Jump to content

Insulation - DIY spray foam?


Featured Posts

I am fitting out a spare room as an office/guest room. At present it is very rough. Sterling board lines the floor and a third of the walls, original Black Prince fiberglass laminate another third, and the last third is missing its lining. Behind this lining is 50mm thick polystyrene slabs that are variously balanced in place on the struts or stuck down with a blob or two of Gripfill-style grab adhesive.

Needless to say this room gets very cold in the winter, and I presume it will get very hot in the summer. Moreover, there are flecks of surface rust on the hull behind the insulation, and I'd like to prevent air and therefore condensation from getting to the metal.

 

I would like to strip the linings entirely from this room and re-line it with thin (e.g. 6mm) plywood. I want to look into insulating this room better, and the advice I have seen from scouring old threads on this site is that spray foam is the way to go, though expensive.

 

Is there any difference between the spray foam installed by professional companies and the spray foam in a can like this: https://www.ebay.co.uk/itm/370892389649

I've also seen bigger DIY kits like this: https://www.ebay.co.uk/itm/293040411232

What would be the most effective and what would be the most cost-effective way of insulating this room from cold, heat, noise and especially condensation?

Link to comment
Share on other sites

I've used the 2 pack foam successfully in buildings but my choice for the boat was Celotex type boards (50mm) stuck with aerosol spray foam. The aerosols would be quite hopeless on their own. It would be very difficult to build up to the desired depth, it's open cell, and not dense enough. If using aerosol foam to stick and seal the boards, invest in a foam gun and use gun-grade foam (B1 fire-rated). 

IMG_20190510_102324.jpg

Edited by stegra
Add pic
  • Greenie 1
Link to comment
Share on other sites

1 hour ago, stegra said:

I've used the 2 pack foam successfully in buildings but my choice for the boat was Celotex type boards (50mm) stuck with aerosol spray foam. The aerosols would be quite hopeless on their own. It would be very difficult to build up to the desired depth, it's open cell, and not dense enough. If using aerosol foam to stick and seal the boards, invest in a foam gun and use gun-grade foam (B1 fire-rated).

Did you apply a say 10 to 20mm layer of aerosol spray foam and then press the Celotex board into the foam before it cured? Does this aerosol layer sufficiently cover the steel and seal against moisture?

Link to comment
Share on other sites

I used a kit to sprayfoam a boat, it was successful but I will never, ever do it again. I am still finding bits of the damned stuff in nooks and crannies. Anyway, its much the same if not identical to that Celotex stuff so if its a room with nice flat walls then use that. The only way we could find the cat after I'd done the boat was to prod lumps of the stuff till we found one that meiowed. Definitely Celotex or something like that.

  • Greenie 1
  • Love 1
  • Haha 1
Link to comment
Share on other sites

54 minutes ago, ivan&alice said:

Did you apply a say 10 to 20mm layer of aerosol spray foam and then press the Celotex board into the foam before it cured? Does this aerosol layer sufficiently cover the steel and seal against moisture?

Yeah. Just ran a few beads of foam far enough apart that they would squash together and join up. I'm satisfied that there is ample protection against moisture but my steel work is primed anyway. I pressed the slabs into place and supported them with a plank until the foam had cured. 

  • Greenie 1
Link to comment
Share on other sites

20 minutes ago, Bee said:

I used a kit to sprayfoam a boat, it was successful but I will never, ever do it again. I am still finding bits of the damned stuff in nooks and crannies. Anyway, its much the same if not identical to that Celotex stuff so if its a room with nice flat walls then use that. The only way we could find the cat after I'd done the boat was to prod lumps of the stuff till we found one that meiowed. Definitely Celotex or something like that.

The hull is made up of flat plates but not necessarily parallel with where the walls are going to be. Besides, the Celotex is not going to be bonded to the steel so I'd be worried that it doesn't seal out the condensation.

 

2 hours ago, ivan&alice said:

Is this the kind of kit you used?

 

 

3 minutes ago, stegra said:

Yeah. Just ran a few beads of foam far enough apart that they would squash together and join up. I'm satisfied that there is ample protection against moisture but my steel work is primed anyway. I pressed the slabs into place and supported them with a plank until the foam had cured. 

Our steel work is primed, too, but the moisture/rust has worked it's way through. It looks quite superficial so I don't think there is anything to worry about yet, I'm planning on cleaning up the rust and repainting with primer before insulating anyway. But still, I'd rather keep the condensation completely away from the hull if possible.

Do you think it's anything to worry about? Here are a couple of pics of what I'm talking about:

IMG_20190510_125314.jpg.f692a00aefd4e366afce30f9c1f7c1f9.jpgIMG_20190510_125259.jpg.3a5b3ce2d6c6937aae1b69318448a528.jpg

Link to comment
Share on other sites

Ive done a few using celotex (or equivelant) I make sure the panels are cut ever so slightly oversize so they are a tight fit between the battens. Glued to the steelwork if needed using stixall. 

All gaps /missing bits are meticuosly filled and then using alumininium tape every single joint and edge is sealed to battens etc so making a vapour barrier. Takes a while but if done well will still be better than a poorly done sprayfoam. And there is a good few of them about with mm's of coverage in awkward spots..

 

  • Happy 1
Link to comment
Share on other sites

1 hour ago, ivan&alice said:

The hull is made up of flat plates but not necessarily parallel with where the walls are going to be. Besides, the Celotex is not going to be bonded to the steel so I'd be worried that it doesn't seal out the condensation.

 

I think there's a common misconception here. If you stick Celotex or kingspan boards to the steel using a flexible PU adhesive sealant like Marineflex or Stixall (or even sticking them up with cans of sprayfoam), then any small air gaps left behind will contain such a small volume of air that any moisture contained in that air will contain negligible (and finite) amounts of moisture. Remember that even if there was enough moisture to start to cause a tiny bit of rust (which is highly unlikely), a finite amount of moisture can only create a finite amount of corrosion.

 

It's the unlimited and continuous amounts of moisture that get through insulation systems such as loose expanded polystyrene sheets or unlined rockwool, without any vapour barrier that will eventually cause the insides of steel boats to corrode badly. However, Celotex or Kingspan PU boards will act as a vapour barrier to prevent moisture getting behind the insulation and you can just seal any gaps between the boards with handheld sprayfoam or aluminium tape so that the whole thing is vapour proof.

 

If it's sealed properly then a tiny and finite amount of moisture held in the air gaps behind insulation boards isn't going to do any damage. In fact, the instructions on some brands of sprayfoam actually recommend using a plant sprayer to give the surface a fine coating of water before applying the sprayfoam to help it cure. There's going to be far less moisture in any small air gaps left behind your Kingspan or Celotex than that applied with a plant sprayer so I really wouldn't worry about it.

Edited by blackrose
  • Greenie 2
  • Happy 1
Link to comment
Share on other sites

4 hours ago, ivan&alice said:

Do you think it's anything to worry about? Here are a couple of pics of what I'm talking about:

IMG_20190510_125314.jpg.f692a00aefd4e366afce30f9c1f7c1f9.jpgIMG_20190510_125259.jpg.3a5b3ce2d6c6937aae1b69318448a528.jpg

Looks to me like the perfect candidate for Vactan. Paint it on, insulate the boat, job done. 

Link to comment
Share on other sites

Yes, I personally wouldn't use vactan unless I wasn't able to remove the rust with a wire wheel on the end of an angle grinder (I think vactan is over-rated). Most of that just looks like surface rust, so however you treat it, it doesn't look like a major issue. The areas around the windows are the most important. 

Link to comment
Share on other sites

4 hours ago, blackrose said:

Yes, I personally wouldn't use vactan unless I wasn't able to remove the rust with a wire wheel on the end of an angle grinder (I think vactan is over-rated). Most of that just looks like surface rust, so however you treat it, it doesn't look like a major issue. The areas around the windows are the most important. 

 

In my experience if you can remove the rust, vactan will have nothing to work on so will be wasted.

 

I would certainly use a rust converter before/rather than priming. There are several to chose from - I would pick vactan.

Link to comment
Share on other sites

Just now, frahkn said:

In my experience if you can remove the rust, vactan will have nothing to work on so will be wasted.

Agreed. Likewise all rust converters, but particularly pertinent to those which also prime (like Vactan, there are many others). That surface rust needs nothing more than a wipe with a damp cloth to remove the loose stuff, then a coat of Vactan, then get on with your life. Why make the job harder for no benefit?

Link to comment
Share on other sites

Because in my experience after using vactan the rust comes back in a few years. That was in my engine hole, not behind insulation, but I just don't think it's that great. How many professional boat painters use Vactan? Also I'm not sure how well it bonds and if I'm sticking insulation to it then I'd want to be sure. Personally I'd rather get rid of the rust properly and prime the steel.

 

Anyway, we're going slightly off topic. Treat that rust any way you want. The important bit is getting it properly insulated.

Edited by blackrose
Link to comment
Share on other sites

8 hours ago, blackrose said:

Personally I'd rather get rid of the rust properly and prime the steel.

 

But the photographs on Post 6 ARE of primed steel. Primer is moisture permeable and doesn't stop rust. We all know this surely. 

 

 

Link to comment
Share on other sites

5 hours ago, Mike the Boilerman said:

 

But the photographs on Post 6 ARE of primed steel. Primer is moisture permeable and doesn't stop rust. We all know this surely. 

 

 

Prime and one or two coats of top coat to seal the surface. An ideal opportunity to use up all those odd half cans of miscellaneous colours which you will never need again.

Link to comment
Share on other sites

5 hours ago, Mike the Boilerman said:

 

But the photographs on Post 6 ARE of primed steel. Primer is moisture permeable and doesn't stop rust. We all know this surely. 

 

 

 

Clearly what you don't know is that not all primers are permeable to moisture! 

 

3 hours ago, Neil Smith said:

yes normal primer is porous, use 2 pack primer or even a coat of hammerite.

Neil

 

Yes two pack primer isn't porous and neither is a good alkyd resin based primer like Bonda Primer. I've primed steel with Bonda Primer and it's been left out all winter before I've had a chance to get the undercoat and topcoats on and it's been fine.

Edited by blackrose
Link to comment
Share on other sites

Anyway, the reason that the steel has rusted in that picture is because the insulation system used didn't have a vapour barrier. Bond your kingspan, Celotex, etc, to the steel and make sure it's acting as a vapour barrier by sealing or taping the joints and you can use Vactan or any old primer because no moisture will get to the steel so the steel will not rust.

Edited by blackrose
  • Happy 1
Link to comment
Share on other sites

1 hour ago, blackrose said:

Anyway, the reason that the steel has rusted in that picture is because the insulation system used didn't have a vapour barrier. Bond your kingspan, Celotex, etc, to the steel and make sure it's acting as a vapour barrier by sealing or taping the joints and you can use Vactan or any old primer because no moisture will get to the steel so the steel will not rust.

Spot on. 

Link to comment
Share on other sites

If the rust inside the cabin gets up to 40mm thick, you will have holes.

So why lose sleep worrying about rust inside?

 I've seen loads of shells spray foamed onto bare unpainted steel, the foam eventually loses it grip on the steel and the condensation gets in. I hate cutting back spray foam and there are always bits missed or too thin.

Anti condensation paint may be a good idea, presumably it is not water permeable.

Kingspan and aluminium tape for me every time

Link to comment
Share on other sites

Thanks for all the advice. Here is my plan of action:

1) strip out existing chipboard lining and polystyrene insulation

2) remove loose rust with wire brush (no angle grinder)
3) if there is any rust remaining, dab on vactan

4) if not, coat of primer

5) coat of topcoat

6) thin layer of aerosol spray foam (to bond celotex and fill any gaps)

7) press celotex boards into spray foam before it has set

? aluminium tape all joints to create an effective vapour barrier

9) re-line in 6mm plywood

10) finishings as per wife's orders

Link to comment
Share on other sites

Whilst getting rid of gremlins in a boat I've been stripping out I've used a layer of gun grade can foam to ensure no thermal breach. All holes filled and no gap left unplugged.. If moisture can't get to the structure I'm happy, there's then a 10-20mm bilge vent gap depending on where my lekky is being run, this air gap allows any problem moisture to evaporate from the bilge or as it travels to the bilge.. and then a selco vapour barrier and Screwfix aluminium bubble wrap layer.

 

Have been super impressed with the ability of gun grade to seal an area and would not use more than 15mm of it to get that seal, after which I'd use some metallic foil or something that has a decent thermal rating. Foam for thermal breaches (screw head of metal exposed becomes a waterfall in an otherwise we'll insulated boat) then foil for doing the actual work of keeping the warm in. Also could paint your wood after for another vapour + air barrier

 

Am told the other school of thought is to completely kack the gap with insulation so 'no water can ever get in so you don't need to air it out' however we all know water finds a way

 

Also comes in a variety of wonderful colours

IMG_20190226_101133311_HDR.jpg

Link to comment
Share on other sites

1 hour ago, ivan&alice said:

Thanks for all the advice. Here is my plan of action:

 

6) thin layer of aerosol spray foam (to bond celotex and fill any gaps)

 

?

 

You'll find it's easier to apply the foam to the Celotex on a flat surface then press it into place. 

Link to comment
Share on other sites

4 hours ago, stegra said:

 

You'll find it's easier to apply the foam to the Celotex on a flat surface then press it into place. 

Unless you want to be stood ankle-deep in foam of course ;)

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.