Sub Base

[HJB]

Hi

 

I am having new patio put down, sand stone.

 

There has been Type1 min 100mm whacked down.  The next step I thought was a sand/cement mix mortar that the sandstone is laid onto, on a 1 by 1 basis.

 

However they are going to do the above, but before the mortar mix goes down, Geo fabrix is going down and sharp sand then whacked down?  I've never heard of it being done this way?

[Carrerahill]

I don't see the point of the Geo and the sand, I would go direct to a FULL cement/sand bed. 

 

Do that and no Geo is needed and will be quicker and save a little without any detriment to the install.

 

The sand blinding is done for certain things but in this instance I cannot be sure why they want to do it.

 

If they do insist on the sharp sand, ask for it to be bound up 1:7 or 1:8 ish (min) with cement so that it becomes a ridged base. The sand layer in there could, wash out and cause issues depending on how it is installed.

 

I shall caveat the above by saying that without full view on this we may not know things for sure.

 

 

[Carrerahill]

This is website is considered as the authority on all things paving:

 

https://www.pavingexpert.com/layflag1 - note how they do it. Sub then bed i.e. the sand/cement.

[HJB]

I can not see the point in this layer of sharp sand either. if anything add more type 1 and whack to level.

 

They said they do it this way all the time and have really good reviews but a guarantee on install for 10 years.  I have just never heard or seen it done this way.

 

Should I be a concerned with this layer of sharp sand?

 

He said on top of type 1 is geo fabric,   sharp sand to level out, whacked down, sealed and then the mortar mix (not dot and dab) full bed per slab as it is laid.

[saveasteading]

Yes be concerned. I think this is just easier to lay flat than stone. It can't really be rolled or whacked hard either.

The problem I see is of rain running through the joints (perhaps in 2 to 3 years, and washing away the sand.

 

As suggested above, if it has enough cement in it then it will be ok. but I think this is just to suit themselves as it is difficult to impossible to lay stone exactly within a few mm..

[HJB]

Yeah that is my exact worry is the sand underneath starts to wash out, there is no need to put the sand between there levels other than as you said its easier to level sand than it is onto type 1.

 

The company comes with good reviews, but from Day 1 I have been extremely worried, the sharp sand between the layers has just made me loose all confidence in them. To far in to say just walk off, and its the way they do it, already said I've never head of sharp sand between Type1 and Cement.

[Makeitstop]

8 hours ago, HJB said:

I can not see the point in this layer of sharp sand either. if anything add more type 1 and whack to level.

 

They said they do it this way all the time and have really good reviews but a guarantee on install for 10 years.  I have just never heard or seen it done this way.

 

Should I be a concerned with this layer of sharp sand?

 

He said on top of type 1 is geo fabric,   sharp sand to level out, whacked down, sealed and then the mortar mix (not dot and dab) full bed per slab as it is laid.

 

Sealed...???

[HJB]

Yes this is what he said, I have no idea what he meant by this, I can only think he is referring to the Geo Fabric as a seal !!! 

 

He has told me the process is....for all sandstone paving is a sub base of type1 then compact, then the layer of sharp sand and compact followed by the mortar and slabs. 

 

He has put this in writing so I  now have some come back should I need it, he never mentioned  the Geo fabric in the email, but  I have gone back to confirm that he is putting Geo fabric betweem Type 1 and sand.

 

I know form what I've read across various websites, inc manufacturers and watched many installs online this is not correct.  I have read on some occasions sharp sand can be used as a very thin coating to bind into the type 1 and fill any gaps.  However if he uses Geo fabric between then that eliminates any binding.

 

 

[Carrerahill]

14 hours ago, HJB said:

Yes this is what he said, I have no idea what he meant by this, I can only think he is referring to the Geo Fabric as a seal !!! 

 

He has told me the process is....for all sandstone paving is a sub base of type1 then compact, then the layer of sharp sand and compact followed by the mortar and slabs. 

 

He has put this in writing so I  now have some come back should I need it, he never mentioned  the Geo fabric in the email, but  I have gone back to confirm that he is putting Geo fabric betweem Type 1 and sand.

 

I know form what I've read across various websites, inc manufacturers and watched many installs online this is not correct.  I have read on some occasions sharp sand can be used as a very thin coating to bind into the type 1 and fill any gaps.  However if he uses Geo fabric between then that eliminates any binding.

 

 

You are the customer, I think you should set the spec as per discussed and the paving expert site.

 

Geo is only really going to do anything where there is a loose covering like gravel or bark. Once a fully bed of paving mortar is laid no weed will come up through that! 

 

Unfortunately there are a lot of trades who think they know things and don't really. Some of them don't really think, they just, try and copy and make up their own minds on things and carry on oblivious to what is going on or how things work. 

 

I saw a push-fit coupler installed by a plumber, with PTFE tape last week! I do not joke! I fixed it, the neighbour wanted to get the plumber in to check it... I pointed out the plumber was totally incompetent and that I did know what I was doing and had replumbed my whole house in soldered copper when I built the extension  (I was so proud of my under sink work etc. I posted it on this site to receive many comments of how good it looked) and that although I am no plumber, I probably carry out better work than at least 60% of professional plumbers because I care and I take my time and I want it to look like a work of art. 

 

Sorry, I digress, but you get the point.

 

 

[HJB]

I've been through this with them but they are amendment this is the way its done and the way they do it all the time, they have done load and good reviews.  By not doing it this was could impact their 10 year guarantee also...apparently. 

 

It's bizarre as its actually extra work for them to put in this extra layer of sand that is not needed, more effort moving it all round to the back garden...I am trying to work out if its corner cutting and if so what corners are they cutting.

 

In my eyes its more work, more martial that is not needed and its only adding risk to the sub base build that is not needed. 

 

I am baffled!! 

Edited November 12, 2021 by HJB

[saveasteading]

22 hours ago, HJB said:

sharp sand between Type1 and Cement.

It is standard in laying big concrete slabs, but must have a dpm above it.

 

1. it makes the slab a consistent thickness and therefore controllable

2. it provides a sliding layer for shrinkage

3. it is cheaper than concrete.

 

The problems come when it is much too thick, as it isn't compacted well, and then gets footprints in it which may remain as voids under the dpm and cannot help crack control.

[Carrerahill]

11 minutes ago, HJB said:

I've been through this with them but they are amendment this is the way its done and the way they do it all the time, they have done load and good reviews.  By not doing it this was could impact their 10 year guarantee also...apparently. 

 

It's bizarre as its actually extra work for them to put in this extra layer of sand that is not needed, more effort moving it all round to the back garden...I am trying to work out if its corner cutting and if so what corners are they cutting.

 

In my eyes its more work, more martial that is not needed and its only adding risk to the sub base build that is not needed. 

 

I am baffled!! 

Throw them off the job and fine some pro's.

[HJB]

1 hour ago, saveasteading said:

It is standard in laying big concrete slabs, but must have a dpm above it.

 

1. it makes the slab a consistent thickness and therefore controllable

2. it provides a sliding layer for shrinkage

3. it is cheaper than concrete.

 

The problems come when it is much too thick, as it isn't compacted well, and then gets footprints in it which may remain as voids under the dpm and cannot help crack control.

The slabs are sandstone though not Concrete slabs

 

The sandstone will be going on a full bed of cement and sand mix as per how sandstone should be.

 

Everything I read or watch says that above the 100mm type 1 should be sand/cement full bed mix, but these guys are putting in a layer of sharp sand, it just makes no sense, and its more work...I am hoping someone can shine some light to it. 

 

Its not cost as from what I can see type 1 and sharp sand is about the same, so if anything if costing me more for this layer, and costing them more time...pointless

 

As it turns out the Geo Fab has not been placed between the Type1 and Sand, so god knows where this is going now possible between the sand and sand/cement mortar mix

 

 

Edited November 12, 2021 by HJB

[HJB]

1 hour ago, Carrerahill said:

Throw them off the job and fine some pro's.

Too far into in now, and cant have the garden left the way it is over winter.

 

I've taken photos through their work, have it in writing what they are saying so if it all goes wrong I will hopefully have some come back!

[saveasteading]

Can you ask them to show you any drawing or written spec that confirms their proposal?

A lot of people on here will be surprised if they can.

[HJB]

My question to them was what is the added benefit of this additional layer of sharp sand.  The response was and I quote "for all sandstone paving is a sub base of type1 then compact, then the layer of sharp sand and compact followed by the mortar and slabs. "

 

No other evidence other than that.

 

They have photos going back 6 years on Insta/facebook...have 5 stars and recommended a lot. I cant be the only one to have questioned this...surely! Maybe just nothing has gave way yet on the work they have done.

[Makeitstop]

Surely, the point of mortar straight onto type 1, is to enable a bond into the very solid surface that the compacted type 1 offers.

 

No matter how much you whack sand down, even sharp sand, it's not going to be as tight as type 1.

 

I'd be concerned that the mortar bed will simply sit on a surface that isn't properly bound to the sub base.    

 

 

[HJB]

17 minutes ago, Makeitstop said:

Surely, the point of mortar straight onto type 1, is to enable a bond into the very solid surface that the compacted type 1 offers.

 

No matter how much you whack sand down, even sharp sand, it's not going to be as tight as type 1.

 

I'd be concerned that the mortar bed will simply sit on a surface that isn't properly bound to the sub base.    

 

 

yeah fully agree with you. 

 

I cant understand why they are so amendment by this way. Like I said before cant be cost, and its not to save on labour as its more work, work comes with 10 year guarantee also so in my eyes they are setting themselves up for a massive fail.  I just cant comprehend why they would do more work for something that isnt needed, its normally the other way round.

 

There are amendment that the sand is needed to provide the bond and fill the space in the type 1.  It seems to be a bed of about 300 -400mm sand, its hard to tell. 

Edited November 12, 2021 by HJB

[markc]

Lot of civil engineering going into the Patio

[HJB]

10 minutes ago, markc said:

Lot of civil engineering going into the Patio

I'd say a lot of wasted unneeded materials and labour going into it, just to increase the chances of something going wrong

[saveasteading]

Until you have tried to lay stone to a level it sounds easy. The sharp sand is similar cost to the stone and much easier to lay, so saves labour.

 

This will work fine for a number of years then will fail, and when that starts it continues.  The guarantee, I guarantee, will be worthless as it will take you £1,000 of legals to get £500 of repair done.  Unless thy of course the contractor admits a problem and just does it for you with a smile.

 

be sure that they do proper pointing with wet mortar and don't just brush in a dry mix and assure you this is the best way. If they do this properly it will allow the rain to run off the edge and away, rather than through the sand. It is on a slope isn't it?

[HJB]

Partner is a solicitor so that’s covered, I imagine it will be a claim against the full lot not just a repair.

 

yeah I checked and it will be a proper pointing that’s wet.

[Makeitstop]

4 hours ago, HJB said:

yeah fully agree with you. 

 

I cant understand why they are so amendment by this way. Like I said before cant be cost, and its not to save on labour as its more work, work comes with 10 year guarantee also so in my eyes they are setting themselves up for a massive fail.  I just cant comprehend why they would do more work for something that isnt needed, its normally the other way round.

 

There are amendment that the sand is needed to provide the bond and fill the space in the type 1.  It seems to be a bed of about 300 -400mm sand, its hard to tell. 

 

Sorry, 300 to 400mm sand?....... you must mean 30 to 40mm surely.

 

If the former, that's 12 to 16 inches of sand. Fine for sand castles, not so cool under a patio...? Haha.

 

I cant see for the life of me why anyone would use any sand layer over the sub base. Once type 1 is worked to levels and compacted down, it's perfect for taking a mortar bed. Once laid, it would be well tricky to pull stones up, as they'd be solidly bonded to sub base, which itself is damn hard to lift once tight. To my thinking, if you've got a sand layer sat on top of sub base, a strong bar wedged under a sandstoned slab could lift the slab up off the sand layer with the mortar attached firmly to the back of it still. It just sounds odd.

 

 

 

Edited November 12, 2021 by Makeitstop

[HJB]

1 hour ago, Makeitstop said:

 

Sorry, 300 to 400mm sand?....... you must mean 30 to 40mm surely.

 

If the former, that's 12 to 16 inches of sand. Fine for sand castles, not so cool under a patio...? Haha.

 

I cant see for the life of me why anyone would use any sand layer over the sub base. Once type 1 is worked to levels and compacted down, it's perfect for taking a mortar bed. Once laid, it would be well tricky to pull stones up, as they'd be solidly bonded to sub base, which itself is damn hard to lift once tight. To my thinking, if you've got a sand layer sat on top of sub base, a strong bar wedged under a sandstoned slab could lift the slab up off the sand layer with the mortar attached firmly to the back of it still. It just sounds odd.

 

 

 

I yes typo on my part 30-40mm

 

Yes what you are saying is spot on about it lifting, the sand to type 1 is weaker than mortar to type 1.

[HJB]

I also think he lays the gro fabric on top of the sharp sand before the mortar mix which would make the bond even worse...?