Pouring concrete

[Tomw84]

The last owner of my flat hacked great chunks out of the flooring slab to make way for pipes then did a shocking job of refilling with concrete. I've chipped away all the crumbling old concrete from around the pipes so it's now in this state:

What I'd like to do now is pour concrete so that it comes to the top of the joists at the left and right of the photo, but without encasing the pipes. Then I can put in floorboards, screw them to the joists, add some reinforcement to protect the pipes, then lay a new floor over the top.

Couple of questions:

1. I'll give the cavity a hoover and a dusting before pouring, but is there anything else I ought to do beyond that to make it ready for the concrete?

2. If I were to encase the pipes in cardboard tubing before pouring, would that keep the concrete out?

Cheers

 

[biryani_boy]

1. PVA solution to act as an adhesive?
2. pipe protection foam

 

[jks7492]

Have you measured how deep the concrete infill will be? If it’s very thin then it’s likely to just crack and break up again, which is probably what has happened when the previous person has done it.

If you’re going to do it, I’d get a piece of guttering and place it underneath the pipes and then pack between the pipes and guttering to keep it in place. Pour the concrete and encase the piece of gutter and then remove whatever you packed between the pipe guttering with after the concrete has cured

 

[Tomw84]

It's around three inches deep. For the bit in the photo I might be able to get away with not using concrete because there are conveniently located joists, but there's another bit off to the side where there's nothing for the boards I'll be putting down to rest on, so filling that is going to be essential - I figure I'll use the bit which doesn't strictly need filling as a practice run.

If the concrete does break up somewhere down the line, that should be fine I hope. The main problems with what happened last time were that the concrete was proud of the tops of the floorboards, and the pipes had worked their way upwards and started bursting through!

 

[denso13]

What are the pipes for?

 

[Tomw84]

Hot water to the radiators. The ravine through the floorboards goes all the way through the hallways and back to the kitchen

 

[Hugh Jaleak]

All that screed covering the pipes needs to come out. Cementious products, (concrete and screed) attack copper, you will have a multitude of leaks before long if you dont do something. Copper piping underfloor needs to be either run through a duct, or sleeved with a suitable protective material to protect it from the concrete.

Otherwise it will rot, go brittle and leak everywhere.

 

[kingandy2nd]

Wrap the pipes in Denso tape before covering in concrete. As has been said, clean those pipes up or replace them first.

 

[Tomw84]

All that screed covering the pipes needs to come out. Cementious products, (concrete and screed) attack copper, you will have a multitude of leaks before long if you dont do something. Copper piping underfloor needs to be either run through a duct, or sleeved with a suitable protective material to protect it from the concrete.

Thanks for the heads up. Annoyingly, that'd involve ripping up the bathroom floor, and I'm not in a position to do that at the moment - just don't have the money - so I'll have to hope for the best

 

[Notch7]

Wrap the pipes in Denso tape before covering in concrete. As has been said, clean those pipes up or replace them first.

is that where the forum member gets his name?

 

[denso13]

is that where the forum member gets his name?

*cough*, yes actually, I take it you mean me. Goes back to technical college during my apprenticeship many moons ago. It was funny at the time

 

[Hugh Jaleak]

Thanks for the heads up. Annoyingly, that'd involve ripping up the bathroom floor, and I'm not in a position to do that at the moment - just don't have the money - so I'll have to hope for the best

I'd try and arrange something so you have a clean section of copper available to couple onto for future needs, as and when you come to/need to replace the sections under the bathroom floor.

 

[Tomw84]

Yeah, I'll look into it for sure. The pipes actually seem to be in fairly good nick for the time being, once they're wiped clean, so with a bit of luck it'll be a few years before there are any problems, by which time I'll have finished the main refurbishment (still need to put in a kitchen, rewire, replace the boiler, put a floor in and plaster a few walls) and hopefully saved some money!

 

[Tomw84]

Well here we go - hope this works!

 

[biryani_boy]

what about the elbows? those have to be protected too.