new floor screed has cracks and sounds hollow

[P.Pipe]

Hi, I recently had some screed installed by a local builder, approx 6 weeks ago.

It's since started to show small cracks and, when I knock on these sections it sounds hollow. Where as the non cracked sections sound solid. It was about 40mm depth and was sand/cement/pva based.

Now it's cracked I'm concerned it'll start to curl or get worse, and need re-doing.

So I'm after a second opinion, there's some pics and a video below. Is there any rescuing this? should it get redone? Will it be ok as it is?!

thanks in advance...

 

[Notch7]

Is the screed, bonded, unbonded or floating?

If the screed is laid over insulation 40mm is too thin

 

[Doggit]

It should be 60mm minimum, and there shouldn't be any PVA in it. Was it sharp or building sand, and how thick was the insulation underneath, and what was below that.

 

[P.Pipe]

It should be bonded to the concrete base below it (there's no insulation, it's an old 60s house).

I believe they used sharp sand, and PVA as a bonding agent.

 

[Doggit]

PVA is designed to reduce suction. Now it can be put on, left to dry, and then a second coat applied, and the screed put down before it goes off, but SBR should really have been used, not PVA, and it should still have been 60mm.

At 40mm, you'd have been better off applying acrylic primer to the floor, and then using self levelling compound.

 

[P.Pipe]

Yeah the cost of 40mm of self levelling compound soon adds up, there's quite a few places online (e.g. https://www.concretecentre.com/Building-Elements/Floors/Floor-Screeds.aspx) that suggest a bonded screed can be laid at depths of around 25mm, so I was lead to believe this would be ok and reassured by the builder.

I guess I'm unsure what to do next, as essentially I need to know if it's a lost cause and has to come up or can it be remedied? Should I get the builder do it again but with SBR to make sure it bonds correctly?

 

[Doggit]

I'd definitely call the builder in; especially as he said that it could be done, and it hasn't worked. Under the circumstances, this should be down to him to rectify the problem.

And having had a look at the article, I suspect it's the bonding that's failed. It's the typical sand and cement screeds that's the appropriate section. I'll have a look at it in more depth tomorrow, but he's definitely mad a mistake.

 

[Notch7]

Yeah the cost of 40mm of self levelling compound soon adds up, there's quite a few places online (e.g. https://www.concretecentre.com/Building-Elements/Floors/Floor-Screeds.aspx) that suggest a bonded screed can be laid at depths of around 25mm, so I was lead to believe this would be ok and reassured by the builder.

I guess I'm unsure what to do next, as essentially I need to know if it's a lost cause and has to come up or can it be remedied? Should I get the builder do it again but with SBR to make sure it bonds correctly?

How good was the prep? It seems the concrete needs cleaning and maybe keying to create a good bond and Shot blasted or scabbled

http://www.screeding.org/html/body_traditional_screed.html

 

[P.Pipe]

Thanks Notch7/Doggit for your help and replies. Yeah I suspect you're both right, I don't think it was prepped properly, I don't believe the base was scabbled or shot blasted. I'll get in touch this week.

I know it's hard to tell from the video and pics, but does it seem like the screed has failed to you guys?

 

[Doggit]

The video was a good one, but using SBR, possibly as a slurry first, would negate the need for shot blasting the floor.