Rockwool insulation

[Donald]

I need to re-insulate the kitchen floor over a crawl space. It currently has falling down fiberglass batts. Mice have made little messes here and there. So rather than replacing the damaged fiberglass batts I was thinking of replacing all the fiberglass batts with rockwool.

Never worked with rockwool but looks like I can just push up these flexible rectangles of rockwool and they will stay put. I could even get a higher R-value and then have the insulation stick below floor joists.

Currently the hot and cold water pipes freeze when below 5F (typically at night) and they are at the top of the floor joist where the joist meets the floor covered in a batt of insulation.

So how is rockwool to work with? Most people seem to use fiberglass.

 

[Warstud]

It's easy to work with. I used a bread knife to cut it and it needs to be around 3/4" oversize to keep it from falling out.

 

[Donald]

Originally Posted by Warstud
It's easy to work with. I used a bread knife to cut it and it needs to be around 3/4" oversize to keep it from falling out.


If for example there was a 3/4 pipe in upper corner would it flex around it, or stop when it hits it?

 

[jalf]

Sounds like a 100-pack of 16-inch metal insulation support rods is what you need, regardless of whether you go rockwool or fiberglass.

 

[Warstud]

Originally Posted by Donald
Originally Posted by Warstud
It's easy to work with. I used a bread knife to cut it and it needs to be around 3/4" oversize to keep it from falling out.


If for example there was a 3/4 pipe in upper corner would it flex around it, or stop when it hits it?

You could either cutout for the pipe or split the insulation and wrap around the pipe.

 

[atikovi]

Isn't rockwool a mineral product like asbestos?

 

[maxdustington]

Originally Posted by jalf
Sounds like a 100-pack of 16-inch metal insulation support rods is what you need, regardless of whether you go rockwool or fiberglass.
Never even heard of those and I've insulated a few houses in my day.

Like mentioned above, cut it 1/2-3/4 oversized. My co-worker is really good at it and he told me 1/2 oversize. If it gets too compressed, it loses R value.

Rockwool can be cut by a knife, I would recommend a the 25mm Olfa over the 18mm. You can also cut it with a bread knife, I have a Roxul branded bread knife in my kitchen that my Dad got from somewhere, probably by buying a bunch for a project. I would be trying to minimize fibres flying everywhere, so a knife is probably better. It kills knife blades because it is mineral, not fibreglass insulation. It's funny when you go into a house that is/has been insulated and there are numerous completely whole but completely dull utility knife blades all over the place.

Get a real respirator and possibly a Tyvek suit/ goggles that can seal the fibres out of your eyes. You are going to be up close and personal with it insulating a crawl space so quality of life equipment can make the difference between a gross tedious job and a nightmare that you will never attempt again.

 

[KGMtech]

Originally Posted by atikovi
Isn't rockwool a mineral product like asbestos?

It is not like the nasty asbestos. It is made from injecting slag from steel production into a hot air jet, so it's doing the environment multiple favors. It is nice stuff to work with, and doesn't absorb water either.

 

[atikovi]

Then why don't they call it slagwool? What does rock have to do with it? Is that how steelwool is made too?

 

[KrisZ]

I've worked with it in my previous house. A nice serrated knife works really well.
If you have to go around big pipes, cut out where the pipe will sit. Compressing the bat makes it lose its R value substantially.
It's good stuff, water and mold resistant. And once you get a hang of it, it quite easy to work with.

 

[PimTac]

I've worked with it and it performs well. I second the suggestion of full protective clothing and respirator mask and goggles. The stuff can work in between openings in your clothing. I used masking tape on my wrists and ankles to eliminate that. This was before full suit coveralls were available to the general public though.

 

[jalf]

This is what I'm talking about. (Link below.) Keeps insulation in place in crawl spaces below kitchen floors.

https://www.homedepot.com/p/Simpson-Strong-Tie-16-in-Insulation-Support-100-Qty-IS16-R100/100375163

 

[Warstud]

Originally Posted by jalf
This is what I'm talking about. (Link below.) Keeps insulation in place in crawl spaces below kitchen floors.

https://www.homedepot.com/p/Simpson-Strong-Tie-16-in-Insulation-Support-100-Qty-IS16-R100/100375163

Good suggestion...Although you probably wont need it with Rockwool.... since it's alot more Rigid than fiberglass insulation.

 

[Donald]

Originally Posted by jalf
This is what I'm talking about. (Link below.) Keeps insulation in place in crawl spaces below kitchen floors.

https://www.homedepot.com/p/Simpson-Strong-Tie-16-in-Insulation-Support-100-Qty-IS16-R100/100375163


I have some of these. A recent article said to use thin lath boards as the insulation supports tend to compress the insulation.

When you put in the insulation supports do you have the slight bow going up or down or sideways.

 

[wag123]

Originally Posted by Warstud
Originally Posted by jalf
This is what I'm talking about. (Link below.) Keeps insulation in place in crawl spaces below kitchen floors.

https://www.homedepot.com/p/Simpson-Strong-Tie-16-in-Insulation-Support-100-Qty-IS16-R100/100375163

Good suggestion...Although you probably wont need it with Rockwool.... since it's alot more Rigid than fiberglass insulation.
Yes, but it is also heavier. Insulation contractors always use these support rods in installations like this. Rockwool is also more expensive than fiberglass.

 

[jalf]

If you look at the illustration on the right side of the box in the link, you can see how the metal rods are intended to be installed. No doubt over time, some of the wire supports will go from an upward bow to a downward bow. As long as the insulation is in close proximity to the under side of the kitchen floor ... and not lying on the ground ... that's all that matters to me. Yes, wood lath is more stable but not nearly as quick to install. I recall that I had to use wood lath several years ago under my kitchen floor when I discovered that a couple floor joists were spaced closer to 17 inches than 16 inches apart, thus making the metal wire supports too short to work.

 

[ecotourist]

Originally Posted by KGMtech
Originally Posted by atikovi
Isn't rockwool a mineral product like asbestos?

It is not like the nasty asbestos. It is made from injecting slag from steel production into a hot air jet, so it's doing the environment multiple favors. It is nice stuff to work with, and doesn't absorb water either.

Slag wool and Rock wool are intermediate in hazard between fibreglass (least hazard) and asbestos (greatest hazard). So if you're going to use rockwool, full respirator protection (half or full mask respirator with Hepa filters) would be a good idea. (And if I were advising a friend or relative who insisted on installing rockwool, I'd tell them it was essential).

But I prefer not to use slagwool or rockwool at all. Fibreglass is itchy on the skin, but it's easy to use and relatively safe.

I think you'd be better off finding a good way to support fibreglass bats.

 

[JC1]

Originally Posted by KrisZ
I've worked with it in my previous house. A nice serrated knife works really well.
If you have to go around big pipes, cut out where the pipe will sit. Compressing the bat makes it lose its R value substantially.
It's good stuff, water and mold resistant. And once you get a hang of it, it quite easy to work with.


+1. Insulated my basement with it. It's much better than Fiberglass pink. It won't sag over time like fiberglass will.

 

[Donald]

The other issue is Home Depot does not have one bag of the rockwool batts (I would like to use) locally, If you try and order some you need to order several.

 

[maxdustington]

Originally Posted by Donald
The other issue is Home Depot does not have one bag of the rockwool batts (I would like to use) locally, If you try and order some you need to order several.
They should have them on the shelf at a building supply store.