Screed or Cement?

[Callismichael]

Hi all

I have variouse voids to fill in my hallway. one void is about 200mm down, another is where pipework runs in my conrecte block about 100mm down. Should i use a screed or a make up concrete with sand, gravel and cement?

I have a bag of self levelling compound. When people advise a screed for a depth maybe this size. Di mix the levelling compound with sharp sand or is there a different compound for this as the bag of levelling compound i have only describes levelling a floor to say 8mm thickness?

Sorry to sound simple but it's mind boggling.

 

[^woody^]

Any hole deeper than 10mm or so should be cement and screed sand mix or a cement and sharp sand mix. 3 sand one cement ratio.

Self leveller just requires water

 

[Callismichael]

Hi Woody

thank you. Was confusing me as most people advise to 'screed fill across a cavity' as opposed to concrete across cavity. I will have an upstand of insulation at my door. What would be most suitable? I already have sand, cement and ballast so would I just be over complicating things?

 

[cjard]

What floor covering will you use over this cavity?

 

[Callismichael]

Well the cavity is going to be filled 2 brick course below dpc. DPM in void, then fill to FFL and then either laminate or Karndean on top.

 

[^woody^]

Your not filling a hole then, but filling a door threshold?

 

[Callismichael]

Hi Woody

Both, filling over service pipes and then the door threshold (cavity)

 

[cjard]

karndean will require a good, solid, consistent surface to adhere to that is relatively flat (self levelling.. though verify that the SL compound you use will work with the glue for the karndean (possibly F46) - you may need a primer (P121) if the self levelling compund and glue are incompatible.

Laminate/wood flooring will be more tolerant of a poor subfloor and depending on the cavity width and thickness of the planks you wouldnt necessarily need a solid fill; for example, an engineered wood floor with oak veneer at around 15mm thick would bridge a 50mm gap filled with insulation without too much worry (don't land any plank ends on the gap) but a 9mm mdf laminate on a 100mm cavity will need a decent solid fill to the cavity

 

[Callismichael]

Thank you. so is it best to say cement from DPM up to floor level as I already have the materials and then if I require Karndean I can floor level through the hallyway? Just confusing why people use the term screed above DPM and not concrete

 

[cjard]

concrete is grey stuff with stones in. screed is grey stuff without stones in. cement is what makes the grey stuff grey; it crystallizes in the presence of water, making screed and concrete hard. using it with sand and stones means you get more volume of grey stuff and varying the quantities alters the properties of the cured mixture

people tend to use the relevant name to refer to the presence of stones, not the location in the building, though to be fair there are some screeds that, were they holding bricks apart in a wall, would be called "mortar"

ps; personally i'd use some scrap kingspan or polystyrene insulation up to 50mm or so, then screed it if I were karndeaning or thin laminate, and insulation all the way if I were using thick wood

 

[Callismichael]

Thanks Cjard I will concrete then as I have the materials. Regarding the insulated upstand U have plenty of Celotex, are you saying if Karndean then it would be best to screed over the insulation to provide a bit of strength for it and solid floor not to bother as it will bridge the Celotex?

 

[Callismichael]

regarding under floor dpm. I dont have much to overlap without chiselling out the floor. Would it be best to buy a liquid DPM or would overlapping under 150mm and duck tape be sufficient enough? or overlap what i have and bring up to FFL and cut?

 

[cjard]

, are you saying if Karndean then it would be best to screed over the insulation to provide a bit of strength for it and solid floor not to bother as it will bridge the Celotex?

Yes but it depends on e floor covering. I wouldn't want 9mm MdF laminate to bridge a 100mm cavity, 50mm cavity I would though. I'd be happy for 18mm engineered wood laminate to bridge a 100mm cavity. Karndean will need a solid base. I'd fill the cavity to within 50mm of the top with celotex's, put some 12mm ply on the insulation, put concrete on the ply and then use a cordless in hammer mode to vibrate the ply, settling the concrete into every gap and crack, then polish level with either side of the cavity. I might then used some self levelling compound over that to get a nice surface as Karndean really does settle when trafficked, and undulations would be obvious
Not really getting what you're saying with the dpm, can you draw a picture? If you're on an iPad, use the Notes app, sketch something, save to camera roll and upload

 

[Callismichael]

all sorted now that burden of a void has been filled. I have used an upstand of insulation and the screed butts up to it. We have decided on carpet and also a framed mat in the floor. Should be able to fix the frame to the concrete and then the back end of it will go over the insulation upstand.