Does anyone know how PU injection works?

I have a spot in the ceiling with water mark.
The contractor suggested PU injection grouting.

My question is if he seal the area (water mark spot), where is the water (leaking from somewhere) going?
So if he seal one spot, I am sure the water will find its way to another section of the ceiling right?

If he not sealing the root cause of leakage, the water will flow elsewhere if he targeted seal the water mark area.

You need to find the leak and fix it before worrying about cosmetic stuff

The leak could be from the balcony drain outlet from unit above.
Somewhere somehow the water leaking to my unit ceiling.

the developer now try to use PU injection on my sealing.
if the injection not fully cover all the way to the unit above, I worry the water will find another route to another part of my ceiling.

Since is developer's defect rectification work, then you have to just accept their work. If it leaks again, you need to call them until no leak subject to warranty period.....unless you want to spend money to call a private contractor.

This post has been edited by mini orchard: Oct 29 2020, 01:19 PM

As far as I know PU injection means injecting some substance through some areas perimeter of the walls or ceiling through some holes
And these substance will fill up crack or holes
Anyone can correct me if I wrong
Better ask where the root cause
If rooftop tiles break then need to replace rooftop tiles
If concrete slab then maybe PU injection is not a bad idea
My kitchen extension side walls is leaking badly during heavy thunderstorm. Above is concrete slab.
Suspect is the joint between slab floor with wall side but I dunno
So now I paint waterproofing and it stop the leak

PU will only direct the water to another area ... and hopefully outside ... but over the years mold will start growing and back to square ... find the cause.

This post has been edited by mini orchard: Nov 1 2020, 12:02 AM

Injection is a temporary solution. Got to find the.leak from unit above, no other way. Like you say when the source is not fix, water will find its way out going down

PU injection is only temporary fix for the particular spot. If you don't fix the root cause the water can always find another weak spot to come out, the problem can never be solved this way. Best to find a reliable contractor to rectify the cause and fix the root problem. then apply proper waterproofing and coatings.

I used to PU injection my whole house, cost me RM10K.
Then ended up I demolish that house and rebuilt from scratch again.

But later I sold that house already. Getting old to fix here fix there.