Concrete floor advice - urgent

evilgoose

Hello, I've asked this question or ones simular in several places and I'm struggling for an answer.

I've got solid floors down stairs, I've knocked off the plaster from the walls and there is now a gap of aroung 1cm between the floor slab and the walls.
I've been filling this with concrete mixed 4sand 1 cement and feb waterproofing liquid. Is this ok?? or is the gap for expansion? I'm concerned its letting water vapour up as the plaster around the gap was in poor condition (very powdery).

2ndly - above the concrete slab is a 'smooth' layer which finishes the floor surface, this is broken and loose around the edges and hollow sounding in some spots. Its around 12 to 15mm thick. I can only find leveling compound suitable for max of 10mm. (which was v expensive compared to the ones suitable for 3mm thick)
Can I paint a liquid DPM onto the concrete slab, key it with sharp sand and then lay a 10mm concrete coat ontop, when set then lay a finish of self leveling floor compound? if so, what mix should the concrete be to make it strong enough or is 10mm going to be to thin??

I'm really stuck. I dont want to get a firm in unless I really have to as funds are running out fast!

thanks in advance.

vansboy

The gap around the floor/wall, won't this be hidden with skirting - so no need to fill it?

Wickes have a stronger self levelling compound, which you can build up in thicker layers. http://www.wickes.co.uk/Special-Mortars/Latex-Floor-Levelling-Compound/invt/224669

We used this for our very uneven bathroom, it was cheaper than some of the branded products & worked well enough.

If you're not in a hurry, then B&Q & Wickes both stock a cheaper item, which does take longer to dry out.

Hope that helps.

VB

evilgoose

thanks, I think the gap is allowing water vapour through so causing rot in the skirting, so I think I have to fill it.

I'll check that out.

I need to get the floor done as new door going to be installed soon so floor needs to be in place where the doorstep will sit.

I had wondered about laying quarry tiles by the door to just above the level of the floor so that the threshold strip can be fixed to that and give me more time to sort the floor out.
Sadly I think the whole ground floor will need to be done at somepoint.

evilgoose

BUMP! - Any other suggestions? the weekend is almost upon us, so need to crack on.

illzlee

right, more info needed here.
the gap around the edge could be for a multitude of reasons.
1. expansion/movemen as you suggested, but this is unlikely
2. to stop cold-bridging between floor and walls
3. poor workmanship in the first place

however, the rotten skirting points to a different problem,
if you have a cavity wall the cavity could be full and bridging the dpc via the internal slab
a lot of this depends upon the age of the house etc...

To be honest i would be more concerned about the damp than the gap around the edge that woul dbe covered by skirting.

As for the levelling compound, lay it in stages and build up the levels? It's what i've done in my workshop and that survives me dropping engine parts regularly...

evilgoose

Thanks for the reply, the house was built in 1950.
The cavity is blocked in several locations, I've looked for spots of damage on the internal plaster or where its not the black mortar but been redone. I've been removing bricks to get access and clean it out, (though the house doesnt smell damp or feel damp). I've had several sacks of rubble out of the spots around the house where I've done this.

Nothing like a saturday with your arm wedged up a cavity!

webwalker

evilgoose wrote: »

thanks, I think the gap is allowing water vapour through so causing rot in the skirting, so I think I have to fill it.

I'll check that out.

I need to get the floor done as new door going to be installed soon so floor needs to be in place where the doorstep will sit.

I had wondered about laying quarry tiles by the door to just above the level of the floor so that the threshold strip can be fixed to that and give me more time to sort the floor out.
Sadly I think the whole ground floor will need to be done at somepoint.

The gap around the concrete floor is quite normal and when it was first laid would have had some make of flexiboard in it, anything it is filled with needs to be flexible to allow for the floor to expand and contract, if the gap is out of the light I would go with one of the many expanding foams available. You can use a sand/cement screed to level the floor but the existing floor must be sealed first, a couple of coats of diluted pva will sort that, also add pva to sand/cement mix to help it bond.

andrew-b

I'd leave the gap and cover it with a skirting. We have the same gap but in our house i think it's actually there for a reason. In the past damp proof course injection work was carried out on our house and from the original invoice it mentions "cutting out plaster from above the floor". I'm told that the reason this is done is because standard plaster is hydroscopic (sucks up water) so by having a gap damp is less likely to rise up the wall.

With regards to the concrete floor itself, i had a similar thing in the bathroom. Someone in the past had dug up the floor, laid pipes in it (unprotected) and then badly finished the floor with a thick layer of self-levelling compound which was higher than the rest of the floor. They had left air pockets under the pipes too so it all sounded hollow and was starting to crack up. I had to remove it all and fill it back in again properly.

I was faced with much the same problem of finding suitable material to replace. Though in places the hole was a couple of inches deep. I did actually buy the Wickes self-levelling for thicker layers but took it back because it mentioned that it was not suitable for laying vinyl floor on top which was my intention. All the advice i saw was to use a sharp sand/cement floor screed mix but in the end i took the cheap and easy option and just bought a few bags of Wickes patch repair mortar (mentioned on it suitable for patching floor screeds) that you add water to and used that. I primed the area to be filled with PVA first and used 5:1 water:pva mix to mix the mortar up with. I think it must have taken a week or so to dry out fully because of the thickness but it seems fine now and sounds totally solid. I'm planning on getting some standard self-levelling to finish it off properly as it's a bit uneven still but it will have worked out cheaper than if i'd used the thick self-levelling.

The liquid DPM may or may not be worth doing. If there's already a damp proof membrane in the floor (usually a plastic sheet of some sort if it's there - might not be for a property of your one's age) it's probably a waste of money or may even cause further problems (if moisture gets trapped underneath). If there isn't a damp proof membrane then it may help though it won't stop damp rising through the floor elsewhere. Personally i didn't bother and it looks like i got away without needing it ok. If i'd had some already i'd probably have used it though as i didn't come across any damp proof membrane.

With the rubble in the cavity ...we have some of that too which i found whilst opening up the bathroom wall for running a waste pipe through. I just extracted what i could though we have cavity wall insulation which i don't want to displace. It seems to me that the 1950s wasn't the best time for buildings!

Hope that helps

Andy

HairyApeMan

evilgoose wrote: »

Hello, I've asked this question or ones simular in several places and I'm struggling for an answer.

I've got solid floors down stairs, I've knocked off the plaster from the walls and there is now a gap of aroung 1cm between the floor slab and the walls.
I've been filling this with concrete mixed 4sand 1 cement and feb waterproofing liquid. Is this ok?? or is the gap for expansion? I'm concerned its letting water vapour up as the plaster around the gap was in poor condition (very powdery).

2ndly - above the concrete slab is a 'smooth' layer which finishes the floor surface, this is broken and loose around the edges and hollow sounding in some spots. Its around 12 to 15mm thick. I can only find leveling compound suitable for max of 10mm. (which was v expensive compared to the ones suitable for 3mm thick)
Can I paint a liquid DPM onto the concrete slab, key it with sharp sand and then lay a 10mm concrete coat ontop, when set then lay a finish of self leveling floor compound? if so, what mix should the concrete be to make it strong enough or is 10mm going to be to thin??

I'm really stuck. I dont want to get a firm in unless I really have to as funds are running out fast!

thanks in advance.

From what I remember they leave a bit of a gap to allow for settling, that's why the skirting board to cover the unsightly gap.