Polystyrene instead of studs+chipboard?

[B6304S1]

Hello!

I have just inspected our newly purchased house. There is a moisture damage in the upstairs bathroom that I was aware of. Since it seems difficult to have a split contract with a wet room certified craftsman, I have decided to do the bathroom renovations myself.

Now to the actual question; Currently, the existing construction consists of

1. Concrete vault (Intermediate floor)
2. Studs (Presumably 45x95) with insulation between the studs.
3. Floor chipboard
4. Floor gypsum (probably)
5. Self-leveling compound
6. Tiles

When I talked about the construction with the inspector (structural engineer), he said that instead of building a new floor with the old construction, I should build it like this instead:

1. Concrete vault
2. Dimensionally stable styrofoam
3. Aging-resistant plastic.
4. Self-leveling compound (fiber-reinforced)
5. Tiles

The reason for this is to avoid bringing organic materials into the floor construction in the bathroom. (This way, you eliminate the studs and chipboard)

Styrofoam is used so that you don't have to pour more self-leveling compound than necessary; otherwise, I would need to pour about 14 cm... That extra weight would not have been supported by the concrete vault without me having to put pillars on the ground floor!

Does this seem like a good construction? Opinions are gratefully received!

Best regards, Kim

 

[jon_h]

Nah, it doesn't sound quite right to have a liquid cake spackel on the styrofoam. I think you should rather cast up to the same thickness with EPS concrete or Lecakulor mixed with cement slurry. Or as you thought, but with at least a 50 mm thick slab of rapid concrete (floor mortar, floor grinding compound) before the self-leveling compound.

 

[Mikael_L]

I think it seems like you can also use foam plastic + concrete.
We have discussed such a construction here:
http://www.byggahus.se/forum/badrum/64564-ny-betongplatta-pa-cellplast.html

The only difference is that here it is a concrete slab on ground, in your case a concrete floor.

edit: I just saw that Jon wrote that , but in the thread, you'll at least find some more thoughts on the construction.

 

[jon_h]

That was what I was trying to write in the last sentence, but I suggested a quicker variant than regular concrete, which needs to set for so long. But concrete is obviously also fine if you have plenty of time.

 

[Mikael_L]

Jon, writes faster than his own shadow ...
or at least faster than me

 

[jon_h]

Hehe, yeah..

 

[B6304S1]

Thanks for the quick and good responses

Judging from the post you recommended, should I, to be safe, cast "support legs" for the concrete vault? (In case I use polystyrene)
I was thinking of using "hard" polystyrene that shouldn't compress.

But I wonder why I should use EPS cement or quick-setting concrete instead of, for example, screeding above the polystyrene?
I was mainly thinking about keeping the weight of the concrete vault down.
Or is it that EPS cement weighs less than regular concrete?

// Kim

 

[jon_h]

Self-leveling compound cannot handle the deflection that occurs under point loads. Therefore, a more substantial slab of concrete or equivalent is needed underneath.

And why would you need legs down to the vault, you ask? Ensure that the styrofoam is not hollow anywhere and has support everywhere.

 

[Mikael_L]

Thanks for the quick and good answers

Judging from the post you recommended, I should, just to be safe, cast "support legs" for the concrete arch? (In case I use styrofoam)
I was thinking of using "hard" styrofoam that shouldn't compress.

That idea, to attach the concrete cake, was mine because I saw a small potential risk with the styrofoam compressing a little. That's why I posted the question in that thread, and we worked it out so that since the strips in the floor-wall angle absorb some movement, extra support in the construction is not necessary. If you use XPS foam instead and with a strength of 200, the load and long-term properties will surely be satisfactory.

But I wonder why I should use EPS cement or quick-set concrete instead of, for example, self-leveling compound over the styrofoam?
I was mostly thinking about keeping the weight of the concrete arch down.
Or is it that EPS cement weighs less than regular concrete?

// Kim

I would imagine it’s the durability and cost. A concrete cake can handle much more load. And the price, well, big difference. The weight is not a big problem, consider that all floors and joists are dimensioned for many people or that you should be able to place, for example, a piano there. The concrete cake weighs much less after all.

 

[jon_h]

I think that TS might have referred to Ardexsmittens' customer's poor laying of the EPS, which led to the casting of the support legs.

Numbers guy, EPScement weighs 450 kg per cubic, compared to concrete which is maybe 2400 kilos. I agree with Mikael that the floor structure would likely handle the extra load without problem, but there's no reason to haul that much concrete there. If you're going to go with concrete or similar, you might as well bottom with EPS as you originally intended.

Edit: I mean bottom with EPS plastic, that is styrofoam. Not bottom with EPS cement.

 

[Mikael_L]

The Number Guy

EPS-cement weighs 450 kg per cubic meter, compared to concrete which is maybe around 2400 kilos. I agree with Mikael that the floor structure would likely handle the additional load without problem, but there's no reason to bring in so much concrete. If you’re going to use concrete or similar, you might as well use EPS as a base like you originally planned.

I think it feels like a choice between polystyrene + concrete layer or EPS-cement all the way. Between these two choices, the weight difference is probably not that significant.
But the more I think about it, the more I believe that EPS-cement all the way is the most suitable option. A single work operation, no risk at all of sinking polystyrene insulation that could jeopardize the waterproofing layer, and since it’s an intermediate floor, not much concern over energy loss downward, as it will heat the house anyway.

But, how quickly is the EPS-cement ready to lay the surface layer on? Is it possible to get EPS-c that's sufficiently hardened and shrunk in a short time if you’re in a hurry?

 

[jon_h]

Agree.

The EPS cement sets very quickly, it can be coated as soon as you can walk on it, and in fact, it should be coated with leveling compound within three days to prevent it from drying out too quickly and too much.

Edit: I just realized I was a bit careless in using the term EPS to refer to Styrofoam while also discussing EPS cement. Naturally, I didn't mean to use EPS cement as a base, but rather EPS, meaning Styrofoam, under the concrete.

 

[Mikael_L]

Wait now, clarification:
either EPS insulation with concrete on top or
EPS-cement "all the way," is that what you mean?

That's how I understood it at least.

 

[jon_h]

You understood perfectly right.

 

[B6304S1]

What night owls

EPS insulation with concrete on top?
You mean EPS insulation with self-leveling compound on top, right? Why concrete

EPS Cement otherwise sounds like the safest option if weight is not an issue?
Sounds like I should read up a bit on EPS Cement...

Thanks for your engagement!

P.S.
Is it "forbidden" to use joists+flooring chipboard+fiber-reinforced self-leveling compound after July 1st as a floor construction?

Regards, Kim