Lean mix concrete bond strentgh for cobbles/cubes

[james-78]

I have project to start this weekend laying reclaimed cobbles/cubes (guy at yard said they're whinstone) in my garden. I was planning on laying cobbles/cubes on "moist lean mix concrete" as recommended in website.



LEAN MIX CONCRETE:

I was wondering what the bond strength of "moist lean mix concrete" would be like? The cobbles/cubes are approx 3 inch/75mm so to butter the edges would likely cover the entire base of them, so in effect I would have a layer of lean mix with a thin layer of a stiffer mix on top.

Will "moist lean mix concrete" give me strong enough bond or should I use a stronger mix so I don't need to butter cubes/cobbles? Any suggestions on what concrete mix to use?


POINTING:


I will probably point area using 3-1 dry mix and sweep it into joints and then compact/smooth with tuck pointer trowel and then mist with garden hose and top up later if necessary.

I've read that "Blue Circle Mastercrete" cement contains premixed plasticisers, am I correct in thinking this would be best cement to use because I wouldn't be able to add a liquid plasticiser to a dry mix?

I've got my materials getting delivered on Saturday and it's just normal cement (Castle), and Cementone plasticiser.
I would rather go and get some Mastercrete just for the pointing if it will make it stronger.



Thanks in advance for any help!!!!

[cookiewales]

Okay I would be surprised at whinstone at 75 mm pic would be good don't use lean mix concrete on these make sure proper subase min 100mm use 4/1 sharp sand cement semi dry mix some cement water as slurry pour some on a row at a time and tap in . Do not use you're pointing it will fail use slurry same mix 4/1 use little window sweegie to push in wash of with sponge do small area at a time look on my blog page you will see us laying and pointing cookie

[Tony McC]

You could lay on a lean-ish mix (1:3:6) as long as there's no vehicular usage, but with whinstone being almsot impervious, I'd strongly recommend dipping the bases into a Bond Bridge just before placing each sett.

Dry or even semi-dry jointing is a recipe for disaster with setts. You *must* use a wet mortar and a slurry, as suggested by Cookie, is usually the simplest method of application as long as you are confident with your clean-off strategy. How rough or smooth are the heads of these whinstone cubes?

[james-78]

Brought one of the cobbles/cubes inside and there is a slight glisten/sparkle coming off them.

To describe texture I would say they are closer to being smooth than rough. I tried to break a particle/crumb off with my fingernail but they're solid.

I will do a small test area with slurry mix, if it goes t!ts up I will prob go to PLAN B and get pointing gun.

Will go to local builders merchants and try get some bond bridge.


Cheers

[seanandruby]

here for bond bridge

[Tony McC]

And beware the prices being charged for SBR by some outlets. One contractor whi uses this forum was recently quoted the best part of 60 quid for the same stuff you can get for 11 quid at Screwfix Direct.

The smoother the heads of the setts, the easier it will be to clean them of the slurry.