How do I patch up holes from the old waste pipe and old floor heating vent?

[seri]

Batheoom renovation, rearrange shower and remove the bathtub. Do I need to close off or how do I 
fill up hollowed holes from the old bathtub and the subfloor heater hole

[JacobZ]

Hi @seri,

Thank you for your question and welcome to the Bunnings Workshop community, it is brilliant to have you with us.

I would suggest that these holes need to be repaired to allow for a proper waterproofing membrane to be applied over the top.

Can you advise whether the concrete is a suspended slab, or if it sits on the ground? 

You will need to fill the hole with a low shrink structural grout such as Lanko 701 Duragrout. The method of application will change whether there is a surface underneath or not. If there is not, you will need to add some kind of formwork and reinforcing to allow the grout to set and be supported in place.

If you can advise on my above question, I am happy to assist further.

Jacob

[seri]

Hi Jacob,

Thanks for a prompt reply.  The concrete is a suspended slab, I can see the basement underneath where plumbing pipes etc running under.  So nothing underneath.

Thanks

Seri

[JacobZ]

Hi @seri,

I would suggest that you need to contact a professional for this job as it is likely the hole will need to be widened in order to install reinforcing dowel bars to support any grout added to the hole.

Their method of repair will likely involve installing a formwork underneath the slab to support the concrete or grout while it is hardening. Once the grout is dry, they will remove this formwork, and the grout will be supported by the dowels and the surrounding structure.

Unless you've conducted this type of work before, I wouldn't advise attempting a D.I.Y repair.

Let me know if there is anything else I can assist with. 

Jacob