bounce in my floor insulation

[pilsbury]

Had a right day today laying my DPM single handed with the wind! Anyhow, that is down as is my 100mm insulation boards. Problem is, with corner folds, drainage pipes coming through the floor etc, the insulation has a bounce to it. Efforts to get my sand blinding flat have not payed off.

My only thought is that will 6" of concrete pin it down? Bit pi55ed off really. Was hoping for a solid stable insulation layer, not a bouncy castle.

Thoughts?

 

[tony1851]

It will be OK once the concrete is on.
But have you included the separation layer between insulation and concrete?

 

[Doggit]

How about putting the concrete down first, then apply some SLC, and then the insulation. Did you use screed rods to level the sand, or just do it freehand.

 

[pilsbury]

Tony - what's this separation layer? Thought I just poured directly on the EPS70 insulation?

Doggit - freehand. And looks like I didn't do the best job. To take it up again would make me cry.

 

[Doggit]

To take it up again would make me cry

Not wishing to put a damper on things, nor impune your capabilities, but would it be better to cry now, or after the next stage. Is there's any bounce in the insulation, will it bend and crack when you lay the concrete; and if it does, then you'll have to use SLC afterwards to level again. If there's a possibility of that happening, then maybe adding just 5" of concrete, and then an inch of SLC might be e better course of action. It's also so allow you to drill the concrete and add rawlplugs and screw to give you a working level for the SLC, and it never levels as well as it should. What's the floor area.

 

[pilsbury]

The floor area is 30m sq, then going through a doorway to 8m sq.

Just to clarify, when you say I add the concrete the insulation will bend and crack, what's the problem? Surely this will happen under the weight of the wet concrete giving me a stable base? My worry is the insulation not bending and cracking leaving hollows once the concrete has set making the floor prone to cracking or subsidence.

I do intend to use some SLC after, my initial intention was a couple of mm to iron out some of the out of unlevel bits. Might go for more on your suggestion.

 

[tomfe]

Don't lay the concrete if your insulation is moving, at best it might move slightly when you move across the floor. Foam it in place under the boards if neccessery, unless you do a proper screed type job with the sand it's never going to be flat and level all over so it's best just to foam it.
EPS has much more give in it which so the sand etc can be less level.

 

[pilsbury]

Foam it in place? With what? Canned expanding foam? Just squirt a load down and press the boards into it?

 

[tomfe]

Your base hopefully wont be that unlevel you need to put loads under, but if you have a wobble board put some under one edge.
If your boards are cupped lay them with the concave side down and the concrete will push it down. If your boards are extremely cupped send them back.

 

[John D v2.0]

I'm not an expert at all, but I can't imagine having any voids or weak spots whatsoever is a good idea. The slab/screed needs to be fully supported. The compressive strength of pir and sand/hardcore is good when the load is spread, but expanding foam won't be. I think you want to aim that the pir will be completely supported by the sand/dpm layer before the concrete is starting to cure.
As I say, not an expert, and the pros may know more of what you can get away with in reality.

 

[tomfe]

If it was a screed you'd more concerned but concrete will be fine.
You'll never get a perfectly flat and level sub-base unless you put in screed rails and who is going to do that?

 

[pilsbury]

So I've put a bit of sand under the worst bits and I've made some "relief cuts". This way the insulation is not so level but some of the bounce is taken up.

I've done a test and stuck a few blocks on the worst boards and they seem to press the insulation to the ground. I'd bet that 6" of concrete is heavier.

Dreading tomorrow. Me being a have-a-go-hero, I can do most things..... just takes me 10 times as long. With the concrete I don't have 10 times as long. I've got to be a pro straight from the off. This is something that if it goes wrong, it really goes wrong - a world of pain.

 

[garyo]

Have you put another layer of DPM (or even vapour membrane) over the top of the PIR? You don't want the concrete getting through cracks and under your foam and making it float. Also, it's not advised to allow the concrete come in direct contact with the aluminium foil because it reacts.

 

[pilsbury]

Not used foil backed PIR. I've used EPS70 polystyrene. Didn't think I needed to cover?

 

[freddiemercurystwin]

Concrete may seep through the gaps between the insulation boards and if it does will lift your insulation, a 500 gauge vapour barrier will prevent this.