Concreting

[neddy]

I've attempted some small concreting jobs before (paths, small shed) and follow what the books say. But always have trouble when trowling and especially when using the grooving tool...the rocks seem to be to close to the surface. I beleive I'm getting it wrong with the floating....After the screeding what is the exact way in which to float the concrete? I watched a driveway get done before and vertually straight after the screeding he used whats called a bull float (metal float on a very long extension pole) he only went over each section once and of course made it look all so easy. So my question to all guys out there is what is the art to floating concrete?

[seriph1]

I will certainly be watching THIS one with great interest

I am concreting DISLEXIC!

[ozwinner]

Firsta up you have to be an Italiano, if you havea no Italiano blood in youa vains.
Give hima miss.

Cheers, Juseppie

[journeyman Mick]

Neddy,
The bull float is made of magnesium alloy (that's why they are horrendously expensive). For some reason mag floats push the aggregate down and bring the fines up waaay better than wooden floats. Maybe someone who knows more about concrete chemistry can explain why. Anyway, if you get yourself a mag float you'll find that you'll be able to bring more fines to the surface (and more aggregate pushed down) this will give you a stronger, denser top layer and should minimise your problems. Also, did you pay attention to what he was doing with the float? The handle controls the pitch of the float, as you need to have your leading edge up at all times. The pressure should be on the trailling edge to prevent dig in. If you are still having trouble with your edges or control joints then use your float in a patting motion in these areas to start with, this will ensure the aggregate is pushed well down. Good luck,

Mick

[bitingmidge]

Try this link for a very brief overview of the process and tools:Marshalltown.com (http://www.marshalltown.com/howto/concret06.htm)

The magnesium float is used as I understand it because it is light weight and easier to "float" over the surface, as was the original intention of "wood" floats. Probably no chemistry, more a question of ease of use, particularly when one is holding a large bull float at the end of a long pole.

Sharing the same dyslexia of all things in need of trowelling, I am of the view that concrete, like plaster work is best left to someone whose genetic disposition is more suited to such things.

Cheers,

P

[journeyman Mick]

No, ther's definitely a difference in how the two floats feel. I haven't used a bull float often (and hope never to do so again) but there is a difference in how concrete behaves under a hand float of wood to one of magnesium.

Mick

[neddy]

Thanks fella's...........I did notice the contractor useing the following edge of the bull float so as not to dig it in. Is it possible to use a hand magesium float for large jobs like a drive way or am I being optimistic. Also what's a good size mag float to purchase? Also if you overwork with the float does that cause problems? Chow

[soundman]

the concreete companies should all have some good information that helps. QCL do a real handy brocure.

Don't expect to get good overnight & practise on small sections like a path or a little slab till you get the feel.

If mixing yourself measure accurately.

Marry into an italian family.

[journeyman Mick]

Neddy,
at a pinch you can float a driveway with by hand. I've done a 8 x 3M slab by shifting an ally plank around over the top and floating off of it. Takes ages and is not too good for your back (I pulled the pin on that builder not long after!) Just hire a bull float when required, doesn't cost too much and you'll only need it for the morning anyway. Overworking the concrete can cause problems, you'll end up with a top surface that is always dusty. Not too sure what sort of size range there is for mag floats, mine is about 80mm wide and 500mm long - works for me. I suspect that anything larger (if such an animal exists) would get awkward.

Mick

[neddy]

Thanks Mick.....I'm gunna buy one. How hard is it to use a Bull float....could you practise using it on sand??

[ozwinner]

Hi
I did my own driveway at home all 23x8 M of it, what a pain.
Still it was cheaper than getting it done.

Chow, Juisepie

[journeyman Mick]

I didn't find the bull float too hard to use. I'm not concrete dyslexic but I'm not genetically predisposed to it either. I guess you could practise on sand, that'll help you get the action right, however it won't prepare you for the timing aspect. Working with concrete is all about timing and being able to read the stuff to see if it's ready for the next step. Not something I'm too good at, but I think subconsciously I never wanted to be very good at it. Meant that I was usually one of the last people on a job who got told to drop his nailbag and lend a hand.;) (did I mention I hate the stuff!)

Mick

[ozwinner]

The first job I did on this house was to concrete the back porch, the concrete took soooooooooooooooooo long to go off.
I poured it a 8.00 am, and didnt trowel it off until 4.00 pm.
When I enquired at the local plant as to why? They said, oh that would have been the retarder in it, maybe we put too much in it.
So on the next job, the carport, I said no retarder.
Guess what, it was 35 degres c, and it went off as soon as it come out of the shute, the sweat dripping of my head help it a bit though.
The carport is still rough, but it has got grip.

Al

[journeyman Mick]

When I did the slab for my shed the plant accidently put 3 times too much retarder into the last batch. All the rest of the slab was steel trowelled and there was this section which I couldn't even float yet. Ended up floating it under lights at about 10pm and trowelling it at 6am. I hassled the plant about it and got the bill reduced.

Mick

[neddy]

What actually is the retarder. It's not just adding water to give more time before going off is it?

[journeyman Mick]

Neddy,
a retarder is a chemical additive that slows the concrete without having to add water. Tip: if you find that the concrete is going off faster than you can float or trowel it use a sugar and water mix (as much sugar as you can dissolve into the water) and sprinkle it lightly on top, this acts as a retarder. (as does lemon juice in plaster).

Mick

[silentC]

Some concretors like to add extra water to the concrete as it comes off the truck, or they'll ask for extra water to be added when it is mixed. This makes it easier to work and gives them more time. I was told by an engineer not to let them do this as it makes the concrete weaker.

The message is that you need to have a light hand if you're adding water to it (like Mick says 'sprinkle'). Don't think that adding extra water to the mix to stop it going off is not going to have a downside.

[Dion N]

The water in a concrete mix reacts with the cement and is "used up", ie it undergos a chemical reaction with the lime?? in the cement. The reaction happens quickly at first and then gradually tapers off so that your concrete is never 100% completely dry (although 99.9% is close enough for all practical intents and purposes) At 28 days, the concrete is pretty close the maximum amount of hardness and strength, hence the reason engineers specify a "28 day strength of so many MPa" for buildings and why test cylinders are tested after 28 days.

If you add too much water, the reaction between the water and the cement consumes all the cement, but not all the water and water is not a particularly good building material... :)