heard mixed views on them but if its not too big an area then maybe worth a try.
No slabs are rocking. Pointing mix has been installed both wet and dry now and both have failed. Last wet mix was 3/1. I was thinking of using some other type of pointing mix such as polymeric or something which allows a bit of movement. I have no experience of what alternatives there are so I am struggling for ideas.
could the wet mix of dried out to quickly in the sun? geo fix and cementone are polymeric sands easy to use heard people say they don't last very long, become weak etc but personally never had any trouble with them prices are roughly £25 for the big tubs and should cover around 10sqm.
Hi
Was done during the hot sunny spell but we did try to keep the patio damped down and the pointing still cracked. Is polymeric and the stuff you suggested available at b&q or do I need to go to somewhere more specialised. Also, is it brushed dry into the wide joints and does it allow a bit of movement?
2 when you say sharp sand dave do you mean flooring sand i.e sand with bits of grit up to 5mm in it? or do you mean sharp sand that is used for plastering?
3 dry mix is a fail technique except for large unit council flags in professional hands
4 geo-fix is referred to on here as geoshit,you say you have had no problems with it pickwell?? good for you mate. but myself ,MSH,and dig dug dan have had to repoint many many patios at our own cost due to this stuff.
its use cannot be endorsed on this site IOHO
5 is there that much camber on the slabs that they butt at the bottom,but leave 25mm gap at the top??
so thats my questions for you dave
the only polymerics we use here are gftk and romex
your slabs when they are relaid need to have a gap at the bottom and not be butt jointed,
and its best to point as you go so that the jointing mortar bonds with the bedding layer
when we talk about a dry mix,that mix say 1 barrowful would still have 4-8 pints of water in it
cheers LLL
going back to your first post Dave, if the base your flags are on is moving then any pointing no matter what you use will continue to crack and fall out for ever and a day
flags need a good base to hold them in place so you don't have this issue of the pointing falling out so the only way forward if you want to do the patio the "correct way" is to take the lot up and start again
its also made worse by the fact that the sides of the flags taper towards the top so there is nothing to hold the pointing down, it would be advisable to SBR the sides of the flags to help stick the pointing to the sides of the flags
geo fix is not good long term, like Luton says gftk and romex are the best but its a lot more expensive, an alternative way is to use the gun applied pointing from Easipoint which is also a very good product
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Hi,
To fill in some details, I did all of the prep work but a council worker experienced in laying slab footways laid the type 1 and sharp sand. All the materials are what is used for all council footways. What the council worker is used to, however, is not having to joint up slabs but butt them together like block paving. I'm sure all the sub base and sand layer was laid OK as no slabs are rocking and all appears very firm. The prob is finding a suitable jointing material for these wide joints which doesn't break out. In hindsight, I know I should have laid on mortar but I've got what I've got. Thanks to everyone for their assistance.
hi,the joints should be between 7 and 10 mm max for hand pointing with sand and cement.a bit more maybe for random ,indian ,old yorksone paving .the sand you should be using is washed sand for pointing,not grit sand or shap sand if you are up north .names for sand down sarf becomes complicated .lll will tell you exactly what sand you need .how wide are your joints (not from croydon drug squad nothing to worry about)
.lll will tell you exactly what sand you need .how wide are your joints (not from croydon drug squad nothing to worry about)