Retaining Walls Before Or On Top Of Patio Slab Post your questions and get answers regarding all areas of drives, pathways and patios

[burt12345]

Hi,

I'll be needing to complete garden after building an extension. We will be having a sunken type garden patio of slate, level with extension floor (channel drainage across front of extension). The perimeter walls will be about 3ft high.

My question is, do dig a small trench and make foundations for the walls and build the garden walls (7n blocks?), then pour the slab for the patio.

Or should I, retain the soil with soil filled poly sacks (I'll use this method as I need to shift soil about), pour the slab, then build the walls on top of that? then remove the poly sacks.

One other thing is we'd like to have a timber deck in the middle of the patio at the same level as the slate, to create a sort of deck rug! there will be 110mm pipe running under this from the channel drain to the soak away - how would be best to a) create a frame on which the deck can sit on, b) create drainage so the timber does't rot.

many thanks

[welsh brickie]

I think its best you dig out and lay your foundation first. Then build the walls.
For the sunken garden drainage, dig a pit in the centre and line it with weed suppressant material and fill it with gravel, if possible pipe it away from the sunken area to a lower point. As for the decking, if you buy pressure treated timber it will last 20 years

[burt12345]

Great, thank you.

When I lay my concrete slab, do I use a dryish mix like a screed or does it need to be wet? Sorry if that's obvious!

[burt12345]

and is it ok to create the slab first, then lay the slate on that? Only I've seen a site where they are laying the mortar bed and slate at the same time, I'm not sure I'm skilled enough for that. At least if I get the bed fairly level, I can bed up with tile adhesive.

[welsh brickie]

if you lay a semi dry mix you can bed your slate into it.

[burt12345]

Sorry for the delay, the forum only seems to notify me on first reply.

So would it be a 1 cement to 4 ballast mix? And how much working time do I have, ie what happens if I leave a few days between areas? Or is cracking not a problem as it will be between slates if anywhere?

Ta Matt

[welsh brickie]

lay it on a bed of sharp sand and cement, you have about 2 to 3 hours workability

[burt12345]

ok, just checking, this slate is 10-20mm thick, is that still the case?

[welsh brickie]

yes its fine, its best to paint pva on the back of the slate to make it adhere to the mortar

[burt12345]

Great, thank you.

[burt12345]

Quick questions

The idea of the deck in the middle of the slate patio is to provide drainage for the surrounding slate via gravel pit under it, draining to the main soak away, is the mortar for the bed ok right up to deck beams/joists or do I need to have a small gravel channel to allow water drain away from the timbers. The deck will be flush with the slate you see.

And Obviously we are entering the frosty season, if my mortar bed was 50mm thick am I going to be ok with frost proofer - or am I best to wait until spring?

Thanks.