Looking for info on lime bedding mortars for a sandstone slab patio

[mrblint]

I'm across the ocean in Pennsylvania and would like to put in a DIY patio using reclaimed variegated Pennsylvania sandstone, in a random rectangular pattern. The stone is really handsome, some a dull reddish plum color, some orange, some grayish green, and some gray-blue. I've been watching videos of guys from the UK "fettling" riven stone, and guys laying stone slab patios. But so far I've found only videos where the slabs are being bedded in a portland cement mortar. I haven't been able to find good information on making a lime bedding mortar. I'd like to do that because it would preserve the stone in the sense that it could be removed and relocated without getting pretty much ruined in the process. There was a lime mortar for a patio thread here on this PPUK site over ten years ago but the story trailed off, so I don't know how it turned out. I was wondering if anyone here has tried using lime mortars to bed stone slabs, and if so, if they could share some pointers on how to make your own lime mortar for bedding slabs, the materials and the ratios, and if there's any difference in the laying technique compared to portland cement mortars.

 

[Cubist]

Hi There and Welcome,
There may be many regular contributors here who have specific experience and will be happy to share their advice and recommendations. As it would be helpful to them to know a little more about your project, could you tell us please what the patio area will be used for and specifically whether it may need to support heavy static and/or dynamic loads other than normal foot traffic? I ask as this may have a bearing on the 'strength' of the lime mortar it may be best to use and also the curing times needed before such loads can be adequately handled.

Also, I'll try to bump your thread to the more frequently used Discussions forum or alternatively point anyone that may be able to help to this one.

Cheers,
Cubist

 

[mrblint]

Thanks for the welcome and the bump.

It's a small patio 12 ft x 12 ft, with light foot-traffic only, placed on a pre-existing above-grade concrete slab. The slab previously had a brick patio on a portland cement mortar bed, installed back in the 1960s I believe. But previous owners over the decades had maintained the patio poorly, replacing the pointing mortar in multiple places with plain swept sand where it had fallen out. Many bricks were loose. A foot-high brick veneer wall had also calved away from the face of the slab. I jackhammered all of the brick away. The previous slab had no slope, so I created one (2 inches over 12 foot) by screeding a wet sand+portland cement topping mix (available in 60# bags at the home center) over the now rough slab surface in which the 3/4 to 1-inch aggregate stones had become visible as a result of the tear-off. I know very little about concrete but suspect they had put the brick mortar bed down before the slab had fully cured, so that when I tore out the bricks, the "cream" surface layer of the concrete came off along with the bricks and bedding mortar. I power-washed and broomed the rough surface multiple times to get most of loose stuff off, leaving a fairly intact surface, before screeding the topping mix layer on.

 

[malcolm]

You would want a weak lime mix. Most cost effective is hydrated lime which is the stuff modern bricklayers mix with cement to make it easier to use. 1:3 lime to sand mix. For the sand use sharp sand. That's a mix of sand normally used for patios and contains grains up to 5mm. You might have different names for them over in the US.

I've replaced a few patio bricks bedded in lime where I pulled a tree out of the patio. They seem to be holding up well and plants are not growing in the joints because the lime is flexible and doesn't tend to crack and also it's alkaline which plants don't seem to like. Still more work to do on my patio. I have the cement pointing towers where the bricks have been destroyed by frost because they couldn't evaporate water away but the cement has survived. Lime would have been better.

 

[Zebra]

I laid a small patio with a NHL3.5 lime mortar rather than hydrated. Same ratio as for bricklaying and pointing.

 

[stuart45]

Generally for patios a weak mix is used for the bedding material. This allows for better drainage, and is the same for OPC based mortars.
The pointing can be a stronger mix.
The sub base is better using something like MOT, which would allow water to drain down, while a concrete sub base would hold the moisture for longer.