Building question -- floor matching

[space.dandy]

Hi all,

I've just had a conservatory installed, which involved knocking through an external wall. The plasterer is due next week to put down the floor screed to a level that matches the interior floor. I have a problem figuring out how best to make good the gaps, etc. Here is a drawing showing the problem.

I need to put some kind of barrier, shown in blue, for the screed to sit on, or extend the level of the flooring out to the exterior line of bricks some other way. The two lines of bricks are at slightly different heights and not quite parallel, and also the level of the floor boards is not quite level with the brick work -- I can't simply add more floor boards.

What's the best way of tackling this? I thought about using some kind of fine steel mesh across the bricks and to the floor boards, or is that too much of a bodge?

 

[topchippyles]

Can you not bring the interior floor through to bridge over the brickwork and screed up to it,The brickwork will support the floor and not effect the cavity.Not sure if you have laid a new internal floor or its existing.

 

[user22161]

Maybe knock a brick course or two off, lay some dpc then bed cut paving stones or similar on that, with screed over.

 

[MikeG.]

Graham has it right. Knock a brick off each skin, lay slates across them bridging the cavity, (there should be insulation in the mix somewhere, them screed over. Leave the screed X mm down to allow for a floor finish in the conservatory.

 

[space.dandy]

Thanks for the replies. I think my attempt at a drawing has misled slightly. The conservatory concrete base is already laid and is level with the solid grey line, which is at the base of the top course, on top of which is the old house DPC membrane. I can only see one course of bricks at this point.

The wooden floor boards are pre-existing, and the top of the boards are only 2mm proud of the interior bricks at one end and 12mm at the other, so I can’t just extend the boards over the bricks.

 

[space.dandy]

Forgot to add, the last step of the conservatory flooring is the screed, which is supposed to bring the level up to match the floorboards.

 

[MikeG.]

Thanks for the replies. I think my attempt at a drawing has misled slightly. The conservatory concrete base is already laid and is level with the solid grey line, which is at the base of the top course, on top of which is the old house DPC membrane. I can only see one course of bricks at this point.

The wooden floor boards are pre-existing, and the top of the boards are only 2mm proud of the interior bricks at one end and 12mm at the other, so I can’t just extend the boards over the bricks.

Seriously, do another drawing then, and I'll give you a proper answer based on that.

 

[space.dandy]

Perhaps a photo is better. Excuse the quality, I had to use flash as there’s no lighting in the conservatory at the moment.

The difference in height between the bricks is exaggerated by the photo, but is around 12mm. You can see part of the old exterior of the house on the left that is now an interior wall of the conservatory. At the far left, the floor boards are only about 2mm proud of the brickwork.

 

[MikeG.]

I can't see any problem with my original advice: take the top course of bricks off each skin, bed some slate on mortar, sort the DPM out, and screed up to the required level.

 

[space.dandy]

Ok, thanks. A few follow up questions, and sorry if I’m being dense:

1. If I remove the course of interior bricks, I’ll be left with a big void all the way across. How do I seal that? Just nail some ply to the ends of th joists?

2. When you say slate, is that the type of stuff I’d find at B&Q, or is there a specific type?

3. What exactly needs to be done to ‘sort out the DPM’?

 

[user22161]

Still a bit hard to see existing construction. From your drawing, I guess the floor joists are much deeper than the same depth of the single brick course you show and, in the photo, the inner leaf looks to be level with the underside of the floor boards. How far back under the joists is the supporting wall? What are the differences in height between the different levels - underside of floor boards down to brickwork and from there to new concrete floor?

Bearing in mind the screed needs to be 2 - 3" thick, it appears you could just remove the top course from inner and outer cavity walls and bridge across with slates (old fashioned grey roofing type from most builders merchants) and butt the ends against the wall supporting the joists, with dpc underneath and turned up to underside of joists. Alternatively, knock two courses off and use something thicker such as paving stone. I would be tempted to box the joist ends and underside.

 

[space.dandy]

Here are two more photos in daylight which hopefully show more detail.

The ruler illustrates the height difference. At that point the top of the inner brick is about halfway up the floorboard. There is about a four inch gap between the joist supporting wall and the inside brick line. The ends of the joists are about an inch and a half behind the brick line. The pipe along the internal bricks is either gas or mains water, unsure which.

Is it necessary to remove the brickwork? Could I not just cement the slate bridging the gap on top of the existing bricks?

Where does the DPM go in the slate/mortar/DPM sandwich? If it’s underneath, what stops everything moving? (Does mortar ‘stick’ to polythene?)

I will need a new piece of DPM, since there is not enough excess to use. Do I need to Bond the two pieces together somehow, or is the weight of the final screed enough to ensure a seal?

Sorry, so many questions...

 

[MikeG.]

Take those bricks out, seriously. One floor should run right through to the edge of the other, without brick between. That's just another line at which a crack will occur otherwise. The brick-to-wood height difference is irrelevant, so I am not sure why you keep emphasising it. Get the brick out of there and run the screed through to meet the timber floor.

 

[user22161]

Agreed, knock the bricks off and get a few slates in to bridge the cavity and the guy doing the screed should be able to sort it.

 

[space.dandy]

I really appreciate the advice, even if I’m a little slow understanding it!

I understand your point, MikeG, that the two floors should meet, but that means either the wood needs to extend out or the screed needs to extend in. At the moment there’s a big hole in the floor. Your suggestion is to take all the bricks out and bridge with slate, which will cover that hole but leave an equally big hole along the face between the floorboards and the slate. Screed is just runny cement, isn’t it? So what’s going to prevent the screed from just disappearing down that hole? That’s what I’m trying to understand.

GrahamF is saying that the screeder should be able to work that out, and if so then that’s fine with me. However, following your advice there is one question I need answered: what do I do about the DPM? Do I put something under the slate, or just put the slate down and let the screeder handle any DPM requirements as well?

Again, thanks for the advice, it really is appreciated.

 

[owen]

The screed will be laid on a plastic dpm such as visqueen wont it? Just lnock the bricks out. Fill the gaps between the joists with some timber noggins, slate over the cavity and then visqueen over the top? Or am I missing something?

 

[MikeG.]

I really appreciate the advice, even if I’m a little slow understanding it!

I understand your point, MikeG, that the two floors should meet, but that means either the wood needs to extend out or the screed needs to extend in. At the moment there’s a big hole in the floor. Your suggestion is to take all the bricks out and bridge with slate, which will cover that hole but leave an equally big hole along the face between the floorboards and the slate. Screed is just runny cement, isn’t it? So what’s going to prevent the screed from just disappearing down that hole? That’s what I’m trying to understand.

GrahamF is saying that the screeder should be able to work that out, and if so then that’s fine with me. However, following your advice there is one question I need answered: what do I do about the DPM? Do I put something under the slate, or just put the slate down and let the screeder handle any DPM requirements as well?

Again, thanks for the advice, it really is appreciated.

Screed isn't runny, and it isn't cement, or concrete. It is applied damp, but that's unimportant. Your plasterer will put in a temporary upstand to stop the screed against such that it doesn't "flow" under the floor, and that can be removed a day or two later.

Your questions suggest you haven't much experience with building work, so I reckon your best plan is to have some slates on site ready for the plasterer, and leave everything to him. This is such every-day stuff that he'll know what to do in his sleep.

 

[space.dandy]

Ah, that makes much more sense.

I’m quite comfortable mixing up a batch of mortar and laying a few bricks and slabs, but I know next to nothing about the technical aspects of construction. I’ll knock out the bricks and get the slates ready as suggested.

 

[user22161]

Slate was actually used as a damp proof course many years ago and, looking at the cavity in your photo, I wonder if the course you will be knocking off is above the existing dpm anyway. If the Slates laid lengthwise across the gap don't go far enough, then maybe you could nail some wood across the joist ends. The only screed I have experience with was Staffordshire screeding sand, IIRC 3:1 semi-dry mix so not runny. Pity your conservatory builder didn't finish the job properly.

 

[space.dandy]

Just a quick follow up: I did as advised and removed the bricks, and the plasterer certainly seemed to know his beans -- he did a lovely job of both floors and walls. Interestingly, he put down a layer of polystyrene insulation before screeding, so the gaps weren't an issue.