Loose slabs - How to cure

Wideboy · Post: # 66241Post **Wideboy** Sat Jul 16, 2011 12:07 pm

Just started to lay main patio yesterday and discovered that some slabs(Limestone) haven't bonded and are loose.Checked back on topic history and this has come up before(June) my mix was 4 to 1 with SBR added,LLL stated in previous post that a wet slurry mix could be used to secure lose slabs would this be OK as it would save the hassle of digging out the bedding layer and possibly disturbing fixed slabs.Any suggestions welcome!Previous poster glued his down but this sounds like a bit of a bodge to me!
Cheers Ian

Sat Jul 16, 2011 12:37 pm

you could try but i believe the sbr slurry technique is to bond to mortar thats not gone off, so it adapts to all contours on the underside of the slab other wise youd have to get it exactly realigned or it wouldnt have 100% contact

Carberry · Post: # 66245Post **Carberry** Sat Jul 16, 2011 12:48 pm

The slabs don't have to stick to the bedding layer either unless they're on a free edge. If you want it to stick then I would use a slurry mix, if the bedding layer is too high then I would scrape a little of it off before putting the slurry mix down. Can be a little awkward getting the right amount though to ensure you have the right level, full contact and not loads of slurry squelching out the sides.

Wideboy · Post: # 66255Post **Wideboy** Sat Jul 16, 2011 2:17 pm

I think my mix may have been a bit on the dry side a couple of the slaps aren't loose but sound a bit hollow when tapped in a couple spots so I think I don't have full contact with the bed will investigate further when I stops peeing down! Can appreciate that the slabs don't really need to bond.I assume that the pointing will hold them in place to a certain degree?

Sat Jul 16, 2011 2:51 pm

yes, of course
LLL

Post: # 66275Post **seanandruby** Sat Jul 16, 2011 6:44 pm

When you use a wet slurry, as you sweep it in it will only go as far as trapped air will allow it. So although it might get just under the flag you will still have a void, if the slurry doesn't flow all the way.

Sat Jul 16, 2011 7:11 pm

i never said sweep it in :O
use a measuring jug and a funnel and pour it in the joints really wet
LLL

Wideboy · Post: # 66291Post **Wideboy** Sat Jul 16, 2011 9:19 pm

Can I just lift loose slabs and bond onto bedding layer with a slurry type mix ,more like a mortar with greater ration of cement and plenty of SBR? I realise that any on the unsupported edge need bedding down firmly.
Ian

London Stone Paving · Sat Jul 16, 2011 11:46 pm

How many loose ones have you got Ian ?

haggistini · Post: # 66297Post **haggistini** Sun Jul 17, 2011 5:48 am

lift the loose slabs making sure they are stacked so that they can be replaced in the same position!!! use a hand brush to remove all debris from bedding layer and make a cement/sbr/water slurry mix in a bucket (tomato sauce consistency), then use a gauger and smeer it on the bedding layer a few mm thick then tap slab down. remove any muck that egresses or spills immediately with a sponge and water, leave to dry and then point.
this will hold them from moving but is a patch up job that will proberly stand the test of time (no vehicle traffic) but there is only one right way to do it and thats to remove the bedding layer and and re set them!

Wideboy · Post: # 66300Post **Wideboy** Sun Jul 17, 2011 8:59 am

About half of them are loose Steve I think Haggistini has the right answer that's to bit the bullet and lift the lot dig it out and start again.I'd rather get it right then bodge it and have to do it again in acouple of years time! We all learn from our mistakes when I was an engineering apprentice many years ago I can always remember one of the old boys telling me that the person who has never made a mistake has never made anything!
Thanks again for all your advice cheers Ian:)

DNgroundworks · Sun Jul 17, 2011 10:57 am

Ive got a few thoughts on this common problem, the only time ive ever experienced indian stone sticking to the bedding layer is when bonded with sbr or when ive seen builders lay them on building sand and cement or a very wet mix, which i dont use anymore due to cement leaching/suction if the flag needs re-lifting/and other flags around it moving when you bang it down!

Most of what i lay will probably sound hollow and it probably wont be stuck really strong either, none of it moves as we pack the edges tight, when its pointed its always sound.

So................should the stone stick or not?

We did the site clearance work for alexandra square rejuvenation project at lancaster uni, we stripped nearly 4000m of flags and pre-cast step unit - not one was stuck to the bedding layer!!

Carberry · Post: # 66316Post **Carberry** Sun Jul 17, 2011 12:45 pm

When you say loose do you mean wobbling or do you mean lateral movement? If it is wobbling then it has to come up. If it is moving sideways then that will stop when you do the pointing.

Sun Jul 17, 2011 1:45 pm

I find with my wet technique they all are stuck as well as full bedded,but thats the only way i have done it in the last 15 years so i am used to it now
LLL

Wideboy · Post: # 66324Post **Wideboy** Sun Jul 17, 2011 3:36 pm

Carberry they are just loose laterally not rocking but they do sound hollow when tapped as they haven't bonded to the bedding layer but when lifted they are fully supported The strange thing is we did a small area that a bench sits on at the end of the garden,same mix 4 to 1 with a good helping of SBR and the things sucked down onto the bedding every one was solid only difference was it was a wetter mix.Anyway I will relay them just for my own peace of mind.
Thanks again guys Ian