Rockwool - what are my options?

jonnydecker

Standard Member
Hi, (Please say if there is a better place on the forum for this post?). I would like to install acoustic mineral wool in to the stud walls of my home only I'm struggling to know the best product for this.
Rockwool RWA45 looked like a good option but it only comes in 600mm wide slabs when I need 400mm. So then I look at Rockwool Flexi but apparently the density is less at 33kg/m3 (see description - 100mm Rockwool Flexi Insulation Slab - 1200mm x 400mm | Mineral Wool Insulation). Then I find Rockwool Sound Insulation only I can not find the density of it and most online insulation shops don't stock it yet it is freely available from Wickes which makes me have doubts over it's quality and ability.

Can anybody explain the differences between Flexi and Sound insulation? Has anybody installed either as a general insulation around majority of their home and found them to work well in terms of blocking out noise?

Thanks
Jonny
 

zamwessell

Well-known Member
My acoustic panels are various sizes and shapes. I just cut the RWA45 to fit with a sharp kitchen knife. Was like cutting butter. I did it outside, wearing gloves to be safe.
 

jonnydecker

Standard Member
Thanks Zamwessell. I had considered this but I have over 85 m2 to install with all stud and joists at 400mm centres so it will be more practical and economic to use made to fit slabs.
 

Atomicus

Active Member
I'm not sure the product you want actually exists. Everything that's 60kg/m3 is 600mm as far as I'm aware. If there's a 400mm product at that density, I have not seen it.

I would question how much difference you'd actually notice though to be honest. In and of itself, insulation isn't a magic barrier that will give you a perfectly sound insulated solution.

I've just finished a room with a combination of Knauf RS60 (60kg/m3) and RS100 (100kg/mm) and I can attest to the fact that it's pretty horrible stuff to work with. The equivalent Rockwool product is the same. The irritation from the fibers, for me personally, was pretty horrendous. I found it a thoroughly unpleasant experience and hope to never see the stuff again.

I don't know about the stuff from Wickes, but as I say, I really don't think you'd have any issues with performance, assuming you do everything else right.
 

jonnydecker

Standard Member
No I’m not looking for high end acoustic insulation such as 60kg/m3 as it would be too expensive for size of job. I’m just looking for a solution to making my house reasonably sound proof across all rooms while I have the opportunity. The 2 products I’ve got it down to are these 2 but I don’t know which would be the better choice as their density’s are not clear.


 

Atomicus

Active Member
It really doesn't matter, but I'd imagine they're very similar given they're both Flexi slabs. If there's a difference, it won't make any significant difference to the performance. You should just get whatever is cheaper and easier for you.
 

Harkon321

Well-known Member
Most in the USA just use pink fluffy loose stuff. It's literally to break up the air gap. It's only one of the four sound proofing components.
 

Mr Andy

Active Member
For sound proofing rather than changing the sound profile I think mass is your friend, the thinner stuff you mentioned in Wickes is heavier per volume. I'm far from an expert though and it can get quite complex to do it well.
 

Harkon321

Well-known Member
Mass shouldn’t really come from the insulation. Double up heavy plasterboard for the mass. Insulation needs to fill the space.
 

jonnydecker

Standard Member
Yeah, I’m struggling for density confirmation on the two options I’m looking at and as I need to order so much I’m nervous I buy an inferior product. So hopeful somebody here may of had experience of either or both. Again, it is for general sound proofing on majority of my interior walls.
 

Harkon321

Well-known Member
What else are you doing to the stud walls??
 

AndreNewman

Active Member
Knauf do 455mm slabs for exactly this application, not sure why your centers are 400mm though.

The Knauf Ecose is much nicer to work with than Rockwool, it doesn't send fibers everywhere anywhere near as much also it doesn't outgas like most of the others. I used the rolls for my loft (I think they split at 400mm) and the 600mm slabs for acoustic panels. Next lot of bass traps I need to build I'll use these 455mm slabs and make the traps 455mm instead of 400mm, a lot less cutting.
 

Harkon321

Well-known Member
Typical internal wall boarded on each side with 2mm skim

I honestly wouldn't worry then, it'll make very little difference on its own. Fit whatever cheapest. Money would be better spent on heavier duty plasterboard or double layered if you want to reduce sound transmission.
 

Mr Andy

Active Member
Can you find a spec sheet on sound absorption for the options you have for the thickness you can fit in? You may be able to get information from the manufacturer?

I've found one in the past for various weight slabs, I'm not sure if the R value (insulation coefficient) matters to you as much. I know the thin stuff at Wickes is much denser (and less flexible) it might get expensive if you buy the same volume. Alternatively you might have space for a layer of that plus a layer of other stuff.
 

jonnydecker

Standard Member
Ok some helpful feedback. It sounds like I’m best going for the cheapest out of the 2 products as they will both be adequate.
Thanks
 

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