Laying a patio - sand or cement

cog1

Hello
We're planning a laying a new small area of patio and have someone to do it. My question is whether to lay in sand or cement. I realise cement may be more durable but I'm concerned that this is less environmentally friendly. I live in Dublin and I hate to see peoples front drives being concreted and I've read that this all adds to flooding issues in cities. It's just a small area but I'd rather take the environment into account (yes no patio would be better!). The area is already laid with bricks set in sand and I was considering laying the new slabs on top. Height wise there's already a pretty big step down from the house.
Advice appreciated.

recedite

Sand is fine. Preferably use coarse sand or grit under the slabs for better stability, then brush fine sand into the joints afterwards.
The bricks will be a good solid base, and also discourage any weeds.

smacl

Sand is better environmentally, but in my experience you're more likely to get weeds between slabs as they move slightly over time and seed fall between the cracks. Cement is liable to be impermeable and increases flood risk to yourself and your neighbours, so not a great idea if you're in an area prone to flooding.

Seve OB

i laid my own patio about 10 years ago. i think i laid about 6 inches of hardcore, used a whacker to level and set it for putting sand down on top. then i put a few inches of sand down can't remember how much but 6 inches seems a bit over the top so it might have been 3 or 4.( actually I do recall mixing a lot of sand and cement, but im sure it was just a dry mix, maybe 5-1)
there was weed control membrane in there, can't remember where it went but i think between the sand and hardcore

i was told to just brush dry sand/cement mix between the flagstones which i did....... but it was terrible. weeds everywhere all the time. i soon replaced that with a wet mix. no weeds in general...but did start to get some water lodging. a simple fix was to just drill a few holes around the patio, no more water lodging, but get a few weeds filling them holes every so often

princess poppy

There’s a special silicon sand mix you can get from paving suppliers wihich you brush on over dry slabs and it will harden itself, by far the best thing for the job, much better than the bags of kiln dried sand.
No need for landscape fabric either, just whack 4” layer of hardcore and cover with 2” sharp sand, whack again and use board to ensure levels are correct to lay slabs on

CJhaughey

Romex make a product called Rompox Easy , its an excellent way of filling paving with a permeable joint that won't allow weeds to grow in it.
Its available here.
Its super easy to use, just wet it and brush it in and let harden. Brush off the excess while its wet.

rje66

Wont the water drain off the patio into lawn ,beds or whatever surrounds it? .going to the same place??

corks finest

Seve OB wrote:

i laid my own patio about 10 years ago. i think i laid about 6 inches of hardcore, used a whacker to level and set it for putting sand down on top. then i put a few inches of sand down can't remember how much but 6 inches seems a bit over the top so it might have been 3 or 4.( actually I do recall mixing a lot of sand and cement, but im sure it was just a dry mix, maybe 5-1) there was weed control membrane in there, can't remember where it went but i think between the sand and hardcore

That's the correct method AFAIK

recedite

rje66 wrote: »

Wont the water drain off the patio into lawn ,beds or whatever surrounds it? .going to the same place??

Either that or it could form puddles. Depends on how you arranged the slope.

jmBuildExt

Seve OB wrote: »

i laid my own patio about 10 years ago. i think i laid about 6 inches of hardcore, used a whacker to level and set it for putting sand down on top. then i put a few inches of sand down can't remember how much but 6 inches seems a bit over the top so it might have been 3 or 4.( actually I do recall mixing a lot of sand and cement, but im sure it was just a dry mix, maybe 5-1)
there was weed control membrane in there, can't remember where it went but i think between the sand and hardcore

i was told to just brush dry sand/cement mix between the flagstones which i did....... but it was terrible. weeds everywhere all the time. i soon replaced that with a wet mix. no weeds in general...but did start to get some water lodging. a simple fix was to just drill a few holes around the patio, no more water lodging, but get a few weeds filling them holes every so often

Too much sand... should only be between 35mm and 50mm, depending on the application IIRC
As I do with all my responses regarding paving... refer to www.pavingexpert.com - it really is a wealth of knowledge. Everything you need to know about doing domestic paving is over there.

Seve OB

jmBuildExt wrote: »

Too much sand... should only be between 35mm and 50mm, depending on the application IIRC
As I do with all my responses regarding paving... refer to www.pavingexpert.com - it really is a wealth of knowledge. Everything you need to know about doing domestic paving is over there.

like I say, it was 10 years ago when I did it so can't remember how deep I had sand but it was whatever all the experts told me to do.

in fairness, I've never had an issue with it, still as solid as when it was laid, water drains well, i'm guessing due to the good base of hardcore I laid. which is great because the rest of the garden can get very marshy when the rains come.

magicbastarder

rje66 wrote: »

Wont the water drain off the patio into lawn ,beds or whatever surrounds it? .going to the same place??

not quite. say you've covered half your garden with an impermeable patio; now half the surface is doing the job of soaking up the rain falling on the full surface. it'll be slower to drain as a result, as you've increased the chances of waterlogging the soil which is handling the drainage.

Lumen

magicbastarder wrote: »

not quite. say you've covered half your garden with an impermeable patio; now half the surface is doing the job of soaking up the rain falling on the full surface. it'll be slower to drain as a result, as you've increased the chances of waterlogging the soil which is handling the drainage.

So given that the loads on a patio are quite low, is it worth putting permeable aggregate (e.g. pea gravel) under the sand bedding to provide additional soakage?

Ought to be more stable than topsoil and have more capacity for taking water than 804.

smacl

magicbastarder wrote: »

not quite. say you've covered half your garden with an impermeable patio; now half the surface is doing the job of soaking up the rain falling on the full surface. it'll be slower to drain as a result, as you've increased the chances of waterlogging the soil which is handling the drainage.

This and the fact that the effect gets multiplied where lots of people do it in the same area. Not sure of the effect of patios but I was at a lecture a few years back on the effect of tarmac drives on flash flooding in the UK which advocated return to more permeable solutions with higher soakage.

fryup

CJhaughey wrote: »

Romex make a product called Rompox Easy , its an excellent way of filling paving with a permeable joint that won't allow weeds to grow in it.
Its available here.
Its super easy to use, just wet it and brush it in and let harden. Brush off the excess while its wet.

if i lay the patio slabs loose...will the rompox permanently set them in place?

jack of all

The best type of bedding material for paving/ slabs is "pinhead" sand, laid on a well compacted hardcore base. The pinhead is coarse, compacts well and is readily permeable with very little fines (which wash out over time).

fryup

is pinhead the same as sharp sand?

Lumen

jack of all wrote: »

The best type of bedding material for paving/ slabs is "pinhead" sand, laid on a well compacted hardcore base. The pinhead is coarse, compacts well and is readily permeable with very little fines (which wash out over time).

The pavingexpert view on "best":

http://www.pavingexpert.com/layflag3.htm#unsuit

"Using clean sand (that is, sand with no cement) as a laying course is all well and good, and is a method still used on many larger commercial projects, but it does require a significant degree of skill to ensure that the sand itself is fully compacted when the flags are laid. If the sand is only partially consolidated when the flags are laid, it will continue to settle due to gravity and trafficking, and so the pavement becomes uneven and loose and unsafe.
Consequently many contractors prefer to lay on a mixture of sand (or other fine aggregate) and cement, rather than on clean sand.

There are good reasons for doing so, not least of which is the fact that a sand/cement mix is a more forgiving material. The cement content binds together the sand grains and therefore any partial consolidation will not result in movement of the flags. Consequently, the degree of skill required to make a bed that will be ‘perfect’ is much reduced compared to that needed to make such a bed from sand alone.

There are other advantages: bound sand (that is, sand bound together with a cement) can't be disturbed by sub-surface water flow; it can't be mined by ants and other invertebrates; it provides full and even support for the flags. That's why sand-and-cement bedding is probably the best laying course material to recommend to low-skill contractors and all DIYers."

And on types of sand, tldr: yes, sharp sand:

http://www.pavingexpert.com/layflag3.htm#gritsand

fryup

Lumen wrote: »

Consequently many contractors prefer to lay on a mixture of sand (or other fine aggregate) and cement, rather than on clean sand.

but what type of sand?..... sharp? builders?

and do you wet the sand & cement base before you lay slabs?

Seve OB

fryup wrote: »

but what type of sand?..... sharp? builders?

and do you wet the sand & cement base before you lay slabs?

no

Seve OB

Some pics of my own job.
10 years old now

Seve OB

A few more

fryup

fryup wrote: »

do you wet the sand & cement base before you lay slabs?

Seve OB wrote: »

no

so how do they set then?

Seve OB

fryup wrote: »

so how do they set then?

As I said above, dry mix

fryup

so you lay your foundation with a dry mix of sand & cement, and then put down wet mortar and then slabs ?

Lumen

No. Honestly, read the paving expert guide.

The main variation where opinions will differ is jointing material.

Use of a compacted aggregate below the bedding layer depends on ground conditions and expected load. Obviously if you've a foot deep of loamy topsoil or squidgy clay then you don't want to be putting the bedding layer on top of that, so you just need to dig down as far as is appropriate to give yourself a stable subgrade, then bring up the level with aggregate if necessary, then bedding for a nice even support for the slabs.

Calibos

I've some concrete paths and steps around the house that I eventually want to clad with granite/sandstone slabs and bullnose lippped steps where appropriate. How does one do this? Just a sand and cement mortar?

fryup

Lumen wrote: »

No. Honestly, read the paving expert guide.

The main variation where opinions will differ is jointing material.

i did read it, i just want to know how the slabs set in place ? will they set in place on a dry mix ?

jmBuildExt

Yes. Rain or damp rising up through the ground will activate the cement.

fryup

^^^^^^^^^^^^^

thanks that's all i wanted to know