Grouting Sandstone Slabs

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I'm about to lay some sandstone slabs of various sizes on a DPM, three inches of compacted sharp sand, and an inch of mortar.
What concerns me though is the grouting/pointing as the mortar could stain the sandstone and i would like to know if there is a way of avoiding this happening.
Is it also neccessary or advisable to coat it upon completion with some kind of sealer or not?

Many thanks, Calum
 
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why are you laying it on a dpm

why are you laying it on a sharp sand bed and then mortaring it down?

point it with a damp 1:3 mix on a dry day and it wont be a problem.

the way you are laying it may be though.
 
Thanks for your reply Thermo.

I have been told that the DPM is a good idea should i decide to build something on top of the patio in the future.

Whe slabs vary in thickness and i thought it would be easier to lay them on a mortar bed which would also be stronger.

Is this not a good idea?
 
You've been given duff, if well-meaning, advice on the dpm front. There is a danger water could pool between it and the sand layer if water can get in. Still, its there now, I presume?

The sand is also redundant as you could lay on a 2" mortar base straight over hardcore. Still, its there now, I presume?

Pointing is done as per Thermo's advice. Just keep a sponge and a large bucket of water to dab off any spills you do make.
 
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moratr bed is a very good idea its the sharp sand base thats pointless. you will be better putting a layer of mot dopwn first or as wabbit poo says go straight off the hardcore.

dpm is an absolute waste of time and could actually cause problems.
 
Many thanks for the replies chaps.
Thankfully though there is nothing but earth and a just finised retaining wall at the moment.
So it's compacted hardcore and 2" of mortar with a damp 1 cement to 3 sand grout.
Would a couple of inches of hard core be enough?
 
It depends on whats under it. I would think that the 2" plus the mortar bed would be fine. Use a mix of sharp and building sand for the mortar to give it extra strength.
 
calson said:
What concerns me though is the grouting/pointing as the mortar could stain the sandstone and i would like to know if there is a way of avoiding this happening.

These multi-head hose attachments often have a setting called "mist" which puts out a very fast flow but hardly any quantity. I have found this to be ideal for cleaning bodged pointing, providing you are not using too wet a mix. You can actually aim dorectly at the stain and erase it quite accurateky without having to blast the rest of the pointing to kingdom come.

My advice for a pointing mix would be 3 parts sharp sand and one part cement mixed dry and wetted so slightly as to just allow the mix to form 'sausages' in your hand, but no wetter.
 
Many thanks to you all ModernMaterials, Wabbitpoo and Thermo i now feel a lot more confident in what i'm about to do.
 
dont worry if you get white stains on the slabs a few days after its dont, thats just the salt leaching out the cement
 
I was about to write a new post but this thread is so closely related I thought I'd add on...

I'm about to lay 480x480 sandstone slabs, 22mm thick, supplied by Stonemarket. They are smooth-cut both sides.

Here:

http://www.stonemarket.co.uk/horizon.asp

When I read the technical details, Stonemarket recommend:

1. A 40mm compacted sharp sand bed as minimum for light use.

2. 25mm motar bed, using White Cement as a substitute for Ordinary Portland Cement to prevent discoloration.

Is this advice OTT then? My sub-base is (was!) going to be just the exisitng earth since it's rock solid and not prone to wet. My problem was how to level this though as it's such rocky ground I could almost do with some blinding before the sharp sand bed.

Having read this thread I'm now thinking scrap the sharp sand and use a 40mm bed of hardcore (which would help even the ground) and then motar the slabs straight onto the hardcore.

Another (builder) mate of mine said I should consider screeding the existing earth to level it before laying with motar.

What do you reckon? I'm a little cautious to ignore the technical instructions of the stone manufacturer...

Thanks in advance.

Ben
 
If you wish to lay on mortar on top of earth, then its probably OK so long as the earth is quite stoney and compacted. If you do so, and I have done many paths and patios this way, make sure the mortar is a strong one, with a mix of sharp sand and building sand, and that it is quite thick.

If you need to raise the levels by a large distance then yes, you'll have to add hard material first, such as compacted hardcore and/or crushed stone from a builders' merchant.

Either way, always lay slabs on a mortar bed, not screeded sand as you'll get a better result as a beginner and it'll last longer.

If using natural stone then paint the backs of each slabs (ie the underneath) with a slurry of cement and water before bedding them down.
 
WabbitPoo said:
If you wish to lay on mortar on top of earth, then its probably OK so long as the earth is quite stoney and compacted.

I've actually dug down about 2 inches thinking I'd be using a 2 inch sharp sand bed. So I suppose I'm really asking which you reckon would be better to mortar onto? compacted hardcore or sand?

If you do so, and I have done many paths and patios this way, make sure the mortar is a strong one, with a mix of sharp sand and building sand, and that it is quite thick.

So a strong mix with half sharp, half building ok?

If you need to raise the levels by a large distance then yes, you'll have to add hard material first, such as compacted hardcore and/or crushed stone from a builders' merchant.

I've actually be digging down to get some depth for a bedding layer. Also glad I've done this becuase this ground is so stoney/rocky it will help to get a more even surface for a mortar bed.

Either way, always lay slabs on a mortar bed, not screeded sand as you'll get a better result as a beginner and it'll last longer.

If using natural stone then paint the backs of each slabs (ie the underneath) with a slurry of cement and water before bedding them down.

Thanks for the advice.
 
Cheers Thermo.

I get the feeling you've had to say the same thing a few too many times recently...? ;)
 

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