The Brew Cabin

Posted: **Mon Apr 07, 2014 11:12 am**

Hi All,

I have read most of the paving expert and understand laying over an old patio is considered a no no and think I understand the reasons why. It still hasn't put me off from asking this question though.

My existing crappy patio is about 400 mm below the DPM. I want to raise the level of the patio. Down the side of the house is a solid concrete base that is at a higher level that I also want to lay flags on to.

I was considering laying a 100 mm concrete base over the existing patio in order to raise the level to the same level as the concrete down the side of the house. I would bond the concrete to the existing patio by jet washing and then coating it with an EVA coating which aides bonding to the new concrete.

I was then intending to lay a bedding mix with the slabs on top of this over the whole concrete area. Its about 40 m2 of existing patio plus 10m2 down the side of the house.

Is this a stupid plan taken in to account its only for a garden patio?

Posted: **Mon Apr 07, 2014 3:09 pm**

yes it is :;):
I know it always seems like hard work breaking up something existing but if you leave it you run the risk of your lovely new patio cracking and dropping
without seeing the site,the best way is to break everything that is going to be flagged but leave the hardcore in situ
then add type 1 and compact with a wacker plate

there are loads that will say just go over the old stuff but it is *NOT* correct and you may live to regret it

better to do it right once and have it last a lifetime

cheers LLL

Posted: **Mon Apr 07, 2014 6:52 pm**

Many thanks, I thought as much but still had that "why not" niggle.

So are you saying hardcore, type 1, binder and no need for concrete layer???

Posted: **Mon Apr 07, 2014 10:36 pm**

concrete layer would be a waste of money
LLL

Posted: **Tue Apr 08, 2014 12:04 pm**

So, if existing patio os 400mm below DPC, that means you have a maximum of 250mm to overlay.

Admittedly, it would be better to rip out the old patio, but if you did want to leave it in situ, a 100mm thick (any less than that will just crack) layer of mass concrete on top would be OK, I reckon, as long as that existing patio is sound, and not moving or settling. I wouldn't obsess about the over-layer bonding to the old, either: at 100mm thick, it's not going anywhere and as a patio, the loadings are minimal.

You could lay the new flags directly onto the concrete or use a 20-30mm bed of 6:1-ish mortar

The Brew Cabin

Diy help - Overlay existing base