The Brew Cabin

Hi Tony,

I am planning to lay a block paved patio but have a few questions:

The surface will only be subject to fairly light loads (i.e. people, patio furniture but no cars) Is it still necessary to have a 100mm sub base and a 50mm bedding layer, or can one/both be reduced?

Also the soil is fairly clay-rich, but given the light loading is a geo-textile cover overkill?

Finally, the garden slopes very slightly away from the house, so I'll have to lay a concrete kerb base where the paving borders the lawn, but do I need to put such a base under the edges of the paving that butt up to the house wall?

Hope you can help,

Greg

p.s. Website is great!

Hi Greg,

yes - you still need a sub-base and a bedding layer, even though it's only a patio. If you have really firm and stable ground, you could get away with 75mm of sub-base, but any less than that isn't really a sub-base: it's just a fill layer, with no inherent strength.

The strength of a sub-base comes from having a minimum thickness, 75-100mm, of a certain mixture of stone and fines. It is the load bearing layer of the block pavement and it's a false economy to skimp. The biggest single cause of sunken paving is inadequate or missing sub-base.

You don't need a geo-membrane. They're handy on bad ground, but for a lightweight application such as this, they are, as you say, overkill.

And as for the bedding layer, you need enough to 'cushion' the blocks, enough to allow them to bed in, but not too much so that there's a risk of settlement. The minimum recommended thickness is 35mm, but that relies on your sub-base being accurate to not more than +/- 10mm.

It's not worth spoiling the ship for a ha'porth of tar. It's a lot easier to do a bit of extra digging, and use a few barrows of extra sub-base at this stage than face having to lift and relay next spring. :)


You don't need concrete under the blocks adjacent to the house. We do it that way so that, when we screed off using those blocks as a level guide, they won't be dislodged. The house wall will act as the restraining edge.

For your kerbs, though, they must be on concrete and haunched with same. If you're draining towards the kerb and hoping to allow surface water to find it's way through onto the garden, you may need to leave an open joint in the kerb line every 500mm or so.

How's that?

Great - many thanks

Greg