Yet another first time patio layer...

[MRA2]

Hi,

I'm about to attempt my first (DIY) patio project.
It's a 7m x 3m rectangle.
It's at the bottom of the garden away from any houses so what's the worst that can happen!?!

My plan is this:
a, Dig out the area to a depth of 150 mm from where I want the top of the finished patio to be.

b, Tip in 70 mm of type 1 MOT and compact.
I'd like the patio to drain across the 3m run so if I put 75 mm of type 1 along 1 edge and 70 mm at the opposite I should have a fall of 1:60 which I think is right for drainage.

c, Tip in 50 mm of mortar (6:1), level it (using a plank and some rails).

d, Put the slabs on top, tap down with a rubber mallet. Done.

Questions:

1. Is the plan about right?

2. How much will the type 1 compact?
I'm hiring a medium size compactor from a generic plant hire shop.
How many passes should I do?
In terms of digging out, the 150mm was based on 70mm base, 50mm mortar and 30mm slabs.
If the 70mm base is going to reduce though, I'm going to be 'out' on my finished level.

3. Do I need to add water to the mortar mix at all?
How about misting it with a hose before I put the slabs down?
I'm especially thinking about the edges.
There's nothing to retain them so I've read it's a good idea to put the edges on a 'wetter' mix.
How wet?


Thanks for any help or advice...


Chris.

[Carberry]

1. I would go for 100mm type 1. 25-40mm bedding layer.

2. 4-5 bulk bags of type 1 will do 100mm. 8 passes, once in each direction (up down left right diagonal right diagonal left)

3. Yes. How much depends on who you ask. I work with semi dry mix, some prefer wetter than that. Don't mist it with a hose, the water needs to be mixed in.

For the edge slabs put some SBR in the mix and or bond bridge on the slab (read up on bond bridge on main site). Job will probably look better having some sort of edge restraint though.


Your levels are off, that is a drop of 5mm over 3000mm ie: 1:600. You need a drop of 50mm for 1:60 which will be fine for most projects.

[local patios and driveway]

What carberry said, although i would go thicker than 40mm on the bedding layer but carberry knows what he is talking about, probably more down to personal preference.

[MRA2]

Carberry,

Many thanks for your help - and yes - I just realised my calculations about the gradient were out.

I need a 5 cm drop over 3 metres which is 50mm (not 5!!).
Therefore, according to my original plan, that would have been 70mm at one side and 120mm at the other.
Going with your guidelines, we're looking at 100 and 150, I was thinking I'd need 4 bags anyway and just spread it out evenly.

In terms of the edges, I'm laying up to a fence on 3 sides and the 4 side is lawn.

My plan when digging out was to leave a couple of inches from the fence so I don't disturb the fence when laying/compacting the base.
When I lay the slabs, I can hide those couple of inches and get closer to the fence. Hence my thought about using a wetter mix to lay the edges to try and stop them moving.

When I'm done, I was going to fill in the gap between the slab and the fence with the same mix as the pointing.

Is that a particularly bad idea?

Finally, the 4th edge is going to be laid to lawn, this is the edge I'm most concerned about the level.
We can go up from here because this is the lowest point I want the rain to run off onto the lawn.
If this is the lowest point, how much is the type 1 likely to compact if I do the 8 passes you suggest?

Thanks again, much appreciated.


Chris.

[Carberry]

Carberry,

Many thanks for your help - and yes - I just realised my calculations about the gradient were out.

I need a 5 cm drop over 3 metres which is 50mm (not 5!!).
Therefore, according to my original plan, that would have been 70mm at one side and 120mm at the other.
Going with your guidelines, we're looking at 100 and 150, I was thinking I'd need 4 bags anyway and just spread it out evenly.

In terms of the edges, I'm laying up to a fence on 3 sides and the 4 side is lawn.

My plan when digging out was to leave a couple of inches from the fence so I don't disturb the fence when laying/compacting the base.
When I lay the slabs, I can hide those couple of inches and get closer to the fence. Hence my thought about using a wetter mix to lay the edges to try and stop them moving.

When I'm done, I was going to fill in the gap between the slab and the fence with the same mix as the pointing.

Is that a particularly bad idea?

Finally, the 4th edge is going to be laid to lawn, this is the edge I'm most concerned about the level.
We can go up from here because this is the lowest point I want the rain to run off onto the lawn.
If this is the lowest point, how much is the type 1 likely to compact if I do the 8 passes you suggest?

Thanks again, much appreciated.


Chris.

It wouldn't do any harm having 50mm more of type 1 at one side than the other but imo the best way is to dig out a slope, rather than a flat area and sloping it with the type 1. It will be less laborious and it cheaper because you don't have to take so much muck away and fill with more type 1 than necessary.
Setup a string line to the correct gradient and use that as your guideline for digging out.

Laying up to a fence can be awkward because of the concrete that the fence posts are sunk in to. You won't disturb the fence unless it is just put in with those daft spikes but you may have trouble getting your required depths etc if your posts are concreted in.

Your type 1 should be 100mm deep after compaction. I couldn't tell you how much it compacts down, it's not something i've ever paid attention to or tried to calculate I just have a feeling for how much to put down before compaction to get it to the finished level.


to expand on what Lpad said, if you're flags vary in thickness by a large amount then you may need a deeper bed than 40mm.

What is your fence made of? If you have concrete gravel boards at the base then filling the gap with mortar would look ok, but if it is timber then it would look cr*p.