Re-laying patio advice

[paul81c]

Hi,

I was wondering whether I could ask for some advice from you fine people...

I'm in the process of replacing my very old patio. I've taken up all the old slabs and want to re-use the old sub base. It feels solid, however, now I've taken up the old slabs it is covered in powdery/gravelly pieces of the old mortar/cement.

I've attached a photo of the current state of play. My question is: What would the best way to proceed from here, given that I want to retain the base? is it OK to lay the new mortar/slabs on top of this gravelly/powdery mortar/cement material, or should I try and remove as much of it as possible? Woud leaving it there affect the adhesion of the new mortar/slab? And how would be best to level it out to proceed, given that there are some lumps left behind?

I can find lots of information online regarding laying a new patio from scratch, but not much at all regarding replacing old slabs and re-using a sub base. I've had a look at Paving Expert and can't find info regarding this scenario.

I realise that to get the absolute best result, I should dig out the sub base entirely and lay a new one, but that's not an option at the moment. This is the first time I've tried to lay a patio and my DIY skills are modest. I really want to give it a go myself though - It doesn't have to be perfect, if it looks better than the old one and looks alright for a few years that's fine. It won't get too much footfall.

Really appreciate advice from people who know more than I do

Many thanks,

Paul

 

[yorksbuilder]

Is that the old mortar, and beneath it is compacted hardcore? How thick are both layers? I think you should do some investigation and see exactly what you are working with

 

[paul81c]

Thanks for your reply! Yep, I believe so. I've just been outside now and dug down - it looks like this. Does that help? It looks to have been built on top of another surface

 

[yorksbuilder]

If your top surface is loose and not made of hydraulically bound material (ie solid mortar) then i would rake it all over, get a plate compactor and re-compact it all. Have a couple of bags of ballast & sharp sand on hand to fill and level any dips that appear. If all remains solid and the surface is 'tight' then you should be OK to go ahead with the new patio.

in terms of levels, it would be best to remove the old mortar first and then do the above mentioned compacting, as this means your new one wil not be higher than the old, which could cause problems with access/proximity to DPCs etc.

as always, ensure your falls are correct and in the right direction for drainage

 

[paul81c]

Thanks for this.
So after you said to find out what I'm working with, I dug down further and discovered that the patio was built on top of another patio. I've attached a photo, but it's difficult to show.

I realise it's not best practice, but I know that you can lay a new one on an old one.
Tearing the old one out isn't an option right now, so I'm intending to build on top again. I'm working on my own and can't pay to have it professionally rebuilt.

However, the old one isn't flat - it looks almost like shallow steps! Its very strange. A total bodge.

I appreciate this isn't ideal at all, and I should replace the whole lot. But are there any tips as to how I can make this work, at least for a while?
Many thanks.

 

[yorksbuilder]

Wow. Try remove all loose & crumbling stuff on top and then you can lay your new one on top of a full bed of wet mortar levelling each slab as you go

 

[paul81c]

Wow. Try remove all loose & crumbling stuff on top and then you can lay your new one on top of a full bed of wet mortar levelling each slab as you go

They're so wonky... I decided to see whats's underneath one of the slabs and its just type 1 - they didn't use any mortar underneath.
Pretty sure it's all too high as well, its less than 150mm from the DPC.
I'm going to pull up all the slabs and start again. I'll be more confident the new patio will last then, and won't be too high.

 

[yorksbuilder]

You won't regret it. Best to do it right

 

[paul81c]

You won't regret it. Best to do it right

I'll let you know how I get on! Will probably post again asking for advice no doubt, I'm very much an amateur!