Tom Posted June 5, 2023 Share Posted June 5, 2023 (edited) So I'm currently prepping for the pour of our floor which is 20cm reinforced concrete over insulation. We have several 110mm pipes coming up through - one for an internal stack, another for the loo waste. The chap that will be pouring the floor wants all these terminated below floor level - so that he can powerfloat and then polish over the top. He suggested capping the pipes with a square or round of ply, this would then be evident after the floor had been poured as the concrete would colour differently as it would just be a ~10mm thick cover over the ply, the concrete can then be carefully chipped out and the pipes exposed. This might work well for him (and we're going to do this in another few areas where we have conduit coming up for floor sockets) - but is it OK from a plumbing point of view? I would presumably have a 110mm connector to be able to extend the stack, but not ideal I'm guessing. Any thoughts? Thanks all Edited June 5, 2023 by Tom typo Link to comment Share on other sites More sharing options...
JohnMo Posted June 5, 2023 Share Posted June 5, 2023 I used left over PIR insulation, around areas like this, was easy to break out later, make big enough to give some wiggle room to move around later and make connection easy. Once you are ready back fill these areas with concrete if the need too, or leave as is. Our construction is slightly different from yours, 200mm reinforced concrete, 200mm insulation, 100mm concrete. First image is prior to first concrete. Second image just prior to second concrete, where you see the pipe stubs coming up, these were encased in PIR but only on the second pour. Link to comment Share on other sites More sharing options...
Tom Posted June 5, 2023 Author Share Posted June 5, 2023 Thats brilliant @JohnMo, thanks for posting and sharing the pictures. Good idea re the PIR, can I ask what depth of this you used and what depth of concrete went over? Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 5, 2023 Share Posted June 5, 2023 I assume you’re putting straight couplers onto each, and then the blank plug goes into that just below the surface? Link to comment Share on other sites More sharing options...
JohnMo Posted June 5, 2023 Share Posted June 5, 2023 I used 100mm PIR and there was 100mm concrete Link to comment Share on other sites More sharing options...
Tom Posted June 5, 2023 Author Share Posted June 5, 2023 29 minutes ago, Nickfromwales said: I assume you’re putting straight couplers onto each, and then the blank plug goes into that just below the surface? Yessss... though I was thinking to leave enough space around the top of the pipe (by using PIR or whatever) to give enough room when this is hacked away to be able to add the coupler, makes sense to add the coupler first though I guess, then just stick a bit of PIR/wood on to the top of the blanking plug and have this 10mm below the surface of the poured concrete. Does this sound OK? Link to comment Share on other sites More sharing options...
Tom Posted June 5, 2023 Author Share Posted June 5, 2023 32 minutes ago, JohnMo said: I used 100mm PIR and there was 100mm concrete Ah, gotcha, so full thickness of the pour Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 5, 2023 Share Posted June 5, 2023 17 minutes ago, Tom said: 10mm below Depends on the size of the aggregate I suppose, as the float will just roll over them if they're bigger than the gap. Just take some measurements from datum timbers set into the ground outside of the slab and you'll not struggle to find them afterwards, then you can make them an inch lower than TOC to guarantee the power-float can whizz over them. Take lots of pics / measurements You go and pick these out whilst the floated concrete is 'green', like literally as soon as you can walk on it. Link to comment Share on other sites More sharing options...
Temp Posted June 5, 2023 Share Posted June 5, 2023 I think using insulation is much better idea than plywood. Less chance of damaging the pipe fitting when removing it. Link to comment Share on other sites More sharing options...
saveasteading Posted June 5, 2023 Share Posted June 5, 2023 My preference is to box around the pipe by about 100mm. It needs to be spiked down, or tied to by wires, or filled with sand to stop it moving when kicked or knocked by a float. The concrete is simply placed around the box to remove the fear of bashing or filling the pipe. When the concrete is hard you can leave the box in place or remove it. If being left open for a while, fill with sand to avoid a trip hazard. Then when the time comes for drainage connections, the pipe is undamaged and there is tolerance for the plumber to adjust it. Then a shovelful of concrete fills the gap. In theory the box out can be eps or pir, but it moves and floats. It takes time to make the boxes but it can be repaid many times over. Link to comment Share on other sites More sharing options...
Tom Posted June 5, 2023 Author Share Posted June 5, 2023 Ah, good point re the aggregate. And the straight coupler - on before or after? Link to comment Share on other sites More sharing options...
Tom Posted June 5, 2023 Author Share Posted June 5, 2023 3 minutes ago, saveasteading said: My preference is to box around the pipe by about 100mm. It needs to be spiked down, or tied to by wires, or filled with sand to stop it moving when kicked or knocked by a float. The concrete is simply placed around the box to remove the fear of bashing or filling the pipe. When the concrete is hard you can leave the box in place or remove it. If being left open for a while, fill with sand to avoid a trip hazard. Then when the time comes for drainage connections, the pipe is undamaged and there is tolerance for the plumber to adjust it. Then a shovelful of concrete fills the gap. In theory the box out can be eps or pir, but it moves and floats. It takes time to make the boxes but it can be repaid many times over. Thanks mate, I can certainly see your logic but not sure we can do exactly that given the make-up of our slab. It's 200mm thick with four layers of rebar mesh passing around the 110mm pipes Link to comment Share on other sites More sharing options...
saveasteading Posted June 5, 2023 Share Posted June 5, 2023 5 minutes ago, Tom said: given the make-up of our slab So vary it for your own circumstances. The mesh makes the box easy to fix in place In the majority of cases when I've had this done, the slab has been 175 thick, with mesh. Mesh can be cut....more about that if you want. 4 layers of mesh. I'd love to hear why. Link to comment Share on other sites More sharing options...
Tom Posted June 5, 2023 Author Share Posted June 5, 2023 2 hours ago, saveasteading said: 4 layers of mesh. I'd love to hear why. You're not the only one! For layers of A393. It's a suspended slab and is going to be built on with blocks. The SE was adamant it was needed... Link to comment Share on other sites More sharing options...
saveasteading Posted June 5, 2023 Share Posted June 5, 2023 SE will be right that it is needed but not necessarily in that way. At some stage it is cheaper to use bars and a steel fixer. SE for theory and calculations, contractor for cost knowledge. What span is the floor between support walls? Is there any reason ( such as span) why you can't use beam and block? Link to comment Share on other sites More sharing options...
Tom Posted June 6, 2023 Author Share Posted June 6, 2023 Waaaay too far down the road with the suspended slab to consider alternatives now. Each of the four sections of floor is approx 8x4.5m, supported around the perimeter. First layers of rebar are down, I need to spend the next few weeks zip-tying the ufh pipes down, then wiring the deckchairs in before the final few layers of mesh. Link to comment Share on other sites More sharing options...
saveasteading Posted June 6, 2023 Share Posted June 6, 2023 4 minutes ago, Tom said: Waaaay too far down the road Ahhh yes. Clearly. So back to the question. The builder wants to power float without hindrance, but doesn't care that you would have to break out the floor to find the pipes. With that fort knox floor there is no way you should break it out. So protect the pipes against impact. Assume the worst,that they WILL bash hard with a power float. Best to box with timber...as it will only be about 50mm above the mesh you can use 4x 2 or similar. You don't want concrete in the pipes so close the tops. Stuff in sponge then cover with plastic bag. The concretor doesn't seem experienced or this would be normal. Therefore stay present throughout . NB power floating is once when the concrete is stiffening, then again hours later if a hardening polish is required. Link to comment Share on other sites More sharing options...
Jenki Posted June 6, 2023 Share Posted June 6, 2023 17 hours ago, Tom said: Yessss... though I was thinking to leave enough space around the top of the pipe (by using PIR or whatever) to give enough room when this is hacked away to be able to add the coupler, makes sense to add the coupler first though I guess, then just stick a bit of PIR/wood on to the top of the blanking plug and have this 10mm below the surface of the poured concrete. Does this sound OK? Personally would steer clear of plastic bags etc, as per @JohnMo photo above, coupler and a proper blank these could be set at finished height or a few mm below, then there is 100% zero chance of concrete entering the pipe. the power float will be over the top / skim the blanks and they will be easily visible. the coupler then allows you to connect whatever you need to, and if you do want wiggle room, follow the advice above, re timber boxing or PIR. 1 hour ago, saveasteading said: The concreter doesn't seem experienced or this would be normal. Therefore stay present throughout . +1 to this - - You do not want the chance of concrete entering the pipe by a bit of ply moving when tons of concrete are sloshing about. Link to comment Share on other sites More sharing options...
saveasteading Posted June 6, 2023 Share Posted June 6, 2023 17 hours ago, Tom said: And the straight coupler - on before or after? That is also worth considering. A straight coupler then a length of pipe sticking up a metre or so, which flags the pipe. Concrete pumping is a very arduous job, fighting a pipe that is very heavy and pumping. The guy on that isn't looking for your pipe, so make it obvious. Then later the helicopter come dodgem, banging into edges and anything else. All this still inside the wooden box. Try to get them in exactly the right position so they are not clashing with walls (mm count), and completely vertical as the concrete is encasing through for ever. You can tie them to the reinforcement and to your top boxing. This all protects the end of the pipe for easy connection later. A big pour is exciting as well as stressful. Be there, but stand back. Oh....where is the washout water going? They have to clean the pump pipes and it is messy. Link to comment Share on other sites More sharing options...
Tom Posted June 6, 2023 Author Share Posted June 6, 2023 Thanks for all your responses, really helpful. How about this for a solution: I'll sleeve the 110mm pipes with 150mm plastic ducting (eg https://www.screwfix.com/p/manrose-150mm-round-ducting-1m/207GY?kpid=207GY&ds_rl=1249404&gclid=CjwKCAjwsvujBhAXEiwA_UXnAFPVjHn0tcX-6D__aSDqrLyQNSrKWppXkC81Ba1cUv1O8ZFA7Gy9BxoC-1UQAvD_BwE&gclsrc=aw.ds). I can stab the ducting in to the insulation layer, then bring it up short of FFL and cap it with a bung of EPS at 20mm below FFL. Within this I'll put a straight coupler on the 110mm with a bung (just in case). 12 hours ago, saveasteading said: The concretor doesn't seem experienced or this would be normal. Therefore stay present throughout . He does seem to know what he's doing, his business is just these floors, it's just me that is slow on the uptake. He has suggested a dry powder sprinkle during the powerfloat stage to harden and give the darker finish we are after, I think. Link to comment Share on other sites More sharing options...
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