Is levelling a subfloor before insulation necessary?

[thompo]

Hello

We are in the process of replacing the ground floor.
Having opted for concrete subfloor-> 100mm Insulation-> 50mm Anhydrate self levelling screed & UFH, we got appointed a builder to pour the subfloor.

Im not 100% happy with it, overall level is about -15mm shy of where i wanted it (some rooms +10mm other areas -40mm!) , which means extra screed, cost and efficiency of UFH.
Builder sent a different contractor than the one that did the floor who said the floor is as good a job as he would have done for a subfloor, so builder says it complies with regs and is fit for purpose and not very keen to finish it any further.

My main concern is that the floor hasn't got a great finish for applying insulation. Im worried about insulation bridging a void and flexing when walked on causing the screed to crack and tiles to go with it.

I hired a concrete planer (grinder with a fancy disc) to remove the high spots and some large ridges left from tamping, just worried about dealing with the low spots and couple of particular high spots of aggregate build up. See photos, am i being too picky for a subfloor?

Untitled

• thompo
• 22 Apr 2013
• 1

Untitled

• thompo
• 22 Apr 2013
• 2

Untitled

• thompo
• 22 Apr 2013
• 1

Untitled

• thompo
• 22 Apr 2013
• 2

Opinions to level the remainder or just put the insulation down?

Thinking of using a water based self levelling compound that can bulked up with sharp sand to give a greater/thicker coverage. This was advised by a local builders yard.

As for the high points of aggregate, either grind down or cheq out the insulation to accommodate?

Thanks for any info

 

[Adrian80]

Depends what type of insulation your using?

I Poured my garage slab, i dont think i was more than 20mm out over 12m.

I used 50mm eps, which is quite flexible.

If your really concerned, clip off the high, fill the low, and the put the insulation down.

For a few bags of self leveling its not worth doing a **** job.

 

[thompo]

cheers for the response, we are using 100mm Xtratherm (similar to kingspan), its pretty rigid but will flex into a void if walked on.

Probably going to go the self levelling route and grind down the build ups.
Unfortunately the self levelling compound only covers 5m² @ 3mm, i need 3-20mm over a total area of about 20m² (joins, door ways, low spots etc) so looking at 15-20bags of levelling compound

Could a sand cement screed be used?

 

[Adrian80]

I wouldnt worry about 3mm, just do the big dips.

I would have thought sand and cement would be ok, when its thin it breaks up, but as you have insulation over it will probably be ok, all your looking to do is provide some support for underneath the insulation.

 

[mattysupra]

most water based compounds can only be used over a dry base ( below 75% RH) . A base takes approx 1mm per day to dry.

As for teh concrete subfloor teh bouilder has supplied, well he should of been given a specification to work to. In domestic property in is normally SR2. SR is a reg that builders have to work to/provide.

Google SR regs for subfloors for more info.

 

[thompo]

Thanks for the info, ill see what i can find for SR regs, quick google seems to pull up New Zeland and Austrailian reg though lol, ill keep digging.

Floor was passed by building control etc, compacted blinding, taped joints in DPM, 100-150mm concrete. But i dont know if building control considers the finish?

We had specified what floor build up we were going with saying we were putting the insulation on top and gave the finished floor level to work to (front door). Im thinking we should have specified a power floated finish to the subfloor, i had suggested it during the initial meeting but was told it wasnt necessary as its just a sub floor

Floor was completed first week in Feb so still a while yet to get to the correct RH i think.

The Sand and cement screed option is the most appealing at the min, mainly due to cost and that ive heard self levelling can be tricky to work with as it goes off quick. As you say not too worried about cracking as its really just to support the insulation where there are currently voids.