Ground floor sub-floor advice part 2

[AndersonC]

Some time ago I posted a question about my ground floor with some pics, and was asked to find out what kind of floor was currently in place.

While some local builders were in this week I showed them some of the material I'd dug out of the "slab" from which the sub-floor is made. They said it was most likely to be a mix of "lime and cinder" which has then been covered with a thin layer of bituminous material and floorboards nailed down over that.

I want to remove these boards as they are in a sorry state through wear, not really through moisture related issues. When I pull them up though the removal of the nails will damage the bituminous layer which is acting as a surface DPM I guess.

I intend to create a new wooden sub-floor layer over the lime & cinder on top of which I will then fit solid oak. The advice I am after obtaining is:-

DPM? Do I need to apply a new one if the bituminous layer becomes damaged?
Foams/underlays? Are they worth putting down under the wooden sub-floor I intend to fit?
Board material for the sub floor - ply/chip?

I was considering the following course of action:-
Rip up old boards and remove nails from lime/cinder slab
Fill holes/gaps with self-levelling compound
Install a combi-underlay (DPM backed foam)
Sit the ply/chip on top (but I dunno how I'd hold it down?)

Any advice on this would be extremely helpful, thank you.

 

[mattysupra]

I would really consider digging old floor out and laying new concrete/screed etc with working dpm/ insulation. You have alot of work to repair existing floor.

 

[AndersonC]

Matty

Thanks a lot for getting back to me on this. Is the level of work needed to repair this floor greater than that needed to dig out and screed?

It's going to be extremely awkward for me to dig out and re-lay screed (we're living in the house for starters).

Surely there is some way of providing a reasonable moisture resistant layer over the top of the lime&cinder slab?

If you could do so, I'd appreciate if you'd scope out what you'd reckon would need doing to repair the existing sub-floor.

Once again thanks a lot for your input (pity I can't send you an E-beer!!!)

 

[mattysupra]

You would have to remove all the bitumen from the top. Im guessing this is acting as a dpm. Its not recommended to lay surface dpm over the top of this. Also the type of concrete base you have has a limited life span which is i would guess be coming up to its end. When you try to re seal with dpm or levelling compound over the top, you have an increased risk of it failing. Thats why you may be better starting from scratch. You will also benefit from proper dpm and insulation. But you will also have to wait for new concrete etc to dry. ( approx 1" a month) until you can lay on it. You could put a surface dpm on top of this to speed things along but i always look at this as false economy. But if its my floor i would just lay acrylic compound over existing floor using bonding primmer and the surface dpm and then water or acrylic based compound over the top. This is not the correct method. I would never do this in a customers house, Only in my own as i change my floors every 6 months and i dont pay for the products as i am given them by manufactures to test. Its my job to see what makes products fail and how much i can bend the rules until i make them fail! In your case its different, Your paying and its at your own risk.

 

[AndersonC]

Thanks for your understanding and advice Matty.

Would you remove the bitumen (I'm assuming a sharp scraper), then apply the acrylic compound? Could a self levelling compound go down as well to level things up?

If this method was used to 'repair' the sub-floor, are the sonae P5 chipboard panels suitable to put down to provide a base for the solid oak?

Changing floors every 6 months? My missus would go mad!!

 

[JohnD]

rather a bodge job on that weak and crumbly base

you'll be annoyed if it goes wrong and has to be taken up again.

 

[AndersonC]

Tis a very good point that JohnD!!

hmmmm

 

[mattysupra]

Changing floors every 6 months? My missus would go mad!!

Guess thats why i live on my own!
If your going to bodge the job, you may as well go over the top of every thing. You dont put any type of chip board/ ply/ hard board on top of concrete base. You install your new wood floor on top of the levelling compound you put down. Either glued all over or floating. You have more of a chance of floor staying down on floating method. But there are very little u.k suppliers that will guarantee the floating method. But then again without correct floor prep you have no guarantee anyway and the only thing that goes wrong with wood installs is always down to fitting error. I must say that you really should dig up base and do properly tho. Wood will not forgive any mistakes or bad floor prep.