Garage floor - Digging up and laying to a new level

[dig dug dan]

I wonder If someone can answer this.
I have to block pave a drive up to a garage door. At present the drive continues into the garage(it used to be a car port), and it slopes left to right by about 4in. The client wants the floor screeded to match the height of the new drive, which will be level. Halfway down the garage is a step up in the concrete which we are to match up to also.
I have said that the old floor will have to come out as to try and skim it will not work. Besides which there is a row of slabs runnning up the middle of the floor.
My query is this: If i break out the old floor, do i lay 4x2 against the garage walls to the set height and pour in the 1.5cubm of concrete, level it, let it go off then remove the timbers and fill in afterwards, or is there another way of doing it?

[danensis]

Make sure that row of flags down the middle doesn't cover an inspection pit or you might end up using a lot more concrete than you anticipated!

[dig dug dan]

there is a sewer, but no inspection pit luckily!

[Tony McC]

If I follow you correctly, Dan, you're looking for a way to cast the garage floor inside the existing brickwork and need some help on establishing levels: is that it?

My preferred way of doing this sort of job is to use masonry nails to carry a 20mm screed rail (or cable conduit) against the long walls at the required level (I like to build-in a fall of around 1:100 for internal garage floors). If masonry nails are used at, say, 600mm centres, they should support the rails quite firmly, so you can tamp or beam screed off them. For long garages, I might use a screed rails that are half the length of the garage.

Tamp or screed out as required then lift out the rails as soon as you can, walk back in on the fresh concrete and screed/float the edges as required to cover up where you went back in.

Another option is to use timber screed rails fixed to the walls at, say, 300mm above the required FFL. Build a screed/tamp to ride on the elevated rails and you can screed all the way out, leaving the rails in place for a couple of days while the concrete sets.

I normally used option 1 (when I was fit!) as I had to trudge back in to get a float finish, anyway. The wall-mounted rails workk well if you've doing a tamp finish or plan on going in with a power float to do the finishing, but for hand-trowels, option 1 is simpler.

[dig dug dan]

Thanks tony. I do have one query with what you suggest for option one. how do I remove the rails if the have been nailed. wont the nails be in the concrete? or am i being dumb and the rails rest on top of the nails?

Thanks for your help tony

[Tony McC]

The rails rest on top of the nails.

[dig dug dan]

Thanks tony. I thought I was being dumb!

[skinny d]

I am laying a living room floor (first timer) and was wondering how long after tamping do you leave the floor before you walk (trudge) back in to float the surface?

I want to get a fairly smooth surface as I shan't be screeding the surface but laying a combination of carpet and slate floor tiles direct onto the slab.

Cheers, Dave

[Tony McC]

There's no fixed time as there are so many factors affecting the hydration of the cement and therefore the 'setting' of the concrete. However, it's usually somewhere around an hour before the concrete is firm enough to float-up without leaving trowel marks. You just have to keep your eye on it!

Usually, with concrete floors for internal rooms, the surface is left low by around 6mm, tamped as smooth as poss when the concrete is poured and then a self-levelling compound can be poured over the hardened surface a few weeks later, when you've done all your other internal works. This eliminates the need to be highly accurate with your levels and to float-up the surface as it sets.