Depth of Sub Base

[800w]

Hi I'm going to do a 3.6m x 3.6m patio, I'll be using, new paving, but nothing fancy just plain 600mm x 50mm, with a mortar base of 40mm.

So what depth should my sub base be, I'm reading that the standard should be 75mm, just wondering though could I get away with 50mm, it isn't soft soil, and fairly untouched, apart from me digging out the weeds.

 

I had a look on paving expert UK, and it seems that the usual depth is between 75 - 100 for patios, but it is a little vague in areas, and says that sometimes no sub base is needed, so I'm thinking then why not 50mm or is that too thin.

 

I'm a novice I've layed a small path, with 3x2 x 50 mm, and done a couple of other jobs, but the patio will be more of a challenge, so I want to get it right and have it look nice, and as I said I'm using 600mm x 50mm, so I'm not sure because of this you can get away with a smaller depth of sub base, or its the total opposite because I'm using a heavier slab I need a thicker base, Thanks.

[markc]

Sub base depends on ground you have and load that will be applied.

Remove the vegetation layer (turf, weeds, roots etc) as that will shrink and swell, also to reduce stuff growing back. Lay a geotextile sheet and your 50mm type1 etc will be plenty for a small patio

[800w]

2 hours ago, markc said:

Sub base depends on ground you have and load that will be applied.

Remove the vegetation layer (turf, weeds, roots etc) as that will shrink and swell, also to reduce stuff growing back. Lay a geotextile sheet and your 50mm type1 etc will be plenty for a small patio

 

Hi thanks for the reply, can I ask have you done this kind of work, or have experience in this kind of DIY job, I'm not trying to be cheeky, but your the first person that has said go with 50mm, most replies have been 100mm on other forums, some have even said as much as 10" of hardcore, it's not for a car lol, I just think some people it is just overkill, or they've read from some site and are passing it on.

 

I can easily read from a paving site, and apply what they've said but every situation is different and you just need a little common sense, and if it is going to work, the slabs I lay will 2x2 x 50, so all I needed to know was if you were laying tiles say 25mm thick are they going to need a thicker foundation or a lighter one, but I'm laying heavy concrete slabs, FWI all the weeds are gone and there was no turf to begin with, Thanks.

[markc]

Morning, yes I’ve done loads of patios, driveways. It all depends on the ground you are working with, many pavements were laid with slabs directly on the ground without any base, most new builds have patios with slabs laid directly on whatever ground they have.

Are you working on clay, sand, peat, infill ? These all have a bearing on what you need to do. I wasn’t saying 50mm is ok for everything but you are not laying a road or driveway or say a base for a oil or water storage tank.

Dig a small hole and post a pic to show the ground conditions

[Gone West]

I've used the Paving Expert website for many years for stuff like that.

 

https://www.pavingexpert.com/

 

 

[Radian]

My last project was laying over 500 slabs for our paths and patios over a variety of different bases. On new areas bordering a couple of building extensions I used 100mm of type 1 on top of broken-up hardcore left over from the building work because the clay had been considerably disturbed. On areas that were original patios, just laid laid on a uniform bed of sand, I carefully lifted the old slabs, whackered it and replaced with the new slabs on a full 30mm mortar bed. The old patio had been down for over 20 years on sand and not misbehaved at all so I figured the ground below was good enough. As a point not often mentioned, it helps if there's lateral restraint i.e. a kerb set in concrete or wall. This contains the ground below and stops it spreading. If it has no where to go, the patio can't go anywhere except for up and down. If the ground was well compacted or not disturbed then it's down to moisture content. Good surface drainage then becomes important with the aim being to maintain constant conditions beneath the patio.

[Mr Punter]

I have done 50mm MOT on chalk for a patio and 300mm hardcore, terram and 100mm MOT on clay for a driveway.  It really depends on ground conditions.

[Conor]

The depth isn't important as much as how compacted everything is. 100mm would be the default as it allows you to get away with an uneven ground below, e.g. if you are on stoney ground you don't have to worry about picking out every protrusion. We dad did ours 20 years ago, we just put 50mm of quarry dust on the (rock hard) ground, and it still hasn't moved. Hire a vibrating plate compactor and make sure everything is firm.

[800w]

7 hours ago, markc said:

Morning, yes I’ve done loads of patios, driveways. It all depends on the ground you are working with, many pavements were laid with slabs directly on the ground without any base, most new builds have patios with slabs laid directly on whatever ground they have.

Are you working on clay, sand, peat, infill ? These all have a bearing on what you need to do. I wasn’t saying 50mm is ok for everything but you are not laying a road or driveway or say a base for a oil or water storage tank.

Dig a small hole and post a pic to show the ground conditions

I had to crop the pic for upload, this is my ground, the wood surrounding it is 160mm high just to give you an idea, so I was thinking just to go down another 5mm, and with 75mm mot1, 50mm paver 40mm full mortar, that would be overall height of 165mm level with the wood or there abouts, I know you can't see the soil clearly but I thought a pic would help.

 

 

 

 

 

[markc]

Yes, get on with it! Main thing here is compaction to prevent settlement later on.

hire a wacker  plate go over it a few times, spread the type1, plenty more wacker ing and you are sorted

[800w]

10 minutes ago, markc said:

Yes, get on with it! Main thing here is compaction to prevent settlement later on.

hire a wacker  plate go over it a few times, spread the type1, plenty more wacker ing and you are sorted

Thanks, so should I whacker the soil first as well, before adding type 1? I also have a question about the fall, I know the standard is 1:80, but I'm nowhere near the house as you can see, so should I still stick to the standard, if I did with the size I'm doing, the patio would drop gradually around 4-5cm from one side to the other.

 

Also regarding the fall should I incorporate that straight away on the soil as you see in the picture eg have it  sloping down slightly by removing a little soil, in other words create a little slope and keep it there as I add in my type 1, hope that makes sense.

You can maybe tell I'm a little nervous about the fall or slope, when It comes to putting down my paving I think I'll be ok, it's just the preparation I'm inexperienced with.

 

Maybe you could help and explain how you go about preparing the area from the start, up untill laying the paving, if you wouldn't mind, I'm just preoccupied thinking about the slope, that when it's finished it's going to look stupid, hope I'm making sense, Thanks.

[markc]

2 hours ago, 800w said:

Thanks, so should I whacker the soil first as well, before adding type 1? I also have a question about the fall, I know the standard is 1:80, but I'm nowhere near the house as you can see, so should I still stick to the standard, if I did with the size I'm doing, the patio would drop gradually around 4-5cm from one side to the other.

 

Also regarding the fall should I incorporate that straight away on the soil as you see in the picture eg have it  sloping down slightly by removing a little soil, in other words create a little slope and keep it there as I add in my type 1, hope that makes sense.

You can maybe tell I'm a little nervous about the fall or slope, when It comes to putting down my paving I think I'll be ok, it's just the preparation I'm inexperienced with.

 

Maybe you could help and explain how you go about preparing the area from the start, up untill laying the paving, if you wouldn't mind, I'm just preoccupied thinking about the slope, that when it's finished it's going to look stupid, hope I'm making sense, Thanks.

Yes wacker the soil if it has been disturbed, in an ideal world you remove the top without disturbing anything.

1:80 is really aimed at soil pipes and drains to ensure they take “solids” with them.

as this is a patio and away from your house then it can effectively be level, but a small crest in the centre is a good thing to prevent pooling.

sequence

remove any loose soil, vegetation etc.

Lay out the working area,

wacker the area

throw in some sub base … type 1 etc and give it a good compacting,

add more type1 and wack again

bring up to your level.

using a spirit level and straight edge level the surface and ideally give a bit of fall to the edges.

laying slabs is just like tiling, start with centre and work outwards, mortar should be 5 or 6 sharp sand to 1 cement, fairly soft mix.

some good vids on YouTube regarding laying slabs as it’s easier to watch than explain.

[800w]

1 hour ago, markc said:

Yes wacker the soil if it has been disturbed, in an ideal world you remove the top without disturbing anything.

1:80 is really aimed at soil pipes and drains to ensure they take “solids” with them.

as this is a patio and away from your house then it can effectively be level, but a small crest in the centre is a good thing to prevent pooling.

sequence

remove any loose soil, vegetation etc.

Lay out the working area,

wacker the area

throw in some sub base … type 1 etc and give it a good compacting,

add more type1 and wack again

bring up to your level.

using a spirit level and straight edge level the surface and ideally give a bit of fall to the edges.

laying slabs is just like tiling, start with centre and work outwards, mortar should be 5 or 6 sharp sand to 1 cement, fairly soft mix.

some good vids on YouTube regarding laying slabs as it’s easier to watch than explain.

Thanks, couple queries what is a crest in the centre, and start from the center when laying, I'm not telling you how you do your job, but would you not start from the corner, if I started from the center that would confuse me even more lol, I've no cutting my patio is 3.6m so 36 pavers no cutting and just a simple square.

[markc]

2 hours ago, 800w said:

Thanks, couple queries what is a crest in the centre, and start from the center when laying, I'm not telling you how you do your job, but would you not start from the corner, if I started from the center that would confuse me even more lol, I've no cutting my patio is 3.6m so 36 pavers no cutting and just a simple square.

Hi, if you don’t have to force the water in one direction I.e away from a wall then you can slightly raise the centre of the area, sort of a very slight hump in the centre so water runs off in any direction.

if you are using whole slabs then yes you can start in a corner, most pavers and tilers have a set size so starting in the centre gives even cuts around the outside edge.

it is always easiest to start at the highest point tho regardless of where the slope runs and work your way downhill

[800w]

34 minutes ago, markc said:

Hi, if you don’t have to force the water in one direction I.e away from a wall then you can slightly raise the centre of the area, sort of a very slight hump in the centre so water runs off in any direction.

if you are using whole slabs then yes you can start in a corner, most pavers and tilers have a set size so starting in the centre gives even cuts around the outside edge.

it is always easiest to start at the highest point tho regardless of where the slope runs and work your way downhill

 

Thanks so I think I'll just have it running with a slight slope, but not as much 4-5cm, but just enough to stop pooling, I think the crest idea would be fine if you were starting in the centre, and slope down gradually as you get to the edges, so if I go with where my garden naturally has a fall, and follow that for my paving, instead of trying to create a fall, then my first row of pavers should run that way naturally sloping down slightly.

I've watched YouTube videos and they're good info, all there patios seem to be close to the house though, and they always bang on about the fall, there never seems to be someone creating a patio, in the middle of the garden like mine lol.

Edited August 22, 2022 by 800w

[Radian]

The problem with not having sufficient fall is that you'll not manage to lay the slabs on a perfect plane whatever slope. So without more fall than your worse laid slab, you may end up with a local puddle. If your ground already falls somewhere around 1:80 follow it but I wouldn't risk going to 1:100

Also, by starting in the middle you automatically halve the inevitable laying error so you make it easier to keep your rows and columns square. You'll always be fighting a tendency for them to creep out of line so the more help you can get from your initial set-out the better.

[800w]

56 minutes ago, Radian said:

The problem with not having sufficient fall is that you'll not manage to lay the slabs on a perfect plane whatever slope. So without more fall than your worse laid slab, you may end up with a local puddle. If your ground already falls somewhere around 1:80 follow it but I wouldn't risk going to 1:100

Also, by starting in the middle you automatically halve the inevitable laying error so you make it easier to keep your rows and columns square. You'll always be fighting a tendency for them to creep out of line so the more help you can get from your initial set-out the better.

So better to follow the natural slope then and not to fight it, still not starting in the center though just wouldn't feel comfortable with that.