Concrete Floor Problem

[IanF]

Hi,

Apologies if this is in the wrong section but it seems most relevant to me.

Firstly, this is a problem I'm encountering as part of a larger project, but I'll try to focus on the actual problem itself and not wander off onto the project.

My house has an outside toilet which is part of the main structure of the house with a bedroom above it. There's a rough diagram of the floor plan at the following URL:
http://www.verses.free-online.co.uk/kitchen/kitchen.jpg

I plan on having a builder block up the outside door and knock through a new door (labelled Door 2) and use the outside loo as a utility room.

At the weekend I removed the toilet and associated plumbing. In doing this I broke apart some of the concrete floor so I could remove the top of the soil pipe and cap it off. At the time I noticed (and since then the Building Regs bloke has commented on) the fact that there appears to be a cavity under the concrete floor. The concrete looks to be about 1 to 2 inches thick and broke apart quite easily when I removed the soil pipe. There also doesn't appear to be a damp proof course under the floor.

The Building Regs bloke suggested breaking up the concrete, using it as hard-core then laying a DPC over it and concreting over that. Does this seem like a good suggestion? Can anyone think of other options available to me?

I've little to no experience of laying concrete and while I don't mind tackling it myself I can't see how I'll get it flat as the room is about 8ft long and I'll be working from the outside doorway.

Can anyone offer any tips/advice/suggestions?

Cheers,

Ian

MOD

moved as posted in wrong forum

 

[masona]

This is the nearest drawing I could find.

You may have to dig down a bit deeper to allow approximately for 100mm hardcore or rejects > a layer of soft wash sand ( to protect the DPM from the sharp edge of the hardcore) > DPM (damp proof membrane) to pass the dpc level on the wall > 75-100mm 3/4" concrete > 50mm floor screed for top floor finish (floor screed: sharp sand & cement).

 

[IanF]

Thanks very much for that, looks just like what I needed to know. The only other thing is how long do I leave the concrete to set before applying a screed, and are screeds fairly easy to get level?

Cheers,

Ian

 

[masona]

Got to rush out now unless someone beat me to it , if not I will reply later.

 

[Thermo]

poor old masona, rushing off to the loo again! Ideally you should leave the concrete to set for as long as possible (approx 28 days) this allows it to get to full strength (well not actually as it never stops hardening but thats another story!) and dry out. If this is too long then give it as long as you can. When you do the fllor screed you use a semi dry mix. its wet enough that you can mould it in your hand but no water will drip out if that makes sense. Its fairly easy to get level if you set up right in the first place. if you run two battens down each side of the room and get them levelled up to the right height, you can then fill in the screed in between and use another batten across the top of them to level it off. I always put a nail in each end of the batten protruding upwards and give them a coat of cooking oil so its easy to pull them out when its all done. Hope it makes sense and good luck!

 

[masona]

poor old masona, rushing off to the loo again!

No I don't have that problem anymore

 

[Thermo]

always wondered what you looked like masona!

 

[IanF]

Cheers for the help and advice given

However, problem 2 has arisen.

Last night I broke up the old concrete floor and re-laid it as the hardcore base. Looking at my plan diagram (http://www.verses.free-online.co.uk/kitchen/kitchen.jpg) where the old doorway is to the garden I can now see both skins of the wall.

The doorway is on top of one of them and then theres an inch or so gap then the 2nd layer. Under the concrete there are a few bricks that are placed (not cemented) over the gap. The inner layer is lower than I will need to go with the new concrete floor. Should I build up the inner skin, or should I do like had been done before and just place bricks over the gap and concrete over them?

I'll post a photo of it on my web-space later tonight if that'll help.

Cheers,

Ian

 

[IanF]

Hi,

I've now laid the sand and as promised, I've uploaded the pictures;

http://www.verses.free-online.co.uk/kitchen/loo1.jpg
http://www.verses.free-online.co.uk/kitchen/loo2.jpg
http://www.verses.free-online.co.uk/kitchen/loo3.jpg

As they show the sand comes up level with the inner brickwork. So should I add a row of bricks for the new concrete to go up to? Or is there another route I should follow?

Cheers,

Ian

 

[masona]

Where the door frame is, can you see the damp proof course? If so, is it just under the door frame or the next brick down etc?

 

[IanF]

There doesn't appear to be a damp proof course, as part of this project the doorway is being bricked up and a DPC will be put in as part of that.

Ian

 

[masona]

Okay,

Insulated in the cavity and there's normally a dpc under the door frame cill which should overlap 150mm whenever possible then the dpm (damp proof membrane) goes under the dpc.

Also where the wall meet the outer wall there should be a dpc positioned behind door or window frames so that the wall plaster will not bridge it, this is to prevent rain/dampness entering into the wall. If no dpc, you will have to use a grinder and slot a new dpc.

 

[IanF]

masona, thanks for the advice, but I have to confess to getting a little lost here. I'm inexpereinced at this kind of work so have perhaps missed what you're saying.

My problem is that my layer of sand is level with the existing inner layer of brickwork, so if I just poured concrete on to my damp proof membrane the concrete would pour down into the cavity. I need to know what I should do to prevent this, should I build up the inner brickwork another layer before laying the concrete? Also, if this is what I should do, should the damp-proof membrane go under this new layer of bricks?

Sorry for being a bit dense

Ian

 

[masona]

Use something like Polythene Cavity Wall Insulation to the sand level as it will not transmit water to the inner leaf and also support the concrete base. Remove bottom section of door frame or all of it, a layer of cement with dpm on top at the outer cavity wall, dpc on top of the dpm then a couple row of bricks. Next day pour 3/4" ballast concrete ready for the top floor screed.

 

[IanF]

Thanks again for your help, I think I'm sorted now. A busy weekend awaits.

Cheers,

Ian