patio- use existing base or start again?

[dendenden]

Hello all.
I could do with the advice of some people with more experience than myself at preparing a base for a patio.

I recently bought a house and the patio in the back garden (made from two different levels) had loose slabs, which were far from our taste. Most of the slabs came up easily by hand; they were attached by dabs of mortar as you can see from the photos.

I’d like to prepare another base, all of one level, and extended it back toward the house slightly more and into the space where the metal tank is in the first photo.

The existing concrete lower base is in fairly good condition, apart from the patch as seen in photo 4. My original plan was to knock the lumps of mortar off the lower area so that’s flat, hire a breaker and remove the higher level section, make a frame and pour concrete into the areas that need it to the same level as the existing lower section (I’d ensure there was a slight slope for water run-off away from the house as there is now.)

I’m now thinking though that it may be best to break up both areas (higher and lower), then hire a compacter to for the hardcore to make a flat bed of at leat 10cm to the level of the tarmac, then lay slabs onto this onto a full bed of mortar. My slight concern with this approach though is that the level of the patio would then be an inch or so below the soil level, taking into account the mortar and the slab thickness.

Can anyone see a problem with this plan? It would involve laying mortar onto some of the tarmac sections with the slabs on top of that, and then having the run off a little lower than soil level. Or would it be best to build up a concrete base at the same height as the existing lower section, then paving on top of that.

I hope this makes sense, if anyone’s cringing at my obviously inexperienced plan, please do let me know what I’m missing.
Thanks in advance, Den.

 

[Halitosis]

I'm certainly no expert (so take my comments with a pinch of salt) but why break up what appears to be a solid/proven base and then try to compact it? A good base is usually made of MOT/type 1: specified amounts of various sized parts (stones down to dust) that compact to make a firm, stable, and gap-free platform. I imagine smashing up what you've got would lead to large pieces with gaps between (no matter how much you try to compact it) which might cause problems down the line.
I prefer your original plan, though be sure not to compromise the damp proof course on the house - I brought my patio up to house floor-level and it makes the patio more like another room with no difference in level. This website has a wealth of information: http://www.pavingexpert.com/dpc01.htm

 

[r896neo]

If you plan to fall the patio towards the grass then it obviously must be high enough to allow that? You could alternatively install drainage between the grass and patio but that seems unnecessary.

What will the finished surface be on the path near the house? Can you fall the patio back to the house? It looks like your dpc might be miles up in the air? what level is it at?

 

[dendenden]

Thanks for the advice above both of you. Yes, it would seem a shame to remove a perfectly good surface, but once the higher section is removed, I'm thinking that I would then have to raise the other areas in order to bring them up to the same level. Thanks for the info on MOT- type 1- I assumed the hardcore would be enough but understand the logic of needing a base you can compact.

As for the runoff onto the grass, it would be a little below soil level (approaching an inch after allowing for the height of the flags and the mortar). I can't see the DPC level, so Im assuming it would be above where mortar covers the brickwork otherwise it would bridge it? In which case I would still have plenty of height if the patio went back to the wall.

I'm planning on using natural sandstone.

I'll do a little more research then make a decision. Thanks again for the help.