Perished polystyrene under gunnels fix

[LIEFbristol]

Hi,

 

I've just purchased a narrowboat and have noticed under the gunnels the polystyrene sheets have begun to perish. The spots seem to correspond to leaky windows nearby (another job on the list, bodged with tape at the moment). 

 

What would be the best way to reseal these areas to stop cool spots and condensation forming? 

 

Regluing on polystyrene is one option I'm looking at, using aluminium tape to cover any gaps. 

 

I'm currently living aboard and plan in the summer to redo the lot but looking at an interim fix for now. 

 

Cheers 

[Tony Brooks]

It looks to me as if you might be well advised to do something about the rust on the hull before trying to do a more permanent job. In the interim how about a can of non-expanding spray foam.

 

I doubt the polystyrene was glued to anything, it is typically just cut slightly oversize and pushed into position.

 

I would suggest that for the good of the hull and bilge the leaking windows should be a higher priority than a bit of missing insulation.

Edited January 11 by Tony Brooks

[BEngo]

Spray foam in tins from Screwfix et al.  Supposedly sticks to damp steel. May or may not like existing polystyrene.

 

Regluing some polystyrene and adding Aluminium tape may be easiest.  Keep the polystyrene away from PVC cabling if there is any about.

 

When renewing, polyurethane foam (Kingspan/celotex)   is better than polystyrene.

N

[LIEFbristol]

36 minutes ago, Tony Brooks said:

It looks to me as if you might be well advised to do something about the rust on the hull before trying to do a more permanent job. In the interim how about a can of non-expanding spray foam.

 

I doubt the polystyrene was glued to anything, it is typically just cut slightly oversize and pushed into position.

 

I would suggest that for the good of the hull and bilge the leaking windows should be a higher priority than a bit of missing in

 

Cheers thanks for the info, spray foam seems to be the go, I'll try a bit on the polystyrene first to see if it reacts. 

 

 

I'm planning to take her out onto hard standing for a few months and redo all the windows and installation in the warmer months. 

 

 

Working on the leaky window, tape is holding well for now, condensation is becoming more of an issue hence the post. 

[dmr]

We have exactly the same issue.. Your "under gunnels" look to be done in the thin (3mm?) polystyrene. Polystyrene is not 100% waterproof and the thin stuff will enentually become waterlogged and break down/come unstuck.

It needs to be scraped off, any loose rust removed with a wire brush, and then this is one of those jobs where Vactan is good.

Spraying on foam would be good but I doubt it would work upside down and you wil just make a huge mess. If you do try then do let me know how it goes.

I used extruded 20mm polystyrene, carelful cut to size in lengths of about 1m or less, and stuck on with lots of silicone sealant. I used silicone on the joins also to try to get a seal. Aluminium tape will not stick to polystyrene. I am still working on this project but the first bits were done 2 years ago and are performing well.

 

Extruded Poly is much better than expanded poly. Proper foil backed insulation board would be even better but is not easy to get in thicknesses of less than about 4 inches, but if you can find any then get it.

[LIEFbristol]

15 minutes ago, dmr said:

We have exactly the same issue.. Your "under gunnels" look to be done in the thin (3mm?) polystyrene. Polystyrene is not 100% waterproof and the thin stuff will enentually become waterlogged and break down/come unstuck.

It needs to be scraped off, any loose rust removed with a wire brush, and then this is one of those jobs where Vactan is good.

Spraying on foam would be good but I doubt it would work upside down and you wil just make a huge mess. If you do try then do let me know how it goes.

I used extruded 20mm polystyrene, carelful cut to size in lengths of about 1m or less, and stuck on with lots of silicone sealant. I used silicone on the joins also to try to get a seal. Aluminium tape will not stick to polystyrene. I am still working on this project but the first bits were done 2 years ago and are performing well.

 

Extruded Poly is much better than expanded poly. Proper foil backed insulation board would be even better but is not easy to get in thicknesses of less than about 4 inches, but if you can find any then get it.

Thanks for the great info, tried and tested too. 

It's quite a fiddly spot and this seems more doable. 

[David Mack]

22 minutes ago, dmr said:

Proper foil backed insulation board would be even better but is not easy to get in thicknesses of less than about 4 inches, but if you can find any then get it.

Wickes sell 25mm and 50mm thick Kingspan.

[dmr]

3 hours ago, David Mack said:

Wickes sell 25mm and 50mm thick Kingspan.

 

Thanks, 25mm would be ideal. I had a Wickes eCoal delivery just two days ago as they had a 15% off everything deal, so just missed a free delivery 😀. I will get a sheet of Kingspan next time I do an order.

It was a couple of years ago that I got the extruded poly, the only Kingspan that I could find had to be purchased in huge quantities, but I think there were supply issues at that time.

[beerbeerbeerbeerbeer]

What’s wrong with shoving some rockwool in the gaps?

fix any leaks first mind

[blackrose]

I'm not sure that sprayfoam is a good interim solution. It's very messy and then once it's gone off it's difficult to remove.

[kevinl]

Sorry to sound trivial, but I read the title to the thread and wondered if it was a medical condition.

K

[dmr]

1 hour ago, beerbeerbeerbeerbeer said:

What’s wrong with shoving some rockwool in the gaps?

fix any leaks first mind

I think the photo is sort of upside down, so looking upwards at the underside of the gunnels, so any fix needs sticking on in some way as gravity is working against it.

[Tony Brooks]

7 hours ago, dmr said:

I think the photo is sort of upside down, so looking upwards at the underside of the gunnels, so any fix needs sticking on in some way as gravity is working against it.

 

Whichever way up the photo is there are still two horizontal edges to force any insulation between. If it happens to be Kingspan type or expanded polystyrene board cut into suitable strips, it should stay in place. Possibly not aesthetically pleasing, but should do the job for now.

[dmr]

35 minutes ago, Tony Brooks said:

 

Whichever way up the photo is there are still two horizontal edges to force any insulation between. If it happens to be Kingspan type or expanded polystyrene board cut into suitable strips, it should stay in place. Possibly not aesthetically pleasing, but should do the job for now.

 

Assuming the lining on the (upper) cabin sides drops down a little lower than the gunnel (as it should) then the insulation repair should be invisible....unless you are lying on the floor.

There are cans of spray on foam available:

 

https://www.ebay.co.uk/itm/374511641514?var=643477175753&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338749386&toolid=20006&_ul=GB&customid=GB_12576_v1|374511641514|643477175753.151379355311~1869633454526-g_CjwKCAiA44OtBhAOEiwAj4gpOTU8_NQCjIknZN5EWXFUK6KvdFkf_4-XE6AyE5EEFhkIiIHbggJ_7hoC_74QAvD_BwE&gclid=CjwKCAiA44OtBhAOEiwAj4gpOTU8_NQCjIknZN5EWXFUK6KvdFkf_4-XE6AyE5EEFhkIiIHbggJ_7hoC_74QAvD_BwE

 

I know nothing about these but they look interesting and should be much more suitable than expanding builders foam. I don't know if they would work upside down, and a large amount of carefull and comprehensive masking up would be required.

Has anybody tried these?

[plato]

If you go for Kingspan or similar foil backed board, try your local builder’s merchant. A sheet of 25mm was £35 in wickes. I paid £18 including vat at my builders merchants.

[LIEFbristol]

On 12/01/2024 at 07:46, Tony Brooks said:

 

Whichever way up the photo is there are still two horizontal edges to force any insulation between. If it happens to be Kingspan type or expanded polystyrene board cut into suitable strips, it should stay in place. Possibly not aesthetically pleasing, but should do the job for now.

It's a tight space but once it's all done it won't be seen