The Brew Cabin

Posted: **Sun Apr 10, 2005 8:15 am**

I need to lay a large floor slab that is up against the side of a house, it is approx 5m wide by 8m long.

When i did a smaller area for a garage base as we barrowed in the concrete we tamped it with a beam and then finished with a trowel as we moved along approx 0.5 meter at a time. however with the size of the area above using a barrow to move the concrete is out of the question (approx 6 cubic meters) so i was going to have a pump as the nearest access is approx 10meters away. this gives me a problem with the compacting / leveling as they are not going to want to hang about half a day with mixer and pump whilst i lay and tamp 0.5 meters at a time. so my cunning plan was to use a vibrating beam. but then i have a number of issues.
1. one side of the slab is up against the house so i have nothing to rest the beam on at that side
2. do i go for very wet mix or a more stiff mix
3. do vibrating beams level in one pass ? if they dont then i have the same problem as in 1. i.e. i can only get at one side of the slab.
4. do i just put the concrete in as wet as i can and then use an easy float to finish it ?

or is there another method that i have missed ??

Posted: **Mon Apr 18, 2005 9:04 pm**

What about using a "Mix & Lay" contractor? It's got to be considered as handling 6mÂ³ on your own is just silly. It will kill you!

The usual method is to attach a rail to the walled side of the slab. The vib beam rides on/from the rail on that side and on the free edge on t'other. The exact detail of the rail depends on the site.

Wet mixes may seem easier to handle but it's a mistake to think they stay workable for longer. The way that concrete hardens/cures has little to do with the water content: it's all anbout cement content. If you want to delay the curing process and give yourself more working time, you need to request a retarder from the batching plant.

Vib beams do a very reasonable 'level' in a single pass, but we usually make 4 ,6 or 8 passes to get the slab as accurate as poss, and to reduce the amount of float work needed.

For a 6mÂ³ pour, I can't emphasise too strongly the suggestion that you get a Mix & Lay contractor or help from someone that has laid concrete in this manner on previous occasion(b]s[/b] (note use of plural!)

Posted: **Thu Apr 21, 2005 7:54 am**

thanks for the advice.
i had decided that i had two options
1. was to attach a beam to the wall and then cut out the creed beam to fit over it, this way the bottom of the wall battern would be the top of the finished concrete level. disadvantage of this method would be that it's bloody hard work screeding by hand with a wooden beam!

2. use something like an "easy screed" vibrating beam and a couple of chums. i was going to get the concrete pumped and get them to send a lines man so that me and my mates could get stuck in with the screed beam straight away. the only problem that i can see with this is that the battern on the house side of the slab will have to be in the slab, i.e. top of battern level with top of finished floor level. so how do i get the battern out afterwards ??
one of the down sides of this is that the screed beam will cost me approx 150 a day to hire ! and then the bull float will cost me another 30 a day.

not sure what a mix and lay contractor would charge, do you have any idea ?

Posted: **Thu May 05, 2005 10:14 am**

The batten (aka a screed rail) would need to be prised off the wall and then use a long-handled float to patch in the 'groove' formed by its removal.

On site, we would be more likely to use a screed rail that isn't fastened to the wall, but is supported by 'chairs' (pieces of reinforcement steel set into the structure) set away from the wall by around 500mm or so. Once the beam screed has done its work, the screed rail is lifted out and the resulting 'groove' worked out with a long-handled float or by a couple of careful passes of the beam screed.

These screed rails are usually 30x30mm box section aluminium, and some 'professional' systems include special screed rail supports that carry the rails at the required level but are removed with the rail when initial screeding is complete. It's not an easy concept to describe, and I don't have a photo as it's not something you see being done very often.

Given this isn't a very large area, Option 1 would be more likely.

The Brew Cabin

Large floor slab - Laying and finishing large floor slab