Polished concrete - C20 or stronger?

[seathan]

Does anyone have any experience with this situation?
We're pouring a 80sq/m slab indoors for a kitchen floor. the substrate is Type1 bedded and blinded, DPM, 100mm kingspan for U/F/Heating.
We have allowed for a 100mm slab/meshed but are concerned
a. that the grinder polishers are bloody heavy and vibration is severe.
b. whether or not we should use some admix to enhance the polish finish or is this detrimental to the strength.
I know its a curly one but worth a shot!
Any input would be appreciated even if its speculation.

[Ted]

I think you want to give the concrete at least a few days before you polish it. I'm not sure of the optimum time.

Ideally you want to do a test run so as to have an idea as to what the floor will look like. You will never know 100% how it will turn out as factors pretty much beyond your control such as how humid it is on the day of the piur may well affect the concrete's final appearance.

I would ask an American at www.decorative-concrete.net. Americans love polished concrete floors and you should find a knowlegable contractor who will be more able help to you.

[Ted]

I would say any admix is a good thing as it will reduce water content.

Are you colouring the concrete or using any fancy aggregates?

[bobhughes]

Have a look here and scroll down to "The Specification of Burnished Concrete Finish"

This comes up as a pdf file with a full specification for this type of floor. Over the top for your application but I think you will find it helpfull.

[seathan]

Many thanks guys todays the big day, the only coluorant were using is white (snowcrete) and some beach pebbles inset for effect after polishing. We have done samples and had them polished but who knows the sand will be different the aggregate slightly off ITS A LOTTERY!
Many Many thanks, here we go.

[lutonlagerlout]

let us know how you get on , a picture even
cheers LLL

[Suggers]

If only you were talking about polished plaster, then I'm your man - our new neighbours have just gone for it - have to say it looks fantastic - they have 3 young kids - the crayon just wipes off.......!!

[seathan]

Didn't get started yet the underfloor heating guys didn't get finished on time. Will post some pics but it will be a while before we can polish it up, they reckon a month curing time. better safe than sorry.

[lutonlagerlout]

do you have to powerfloat it when its laid ? or is it just a tamped finish?? sounds interesting
regards LLL

[seathan]

Hi LLL, we mixed with two mixers on site as a delivery was out of the question. we managed the finish with tamping and then a fresno with all the extensions, we had a laser level set up to double check all the way through, it has a couple of lowspots but the grinder polisher should take them out, we ended up using an all in ballast at 4:1:with ronafix as an additive, not cheap stuff but I'm assured it with give us a much better finish. We threw in some interesting stones on top to expose when we polish cant wait to see the end result I will have to sus out posting a photo or two.
I found out an interesting thing about normal admix/plasticisers thats probably common knowledge to everyone else, they work but entraining air into the mix, so not the best for a polished finish, would probably end up looking like a crunchie bar!

[Ted]

Not all ad mixtures entrain air. For instance, if you just add some latex to your gauging water that is not going to entrain air, is it!? Adding some latex will reduce your water content and thus make stronger concrete. You can get ad mixtures in the US specifically for polished concrete.

When are you going to polish it?

Assuming it is Type 1 OPC that you used I would guess that at about seven to 10 days is about right. At this stage the concrete will have a lot of strength but will not be at full strength which it reaches at about 28 days. I think that if you leave it too long it will cost a fortune in diamond grinding and polishing pads.

But you don't want to do it too early either.

BTW: I have a book on polishing concrete but it is in storage but I am hoping to retrieve it on Thursday so may be able to answer some of your questions then.

[lutonlagerlout]

cant wait to see the results,you mentioned a fresno is that one of the tools they use for getting concrete flat??
i am a bit ignorant on concrete finishing ,other than brushed and a bevelled trowel
i think concrete as a surface has been much maligned because of some of the crappy ballast you get served up at a lot of builders merchants
cheers LLL

[lutonlagerlout]

??? a gremlin in here?
LLL