Gradient

[rks]

Please could you advise , my drain is sited against the house , so could i have the 1:80 gradient towards the house when laying riven slabs if im fitting a drain channel against the house ? also how much water is reccommended if using a 10:1 mixture of sharp sand / cement ?
thanks for any advice .

[lemoncurd1702]

It say's 1:80 Here if that's where you found the info.
It's fairly tight if using riven, particularly if they are roughly hewn. If it's a short run it shouldn't cause any problems though.

Hard to give a measure of water because the sand can have varying degrees of moisture. Chuck 1/4 bucket then about half you mix then add more if needed and chuck in rest of mix.
Also depends on whether using a wet or dry mix. If wet chuck a splash of plasticiser in also to get a nice flexible mix.

10:1 would be a bit lean for me. Most on here go for 8:1, but personally I prefer a bit stronger than that.

[rks]

ok thanks and should i add plastisicer or sbr ?

[lemoncurd1702]

Some do, I don't see the need. Maybe good to use sbr mixed with cement to make a paste and paint on bottom side of slabs.
This will help it to adhere to the mortar bed. A must if using a semi dry mix.
Don't worry about covering all of the bottom of the slab but don't get any on the surface, wash off quickly if you do!

[lutonlagerlout]

i add around 100ml of SBR to every gauge,with a wet mix never used a bond bridge and never had any problems
LLL