Slabs not stuck to mortar-bed.

kiddo · Post: # 37522Post **kiddo** Fri May 08, 2009 6:25 pm

Hi folks.

I've laid my sandstone on a full mortar bed, but about half-dozen slabs (mostly the smallest ones) are not adhering to the mortar, and can be lifted straight upwards.

They've been down almost a week, but I haven't started the pointing yet.

Does it matter that they have not stuck to the mortar and can be lifted straight up, or will the pointing stop that from happening?

Thanks everyone.

Sat May 09, 2009 2:33 am

i think you posted that you laid on a dry bed previously?
theoretically if they cannot move downwards then pointing should hold them,
why are you lifting them?
were you suspicious ?
LLL

henpecked · Post: # 37542Post **henpecked** Sat May 09, 2009 10:33 am

My missus said the same when I laid the patio. I explained the reasoning to her and her eyes just glazed over

I thought, wait till the grouts gone off and say Ive relaid them, worked a treat :laugh:

kiddo · Post: # 37548Post **kiddo** Sat May 09, 2009 3:53 pm

I was testing to see if any rocked, and got over-enthusiastic and tugged at a small one. When it lifted, I had to see if others did the same.....

They weren't rocking, but they did once I had pulled them up

I had to chistle the mortar out and re-lay the few I messed with. grr.

Marty C · Post: # 37659Post **Marty C** Mon May 11, 2009 5:14 pm

Sorry if I've done this wrong but I've never posted on a web site before. Anyway, I have a similar problem with the flags not sticking. My builder seems clueless. We have a mixed size of raj green sandstone flags newly laid and about 25% of the stones are lose, i.e. they can be made to move just by standing on them. The larger ones are the worst. I watched some go down and the mix looked reasonably wet and I'm told was 8.1. When lifting them, the stones come up clean. He left it unwalked on for over a week and it is pointed. He is now relaying them but its making a mess of the job and I'm still not sure that the remainder will not also come up. My initial thought was that the stones were sucking the moisture out too quicly. Any help would be gratefully received - he's back tomorrow to lift and relay some more and I'm desperate!

henpecked · Post: # 37686Post **henpecked** Mon May 11, 2009 9:06 pm

With an 8.1 screed bed your effectively making a hard bed for the slabs to lay on, as LLL said, it when theyre pointed that does the trick. Your builder may not be consolidating the screed underneath properly(compacting) this will cause a rock. Walking on them before theyre set will make them rock too.

HP

Mon May 11, 2009 11:20 pm

i have never experienced this with a wet mix,is he laying a full bed or the 5 dot method?
something really strange there?
LLL

Marty C · Post: # 37705Post **Marty C** Tue May 12, 2009 8:45 am

Thanks to both of you. I know he used scalpings and then compacted them over a hard core base although I didn't see how deep the scalpings were, i think it was a reasonable depth. He's used a full bed but I wonder if the weight of some of the larger stones has made them very hard to avoid one corner or edge going down first, and therefore leaving a low point which when stood on pivots the slab up fractionally. but that doesn't account for the smaller ones being loose.

What surprised me most was that the slabs come up clean. The underside looks like there is a round dark mark which I assume is showing where there was a better contact but all round the edges they are completely dry. Even though he's grouted they are stil moving.

His latest idea is to wet them first and use unibond and a stronger bedding mix, 6:1. I'll see what he has to say later today.

thanks for your help.

MC