Slab laying methods

[Ratman]

I have done before now on occasion, but usually for bedding my flags on no, just feb/plasticiser, put SBR in my mortar mix for block work though cos they whap moisture out of the mortar that quick sometimes that they sometimes dont get hold as good as i’d like.

[youngsbury]

50-50 sharp-soft half bag of dust as much as the mixer can handle. 3-1 for the pointing mixed so that it just binds together ( like fishing ground bait ? ) so that it doesn’t stain the slab but you can really get it In and strike a nice finish ( finger trowels ). I pva underneath of slabs especially Indian sandstone as found its more dusty and flaky than most. Also use seatbelts to help lay the 4” thick york gravestones ?

[doobin]

1 hour ago, youngsbury said:

50-50 sharp-soft half bag of dust as much as the mixer can handle. 3-1 for the pointing mixed so that it just binds together ( like fishing ground bait ? ) so that it doesn’t stain the slab but you can really get it In and strike a nice finish ( finger trowels ). I pva underneath of slabs especially Indian sandstone as found its more dusty and flaky than most. Also use seatbelts to help lay the 4” thick york gravestones ?

Pva is water based so no good for outdoors. Use sbr as Kev describes ??

[youngsbury]

Used pva for years never any problems use it on plywood as well waterproofs it stops ends splitting lifting and a lot cheaper than marine grade 

[doobin]

5 hours ago, youngsbury said:

Used pva for years never any problems use it on plywood as well waterproofs it stops ends splitting lifting and a lot cheaper than marine grade 

Interesting. I may experiment!

[Guest Gimlet]

I lay full wet bed - troweled on as spots but heavy enough that it becomes a full bed when the slab is pressed down. None will sound hollow after they've gone off. 

I also put down a coarse blinding screed over the whole area on top of the compacted stone before laying the slabs. 30 - 40 mm of roughly raked 4:1 concrete for the mortar to key onto. Mortar doesn't really stick to compacted stone and they can part company if water gets in. With a blinding screen they stick like proverbial to a blanket.

 

Laying mortar is a 4:1 mix of sharp and building sand with 1/2 of hydrated lime. Pointing mortar usually similar but with building sand but may vary depending on the type of slab. As with brickwork, pointing mortar doesn't want to be denser than the material the slabs are made from of frost and wet will push it out.

 

I use a bonding coat on the back of the slabs depending on what sort they are, how much key they have to start with and how damp they are when laying. If I do it will be a wash of water, PVA or SBR and cement dust.   

Edited November 28, 2020 by Gimlet

[dig-dug-dan]

On 26/11/2020 at 20:44, Ratman said:

Always lay on a full bed, spots can cause staining then you end up with a patio looking like a dice once weathered. I personally mix 3 - 1 ((each to their own though) and use plasticiser so they key. Pointing up is again your choice, standard mortar or alot use the modern sweep in stuff or resin based pointing now.

 

Example of spot staining below

 

Plastiscier does not help them key. Its ads microscopic bubbles to,the mix to enable it to be more workable.,that's it. But you have redeemed yourself in saying you use sbr. 

And pva does nothing for paving other than waste your money  

[doobin]

5 hours ago, dig-dug-dan said:

Plastiscier does not help them key. Its ads microscopic bubbles to,the mix to enable it to be more workable.,that's it. But you have redeemed yourself in saying you use sbr. 

And pva does nothing for paving other than waste your money  

Plasticiser actually makes a screed harder to work and key in my experience.