How should i point my bevelled slabs? - Should i use wet grouting or mortar?

[HarryHedgehog]

Hi

Please bear with me on this, as this is the first time I have done any cement/sand related building work.....

I have just completed the laying of 50+ slabs, and I think it looks very nice. I have read almost all the pages of this site to do with laying slabs/flag and I have just one dilemma.

The edges of the slabs are bevelled (ie they touch at the bottom of the slab, but have a 10-15mm gap at the top surface).

My questions are...

How should I point/joint the slabs?
Should I use standard mortar pointing? The edges of the slabs have not been buttered and they have been laid for the last 3 days.

Alternatively should I use a dry grouting?


Is the pointing meant to grip to the slab sides and give a hard joint or is it more cosmetic (finishing off a job and looking nice)?

I say this as the slabs are pretty smooth around the sides and I cant see how anything can 'bond' to them?

Hope you can help,

many thanks

Harry

[alan ditchfield]

I hope these are not indian sandstone flags because it sounds like you have layed them upside down, if they are concrete reproductions then i think they may be too close as the pointing really should meet the laying course to bond properly. The pointing is meant to grip to the flag and form a solid joint you would be suprised how much strength the pointing adds to the paving, as for the mix it should have enough water content to ensure the mortar setts properly ie it should not be a powder more of a stiff mix too much water will leed to a messy job. hope this helps a little.

[HarryHedgehog]

No, definately not upside down

And no they aren't indian sandstones either. One of them was broken at the corner and they seem to be a concrete slab that has a moulding covering it to make the top look like a weathered stone slab. They are about 3-4cm thick and heavy to lift (phew!).

If I measure between the slabs on the upper surface, the distance between the slabs is 2.5 - 3 cm. This is the distance when the bottom edges of the slabs just touch each other. Should I have left a 1 cm gap between the slabs? That would have left a 3.5 - 4 cm gap at the top surface of the slab!?! Is that right?

Have I got a serious problem in having no gap between the bottom edges of the slabs?

[Tony McC]

Are these the silly TopPave wet-cast flags that are wider on the base than the face and give a ridiculously wide joint because some eejit at TopPave thinks folk want to see 40mm wide mortar joints when they're paying 30 quid a metre for paving?

Everything else Alan said is spot on. Get 'em pointed with a mortar: use the semi-dry method described on the Pointing Case Study page or use a traditional wet mortar. You'd be surprised by just how easily even a semi-dry mortar can bond to a concrete flag - you'll find out if you accidentally spill any on the surface! :p

Don't worry too much if the flags are 'just' touching at the base: it's less than ideal but it really shouldn't be a major problem for a patio.

[HarryHedgehog]

Brett Stones
This is the URL of the maker of my slabs. I am regretting not getting proper real stone slabs, but I guess I will have to make do. (sigh)

I have checked all the slabs and 70% of them have a 5-8mm gap, and the rest have no gap. The reason for the difference in gaps is because the slabs are made up of 6 different sizes and fitting them together with the same sized gaps just didnt work.

I will try the semi dry once this current spell of bad weather passes.

Thank you for making a very very worried man a little calmer

[Tony McC]

The problem with joint spacing occurs with most modular flags when laid to a random layout, whether they are concrete or stone. the 'trick' is to mainatin a minimum joint width of around 9mm and then re-space the other joints to 12-18mm as necessary.

This 'problem' is discussed somewhat briefly on the Random layouts page of the main website.