Expanding foam query

[Rutlandcottage]

Hi all, first of all thank you this forum has been very helpful to read as a first time buyer of a listed limestone cottage.

We are seeking to rectify issues and have had a damp specialist strip back the existing plaster to add a lime plaster/render and then wood fiber boards before a topcoat of lime.

I noticed that they have sealed the bottom of the walls with the attached expanding foam, which they are then trimming and covering.

My ignorant question is is this normal practice or is this potentially going to undo all the work by trapping moisture and forcing it up the wall?

Photos attached.

This work is currently being completed so any urgent thoughts and feedback would be hugely welcomed!

Thank you

 

[malcolm]

Normally you would want to leave a small gap between the plaster and the floor and cover it with skirting. Anything waterproof tends to be bad as it stops water moving through the wall and can lead to the materials beside it becoming more wet than they otherwise would be.

Well done for getting it done with lime. Works a lot better than tanking which is waterproofing on a larger scale so more wetness.

 

[Cubist]

The only sensible reason I can think of for doing this would be to limit the effects of damp rising through the floor and into the wall but I can't see that it would be terribly efficient.

 

[Kearn]

The very fact they’ve used that, and in that way/location, bothers me and would make me question their overall experience in lime. Sadly there are a ton of chancers out there who do the modern stuff, then realise they can charge more for heritage work, so have a go… hopefully not the case for you, but this is certainly a red flag. Also, there are images of what looks like finished walls, yet there’s a lot of aggregate visible at the surface, and it looks very large in size. The woodfibre boards, don’t all look the same? Plus, these need to be mechanically fixed to the wall with stainless screws and the special plastic washers.

 

[Lacan07]

Well, I've never seen anything like that before!

How big was the gap between the floor and the wall? What type of floor is it?

Expanding foam should have limited use in old houses, usually only good for filling awkward service voids like drainage pipes knocked through walls, etc.

I agree with Kearn's comments above, where's the mechanical fixings for the wood fibre board? The lime plaster finish looks like its been floated with a sponge. Not the worst I've seen, looks a bit ropey around the sockets but the wall looks relatively plumb. It doesn't look like 'fine stuff' though.

 

[Rutlandcottage]

Ok thanks all. Attached are what is being used to secure. Are these what you’re referring to? Re aggregate, does that mean the sand being used? They are using NHL 3.5 for the lime

 

[stuart45]

NHL3.5 is quite a strong lime for internal plastering. Most plasterers prefer a well matured air lime.

 

[Kearn]

Hate to be the bearer of less good news, but Warmshell is a bit of a modern approach to old methods, fast setting ‘lime’ plaster with lots of nasty additives, non breathable adhesives… NHL 3.5 is far far too hard for what you’re doing. Even a 2 from St A would be strong and liable to potential cracking.

‘Damp specialist’ is a term that tends to give folks the willies. A traditional lime plasterer wouldn’t call themselves such…

Aggregate = sand, yes. Looks like large grain size and has been brought to the surface with some heavy sponging, where you really want your nice fat lime sitting. You’d always want the top coat to be a super fine mix, a couple of mm thick. The sand there looks like 4mm or similar, so assume this a thick coat.

The horse has rather bolted now, but you may wish to have a read of this SPAB study about the possible risks of internal insulation in solid walled properties moving the dew point and increasing interstatial condensation.

It’s generally not considered a good idea compared to simply ensuring dry natural fabric and a low constant heating approach.

https://www.spab.org.uk/sites/default/files/documents/MainSociety/Advice/SPAB%20Building%20Performance%20Survey%20Final%20Report%202019-small.pdf?fbclid=IwQ0xDSwMPD7tleHRuA2FlbQIxMQABHgWM4bUwoVDzB96a32V2kndTvxBQIulFAQD8XODsVV3QgzIzJxfVHQ5i11In_aem_xjdt3Me44mGS3qmNhvPMcQ

 

[Rutlandcottage]

Ok thank you. We’re not at the top coat point yet so I’ll revert back in due course! Thanks for all the points and the study too

 

[a twig]

The horse has rather bolted now, but you may wish to have a read of this SPAB study about the possible risks of internal insulation in solid walled properties moving the dew point and increasing interstatial condensation.

It’s generally not considered a good idea compared to simply ensuring dry natural fabric and a low constant heating approach.

https://www.spab.org.uk/sites/default/files/documents/MainSociety/Advice/SPAB%20Building%20Performance%20Survey%20Final%20Report%202019-small.pdf?fbclid=IwQ0xDSwMPD7tleHRuA2FlbQIxMQABHgWM4bUwoVDzB96a32V2kndTvxBQIulFAQD8XODsVV3QgzIzJxfVHQ5i11In_aem_xjdt3Me44mGS3qmNhvPMcQ

I’ve read this report a couple of times now, it’s 3 long term case studies and to me the conclusions broadly are:

Wall 1: Wood fibre internally reduces heat loss and works with no issues on a soft red brick wall with lime mortar, despite the exterior pointing not being in good nick

Wall 2: Drylining and installing PIR on the inside of a granite wall also reduces heat loss but unsurprisingly doesn’t let the moisture entering the wall from the exterior back out again effectively and causes build up with potential for long term degrading of the wall.

Wall 3 is a cob wall that has been externally insulated with a perlite based insulating lime render so not really relevant to most of the internal insulation discussions.

What am I missing?

 

[Lacan07]

Ok thanks all. Attached are what is being used to secure. Are these what you’re referring to? Re aggregate, does that mean the sand being used? They are using NHL 3.5 for the lime

View attachment 17440

View attachment 17441

View attachment 17442

Yes, those are the correct mechanical fixings for wood fibre boards.

Installing wood fibre board is the accepted way of internally insulating an old house but its recommended to not go beyond 80mm thickness due to potentially moving the dew point into the fabric of the building.

 

[jamest]

What Lacan07 says - even SPAB themselves are up to it, have a look at this place: https://www.inigo.com/sales-list/st-andrews-chapel