Filling cavity

[davecooper]

Some time ago, before I moved into the house, a rear window was removed and replaced by patio doors. The cavity wall was knocked down to floor level and the doors fitted into the outer wall. Up until now, I was not sure what had been done at floor level as there was carpet covering this area. I have now lifted the carpet in preparation for the bitumen floor to be levelled prior to fitting a wooden floor. What I found was that the wall had been taken down to about 20mm below floor level and a wooden board screwed to the top of the inner wall, bridging the cavity and bringing the surface level. A membrane had been laid beneath the board.

I now need to do something about the open cavity before I get the floor levelled. I was going to fill it with concrete or mortar up to top of brick level, re-lay the membrane and then continue filling to floor level. The cavity is about 6' long by 2" wide by 12" deep. However, I thought I would check here first that this is the best course of action.

 

[pinenot]

That's actually what a new build would be, except the concrete should not come above the dpm...pinenot

 

[davecooper]

What should I do about a DPM in this area which will comprise the filled cavity and the inner wall width?

 

[pinenot]

I would have thought the bitumen floor would have provided this?
However you may have to put in neoprene expansion tape for any movement, just to be on the safe side...pinenot

 

[davecooper]

I se what you are saying about the bitumen floor. The only reason I asked was because this newly filled area will have wooden flooring on it. Will there be no risk of damp rising in the inner wall or the cavity filling? If not then that's fine, it makes the job simpler. Just thought I had better ask.

 

[davecooper]

As those in the know will be aware, there is no "inner wall" any more, it is the area of the concrete base where the inner wall was and that is not covered in bitumen that I can see. Therefore, I have the bitumen floor which is about an inch thick, then the concrete base, then the cavity and then the outer wall. I am going to fill level with the floor.

 

[davecooper]

Ok, I have filled the cavity and going to leave to fully dry for a few days. I am now at the level of the external wall DPM on which the door unit sits and the top of the concrete floor base. I now need to make up the 20mm or so to the top of the bitumen floor. Can I put down a brush on type DPM layer and then make up the level with cement mix? This area covers the filled cavity and the exposed concrete base where the original inner wall was, so about 200mm or so in width.

 

[pinenot]

I would try a local plastics company, for an offcut of suitable thickness inert material, it would only be a quick phone call...pinenot

 

[davecooper]

I've actually got a piece left over from a past job, large enough to do this. My only concern was sealing it against the outer wall DPM and against the bitumen which has a very uneven edge. I have a tube of rubberised roof and gutter sealant. Would this be suitable?

 

[pinenot]

I would go for it if I was you...pinenot

 

[davecooper]

Will do, thanks for the help.

 

[davecooper]

I hadn't made up the thickness of the bitumen floor when the guy came to survey the job ready for levelling in a couple of weeks time. He asked what I was going to use to level up the step in the floor and I told him I was going to use a sand and cement mix. He said it would be better done with floor leveller and would do this when he did the rest of the floor. He did not really want a strip of DPM below it as I had planned. I don't have a problem with this, however, do I need to use some form of waterproofer on the exposed concrete base and on the mortar mix that is filling the cavity prior to him putting down the leveller?

 

[pinenot]

When you have to many fingers in the pie things become confusing, for all may I add, so try and get the best answers you can from the tradesman and go with it...pinenot