Laying a patio for the first time

[lms]

Hello everyone, I'm new here, so be carefull with me!

I'm from a mechanical background, not the building trade, but I'm not scared to have a go at most jobs, so is why I'm having a crack at a new patio. I have several questions for you (I have used the search feature and got some answers).

A bit of background first - patio area is to be around 9m square and will stretch the width of the house and up against it. The flags will be 450mm square cast concrete made to look like sandstone type. The existing patio is six 2'x 3' concrete slabs outside the patio doors (standard new house build attire!).

I have already dug out around 4 - 6 inches of soil and luckily that seems to be where the building rubble and clay start. It's very firm. About 1 inch of the foundations is also showing. The existing patio is sitting on a sub base. The slabs surface are 6 inches below the DPC and slope about 1 degree away from the house. They haven't moved in 7 years so all was done correctly.

Question 1 - I have a lot of spare decorative Cotwold chipping gravel 20-30mm. Could I use this for a sub base? I know it would need binding. What would I bind it with..sand?...sand and cement? ratios? It used to compact quite well under foot, so I assume with fines added it should be suitable when compacted with a whacker?

Question 2 - Can I leave the existing sub base where the 6 original flags are? It's very good. Just worried about the joins between this and new base (settlement of the new base)

Question 3 - Would it be better to lay the flags on a bed of sand or a mortar base?

Thanks for your time, any advice appreciated.

lms

 

[Thermo]

whats the sub-base thats already down?

you could use the cotswold mixed with some sharp, although id rather use some mot rather than try to save a few bob.

lay the flags on a wet mortar bed. you can lay it on a dry one but youll be repointing it again next year and relaying it in a few more.

 

[lms]

The existing looks like MOT. After getting an opinion from someone else, and a bit of chin feeling and sucking noises, he came to the same conclusion. Just start afresh and do the job properly with MOT. I cannot quite remember whether he said the existing base should stay or not.

So question now is can the existing MOT base stay and build up around it with more MOT?

 

[Thermo]

yes absolutley.

 

[Hipokondriak]

Excuse me for putting my 10 pence worth in this, but I have laid my own patio with pavoirs and edging stones and I have used a drop of about 1inch over 20 feet.

Right or wrong, this has worked for me and (so far) I have had no problems with drainage or pooling.

My only caveat is that I dug out a half metre wide trench, about 1.5 metres deep, back filled with rubble and shingle to about half way and put a mixture of sand and soil back on top to level with the finished patio.

My patio is 15 feet out from the house and as wide as my garden (about 50 feet wide).

I pegged the ground in one metre squares and laid a 2 metre rigid straight aluminium "I" bar over them and using a spirit level, created a fall away from the house where the bubble in the glass eye was touching the black line away from the house. Just made sure they were level across the sideways aspect.

As for digging out, I went down 18 inches and put down a membrane (don't know what it is for but it is white and looks like glass fiblre), a four inch layer of hardcore, used a whacker plate to get a level and a layer of road scrapings. Whacker plate again, a weed membrane (black and very plastic looking) and another layer of scrapings, then whacked it again and finished off with MOT type 1. A final whacking, then coarse sand levelled off (see fall away above) and pavoirs to finish. Fine dry sand to fill the cracks and whackerplate over the top to settle it all down.

It may not be scientific or right, but it worked for me.

Most pavoirs, sand and edging stones were obtained "free" by an internet website called FreeCycle and the membranes were given to me by a local road laying company, who had offcuts that were only going into the skip as unusable. My only expenses were hiring the digger and buying/delivery of hardcore and scrapings. MOT type 1 was another free gift from someone elses project that went wrong.

My total cost so far, is under 500 quid.

 

[WabbitPoo]

18" of excavations? What you gonna use it for - parking a tank?

 

[Hipokondriak]

Nah?
Duh?
The original garden soil level was about 20 inches above DPC. So, to end up at the right level of 5 inches below DPC (roughly 1 and a half bricks), I had to dig out a long way. As for the amount of backfill, hey, it was cheap and I didn't know any better (at the time). I had read up on it and as it was going to be a dual purpose patio (car park and sun area) I went for the worst case scenario. As I did it myself, paying for tool hire as i went, I had no-one to correct my mistakes.

Sorry, should have given the full story: I moved into "new" council property, and previous tenant had abused the garden and stacked loads of soil near the house, which had to be cleared away. Decided to lay a patio area, hence depth of dig out.

I have a blog going on The Garden Network. I started it after I had been working on the garden a few months and started posting a blog about my experiences. The novelty has worn off a bit, but it is about as up to date as I can keep it.