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Posted: Fri Sep 13, 2013 8:17 am
by Fezbollah
Hi, I have just knocked down a block of horse stables to re build them and found that the 18m x 3.6 slab is cracked in several places across the whole width of the slab. I've been advised that a 75mm thick C35 mix with a mesh additive (is this post tension concrete?) poured on top of the existing slab will suffice for a timber frame building. I have also been told I'll be better off breaking up the old slab before pouring on top of it.
I'm a good chippy but not much of a ground worker so I am not sure which route to go down. The cheaper I can get over this problem the better as it represents a sizable extra!
Thanks for reading,
Fez.
Posted: Fri Sep 13, 2013 11:12 am
by Fezbollah
Answered my own question by having a trawl though older posts. Happy to hear opinions though. Thanks muchly Tony McC! 
Posted: Fri Sep 13, 2013 11:45 am
by GB_Groundworks
You are better off getting rid, but a 100mm slab on top be fine, drill some holes and dowel it with rebar into the old slab, also you want to cut some contraction joints 24 hours after pouring then if it does crack again it'll crack where you want it in neat lines
We always do brushed concrete for stables give them a bit of grip
Edited By GB_Groundworks on 1379094055
Posted: Fri Sep 13, 2013 11:56 am
by Fezbollah
Thanks, Giles. What sort of width are we talking for the contraction joints and how many over the 18 metres? 10mm so I can pop some fibre expansion join into the gap?
Posted: Fri Sep 13, 2013 12:54 pm
by TheRockConcreting
If it's an active crack, or larger than 1/8" you are going to have to remove the slab and start a fresh.
If over laying is your only option then i would be using a liquid floor screed (gyvlon), normally you don't need to cut control joints in gyvlon because it doesn't contract like cement base screeds, but i would cut joints over or near to where the floor is cracked underneath.
Also remember to brake the bond between the two slabs in this case, using a damp proof membrane will be fine for this.
Posted: Fri Sep 13, 2013 6:44 pm
by GB_Groundworks
contraction joints want to be 25% of the thickness of the slab and then seal them with a flexible sealant such as polyshulphide (most big bm will have this in just mastic gun it in)
id do them at say 5m or what ever divides the slab best
also we use a special concrete from cemex for stables as horses urine has a very high urea content, making it hard on normal concrete
Edited By GB_Groundworks on 1379094383
Posted: Fri Sep 13, 2013 6:58 pm
by TheRockConcreting
GB_Groundworks wrote:a 100mm slab on top be fine
contraction joints
id do them at say 5m or what ever divides the slab best
If your putting joints in a 100mm concrete slab the joints will need to be a MAX of 3m apart.
urine affects the steel reinforcement not the concrete its self.
Posted: Fri Sep 13, 2013 7:32 pm
by msh paving
I beg to differ on the urine, it attacks cement, that is why in england stock yard ,stable blocks are poured using sulfate resiting cement commonly call SR by concrete delivery companys. MSH 
Posted: Fri Sep 13, 2013 9:49 pm
by Brucieboy
Under no circumstances should Gyvlon be used for a stable floor - it not designed to be a wearing surface and requires a suitable floor covering. Furthermore, being based on anhydrite / calcium sulfate, if continuously wet for any length of time it will revert to a mushy mess. It is, however, an excellent alternative to traditional sand/cement levelling screeds, particularly when laid in large areas.
The usual concrete mix recommended for a stable floor is an RC35/45 (45 N/mm2) with polypropylene fibres. As Giles states, proprietary mixes are available from most ready mixed concrete producers, e.g. Cemex Stockfloor, Hanson Farmfloor Plus etc.
Posted: Sat Sep 14, 2013 8:17 am
by Brucieboy
ps to my last post. Not so sure about Cemex Stockfloor for a stable - may only be suitable for livestock (not horses with steel shoes). Which ever company you use, check it out first, preferably with their Technical Department.
Posted: Sat Sep 14, 2013 8:58 am
by TheRockConcreting
Fezbollah wrote:Hi, I have just knocked down a block of horse stables to re build them and found that the 18m x 3.6 slab is cracked in several places across the whole width of the slab. I've been advised that a 75mm thick C35 mix with a mesh additive (is this post tension concrete?) poured on top of the existing slab will suffice for a timber frame building. I have also been told I'll be better off breaking up the old slab before pouring on top of it.
I'm a good chippy but not much of a ground worker so I am not sure which route to go down. The cheaper I can get over this problem the better as it represents a sizable extra!
Thanks for reading,
Fez.
I read his OP as he was renovating the old stable for another use, not to be used as a stable again.
Posted: Sat Sep 14, 2013 9:32 am
by lutonlagerlout
personally, and i defer to all the concrete experts here
overlays are never a good idea IMHO
most of the time when we break out old concrete it is laid either straight on topsoil or on a rough mixture of uncompacted brickbats with lots of voids
how about fez getting a digger with a pecker to break it up and dig it out ,then using a crushed to crush the concrete and lay terram over the area then re use your crushed concrete as a subbase
a 3 tonner would break that area out in a couple of hours and it would take 2 men a day to crush with a micro crusher
^^ as above 18M is big so you would probably need to :
pour in 4 bays or use crack control joints
cheers LLL
Posted: Sat Sep 14, 2013 4:52 pm
by seanandruby
I'm with Luton on this one. Overlays on a cracked sunken slab are never a good idea.
Posted: Sat Sep 14, 2013 7:12 pm
by dig dug dan
I'm with luton too, a crusher is a superb idea :p
Posted: Sat Sep 14, 2013 7:40 pm
by mickg
I agree with Luton too