The Brew Cabin

Posted: **Thu Feb 17, 2005 9:52 am**

Hi. An expert opinion would be a great help.
I'm about to lay a smallish flag stone patio in my garden. From the info gained from the site i'm happy with the patio part of the project. But there's a 1m wide (4 inch deep) contrete path/edging between my house and the area for patio'ing, this is casuing me a headache. The issue is... this concrete looks old and is cracked in a couple of places but to patio over will be too high for my DPC and to remove will be lots more work - can i lay my new patio flags about 1 inch higher than this existing concrete path edging and then lay 1 inch of new concrete over the old to make them meet at the same hight. Will this process of laying new over old concrete be strong and will it bond sufficiently?
Advice will be greatly recieved.
thanks, Ben

Posted: **Thu Feb 17, 2005 6:17 pm**

You could try adding a bonding agent into the top layer mix to ensure that it adheres to the substrate sucessfully.

There are a few around based on epoxy, acrylic or polyvinyl acetate.

some info here:

http://www.symons.com/products/brochure/chemical/07ba.htm

Posted: **Fri Feb 18, 2005 2:00 am**

If the old concrete is cracked, there's a risk of what is known as 'reflective cracking', which basically means the new concrete is fairly likely to crack in the same place. As the old bits of concrete move, even if it's only ever so slightly, stresses are created in the overlay and these stresses tend to focus on the pint of maximum movement: the exsiting cracks.

However, there's no structural reason why you couldn't overlay the existing. A bonding agent is a good idea: it won't eliminate the risk of reflective cracking, but it will help the new overly resist the stresses, and, if a strengthening agent is used (such as Ronafix or SBR) then the overlay could help tie together the old concrete pieces.

Would it not be possible to lay one of the mesh-backed paving products directly over the old concrete? These would be much better at coping with any slight movement of the old slab pieces and, if you choose the right product, could look quite snazzy with your new flagstone patio. CarpetStones from Bradstone would be the obvious choice is you're using a concrete paving, but Rock Unique (amongst others) have "real stone" versions that use 25mm slips of porphyry to achieve the same effect.

Posted: **Fri Feb 18, 2005 9:23 am**

Hi. Have to say I had not seen the mesh products and they look great. Thanks for the tip.

The Brew Cabin

Contrete conundrum - Advice on concrete edge of flag patio