Hi
I am having a new patio installed and have a couple questions.
The guys that are doing it are removing some existing turf to extend out and lift the old patio. However they said they can just put type 1 over the existing sand that was under the patio, then on top of the type1 it will be the sand/cement mix for sandstone.
Is this correct or should the old sand be removed also?
Regarding drainage I had asked a drainage grid be put in along the sleeper edge on the far side of the patio where the grass is (grass, then a sleeper height drop to the patio), but they are saying the way it will need to be laid, they would be best running the drainage grid along the house side of the patio. I have always read dont run these along side of house. The pipe is getting tided into the rain water downpipe for info.
There will be a 2 step down from back doors to patio
Any advice on this?
I guess it doesn’t matter what the aggregate is laid down on assuming there’s relatively hard ground underneath. If it’s only a thin layer of sand it’ll get compacted down - I imagine there’s going to be at least 100mm of compacted aggregate - maybe more. I laid a porcelain slab patio recently and that was just over 100mm thick aggregate once I’d wacker plated it. Mine wasn’t sandstone so I had to lay cement down on top then apply a slurry to the back of my Slavs to make it stick as they aren’t porous. I’m guessing sandstone is do no need for flurry. I’d just make sure they aren’t dotting the cement and are applying an even covering - otherwise in time they’ll start rocking potentially.
Not sure on the drainage thing. We have a channel for drainage in our other porcelain slab patio and that drains to a soak away about 5 metres away. I guess as long as what they’ve planned won’t allow damp to gather above your dpc it should be ok.
By 'lift' the patio you mean raise the level? By how much?
The important question is not how many steps down to it, but how it compares to the DPC in the house. It should be at least 15cm below. If there's no DPC because of the age of the house then slope the patio away and put a drain next to the wall.
Otherwise, where the drain goes depends on where the pipe to the rain water system can be laid, but the patio should slope (something like 1:50 to 1:30) towards the drain.
Sorry when I said lift the patio I just meant remove the old slabs, however the new patio will sit higher that the old as there will be min 100mm type 1, plus the sand/cement base and then the slab its self.
There is a vent that sits approx 4 inch above the existing patio, so that gap is going to be reduce by about at inch when the slabs are laid.
My concern is water going towards the house even with a channel drain running along it just seems a bad idea, even more so when the vent is on 1 inch above the slabs, that water straight into the underneath of the house.
I stated from start of the job drainage channel along the sleeper and run off towards that, but as they havent dug down and removed a layer the wont get the run off for the drain towards the sleeper now.
Am I right to be concerned or with the channel drain being there it will be ok?
Also on another point should they have laid Geo fabric between the old sand and new type 1, read online that this is a must. They have geo fabric but havent laid it so I suspect this is going onto of type 1 and below the sand/cement mix.
There is nothing wrong with a channel drain along the house, but this is a method that can be employed when it's difficult to lower an existing surface to the required distance from the damp proof course as it reduces rainfall splashing back up onto the bricks above the DPC. (It doesn't necessarily mean the patio will actually drain towards the house)
So it's possible your builders want to install the channel drain by the house as this allows them to raise the patio closer to the DPC...i.e a bodge to save a few quid on a grab lorry/skip for the old patio base.
Draining towards the house is not ideal even without the vent. If the vent is 4" above and you're getting at least 100mm type 1 it may end up below the level- how thick are new v old slabs? Where is the DPC?
I would not want to raise the level, from what you've said. Why can't the extension go at the same level?
The main reason for geotextile is to avoid the existing ground mixing into the type 1, if it's previously laid sand it may not be a problem.
Patio foundations are often over specified as the contractor doesn't know the ground conditions or its history or what you're going to put on it, and can't afford you claiming it's settled.
We had our sandstone patio laid in the same way your contractor is suggesting (type 1/ then cement) and its been fine. Drain along house has led to no problems and it doesn't get clogged up, it might if closer to the lawn.
Another question on this
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?
Nobody asked yet how Mrs ry33 is? 🙄
Standards.
I dont follow?
There is a reason one builds a patio...and no one wants any suspicious subsidence later on...
haha, I follow now, hectic morning, brain is not multitasking
There is a reason one builds a patio…and no one wants any suspicious subsidence later on…
Last time I had a quote for a patio, divorce seemed cheaper!
Just a general rant that has been building up for some time.
My experience is that foundations for patios are vastly over specified whereas foundations for driveways tend to be correctly specified but are thwarted by builders taking shortcuts.
The pressure on a driveway is around 10 times the pressure on a patio.
I have laid a patio on dabs of concrete. I have supported our decking on nothing more than concrete blocks. Neither have moved at all over the last 10 years.
Whereas, if I take a walk down my road, 75% of the block paving driveways are sunken.
Finally, always use clay pavers not concrete ones. Concrete pavers look okay to start with but the colour always fade and end up looking council. Clay pavers are natural beauties which only improve with age.
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?
It's not my area, but I would have thought whacking down sand on top of geotextile is just going to result in the fabric bouncing, unless they are putting down a very thick layer of sand, which is going to give you problems with your vent. The point of the sand should be to blind the type 1, ie, fill the gaps so that that the mortar has a solid base. My patio is blocks not slabs, and it has type 1 then sand, no fabric.
I am just baffled as to why they are doing this, I can understand some sharp sand over the type 1 as you say fill the gaps in the type 1. absolutely no point in fabric between type 1 and sand.
Can anyone else comment if they are in the industry?
Anyone know how long after you can sue a company? I have no doubt that in 2-3 years I am going to have problems the way it have been layered and not excavated out
absolutely no point in fabric between type 1 and sand
I tend to agree - it's not like weeds are going to grow through if the patio is laid correctly.
Four years ago I laid a patio (onto a solid concrete base as I had some sods of drops to straighten up) and no way would I have considered geo textiles. The same year I built a raised decking area and that DID get a geo textile base.
If anything the Geo Fab is meant is mean to to go under the Type 1 to stop the old mixing with the new Type 1 or so I have read.
I would have thought some of the sand would want to mix with the Type 1 fill the gap kind of thing.
They put the sand down, even though I told them I disagree with the method.
Sharp sand, and type 1 about the same cost so it cant be cost.
Its more work for them to put this sand in so I cant see how this is cutting corners.
I've taken photos, got what they have said in writing and hoping this can be my come back, its too far in to tell them to leave site, as I cant have the garden left the way it is over winter and will prob take me until March/April at best to get someone to finish it off.
Plus I think the damage is already done on day 1 by not digging out what was under the old slabs.
Weird. If you properly whack down type 1 (go over it several times while spraying it with a little water) it will go pretty much solid with very few gaps. The small gaps will help the sand/cement bed on top key in to it.
Here’s mine a did a few months ago. You can see the type 1 on the section I’m flagging.
yes it is very weird the way they are doing it, even more so that is more effort and time for them. Its simply a layer that doesnt need to be there, all it does is add risk to the sub base failing, and me coming back to them down the line.
What you have done is what I expected.
If they lay the geo fab on top of the sand, and place the mortar mix on to the geo fab…would this not be even worse?
This is what they plan to do.
The geo textile serves no practical purpose.
They put it down for three invalid reasons.
1) to stop weeds growing up through
2) to stop mixing between layers
3) everyone else does:
1) Weeds grow on patios/paving because seeds get blown on to the surface and they root in the joints. There is no light beneath slabs so there will be no germination of seeds beneath. The exception is roots from nearby trees and plants but geotextil will not stop those.
2) a little bit of mixing between the layers is no bad thing. It helps to consolidate things. Anyone who has ever put geo textile under gravel will appreciate that after a few years it disintegrated to ugly shreds anyway. It has the long term mechanical properties of tissue paper.
3) everyone else does it because it is very, very cheap and it saves explaining to the customer why it is not needed.
My patio was laid by my step-dad using slabs from where I used to live that my dad had laid. As far as I’m aware, they’re just laid on flattened dirt, although there may have been some sand put down, I really don’t know.
The patio was laid about 1973-4, and hasn’t moved in the slightest since. It’s also pretty level, not that a few mm here or there would notice.
The standard method these days for non vehicular load is 100mm type 1 MOT whacked down then the flags/tiles laid on a solid bed of 4:1 sharp sand:cement in a dry (ish) mortar. If you’re laying porcelain tiles then they’ll need an SBR/cement slurry on the back otherwise sandstone etc will be ok straight onto the mortar.
As said above, nothing will get through the type 1 and I don’t see how sand on top of the type 1 helps anything, to me it would actually worsen the bond to the substrate.
Anyone know if there is a governing body that you can get to check this kind of work?
Major concern now is that the level is not 150mm below the air vents. They have said a thin row of chips and the aqua channels mean it will be ok but tbh I am at the stage now I would like someone authorised to check the work.
An ACO drain laid on the building above the DPC will pass building regs. If in doubt you’d have to ask your local council building control to visit.
There’s good info here:
I suspect then with the channel drain they have done enough to cover themselves.
I guess I wait until the first mass downpour and film the action happening…then the fight begins to get them back, sue them or most likely with these idiots the home owner has to admit defeat and pay out to have it redone…I better start saving now, and purchase osmo floor barriers 😂
