Resin bonded gravel over unenven base - Resin bonded gravel over unenven base

[damiantaylor]

Hi guys,
I want to cover an old, ugly concrete patio with resin bonded gravel and have a couple of questions I'm hoping someone can help me with...

First off, the biggest issue is the fact the concrete isn't level....it dips in places up to just under 20mm.
Ive had a look at levelling it with something like Ardex K301, but that stuff is expensive! It would pretty much double the cose of the whole project.
So, am I worrying too much about levelling the concrete?
Can I just use regular concrete to level the deep bits or would that fail once I put the resin and gravel over it? I don't want the gravel to crack or start peeling off.
If regular concrete is ok to use, would I need to use levelling compound to feather in the edges where the new concrete meets the old or would the resin bonded gravel hide it?

The other question is regarding a manhole that's set in to the concrete.
I have found recessed manhole covers that can be filled with whatever surface you're using to make it look much nicer, but these covers are typically pretty deep, and usually quote for use with resin bound gravel. As I'm wanting to use resin bonded gravel, which is much thinner (3mm gravel), is there a way I can modify the manhole cover so I can fill it with the same resin and gravel I'm using on the rest of the concrete?
Do I just fill it with concrete up to 3mm from the top, then use the resin bonded gravel for the top coat or would concrete be a bad idea for filling the manhole cover?

Thanks for any advice guys, this is turning from a project I was looking forward to, to one I don't even know how to start!

Damian

[seanandruby]

Is your patio very big? Maybe you could scabble it and overlay with grano, a lot cheaper to buy. You can fill lid with concrete. Seal around the edges and eye holes with tape some tape to stop any grout seeping in the joints because can be a right bar steward to lift off otherwise.

[damiantaylor]

Thanks Sean.
The patio isn't very big at all...it's only 2 meters wide and the area that needs filling, we're talking about 4m2.
I've found a couple of builders merchants (jewson and travis perkins) that sell grano dust in 25kg bags, so I'm sold on your suggestion
Do I need to prime the concrete with anything, or just jet wash it, then lay the grano down?
Do you think jet washing is enough or do I need to scabble with something mechanical? Does it mean I need to get down and scrub with a wire brush?

Thanks again for your help!

[seanandruby]

Fine scabble. Get the 6ml to dust for added strength, or jet wash. Use sbr in the mix. Saturate the slab dry.

[Tony McC]

After scabbling, you need to eliminate as much dust as possible, which can be done with a jet washer or an air hose.

On super-critical jobs, we's often acid-etch the exposed surface, although I usually considered this to be belt, braces, and another belt besides, as the 'old' concrete should be well beyond laitence and efflorescence, but some engineers do like to be extra-double-sure.

Then, prime the exposed surface with a bond bridge slurry. This is really important to the long-term adhesion of the grano, particularly if you're feathering it out at the edges.

Don't worry too much about getting a perfectly smooth finish: a wooden float finish is often better at providing a good key for the resin overcoat.

It needs at least 7 days, preferable 28, before covering with the resin. Any sign of laitence should be cleaned off (etched if necessary) before applying the resin bond coat.

[damiantaylor]

Thanks for the extra detailed explaination Tony - much appreciated!