# Forum Home Renovation Concreting  Cutting out part of a concrete slab in bathroom and relaying

## DaleBlack

This is the pad in my bathroom, the top Right corner is the area the old shower bath sat, there is now going to be a shower in that top left corner, 900-900 and bath opposite. 
My question is in terms of levels and fall re tiling, that area is a little raised from where the FFL is, the FFL is just back from the bottom LH side of the above image being the hallway wooden floor. 
One person said make about 30-40mm of cuts and jackhammer out, probably just a 1500w Ozito even as i dont want too much power near that wall.
Another guy and the plumber said    
literally take out the whole section above which is easy to do, slab about 80mm there I think. The 900*900 shower is going in the top RH section, then come another 300mm of space then a 355 wide toilet, there was never a toilet in this bathroom before so a new 100 mm pipe to the drain is coming in according to the plumber. Ie there will be alot of cuts going on in that section. 
But my only concern is the current slab has rod throughout tying it all together, if i cut out this rectangle and the tiler puts a new slab in prior to his screed, could it subside in the future,separate to the existing slab,  which given its tiled and where a shower is, would be very bad for the water proofing , leaks etc? one advisor says it is highly unlikely if the ground underneath (w freshly layed pipes) is watered in and stamped down. 
I was thinking i should drill some rods in from each side and tye them together with wire and then have him pour the slab. 
Or.. just take out 30-40mm and leave it (this seems the slower method compared to a simple bust out of the whole rectangle) 
?
thankyou

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## droog

If the existing slab is 80mm thick and you take out 40mm you are left with a 40mm thick slab as the floor. Doesn’t sound right to me and that would also mean that the existing reo needs to be in that bottom 40mm for it to remain. 
Yes if the floor is cut out dowels should be used to tie the new slab to the old, or cut a smaller section and then expand the opening by removing the concrete but not the reo. The new reo can then be tied to the exposed ends of the existing reo.

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## DaleBlack

> If the existing slab is 80mm thick and you take out 40mm you are left with a 40mm thick slab as the floor. Doesnt sound right to me and that would also mean that the existing reo needs to be in that bottom 40mm for it to remain. 
> Yes if the floor is cut out dowels should be used to tie the new slab to the old, or cut a smaller section and then expand the opening by removing the concrete but not the reo. The new reo can then be tied to the exposed ends of the existing reo.

  
Should I use chemset rather than just belt in dowels?   
also what diameter bars? the ones above are larger than the ones i can see in this slab, they seem about 6mm. 
Also what wire to tie them together?

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## droog

Using chemset is a good piece of mind to help seal them in the holes drilled and prevent rusting. 
Not an engineer but would expect that anything larger than the reo used should be enough, personally would use 8-10mm for stiffness and ease of belting into the hole drilled if it decides to stick half way.
A concrete supply should have the ties used on the reo, short mild steel with loops on the end to assist twitching them, about 120 mm long.

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## DaleBlack

> Using chemset is a good piece of mind to help seal them in the holes drilled and prevent rusting. 
> Not an engineer but would expect that anything larger than the reo used should be enough, personally would use 8-10mm for stiffness and ease of belting into the hole drilled if it decides to stick half way.
> A concrete supply should have the ties used on the reo, short mild steel with loops on the end to assist twitching them, about 120 mm long.

  cheers, from memory though the chemset involves no belting in of the steel as the hole is bigger then the non chemset option ?

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