Page 1 of 1
Posted: Mon Mar 17, 2014 5:33 pm
by thewickedpickett
Hi
I have decided to redo my back garden patio. It is 22 sq m and unfortunately the previous owners have used the dab method for laying the slabs and it is a mess. I had planned just to repoint but that quickly went out the window and led me here.
I am wanting advice on how best to proceed. I can rip up the slabs and remove the gravelly sand that is underneath ready for new sub grade and bedding layer.
The contractor is of the view that the best way is to lay a quarry dust sub grade layer compacted then a complete mortar bed for the new patio flags. He does not favour the screed method.
What are your views? What should I be asking?
Presumably I should not consider a DIY job? I have no experience working with these types of materials at all.
Edit - I should add I don't believe drainage is a big factor as the patio is raised 1 brick above a working drain and is 6ft from the house.
Posted: Tue Mar 18, 2014 9:48 am
by Tony McC
It all depends on how bad is that 'gravelly sand'. If it's well-compacted and stable and free from weeds, then why would you not use it as a sub-BASE? There's no point in digging it out to replace it with summat that won't be anywhere near as well compacted.
And then it should be a full mortar bed. Whether to use individual beds or a screeded bed depends on the layout and the type of flags, but I'd hazard a guess that individual beds would be your best bet.
I can't tell you whether a contractor or DIY is the best option. Laying flags is physically demanding and a contractor might have it all done in a couple of days whereas it could take you 3 or 4 weekends. However, the sense of satisfaction that novice DIYers get when they've completed their first patio is something to behold. 
Posted: Sat May 10, 2014 11:39 am
by thewickedpickett
I got everything repaved and extended the slabs to some previously concreted area. It was done by an experienced contractor.
The two slabbed areas are separated with an ACO drainage channel but with the same slabs. I've noticed there is some slight rocking in a few slab, two that meet the ACO channel and one at the beginning of slight slope to existing drive. The contractor has to come back and add the jointing sand as it was too wet before.
Will this fix the slight rocking?
The slabs are on aggregate, sand compacted then individual beds of mortar.
They are bevelled flags 400mm x 400m and 40mm thick.
Posted: Sun May 11, 2014 5:25 pm
by thewickedpickett
Anyone any ideas on this? I gather they shouldn't move at all but I'm unsure if this means pre jointing or post.
Posted: Tue May 13, 2014 10:12 am
by Tony McC
Never, ever, ever rely on jointing to cure rocking flags. It's a bodge fix.
Flag paving is what we term bed-dependent: the stability of the paving arises from the bedding. Consequently, fiddling with jointing is just masking a failing or failed bed.
There is joint-dependent paving. Setts, espcially smaller cubes, are a good example, and with these, the larger part of the pavement stability is generated by the strength of the jointing with the bed providing little more than resistance to sinking. If setts/cubes are loose.rocking, they can, sometimes, be fixed perfectly well by re-doing the jointing.
However, this is NOT the case with bed dependent paving, so the loose flags must be lifted and re-bedded if they are not to fail again in a few weeks time.
Posted: Tue May 13, 2014 5:12 pm
by thewickedpickett
Thanks I had one replaced that was badly scratched but the problem is replacing one seems to make the one next to it unstable too. Therefore I worry about lifting and changing 3/4. It they're on full mortar beds what is the likely cause?
I should add it appears to be the slabs that butt to the ACO channel which are very slightly rocking when you stand in diagonal corners.
There are a few others too.
Posted: Wed May 14, 2014 12:24 pm
by Tony McC
The most likely cause is some eejit walking on the flags before the bedding has hardened sufficiently, but there are literally dozens of other possible causes.
Posted: Fri May 16, 2014 9:57 pm
by thewickedpickett
Contractor came back and lifted the rocking slabs and jointed with sand.
I've noticed there is still 1 that is rocking slightly when you dance on diagonal corners. It's butted to the ACO channel.
Am I being overly fussy here?
Would I be able to lift it myself and redo it? Can you add additional mortar on top of a full bed or do you have to break the existing stuff?
Posted: Fri May 16, 2014 11:00 pm
by lutonlagerlout
break out the existing bedding
and stop dancing on the bleeding flags :;):
LLL
Posted: Tue May 20, 2014 4:42 pm
by thewickedpickett
All loose slabs have been lifted and relaid.
The whole patio was then pointed with jointing sand brushed in. I'm finding that rain just washes a lot of it out though? They are bevelled flags butted tight so there is only a fine gap in between which means you joint the gap and the recess between the two slabs. This has come out during rain and has covered a lot of the slabs.
Is this normal?
Is polymeric sand worth a shot?
Posted: Tue May 20, 2014 9:26 pm
by r896neo
As for the jointing you can't use anything other than dried sand to joint butt or 1-3mm joints. Anything else just won't go in.
The sand you think is washing out may in fact just be remenants on the surface which weren't apparant until it rained. I wouldn't be too concerned and topping it up in a few weeks is an easy and cheap job.
Posted: Mon Jun 02, 2014 6:32 pm
by thewickedpickett
Thanks. I've taken some pictures to illustrate what's going on.
I've brushed lots of kds in but it just washes out as soon as you apply any kind of hose. I've a dog using part of patio as a toilet so I need to lightly hose at least.
I've sanded the recess on top of the butted join line. This is what washes out so easily. Is there any point using resiblock or similar instead? Should I even worry about the recess being sanded?
Similarly I've an ACO channel as shown. I need to build that up so liquids flow easily into the actual channel. At the minute lots of it just goes down the side of the slab rather than into the channel. I've sanded it but as it's the recess it comes out easily. Is there any benefit to using something else here?
Posted: Mon Jun 02, 2014 7:26 pm
by dig dug dan
The channel needs to be lower than the slabs. In the picture, it appears to be higher. You cannot build up the levels to get the water to go in, it will just flow back over the paving.
Posted: Mon Jun 02, 2014 7:32 pm
by thewickedpickett
The opposite side of the channel is where the slabs slope down to the channel. This is the only place I could put drainage in to connect with existing. I guess there's not much can be done.