new patio concrete too high

[Christo]

I've just returned from 3 weeks away to find that the contractor who poured our new back patio concrete has set it too high! At best it's level with the house floor and we originally had in mind to tile the patio. Water isn't a problem as we will be roofing the whole patio (11m x 6m) and he has put good fall on it anyhow.
Any suggestions for grinding 5mm off the concrete or similar? (Please, no jackhammer jokes...I'm still in a fragile state after discovering this little problem this morning!)
Thanks
Chris

[Terrian]

I've just returned from 3 weeks away to find that the contractor who poured our new back patio concrete has set it too high! At best it's level with the house floor and we originally had in mind to tile the patio. Water isn't a problem as we will be roofing the whole patio (11m x 6m) and he has put good fall on it anyhow.
Any suggestions for grinding 5mm off the concrete or similar? (Please, no jackhammer jokes...I'm still in a fragile state after discovering this little problem this morning!)
Thanks
Chris

Could hire a grinder from Kennards, about $100 mark depending on which state you are in.

http://www.kennards.com.au/

[silentC]

I'd be wary of grinding down a slab in case your steel is higher than you think. It should be deeper than 5mm but you are reducing the cover.

Anyway, if you are planning to tile, taking 5mm off still means you'll be at least 3 or 4mm higher than the slab is now by the time you finish.

What I would do is approach the contractor, pointing out that it's his stuff up, and let him know that you'll accept having him stencil it for the cost of materials. It will be as good, if not better than tiles, only a couple of mm higher than it is now, and cheaper.

[sports fan]

dont know what sort of arrangment you had with the concretor (contract?) but if you dont give them an reduced level (RL) or finished floor level (FFL) what can they be expected to work to?

i would be chipping off the concrete where ever needed to get the right height, if you expose any steel just treat it. it will be covered by the tile bed and tiles which will be under cover anyway... grinding will take ages and make mega dust for you

[dazzler]

What I would do is approach the contractor, pointing out that it's his stuff up, and let him know that you'll accept having him stencil it for the cost of materials. It will be as good, if not better than tiles, only a couple of mm higher than it is now, and cheaper.

Top idea re the stencilling, though to expect him to pay would be based on the fact that he was told the finished height initially.

[silentC]

i would be chipping off the concrete where ever needed to get the right height, if you expose any steel just treat it. it will be covered by the tile bed and tiles which will be under cover anyway... Would you seriously consider doing that? Bashing off the top layer of a slab and exposing the steel and then, what, just whacking on some cold gal or something? And laying tiles over it? Would you really do that?

Yeah, re the payment, if it's your fault and you didn't tell them you didn't want the patio higher than your floor inside, you'd have to suck it up. You can't expect tradesmen to use common sense. :)

[Chumley]

We've got cycle paths and foot paths made out of concrete slabs that lift and buckle - the council workers come by now and then and grind the bits that stick up - looks like some kind of giant angle-grinder track. If your steel is low enough it might be a good way to lower the level, but it's a bit like breaking eggs to see how they work...
Cheers,
Adam

[sports fan]

Would you seriously consider doing that? Bashing off the top layer of a slab and exposing the steel and then, what, just whacking on some cold gal or something? And laying tiles over it? Would you really do that?


the steel should have 30 - 40mm cover of concrete over it so i would doubt he would even expose any steel, it sounds like not that much has to come out... as for laying the tile bed over it the rougher the concrete the better bond the bed will have to it

[silentC]

Well yeah but tile grout is not a real good seal and if any water can get to the reo it will rust and pop the slab. You're also reducing the cover over the steel, which is usually specified as minimum. 30 or 40mm might be 25mm in reality, or even less, depending on how fussy the guy was about getting the chairs level. I'd be thinking carefully before I started hacking away at it. Just seems like not that great a solution to me.

Anyway, I still think the easiest and cheapest solution is to stencil it.

[Ashwood]

Would you consider having a polished concrete finish? I recall seeing some threads on polishing n applying a finish to the concrete and have that as your final floor finish.

[Ronaldo451]

You're not seriously considering grinding down 5mm over 66 sq mtrs of concrete.....seems like a lot of time, effort, expense and dusty inconvenience. The suggestion about stencilling is a great idea, polishing the concrete presumably would not require a 5mm depth but is a job for the pro's and could get xxxx'y.

If the levels are comparable could you extend the same tiles into the room ajoining the entry to the patio area - ie make the indoor/outdoor continuing level a feature? If not, how about just to the inside edge of the entryway reveal with a bit of quad or similar to soften the rise.

I'd really be considering every alternative before hacking into the slab - good luck.

[dazzler]

You can't expect tradesmen to use common sense. :)

Then the complaint might be;

My concreter poured the slab 10mm too low and now I trip on it :p

[Terrian]

I'd be wary of grinding down a slab in case your steel is higher than you think. It should be deeper than 5mm but you are reducing the cover.

errr, if the steel is that close to the surface I would be very concerned what other stuff ups had been done !!!

[silentC]

I'm not concerned about exposing the mesh, it's just reducing the cover, that's all. If it's already a bit high in places or where mesh has been lapped, or if he's used the top slot on a 65mm bar chair you might be starting to get a bit skinny. I guess we have minimum cover - 25mm I think - for a reason, right?

[Ashwood]

How'z bout raising the rest of the house?

er... sorry, bad joke :doh:

[Terrian]

I'm not concerned about exposing the mesh, it's just reducing the cover, that's all. If it's already a bit high in places or where mesh has been lapped, or if he's used the top slot on a 65mm bar chair you might be starting to get a bit skinny. I guess we have minimum cover - 25mm I think - for a reason, right?

the idea is to have the steel close to the middle, or a little lower than middle, concrete, as strong as it may seem is not all that great with compression strength (lay a slab down, start adding weight, the first place cracks appear are at the bottom of the slab)

If the slab was 75mm thick, the concreter has no business using 50/65 bar chairs :)

[silentC]

An old engineer that I hired once told me that he likes the mesh to be no more than 25mm from the top of the slab, because when the slab cracks, as all slabs do, the cracks will be in the bottom of the slab and not the top. This bloke knew concrete - he was the engineer at the Sydney Show Ground and was in charge of making all the suspended concrete ramps and so on that the horses walk on.

He'd been an engineer for 50 years, so who was I to challenge his opinion :)

[sports fan]

stencilling is a pretty big comprimise to make if you originally wanted tiles as i personally reckon its the tackiest look you could go for

[silentC]

It seems to be popular enough, so maybe you have poor taste :)

[sports fan]

if you say so i havent seen any stencilled patios/ driveways in any magazines lately.. just seems to be on mcmansions in the western surburbs of sydney, but if you like it mate no worries

[silentC]

I don't read magazines because they only publish what their advertisers want people to see.

I don't spend any time in the Western suburbs of Sydney either, so I'll bow to your better knowledge on it. No, you're right mate, rip the top off it and whack down some tiles, she'll be right. If you expose any steel, "treat it" whatever that means. We'll be long dead before it becomes a problem.

[Ian Smith]

Christo - Where the bloody hell are you?

[silentC]

He's done a runner.

Sports fan, I'm only winding you up, don't get upset :)

For what it's worth, I reckon tiles can look pretty tacky too. I like the ones with the paver sort of look about them - a bit of texture - not that glazed look. I think they'd be a bad choice for outdoors anyway - slippery when wet.

The stencilled concrete can look pretty good if you stay away from the bright colours. I've got a bit done around my place and it's the blue stone colour. It's only a small area that we wanted to concrete anyway, so thought why not spruce it up a bit. Looks pretty good I reckon. My place is far from being a McMansion though, so maybe that's why.

[sports fan]

silent c you sound like a text book builder, in a perfect world it would be lovely if everything slab/ column etc the proper 35mm cover or whatever it is but that isnt reality...

i have worked for some of the best respected builders in the business and when ever we have exposed reo we treat with a 2 part epoxy a its made by epirez

its just part of building with concrete that sometimes the formwork is wrong or the levels wrong or client changes mind.. you deal with it

what old mate was talking about was a slab on ground with tiles over it and also pergola over hardly the most exposed location? if he said it was a suspended bridge over a river or lake or something i would have offered different advice

[silentC]

Who said I was a builder at all? I'm just a 15 year old kid playing on his parent's computer.

[silentC]

Sorry, I'm being a smart asre now.


it would be lovely if everything slab/ column etc the proper 35mm cover or whatever it is but that isnt reality...But what you said kind of proves my point "in reality". In reality, you don't know where the steel is. I reckon you'd only uncover it if you really had to. I've seen spalling and it makes a mess of a slab. It would lift the tiles up and crack the slab if it happened.

So I'm not saying that even the 'best respected builders' in the business don't sometimes do it, but you'd prefer not to, right? And if there was an acceptable alternative that wasn't going to take a lot of effort you take it, wouldn't you?

I still don't think 5mm would be enough anyway. 5mm tiles, you're back where you started and then you have to allow for the glue and it's already higher than the floor inside.

[bricks]

The Problem here gentlemen, is that the back patio is now illegaly built.

The patio height must be below the height of the main house.

If someone called the local building authority, had them inspect, I'm reasonably sure that the contractor would be told to lower the slab to legal height.

That is of course not a nice way to go about it.

[autogenous]

reo is pretty much placed where the tension will occur

mesh is a shrinkage crack preventative

tile straight up to the door with a good flexible tilers glue and seal between tile and door sill with silicon

[autogenous]

If someone called the local building authority, had them inspect, I'm reasonably sure that the contractor would be told to lower the slab to legal height.

depends where you are but more and more builders are doing this now where there is roof cover to the area

[journeyman Mick]

...............and seal between tile and door sill with silicon

Bad move in my opinion. I was taught a long time ago to build and detail any penetration/possible water entry point as if sealant didn't exist. Sealants can and do fail, gravity never does. If the water can't get under the threshold (sills are under windows, thresholds under doors) then it won't matter if the sealant breaks down. If it can get to the threshold there's a good chance you'll get water into the house even with sealant.

Mick

[Terrian]

An old engineer that I hired once told me that he likes the mesh to be no more than 25mm from the top of the slab, because when the slab cracks, as all slabs do, the cracks will be in the bottom of the slab and not the top. This bloke knew concrete - he was the engineer at the Sydney Show Ground and was in charge of making all the suspended concrete ramps and so on that the horses walk on.

He'd been an engineer for 50 years, so who was I to challenge his opinion :)

to get open cracks on the top in the middle, the ends of the slab have to drop, or the middle has to raise :)

[Terrian]

Who said I was a builder at all? I'm just a 15 year old kid playing on his parent's computer.


:rofl:

[autogenous]

journeyman Mick: Bad move in my opinion. I was taught a long time ago to build and detail any penetration/possible water entry point as if sealant didn't exist. Sealants can and do fail, gravity never does. If the water can't get under the threshold (sills are under windows, thresholds under doors) then it won't matter if the sealant breaks down. If it can get to the threshold there's a good chance you'll get water into the house even with sealant.

Sure Id have at least a 20mm step down from the brick sill. In this case the concrete is level with the sill.

There is fall in his concrete. Silicons are pretty good, especially under cover.
Theres more than one builder who do a level straight through to FFL.
I wouldn't say its great practice but under cover you have two chances of water ingress.
Fat chance and none.

If theres that much water in that area with overhead cover then theres bigger issues of concern.

In this case grinding 15 mm off the top will be a hell mission. It may also reduce the concrete thickness below its structural need.

I agree journeyman Mick, your definitely right. Build with failure in mind.:)

[silentC]

to get open cracks on the top in the middle, the ends of the slab have to drop, or the middle has to raise :)
Yup I'll admit right now I'm no expert on concrete. Only just mastered the broom finish on small areas :-

I think the type of crack he was talking about are the hairline ones you get as the concrete contracts, not open gaping cracks. The idea of the mesh being near the top is that it holds the top of the slab relatively intact and allows the bottom to expand and contract. I should have paid more attention, I was still trying to deal with the concept of the stuff moving once it has set.

[autogenous]

To deal with surface shrinkage cracks is to run a sprinkler on the concrete 10 hours after the initial pour for 24 hours.

Mesh prevents cracking or crazing placed in the place of tension which is 25-50mm below the surface.

There is modern fibres etc which can be added to the concrete to prevent cure crazing cracking.

Too much water can cause shrinkage cracks.

Too much heat such as 38 degree days and over accelerates the curing leading to cracks.

Modern concrete building structure floors are surface sprayed with a resin to slow the evaporation from the surface of the concrete to prevent cracking.

In the past some concrete pads especially multistory were ponded with a mix of 3:1sand/lime around the edge then filled with water to an approx half an inch. Once the slab had been ponded for a few days the lime sand edging was removed with a scraper.

[sports fan]

Who said I was a builder at all? I'm just a 15 year old kid playing on his parent's computer.

i didnt say you were a builder your obviously far far from it, i said you sound like a textbook builder

[silentC]

Yep you're right, I'm not a builder, never said I was, but I do hate dodgey work. I've seen plenty of she'll be right behaviour from builders and tradies too, so don't think that just because you're one of the most respected builders in the business or once worked for one that you're against cutting the odd corner, right?

You just keep hacking at those slabs, mate, she'll be right. Just keep away from my place and we'll all be happy, OK?

[Terrian]

Yup I'll admit right now I'm no expert on concrete. Only just mastered the broom finish on small areas :-

broom finish is good, provides some grip when walking, and getting the brushed look is an art in itself :)


I think the type of crack he was talking about are the hairline ones you get as the concrete contracts, not open gaping cracks. The idea of the mesh being near the top is that it holds the top of the slab relatively intact and allows the bottom to expand and contract.OK, I think I see where he is coming from, I personally would be adding 2 layers of reo, top & bottom if I was that concerned.Or I would use just the 1 layer of reo, and have fibremesh added to the mix


I should have paid more attention, I was still trying to deal with the concept of the stuff moving once it has set.:)

[Terrian]

Mesh prevents cracking or crazing placed in the place of tension which is 25-50mm below the surface.
There is modern fibres etc which can be added to the concrete to prevent cure crazing cracking.


there were times when we would add fiber glass fibers (about 6" long) or steel 'pins' (about 1mm thick, 5" long) to the mix in the barrel, mainly when to pond pours, no need for traditional reo to be used :)