Levelling floors

Rutigur

Hi, I’ve been reading round here for a while and have seen a thread on a vaguely similar topic but theres other questions I have so hopefully its ok to post a new thread.

I’m completely renovating my 50 yr old house. Hall and utility room downstairs had a terrazzo (marble like) floor and I kangoed this up. Sitting room and dining room had floorboards nailed directly into a concrete floor. These were in terrible nick and I pulled them up as they were very uneven aswell.

Under floorboards was a layer of bitumen – would this have been the only dampproofing?

I intend on putting tiles in hall and utility room and solid walnut floors in sitting and dining rooms. So I intend to pour new concrete onto all the downstairs floors as they are very uneven. For the walnut floor would it be best to lay some marine ply and nail into this or go with rows of battons? Do I need to lay additional damproofing?

What would be the best mix ratio for sand to cement for this job?

I will polybond the floors first to get a good adhesion, but I have also heard mention of an additive that can be used to improve the cement mix to ensure that it won’t crack no matter how thin it is – does anyone know what this is?

Many thanks.

Patto

Hi Rutigur,

Firstly I have more questions than answers, hopefully some of you DIYers out there can set me straight on a few things.

I think you are referring to my post on the timber floors. We seem to have exactly the same issues with our floors. I pulled up a few of my own floor boards last night and they are in fact also nailed directly to existing concrete floors. I wonder how the existing floors survived so well without ventilation?

I am debating weather to go down one of 4 routes. 1. Float the floor on the existing concrete 2. Float the floors on the existing timber floors 3. Put down ply and stick the boards to the ply. or 4. Stick the boards directly to the existing concerte floor.

For options 1, 3 and 4 I would consider releveling the existing floors and adding additional damp proofing.

For releveling the floors I was just going to use that auto leveling compound you get in hardware shops. I know there are different sealers you can get that can be painted on after the leveling compound dries. Is this sufficient damp proofing? I hadn't thought of polybond I guess it would also seal the floors?

Rutigur

Hi Patto,

I'm going with solid wood floors as I just prefer their appearance over semi-solid so I don't have the option of using a floating floor.

I guess a question that needs to be answered is: is there a separate damp proof course underneath the concrete floors?

My floors are way too uneven for levelling compound - I will get them nearly there with concrete and use levelinng compound for the finish. The polybond is not for waterproofing the floor - its purpose is to seal the floor so that the concrete that goes on top of it can get a good clean bond to it.

rooferPete

Hi Ruttiger,

Poly Bond and similar brands will seal concrete to a point, it should not be used as the primary DPC, also if using it to get a bond to another concrete surface make sure it does not get a chance to dry because then it stop the new concrete getting a bond.

I have not found the additive that will allow a feather edge of sand / cement to maintain any strength, the usual for floor screeds is 50 mm thick, you might get away with going down to 25 mm although I wouldn't like to be writing a warranty on it.

I would have no problem with Sika products for screeding over existing concrete floors, roofs, even roads, but it must be the correct product from their range.

I am not sure if the bitumen under the timber is the primary DPC but I wouldn't be surprised because 50 years ago timber floors were the norm.

It may be possible to level the floors by flood coating the existing finish with blown bitumen, however it would only be effective as very thin coat.

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