navitron
 
Renewable Energy and Sustainability Forum
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Anyone wishing to register as a new member on the forum is strongly recommended to use a "proper" email address. Following continuous spam/hack attempts on the forum, "disposable" email addresses like Gmail, Yahoo and Hotmail tend to be viewed with suspicion, and the application rejected if there is any doubt whatsoever
 
Recent Articles: Navitron Partners With Solax to Help Create A More Sustainable Future | Navitron Calls for Increased Carbon Footprint Reduction In Light of Earth Overshoot Day | A plea from The David School - Issue 18
   Home   Help Search Login Register  
Pages: [1] 2   Go Down
  Print  
Author Topic: Concrete slab needs to be thicker  (Read 3159 times)
CrowMan
Newbie
*
Offline Offline

Posts: 9


« on: June 01, 2017, 01:33:59 PM »

How would you raise the level of a new concrete slab? I was only laid 3 days ago and needs 25 to 30mm adding to it. (plus it has high and low points +-10mm so needs levelling too)

It covers about 35m sq.

It will eventually have electric UFH on top too so I'm a bit worried about separation with expansion / contraction of different materials


Logged
Sean
Hero Member
*****
Offline Offline

Posts: 641


« Reply #1 on: June 01, 2017, 01:35:46 PM »

Screed
Logged
CrowMan
Newbie
*
Offline Offline

Posts: 9


« Reply #2 on: June 01, 2017, 01:41:11 PM »

Do I have to let the existing slab dry first? Can "self leveller" be added to screed?
Logged
Sean
Hero Member
*****
Offline Offline

Posts: 641


« Reply #3 on: June 01, 2017, 03:26:06 PM »

If you can walk on it you can screed it - screed is usually a dry/slightly moist mix that's manually levelled, liquid self levelling for the depth you want will be a scary price

Who laid the slab ?
Logged
biff
Global Moderator
Hero Member
*****
Offline Offline

Posts: 12642


An unpaid Navitron volunteer who lives off-grid.


« Reply #4 on: June 01, 2017, 03:50:18 PM »

Hi CM,
      If it had been finished to the correct height, what depth is the finished floor supposed to be on top of that.?
                                                                          Biff
Logged

An unpaid Navitron volunteer,who has been living off-grid,powered by wind and solar,each year better than the last one.
CrowMan
Newbie
*
Offline Offline

Posts: 9


« Reply #5 on: June 01, 2017, 10:14:27 PM »

Quote "If you can walk on it you can screed it - screed is usually a dry/slightly moist mix that's manually levelled, liquid self levelling for the depth you want will be a scary price

Who laid the slab ?" unquote


Builder took out the old slabs (2 x 100mm). There was already large gravel underneath the old slabs and insulation boards  (100mm) were put on top of the gravel. The gravel wasn't compacted (not sure it needed to be??).. or level, he told me it was "self compacting" but the insulation boards had voids underneath and sagged markedly when walking on them.

Concrete barrowed in and put on top of DPC over the insulation but he never understood what level I was working to and instead of working to the threshold of the outside door as I asked he worked to the old floorboards in the adjoining corridor. These old boards in the corridor will eventually be over plied, and probably tiled, lifting it above what it is now. So the slab has probably ended up 40mm lower than what I was expecting / wanted.

I was expecting a decent floated finish on the slab ready for the UFH and tiles, LVT or whatever, but it wasn't, it was, as he put it... "lightly tamped"

I honestly despair as time after time I get cr*p job after cr*p job, and its not as if I go for the cheapest either!!

My house is gradually looking more and more like a DIY disaster at the hands of "tradesmen".
Logged
desperate
Hero Member
*****
Offline Offline

Posts: 3624


Backache stuff!!


WWW
« Reply #6 on: June 01, 2017, 10:53:04 PM »

Oh dear, sorry to hear of your tribulations,

a concrete slab is rarely level and true enough to tile on, that's why nearly always a screed goes on top and then the floor covering.If you need to make up an extra 40mm that's no problem.  What bothers me more is the self compacting gravel???, how large was that gravel 10mm? 50mm, bigger? if there were irregular voids and that gravel was large you might have problems. You do need the insulation boards to be well supported over most of its area, if not it will loally crush and settle too much leaving the slab un supported.

Desp
Logged

www.jandhbuilders.co.uk

still a crazy old duffer!
Sean
Hero Member
*****
Offline Offline

Posts: 641


« Reply #7 on: June 01, 2017, 10:56:53 PM »

There was already large gravel underneath the old slabs and insulation boards  (100mm) were put on top of the gravel. The gravel wasn't compacted (not sure it needed to be??).. or level, he told me it was "self compacting" but the insulation boards had voids underneath and sagged markedly when walking on them.

Concrete barrowed in and put on top of DPC over the insulation but he never understood what level I was working to and instead of working to the threshold of the outside door as I asked he worked to the old floorboards in the adjoining corridor.


From what you've said so far, I'd want the new floor ripped up.

The subfloor does need compacting - there should be no voids under the insulation - 100mm isn't really enough (was there any perimeter insulation installed ?) - where is the DPC,  the crete should not have been poured directly onto the insulation ....

I'm assuming there​ was nothing formally agreed in writing (drawings showing FFL ?) before the work where started ?
Logged
CrowMan
Newbie
*
Offline Offline

Posts: 9


« Reply #8 on: June 01, 2017, 11:32:12 PM »

Thanks for the comments, it looks like I need to get someone else in to do a screed good enough to lay electric UFH and tiles (or equivalent).
Would that be a tiler?, or a builder? or another "trade".

Sean:- I would also have expected the subfloor to be compacted, blinded with sharp sand and compacted again, all nice and level. Then that would have supported the insulation properly.
I questioned the "perimeter insulation" and he showed me some white sponge strip about 10mm thick, 100mm wide which he tacked to the wall. It looked more like something you would use as expansion control.

The DPC is over the insulation, under the concrete.
« Last Edit: June 01, 2017, 11:40:30 PM by CrowMan » Logged
Sean
Hero Member
*****
Offline Offline

Posts: 641


« Reply #9 on: June 01, 2017, 11:48:06 PM »

Tacked to wall doesn't inspire confidence - there needs to be a continuous box of insulation enclosing the slab - most BCOs expect to see a second DPC within the "box" onto which the crete is poured, this ensures the fines don't seep down or outward forming multiple cold bridges - the builder won't care, it'll not be him paying the ongoing bills - 250mm below and 50mm perimeter in the norm, and properly load rated for sub slab use (rather than the cheaper versions used for cavity and loft use)
Logged
CrowMan
Newbie
*
Offline Offline

Posts: 9


« Reply #10 on: June 02, 2017, 12:00:03 AM »

Looks like I have been ripped off yet again then.....

I have zero faith in any so called "tradesmen", unfortunately it tars all of them with the same brush.

I know there must be some decent ones out there but I have yet to come across any of them.

New central heating system.... fail
New solar system.... fail
New doors throughout the house ... fail
New driveway gates.... fail
New wetroom ... fail
Rewire throughout   ... fail
Fitted wardrobes   .... fail

Makes me want to sell up and move on away from all this cr*p shoddy "workmanship".

I'm sick and tired of redoing their work (where I can) to some sort of standard, and I'm no tradesmen.
« Last Edit: June 02, 2017, 12:02:25 AM by CrowMan » Logged
desperate
Hero Member
*****
Offline Offline

Posts: 3624


Backache stuff!!


WWW
« Reply #11 on: June 02, 2017, 07:59:13 AM »

Looks like I have been ripped off yet again then.....

I have zero faith in any so called "tradesmen", unfortunately it tars all of them with the same brush.

I know there must be some decent ones out there but I have yet to come across any of them.

New central heating system.... fail
New solar system.... fail
New doors throughout the house ... fail
New driveway gates.... fail
New wetroom ... fail
Rewire throughout   ... fail
Fitted wardrobes   .... fail

Makes me want to sell up and move on away from all this cr*p shoddy "workmanship".

I'm sick and tired of redoing their work (where I can) to some sort of standard, and I'm no tradesmen.

Blimey that is  a sorry tale I feel your pain. Don't take this the wrong way, but if you are managing this project yourself it looks as if you don't really have the knowledge to keep all the trades in order and informed as to how it all fits together. It's never easy getting a load of blokes, who may be very good at their particular job but less good at commun ications, to end up acheiving exactly what you need.

I'm just guessing really but try to have a clear objective in mind with drawings and, or, lists of pointers to hand when you get others in to carry out works. Also always be available to speak by phone at least, and better still visit at least once a day to keep an eye on progress, and don't be afraid to ask questions.

Good luck.

Desp
Logged

www.jandhbuilders.co.uk

still a crazy old duffer!
linesrg
Hero Member
*****
Offline Offline

Posts: 1119



WWW
« Reply #12 on: June 02, 2017, 09:10:17 AM »

CrowMan,

I would agree entirely with Desp, and with all due respect to tradesman everywhere, in that you need to be on site and monitor/ query as required. Almost all the things that haven't gone right with the ongoing projects here at Courtiestown have occurred when I've been at work offshore. I try very hard to ensure nothing occurs outwith my leave periods now.

Having said this the biggest 'disaster' did occur under my very nose. Cutting along story short we had somebody lay the floor in the kitchen after the wet UFH was installed and he did it in two layers to make up the 100mm. The floor wasn't 'flat' on completion and developed a significant crack.

This is why we've gone for the 'poured floor' option this time. On both occasions the contractors 'vibrated' the hardcore prior to laying the concrete sub-base and the insulation went down on a flat base, fully supported and no rocking sheets.

There was a minor unexpected occurrence yesterday. The joiners were in yesterday and started cross brandering the ceiling to lay a new level ceiling (I see they were dealing with up to 30mm deflection of the 160 year old joists) and were using 50 x 25mm battening whereas I'd anticipated them using 50 x 50mm (this is what the joiners used when they did the kitchen ceiling so I assumed that's how it was done.........) and had ordered 50mm insulation accordingly......... fortunately I have 25mm available as well. Mind as there is 200mm of fibreglass stuffed in the spaces between the joists it would be complete over kill - mind there is no such things as too much insulation is there?HuhHuh?

Regards

Richard
Logged

1.28kW on a Lorentz ETATRACK1000 + 1.44kW/ SB3000TL-21 (FIT), 1.28kW/ SB1700 (ROO/FIT). CTC GSi12 heat pump/Ecosol/Flowbox 8010e/Gledhill ASL0085 EHS/3off Navitron 4720AL Solar ET & Immersun T1060/T1070/T1090. 3.375kW/ SMA SB3600TL-21 and a Sunny Island 4.4M-12 c/w 15.2kWh battery and a Renault Zoe.
gravyminer
Sr. Member
****
Offline Offline

Posts: 460



« Reply #13 on: June 02, 2017, 01:35:00 PM »

Crowman

You haven't answered Biffs question regarding the  thicknesses of any layers you had planned above the slab ?

There may be a way to pack the underside of the top layer.
Presumably you were not planning to put the underfloor heating in the incorrectly laid slab ?
Its a heck of a lot easier to pack up than to grind down a concrete layer and most trades that follow other trades i.e. dry trades following wet have learnt to overcome any shortcomings in the previous work.
 I guess thats pretty much what skill and experience is about .....

As for single size aggregates needing compaction, the answer seems to be minimal to zero as theres almost no bulking factor.
Its why we can use it to surround drain pipes, onion shaped septic tanks  and even use as a free draining layer under a slab or foundation pad without the need for compaction.
Its possible your old insulation layer settled because any blinding layer ( if they did one ) migrated down through the gaps in the single size aggregate because no geotextile / hessian layer was put on top of the gravel.
The insulation needs to be fully in contact with layers above and below or it will dent / compress allowing the layers above to move.

Good luck with finding competent people going forward and be mindful that communicating your requirements is the key to getting what you want.
Sometimes diagrams or sketches with descriptions / dimensions are better than words.
Its often the case that you are not understood but people are reluctant to say 'I don't understand' ....

My instinct when this happens is that I failed to communicate the brief successfully.
The skill seems to be knowing the level of competence of the person you are briefing.
Are you talking over their head or patronising them with too much unnecessary info ?


 
Logged

gravyminer
biff
Global Moderator
Hero Member
*****
Offline Offline

Posts: 12642


An unpaid Navitron volunteer who lives off-grid.


« Reply #14 on: June 02, 2017, 01:49:17 PM »

               "It is a heck of a lot easier to pack up rather than to grind down a concrete layer"
  Spot on GM,
       and there may be a rise in the existing wooden floor toward the new floor that can be easily corrected at this stage.
    When you are working out the finished surface for floors or staircases, You start from the top down, that is the only way that you are going to get it right.
                                                   Biff
Logged

An unpaid Navitron volunteer,who has been living off-grid,powered by wind and solar,each year better than the last one.
Pages: [1] 2   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.20 | SMF © 2013, Simple Machines
SMFAds for Free Forums
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!