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Posted: Tue Sep 15, 2020 1:15 pm
by Dean85
On the advice of the wise people in this forum we have thrown our troublesome mint sawn sandstone slabs and are replacing them with a similar looking porcelain pavers (900x600x20mm).

They are being laid by contractors as part on an extention we have had built. To create a level threshold, the contractors have laid a concrete slab 8mx4m). They have left this to dry for a month and have come back this week to lay the slabs. They have sent a tiler to do this who has stated that he is knowledgeable in this area.

1. He is laying the slabs with external tile adhesive - is this ok as every thing I have read states to use a mortar bed and a slurry on the slab?

2. He is claiming the he cannot lay on an area about the third of the concrete slab as it's still damp. My response and concern is that we have a north facing garden and given it's mid September the slab isn't going to dry out much more. I have raised with him about the slurry and mortar, as I imagine this is less of an issue with dampness than tile adhesive. But he has said that he doesn't believe that works and would not do the job if that is what I asked him to do.

So I don't know what the solution is. He has laid with adhesive on the dry concrete.

And advice/reassurances gratefully received.

Dean 👍

Posted: Sun Sep 20, 2020 11:49 am
by Tony McC
Dean,

no problem with the methodology - a well-cured concrete slab and exterior grade tile adhesive would be my prefered method of installation for porcelain, but I think your tiler is being a little over-cautious.

If the damp concrete is a genuine concern, hire a dryer fan and have that runing for a day or two aimed at the damp area - that's what they would do indoors - but I think a suitable adhesive would be more than capable of coping.

I know it's not right, but I've seen it done and the installation sems not to have suffered - porcelain paving laid over a slab that was p[oured 36 hrs previously, so obviously still damp. I said nowt at the time, as I reckoned it's best not to offend the host when you're invited to observe an installation, but I fully expected to hear of problem a few weeks/months later, but here we are, 15 months later, and not a bother!

Ask the installer or the contractor whether they can obtain an adhesive capable of coping with a touch of residual moisture.....or hire the big fan!

Posted: Fri Sep 25, 2020 3:58 pm
by Dean85
Thanks Tony, this is great advice 👍👍