Rockwool insulation?

[Cancunia]

Just wondering on the best insulation on the inside of the hull at about the waterline above where the hull plate meets the sides? I'm getting a lot of condensation on the inside of the hull in the cabin near to the stern, so I'm thinking about putting insulation onto the bare steel. Something like Rockwool glued on with bitumen paint?

 

 

[LadyG]

Others will be along soon.

Rockwool is not used much nowadays, it is more like Cottonwool!

I would go for Celotex type board.

You need to seal edges with silver tape and foam out of a can. Have a look on youtube.

Sounds as though you need to prep the surface, get rid of any loose rust, do the best prep, and ideally coat with a two pack epoxy coating.  It all takes time.

Of course they recommend blasting the steel for best results, but you have to accept the compromise.

Best not to paint on cold damp days.

Best to avoid bitumen inside! , its not the best, and messy.

SML paints will give you technical advice, just ask. They should sell everything you need.  Read the section Marine Paints before you buy!

Read tbe data sheets for each paint you buy . The two pack paints cure fairly rapidly, so you may need a weigh scale to mske up  batches.

I like their pelican paint pot for rolling or brushing.

They sell the correct type of rollers for each paint type, a 4" roller and a short handle plus a pack of their cheapo brushes will  be fine.

 

 

 

Edited February 22 by LadyG

[Tony Brooks]

I agree Rockwool is not a good idea there, it may slump and absorb water.

 

For an alternative for you to consider, think about fire-resistant expanded polystyrene would get you thicker insulation at the same or less cost than Celotext or Kingspan. You can cut to be a push fit between the battens/hull bracing, and cover it with (say) silvered bubble wrap as a vapour barrier. Make sure the metal hull is well painted first. Many boats built in the 90s and probably later used expanded polystyrene and having had welding carried out on the other side of a 4mm bulkhead all that happened is that it melted and ran away from the heat. I also tested a scrap by trying to ignite it. it did catch, but once the match was removed it just went out. If you have wiring in that area, you need to protect it. I just use two lengths of duct tape. One on the polystyrene and one holding the cable in place over the first strip.

[magnetman]

 

People tend to assume Rockwool absorbs moisture because it looks like it would be it doesn't. 

 

Rockwool is hydrophobic. 

 

It will not absorb moisture from the air. 

 

 

[Tonka]

8 minutes ago, Tony Brooks said:

I agree Rockwool is not a good idea there, it may slump and absorb water.

 

For an alternative for you to consider, think about fire-resistant expanded polystyrene would get you thicker insulation at the same or less cost than Celotext or Kingspan. You can cut to be a push fit between the battens/hull bracing, and cover it with (say) silvered bubble wrap as a vapour barrier. Make sure the metal hull is well painted first. Many boats built in the 90s and probably later used expanded polystyrene and having had welding carried out on the other side of a 4mm bulkhead all that happened is that it melted and ran away from the heat. I also tested a scrap by trying to ignite it. it did catch, but once the match was removed it just went out. If you have wiring in that area, you need to protect it. I just use two lengths of duct tape. One on the polystyrene and one holding the cable in place over the first strip.

Can you buy actual fire resistant expanded polystyrene ? 

Or is it just falsely branded as such as used in Grenfall

Edited February 22 by Tonka
Spelling

[magnetman]

 

Apart from handling Rockwool is fine and is good for void filling..

 

I'd definitely use it in an irregular space. 

 

 

[Tonka]

Just now, magnetman said:

 

People tend to assume Rockwool absorbs moisture because it looks like it would be it doesn't. 

 

Rockwool is hydrophobic. 

 

It will not absorb moisture from the air. 

 

 

But once wet it takes an age to dry out

[magnetman]

1 minute ago, Tonka said:

But once wet it takes an age to dry out

It doesn't. 

 

+4

 

No, Rockwool does not absorb water. It's a hydrophobic material that repels water and moisture. 

 

How does Rockwool repel water?

• Allows vapor to pass through: Rockwool can perform well even when there's moisture present. 
   

• Wicks away bulk water: Any water that touches the outside of Rockwool drains away, rather than being absorbed into the insulation. 
   
• Non-hygroscopic: Rockwool doesn't attract or absorb moisture from the air around it. 
   

Benefits of Rockwool's moisture resistance 

 

• Helps protect the health of buildings and the people inside

• Keeps buildings warm and dry during wet weather

• Doesn't reduce thermal performance over time

 

 

People think it will absorb water but it actually doesn't.The water drains away.

 

 

 

Anyway if you are expecting that your insulation is going to end up soaked then there are a lot more questions to be asked than just what material to use! 

 

Rockwool is used in commercial vessels including cruise ships. Its environmentally friendly and fire resistant. 

 

People should be encouraged to use fewer plastics. 

 

ROCKWOOL insulation is a rock-based mineral fiber insulation comprised of Basalt rock and Recycled Slag. Basalt is a volcanic rock (abundant in the earth), and slag is a by-product of the steel industry. The minerals are melted and spun into fibers.

[David Mack]

Unless you have a vapour barrier, rockwool, being permeable, will allow water vapour to pass right through where it will then condense on the cold surface of the steel shell.

[Tonka]

9 minutes ago, magnetman said:

It doesn't. 

 

+4

 

No, Rockwool does not absorb water. It's a hydrophobic material that repels water and moisture. 

 

How does Rockwool repel water?

• Allows vapor to pass through: Rockwool can perform well even when there's moisture present. 
   

• Wicks away bulk water: Any water that touches the outside of Rockwool drains away, rather than being absorbed into the insulation. 
   
• Non-hygroscopic: Rockwool doesn't attract or absorb moisture from the air around it. 
   

Benefits of Rockwool's moisture resistance 

 

• Helps protect the health of buildings and the people inside

• Keeps buildings warm and dry during wet weather

• Doesn't reduce thermal performance over time

 

 

People think it will absorb water but it actually doesn't.The water drains away.

 

 

 

Anyway if you are expecting that your insulation is going to end up soaked then there are a lot more questions to be asked than just what material to use! 

 

Rockwool is used in commercial vessels including cruise ships. Its environmentally friendly and fire resistant. 

 

People should be encouraged to use fewer plastics. 

 

ROCKWOOL insulation is a rock-based mineral fiber insulation comprised of Basalt rock and Recycled Slag. Basalt is a volcanic rock (abundant in the earth), and slag is a by-product of the steel industry. The minerals are melted and spun into fibers.

Well if you search Rockwool use in houses. ( which I appreciate is alien to you) it is frowned upon because of the wet issue. Especially in historic houses. Peter Ward at Heritage House.co.uk especially ia a good source of info on it

[5239]

My boat is insulated with rock wool. Steel work painted with blacking.

The sides and top are as good as new,

It was done back in the 80’s. 

Under the floor was a different matter. The bilges having flooded a few times the rock wool went soggy and horrible, retaining water. 
 

But as I say up the sides are as good as new. I also have an idea that the bitumen blacking has helped prevent condensation. 

 

 

[David Mack]

1 minute ago, 5239 said:

I also have an idea that the bitumen blacking has helped prevent condensation.

How?

[Gybe Ho]

13 minutes ago, Tonka said:

Well if you search Rockwool use in houses. ( which I appreciate is alien to you) it is frowned upon because of the wet issue. Especially in historic houses. Peter Ward at Heritage House.co.uk especially ia a good source of info on it

 

Nonsense, every builders merchant in the east of country will have loads of the stuff in their warehouse, it is sold as "cavity batts". Full fill masonry cavities stuffed with rockwool in houses built in the east of this country, is normal. Partial fill cavities are recommended in the wetter western half of the country.

 

An outer skin of house bricks can absorb and release moisture unlike the steel plate of a narrowboat hull. The usage scenarios are so different there is no point looking for guidance from the building trade when insulating a narrowboat.

 

Edited February 22 by Gybe Ho

[Tony Brooks]

12 minutes ago, 5239 said:

Under the floor was a different matter. The bilges having flooded a few times the rock wool went soggy and horrible, retaining water. 

I do wonder how it would have fared with window or vent leaks that can take ages to show themselves as a problem.

[jim mitchell]

Isn't the difference that of moisture vapour and actual water - the rockwool fibres are Hydrophobic and do not absorb water but the air spaces (that provide much of the insulation are quite capable of filling with water - causing a soggy blanket that  tends to retain the water and destroys the insulating properties.

Hence without a vapour barrier it will let moisture vapour pass freely (and then condense on a cold surface (hull) and if exposed

to a free air movement subsequently dry out. But water saturated wool can not drain unless suspended in some way which i believe is why any that is underfloor or along a bilge are  once soaked stays soaked.

In Houses the problem comes from the same source - if the outer leaf is not water tight  (Water not  vapour !) then the material does become waterlogged and can then cause structural problems.

[David Schweizer]

Our old boat was built in 1981 and was insulated with Rockwool. The cabin sides were lined with pine matchboard and at some time most of it was temporarily removed for re-wiring. In 20 years, we had no moisture issues. We also had no problems with wet bilges. I suspect that much depends on the initial quality of build and the fitting of the insulation.

 

 

Edited February 22 by David Schweizer

[magnetman]

3 minutes ago, jim mitchell said:

 any that is underfloor or along a bilge are  once soaked stays soaked.

 

 

yes but thats obvious. Its like saying 'my foot is in a bucket of water therefore my foot is wet'. 

 

It can be seen that Rockwool is not a closed cell material. 

 

 

It is used widely in steel ships and workboats but that is partly because it is fire resistant. Different priorities offshore. 

 

The aim surely must be to not have excessive humidity in the first place. If one has too much humidity there will be a problem regardless of what insulation is fitted. 

 

Dry bilge is desirable. 

4 minutes ago, David Schweizer said:

. I suspect that much depends on the initial quality of build and the fitting of the insulation.

 

And the way the interior space is managed by the owners. If you have a dry cabin then you have a dry cabin. 

 

If it is damp then it is damp. 

 

i personally make an extra effort to have a dry cabin by having a lot of free air even in very cold weather and a wood burner. 

 

Its much nicer than having damp areas. 

 

 

[5239]

I’m not dead certain, it’s just an idea from observation but..

I have left a section from base to gunnel uncovered for 3 winters now,

no cladding just steel with a coat of blacking (that was put on back in the 80’s) and I’ve not seen any condensation form,

it is a section inside the cabin,

 

so I don’t know for sure other than I have never seen a drop of condensation on the exposed interior section which is blacked. 

And I expected to see some condensation,

lots of other things to consider regards condensation but I can’t help thinking of it were a smooth painted surface there’s be some condensation forming in an exposed surface 🤷‍♀️

 

39 minutes ago, David Mack said:

How?

 

[Ronaldo47]

25 minutes ago, jim mitchell said:

Isn't the difference that of moisture vapour and actual water - the rockwool fibres are Hydrophobic and do not absorb water but the air spaces (that provide much of the insulation are quite capable of filling with water - causing a soggy blanket that  tends to retain the water and destroys the insulating properties.

Hence without a vapour barrier it will let moisture vapour pass freely (and then condense on a cold surface (hull) and if exposed

to a free air movement subsequently dry out. But water saturated wool can not drain unless suspended in some way which i believe is why any that is underfloor or along a bilge are  once soaked stays soaked.

In Houses the problem comes from the same source - if the outer leaf is not water tight  (Water not  vapour !) then the material does become waterlogged and can then cause structural problems.

In some circumstances, water vapour can condense within a wall (or any other vapour-permeable stuff such as Rockwool). It's a phenomenon that has been known for decades, called "interstitial condensation" . With a vapour-permeable wall that is cold on one side and warm on the other, there will be a temperature gradient across the thickness of the wall. If the temperature at a point along the gradient is equal to the dew point temperature of the water vapour, then water vapour will condense there, creating dampness within the wall. Hence the need for a vapour barrier.

[Gybe Ho]

1 hour ago, David Schweizer said:

Our old boat was built in 1981 and was insulated with Rockwool. The cabin sides were lined with pine matchboard and at some time most of it was temporarily removed for re-wiring. In 20 years, we had no moisture issues. 

 

 

Probably because in the good old days building techniques accepted moisture ingress as a fact of life and structures were designed to release moisture. In your case condensation settling at the interface between the steel hull and rockwool would have been released back out to the cabin on a warm day via gaps in the matchboard lining.

 

The modern mentality is to fight nature e.g. smothering the external walls of an old property with an impermeable paint or lining a narrowboat with taped up silver bubble wrap. 

[Tonka]

1 hour ago, magnetman said:

 

yes but thats obvious. Its like saying 'my foot is in a bucket of water therefore my foot is wet'. 

 

It can be seen that Rockwool is not a closed cell material. 

 

 

It is used widely in steel ships and workboats but that is partly because it is fire resistant. Different priorities offshore. 

 

The aim surely must be to not have excessive humidity in the first place. If one has too much humidity there will be a problem regardless of what insulation is fitted. 

 

Dry bilge is desirable. 

And the way the interior space is managed by the owners. If you have a dry cabin then you have a dry cabin. 

 

If it is damp then it is damp. 

 

i personally make an extra effort to have a dry cabin by having a lot of free air even in very cold weather and a wood burner. 

 

Its much nicer than having damp areas. 

 

 

Its only the surface of water that is wet. The rest is dry

[magnetman]

Yes. Also some people call air movement through a cabin a 'draught' which makes it sound undesirable. 

 

In fact having air moving is ideal. Take it to the logical extreme. No air = no breathing .

 

 

[David Schweizer]

But surely boats are legally required to have permanent ventilation via low level cabin side/door vents and roof ventilators. We had both and more than the regulations required, our cabin was always dry.

[Tonka]

17 minutes ago, David Schweizer said:

But surely boats are legally required to have permanent ventilation via low level cabin side/door vents and roof ventilators. We had both and more than the regulations required, our cabin was always dry.

Only advisory now on private boats. Think it is compulsory on commercial boats including hire

Edited February 22 by Tonka
Extra info

[Bee]

Boats, damp, condensation, insulation, Aargh!  Boat insulation must cope with temperatures of minus something at the steel whilst only 3 or 4 inches away on the inside it will be20 - 30 deg. C. that is asking a lot! In my opinion spray foam is the best stuff but even then the internal cladding can be cold enough for condensation and mould. About 6 inches of insulation might work but I'm not convinced.  Even carpet tiles will not work on the ply cladding if there is condensation, a sort of dew forms on them then it all goes horrible and smelly. It really is like condensation on the inside of a car windscreen, if you can blow warm air at it then it will dry, if you can't then it will stay wet. Dark cold unventilated corners are worst and of course warm air will carry more moisture than cold so the more moving air you can get down low the better. Maybe some sort of hot water circuit at floor level might work but it would have to be pumped or some sort of fan blown device?