Previous floor screed has totally delaminated from the concrete slab

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fruitcake

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Hey up,

I was at a house today, the floor screed has totally delaminated from the concrete slab. Its a kitchen floor in an 1900`s house. Its about 45mm thick and is coming up no question about it. There is a concrete slab underneath that has not cracked and therefore leads me to believe the screed on top just never adhered to it. This screed was probably done many many decades ago, 50, 60`s who knows mayby earlier.

Its not going to go back down at 45mm, Im hoping to get it down at about 20mm. (will help eradicate a step after tiling)

Not got much experience of floor screeding but ill be having a go. Its about 12sqm.
I was thinking of SBR/cement slurry 50/50 first onto the slab. letting that set. Then I was thinking 3 screed sand - 1 cement? Should I be adding some SBR to the mix and if so have much. Have I got the ratio above right? Is it ok to do 20mm thick screed?

The concrete slab underneath seems to be a mixture of stones, rocks concrete, cement etc. ???

Thanks for any advice, much needed ta
 
thanks

yes ive been reading up... and it seems theres no chance of it being 20mm. Ive had another look and the old screed is only about 35mm. So theres no chance of it being higher than this. Any thoughts#
 
There is some floor level compound which goes down quite thick, maybe you can build it up to 20mm. Not sure of the cost of gear.
 
We have put down many SBR modified screeds at 20mm, you need to completely clean the slab 1st, consider then if a cement based DPM is required ( Thoro Seal, Vandex etc.).
If not prime the floor to negate its suction, then SBR tack coat, the screed ( SBR in too) needs to be laid over this straight away whilst the SBR/cement tack coat is still tacky. Cover the entire area with 10mm, then you can screed as normal. PM me and Ill give you some ratios for the SBR mixes.
 
fruitcake said:
Hey up,

I was at a house today, the floor screed has totally delaminated from the concrete slab. Its a kitchen floor in an 1900`s house. Its about 45mm thick and is coming up no question about it. There is a concrete slab underneath that has not cracked and therefore leads me to believe the screed on top just never adhered to it. This screed was probably done many many decades ago, 50, 60`s who knows mayby earlier.

Its not going to go back down at 45mm, Im hoping to get it down at about 20mm. (will help eradicate a step after tiling)

Not got much experience of floor screeding but ill be having a go. Its about 12sqm.
I was thinking of SBR/cement slurry 50/50 first onto the slab. letting that set. Then I was thinking 3 screed sand - 1 cement? Should I be adding some SBR to the mix and if so have much. Have I got the ratio above right? Is it ok to do 20mm thick screed?

The concrete slab underneath seems to be a mixture of stones, rocks concrete, cement etc. ???

Thanks for any advice, much needed ta
Click to expand...

So there is not really a slab under the screed then, if that's the case the whole lot needs digging out and you will have to comply with local building controls instructions, that will probs mean excavate down to abot 300mm-350mm then installing 100mm compacted sub base, dpm, insulation (min 75mm phenolic) 150 mm concrete, then screed
 
thanks guys - some helpfull stuff there.

ive enclosed 3 photos.

1- of the old screed coming
2- a bit more -
3- a picture of the concrete subfloor that im on about..

@mark ive pm you - thanks...

when you say prime before the slurry, do you mean with sbr aswell?

you also say 10mm screed ontop of tacky slurry. is this then followed by another layer of 10mm screed to bring it to the desired 20mm, straight away, ??
 

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Fruit,

As Warrior has picked up, there is more to this job than first assumed. Judging from your pictures ( and difficult to accertain from these) . The slab below your loose screed looks suspicious too.

If this too is not sound, a replacement of th whole lot may be in order. Remember, the screed will only be as good as the substrate it is bonded too.
 
ok guys. I think a couple more photos are now in order. Ill try and get them today or tommorow.

Ive only seen that patch of the photo i took, and my in-experienced eye tells me it just rough concrete with a definate aggregate in there. The indentations in the surface of it are where I was hitting it with my hammer.

Ive spoke to my friend on the phone AFTER he has ripped ALL the old screed up and he says there are no cracks or anything like that in the slab. ANd nothing that may suggest it was the slabs fault as to why the screed cracked etc.

So ill get the photos from diff angles and post later or tommorow,.

Thanks for advice so far lads.



Ive just got off the phone to him and hell email me the photos later. Upon more questioning, the floor is basically just a rough concrete floor with noticable aggregate in the surface. No cracks, seperations, lifting or anyhting that would suggest the concrete is failing....


Thanks
 
If its only 20mm Why not use self levelling compound mixed with sharp sand & put a few layers down till you get the required thickness. Depending on how sound the slab is of course & see wether you need a liquid dpm first.
 
Hello again.

Since my last post I have seen the floor for my self... Its definately a rough surface full of cement and small stone. Its been chucked in any old way and is not flat by any means. It also has 2 suspicious looking crevises running across the floor. They seem like they may have been cracks that have closed back up. But my friend reckons there not and there just rough joins of different batches of concrete when it was laid.

Anyway, he got a builder round and old timer who said that all the floor needs is a 1000 polythene sheet and then 50mm of sand/cement screed and wasnt interested in the discrpenicies along the floor. Hes been a builder all his life?

Can you comment on this information and if it sounds like a good plan?
 
deep bed queery..

hi Andy

just wondered how much experiance you have with this product?i do a fair amount of orangaries and connies,and im constantly coming across bases that vary in levels and thicknesses so much that its a bit of a head scratcher to decide which way to deal it..
self levellers are very often not as easy to get spot on as they are made to be,often areas are larger than you can flood in one go and therefore you get overlaps and settling areas faster than you can mix the compound.i work alone usually so as you know it is a mad rush to fire in bucket after bucket of gear and feather the edges off by hand,only to come back the next day and if your as fussy as i am its a bit of a let down when you find the levels are not perfect.
if your levelling this stuff on your own with a depth of anywhere from min/to max recomended depths..how does it fare?whats the coverage like for cost per mtr at max depth compared to screed?overlapping is an issue with most self levellers so does this give you fewer headaches when you cant totally flood the area in one hit at the max depth for instance?
i was in the builders this week and the lads showed me the leaflet on the product,but obviously first hand knowledge is better than a leaflet trying to sell the stuff..

any thoughts or suggestions on this or other products would be great

cheers

Huck
 
Sorry Huck but I don't touch the gear myself but I have seen it done plenty, although when I've seen it done it's mixed/pumped in by machine so I haven't witnessed the problems you mention using buckets. Have a look on Blones' website (google PFT Wales) and there's a clip of the Ritmo mixing/pumping a Weber levelling compound.
Ian would the Ritmo get the gear in quick enough to do a thickness of 60mm or so over a decent area?
 
essexandy said:
Sorry Huck but I don't touch the gear myself but I have seen it done plenty, although when I've seen it done it's mixed/pumped in by machine so I haven't witnessed the problems you mention using buckets. Have a look on Blones' website (google PFT Wales) and there's a clip of the Ritmo mixing/pumping a Weber levelling compound.
Ian would the Ritmo get the gear in quick enough to do a thickness of 60mm or so over a decent area?
Click to expand...

hi Andy..
great looking machine,although youd have to justify the price with the output..its a fairly big outlay and youd really have to make it pay for itself.certainly makes the screed look spot on.
i'll look into it some more(and keep the price away from the missus!

cheers A
 
SBR is an excellent idea I have been using this product for over 20 years, you can go down to 10mm thick. If you go down to anything below 20mm you have to use some washed rendering sand with it. Laten Buzzard is the best by far.
For this: Completely soak substrate floor then apply water and SBR to floor. Mix SBR water and cement with small amount of sharp or Laten Buzzard wash sand and apply to floor as a slurry coat. Mix screed with SBR additive and lay slightly wetter than usual using plastic float rather than standard poly-urethane float. Trowl with proper floor trowl to leave excellent flat finish.

Any more questions or queries: jasper@tylermereplastering.com
 
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