Advice Needed – Localized Floor Collapse Above Plumbing Pipes

[BonnieW7]

Hello everyone, I'm looking for some professional advice regarding a floor repair issue in my kitchen. Approximately 10 years ago, a plumber completely redid the plumbing system in my house. To install the new pipes, he cut through part of the concrete floor, routed the pipes underneath the floor, and then backfilled and repaired the area before reinstalling the flooring. I've noticed that a small section of the floor (approximately 25 cm x 25 cm / 8–10 inches square, under vinal adessive tile) has started to sag and crumble. This area is directly above the plumbing pipes. My suspicion is that the concrete or repair material placed over the pipes was too thin, or that the fill underneath has settled over time, creating a void. The floor has not yet completely collapsed, but it appears to be heading in that direction. One concern is that this area is located in a regular walkway. If the floor eventually gives way completely, someone could step directly onto the pipes, potentially damaging or breaking them. A few additional details: The finished floor is covered with approximately 2.5 mm vinyl flooring. There appears to be only about 20 mm (3/4 inch) between the top of the pipes and the underside of the floor/concrete above. I do not currently know whether the pipes are PEX, multilayer, copper, or another material... probably copper. My current repair idea is: 1. Remove the vinyl flooring. 2. Remove all loose and damaged concrete/fill material. 3. Inspect the pipes and determine the extent of any void. 4. Fill any voids with a non-shrink structural grout. 5. Install a 4 mm stainless steel plate extending beyond the damaged area and bearing on sound concrete around the perimeter. I am not sure if this step in needed.. any thoughts? 6. Apply a thin layer of repair mortar above the plate. 7. Reinstall the vinyl flooring. My objective is to distribute foot traffic loads onto the surrounding concrete and protect the pipes from direct loading. Questions: Does this seem like a reasonable repair approach? Would you recommend a different method? Is the stainless-steel plate unnecessary if the void is properly filled? Are there any concerns with using non-shrink grout around plumbing pipes? If only 20 mm of cover exists above the pipes, how would you repair this area professionally? Is there a better material than a steel plate for this application? Any advice from plumbers, builders, or concrete repair specialists would be greatly appreciated. Thank you in advance.

[Nickfromwales]

25 minutes ago, BonnieW7 said:

Hello everyone, I'm looking for some professional advice regarding a floor repair issue in my kitchen. Approximately 10 years ago, a plumber completely redid the plumbing system in my house. To install the new pipes, he cut through part of the concrete floor, routed the pipes underneath the floor, and then backfilled and repaired the area before reinstalling the flooring. I've noticed that a small section of the floor (approximately 25 cm x 25 cm / 8–10 inches square, under vinal adessive tile) has started to sag and crumble. This area is directly above the plumbing pipes. My suspicion is that the concrete or repair material placed over the pipes was too thin, or that the fill underneath has settled over time, creating a void. The floor has not yet completely collapsed, but it appears to be heading in that direction. One concern is that this area is located in a regular walkway. If the floor eventually gives way completely, someone could step directly onto the pipes, potentially damaging or breaking them. A few additional details: The finished floor is covered with approximately 2.5 mm vinyl flooring. There appears to be only about 20 mm (3/4 inch) between the top of the pipes and the underside of the floor/concrete above. I do not currently know whether the pipes are PEX, multilayer, copper, or another material... probably copper. My current repair idea is: 1. Remove the vinyl flooring. 2. Remove all loose and damaged concrete/fill material. 3. Inspect the pipes and determine the extent of any void. 4. Fill any voids with a non-shrink structural grout. 5. Install a 4 mm stainless steel plate extending beyond the damaged area and bearing on sound concrete around the perimeter. I am not sure if this step in needed.. any thoughts? 6. Apply a thin layer of repair mortar above the plate. 7. Reinstall the vinyl flooring. My objective is to distribute foot traffic loads onto the surrounding concrete and protect the pipes from direct loading. Questions: Does this seem like a reasonable repair approach? Would you recommend a different method? Is the stainless-steel plate unnecessary if the void is properly filled? Are there any concerns with using non-shrink grout around plumbing pipes? If only 20 mm of cover exists above the pipes, how would you repair this area professionally? Is there a better material than a steel plate for this application? Any advice from plumbers, builders, or concrete repair specialists would be greatly appreciated. Thank you in advance.

I’ve done these types of jobs hundreds of times over the past 35 years, and defo zeto need for a stainless plate; I think that would make the repair fail again.

 

Do as you suggest, clear the trough and hoover it all out. Prime (saturate) with 50/50 PVA/water, applying copiously until you don’t see it being sucked into the concrete any more, and then pour in some of this:

 

 

Will be right for life after that goes in there. Mix it with fresh water and to a consistency a-la a thick gravy.

 

If the pipes are bare copper, try and tape these up with gaffa / duct tape. 

 

Lay it directly on to the soaking wet PVA mix and don’t fear that being any compromise to it, it’ll be fine. 

[BonnieW7]

Thank you for the advice, that's very helpful.

One additional question: if the pipes turn out to be bare copper, would it be advisable to cover them with a fairly thick foam pipe insulation sleeve before placing the repair mortar?

My thinking is that the insulation would create a small separation around the pipe and allow for thermal expansion and contraction without the copper being tightly bonded to the repair material. Would that be considered good practice in this situation, or would simply wrapping the pipes with duct/gaffa tape be sufficient?

Given that there is only around 20 mm of cover above the pipes, I'd be interested to hear how you would normally accommodate pipe movement when carrying out this type of repair.

[Nickfromwales]

Are they heating pipes, or a hot & cold?

 

20mm doesn’t leave much (any) room to insulate effectively.

 

15mm pipe with 9mm wall insulation = 33mm diameter, x2.

 

You can buy a thin (3mm) neoprene tape  LINK which may suit and give you that little bit of wiggle room. 

[BonnieW7]

Thank you very much for the advice and for taking the time to explain the repair process in such detail. I really appreciate it.

I'll check what material the pipes are made of and will take some pictures tomorrow.

One question: when you say "Prime (saturate) with 50/50 PVA/water", what type or brand of PVA would you recommend? Would a standard building/bonding PVA sealer be suitable, or is there a specific product you would use for this application?

Thanks again for your help.

[Nickfromwales]

5 minutes ago, BonnieW7 said:

 

 

Thank you very much for the advice and for taking the time to explain the repair process in such detail. I really appreciate it.

I'll check what material the pipes are made of and will take some pictures tomorrow.

One question: when you say "Prime (saturate) with 50/50 PVA/water", what type or brand of PVA would you recommend? Would a standard building/bonding PVA sealer be suitable, or is there a specific product you would use for this application?

Thanks again for your help.

No probs   

 

https://www.screwfix.com/p/no-nonsense-d2-pva-adhesive-5ltr/474ek?ref=SFAppShare

 

👍👍

[BonnieW7]

Thank you again, Nick.

I suspect the original problem may be that there is only about 20 mm of cover above the pipes. I've also received advice suggesting that pipes under a slab would ideally have compacted fill around them and significantly more concrete cover above than I appear to have.

If, after opening up the floor, I find that the pipes really are only about 20 mm below the existing surface, would you still proceed with the repair using the mortar you recommended, or would you be concerned about the lack of cover?

Also, if I discover that the void has been caused by settlement of the original backfill beneath the pipes, would you:

• remove all loose material and fill the area entirely with the repair compound, or
• first try to reinstate support beneath the pipes using compacted sand or pea gravel before repairing the concrete above?

My concern is whether pouring repair mortar directly onto exposed pipes is the best approach, or whether it's preferable to provide compacted support around and beneath them first.

Finally, would you expect a repair with only around 20 mm of cover above the pipes to remain durable in a normal kitchen walkway, or does that depth itself suggest a more substantial repair is needed?

I'd really value your opinion given your extensive experience with these types of repairs.

Thanks again for your help.