The Brew Cabin

Posted: **Wed May 08, 2019 10:53 am**

Hi all ,last year I laid a black slate patio 80 sq m .someone else had laid the sub base ,it wasn't scalpings like I would use,but that recycled crush you get .it had been wacked but it didn't look that great as there were areas where it looked to be thinner than others .he is a friend of a mate an assured me it would be fine.
black slate came an looked pretty good 25-35 mm thickness it was unbranded an no laying instructions. i laid on a full bed sharp cement mix (I have done two slate ones before with no probs)random pattern an came out really well .

anyway he calls me to come an have a look as the 900x600 ones have unkeyed, not rocking but that sound you know!all the other sizes seemed fine.so I done some research an that led me to your fine site which tells me that maybe they should have been sbr`d.I went back an lifted 24 of the big ones an sbr`d them back down,what I did notice when doing this was like 10mm cracks here an there through my bedding mix an subbase (like how it goes on a dry summer )could this have anything to do with it ??.
I gave him three days of labour at no cost,i have said I cant do any more freebies .I don't feel great about it ,but I think the product should have specified sbr on the back of the slabs or is it a combination of both ??bedding course 25 mm to 80 mm.
any advice on how to proceed as he has called again?
thanks dancer

Posted: **Wed May 08, 2019 6:52 pm**

80mm bedding is way too much.
25mm is about right.
Its not the slab manufacturer or supliers job to tell an installer how to lay the slabs, so ypu cant really blame them for the lack of sbr.
When you re lifted, did you do a proper bpmd bridge?
Also, so called recycled crushed tends to be 50% soil from experience, so this would also be a factor.
Unless ypu did a bond bridge on all the slabs, and laid on a wet mix, then its a fail im afraid!

Posted: **Thu May 09, 2019 4:51 pm**

The top suppliers *will* issue installation guides, but then that adds to their costs and the price the customer has to pay. If I had my way, I would require ALL sduppliers to provide basic installation guidance because I encountyer far too many projects where the installer has guessed how to do the work...."I've been doing it this way for 20 years......" and some of the old ways are not appropriate for modern materials.

However, for me, the problem here is most likely to be the sub-base, and it's a salutary lesson that, as soon as you agree to lay paving over a sub-base installed by someone else, you accept responsibility that it is "fit for purpose". I ended up in a court case over this 30-odd years ago when I was a contractor and laid blacktop over a sub-base allegedly "prepared" by the builder that went on to cause all sorts of problems, and it was me that ended up paying for them all!

Trust me: I know how hard and awkward it can be to say "I'm not laying on that..." but that's what we need to do, if we don't want any comebacks.

Slate needs a primer slurry or SBR because it has such low water permeability. It also needs a reasonably regular bed of 20-40mm, 50mm at a maximum.

It's all too late for this, now, on this project. If you can walk away with no further liability, you have to chalk it up to experience and learn the lessons, but, if the client decided to get all arsey, they could probably get you to fix the whole project!

The Brew Cabin

Black slate job