Fibreglass batts for soundproofing

[JohnD]

I want some sound insulation under the bathroom floor. I have not had to do this for a long time and looked for dense, heavy batts in a grey/brown colour, that do not shed dust and fibres like loft insulation (I am somewhat asthmatic)

I found bales of 50mm for cavity walls, and 75mm for going under screeded floors. The 75mm would need a lot of cutting and waste to fit, but the 50mm looks dense and feels suitably heavy when I lift the bale, and is about the right size to fit snugly between my 14" centres joists

However it is marked "For cavity wall Insulation Only"

I wonder why this is? might it have some characteristic that makes it unsuitable for my purpose? Are there different grades for different usage? Or might it just be that it has only been tested and approved for cavity walls?

 

[noseall]

we have used them but have never 'measured' the acoustic resistrance compared to regular fibreglass insulation.

the amount of difference could not be measured or registered by mere humans, i'm fairly sure John.

go ahead and use the batts, we do.

 

[Deluks]

Wear a mask! ? Once they're in, they're in, no probs after that.

It's for sound insulation you can ignore the instructions, they probably only do it to prevent people from mistakenly buying it as loft insulation (for which it would be too thin/costly)

If you are concerned about fibres after installation, I know that rockwool (for example) can be sprayed with a watery pva mix (with a splash of washing up liquid added) to help keep the fibres down.
Once you've done that and allowed it to dry, wrap with weed control membrane (cheapo stuff will do) and tape up. Then install and you'll not see any fibres. The fabric will do little to reduce it's soundproof qualities.

 

[JohnD]

thanks for the tip

I think it probably is Rockwool. I will try the water/PVA/Fairy spray as I have everything I need for it, and I can do that in the garden before I carry it up.

you're right, I do use a mask.