How Not to Plasterboard a Wall : Mould

10 years ago my kitchen walls were dot and dabbed - I'm going to explain why this was a bad idea, what insulated plasterboard you can use and how I'm going to insulate my kitchen walls.

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0:00 Introduction
0:42 Project Recap
1:38 Dangers of Dot and Dab
5:14 External Insulation
6:34 Internal Insulation
9:34 My New Strategy
11:45 Subscribe to Me!

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Charlie DIYte

#plasterboard #insulation #mould

[KnotASailor]

What's important to me from this video is you have taken the time to really think about the insulation - which I find hard to do with work consuming my life. Thank you for the research

[mrjh]

Eager to see how you achieve this.

I am going through a renovation myself and we have decided against internal wall insulation due to several factors. and will therefore try to attempt external insulation in the future.

I spent ages reading about how to insulate, and even airtightness, and too many approaches out there to say the least. It was too confusing and tradespeople did not help.

[jonwilmot]

Great video Charlie, I've been getting involved in external and some internal insulation, I have solid walls and have researched this complicated subject, I have used alutrix vapour barrier and a combination of foam fixing and insulated plasterboard. you can end up chasing cold bridges until the cows come home . Somewhere the vapour barrier has to be breached. As you rightly say, ventilation is essential as moisture will build up eventually. Interestingly I ripped down 4mm conti board pinned to batten on my dining room walls and found the external walls bone dry. Unluckily my lead roof laid 20 years ago on a warm roof where no barrier was installed erupted and dissolved to white dust. You live and learn.

[burnsironwork]

I built a two storey extension as a granny annex in 2003 using 40mm laminate plasterboard dob and dabbed onto 9" solid block work. I recently put new doors and windows in and uncovered a lot of the original wall surface. Not a hint of mould or condensation. External walls are rendered pebbledash. I am now doing the same to the main house external walls as i replace the old leaded light windows. If you try and consider all the issues you come to the conclusion its not worth it bearing in mind the cost and no one can get give a definite way to do it. however I need to be warmer as i get older in the winter. This time I am using adhesive foam which almost removes any gap behind the insulation as it needs perfect contact (keep pressure applied for half-hour plus across the whole board with temporary wood support and of course mechanical fixings). We do intend to open windows as much as possible to reduce humidity issues. in 10 years time I'll let you know if it worked!

[petervine]

When I’ve insulated solid brick walls, I’ve used 50 mm celotex/kingsman straight against the wall, fit the insulation to the walls through 38mm battens, set out to suit the plasterboard, and the 12mm plasterboard to the battens. You can now run cables in the void, cut out drying holes to plasterboard, without damaging the insulation, which is all kept intact & sealed.

[oldboyuk]

Good stuff. Having looked into internal insulation it's clear that it's a murky area with unclear best practices. Props for trying to tackle the issue and bring clarity on different options

[braddempsy]

I will be doing this very shortly in my two front rooms. I have decided use PIR straight onto the brick wall, batten a frame in front of it and screw battens to ceiling and floor joists. This way there is no compromise in the insulation. Socks can go in the void behind the stud wall.

[looopyu]

if you screw your 38mm batons horizontally making a grid pattern you will limit the cold bridge. you could also insulate between the batons. Don't forget you need a ventilation system (ideally a heat recovery system) to deal with all the vapor that can now not pass through the walls. A healthy house requires heat and ventilation working in conjunction. The tighter you make a house the more important this becomes.

[tiktok-xgj]

Interesting video Charlie.
Not to be only pointing out issues but I see two potential problems with this arrangement.
Firstly there are many unventilated cavity spaces right where the dewpoint position is (internal face of the brickwork wall), surely that is perfect conditions for mould.
Secondly, with the batten fixed directly to the brickwall they will act as cold bridges, a studded frame build independently say 20mm off the brickwork would have avoid the cold bridge, or even a "warm" batten with 25mm insulation fixed behind the batten.
Regardless an interesting subject where it is near impossible to satisfy all requiments!

[petefleming]

Amazing to find a builder who actually does understand and considers how to refurb properly and follows or improves on building regs. If only every builder did this.

[alexclifford]

Woodfibre insulation fully bonded to the wall with lime plaster over or Diathonite insulated plaster would have been the best option. Standard best practice is to not leave a cavity next to the wall as you will get mould growth just like you did before. It is almost impossible to prevent air ingress into that cavity. You also need to remember to insulate between the joists in the inter floor void next to the wall having parge coated first around the joists to prevent air ingress.

[andyc]

Thanks Charlie, as always, an open and honest debate covering pitfalls, alternative opinions, ideal solutions and then the rationale of the chosen compromise ! Some great information in this on a subject that is a minefield !

[avisitorhere]

I would use Steico's system of applying wood fiber board to a masonry surface and then finish with either a vapor permeable wallboard or a lime plaster which is also vapor permeable. I would then finish with a vapor permeable paint. You are relying on a cold air cavity to control moisture which will over time probably fail. You are also not allowing the walls to dry out causing them to deteriorate over time. The walls were made to breathe, you have to let them.

[POUSEaroundtheHOUSE]

Nice video, refreshing to see some common sense regarding the lime plaster. It's a nice idea but like you, the end of my house is solid brick wall and without my wood burner I'd be screwed as it gets really cold and if you can make it warmer then go for it. Interestingly I got damp problems in this part of my house after painting the outside of the house using sandtex paint. I think it stopped moisture escaping outwards, maybe a video opportunity for the future! But I think your option looks good. Unfortunately as you say, many manufacturers fail to include how to deal with sockets, ducts etc and it ultimately comes down to you to come with the best solution. Best of luck with it 👍

[togarchitecture]

There are a number of internal wall insulation options that are breathable which is the best option as you get you u-value. These include but not limited to wood fiber insulation and lime render with cork or pumus stone in it put on at about 50m thick. (A friend did the latter on his listed cottage and it's amazingly warm)

[DavidJohnson-ygqm]

Oh dear, this is how the plasterers did my last house in 2001 and I have just checked my current house and it is exactly the same. Well at least I know what the next job is to do.
Thank you for your indepth analysis

[iainwadey]

Love the video and detail! I am in the process of applying IWI on the front external wall of a Victorian terrace. I striped back to the brick work, some which showed clear signs of spalling; not surprising given the air gap caused by Dip and Dab gypsum plasterboarding over the original Lime plaster (creating a cavity where moisture could not escape). I have applied around 30mm of Diaphonite Thermactive, then fixed 60mm Uditherm Woodfibre board on that with insulated screw fixings and using the a wet layer of Diaphonite as lime adhesive. Not sure about the results yet but interested in next winter to perform analysis to the temperature, humidity and thermal imaging (not to mention out gas bill!). Just another thing, it was pointed out to me by a builder who works at CAT that there are common misconceptions about interstitial condensation (dew point moisture) and general moisture caused by cooking, cleaning etc. As I understand it, the latter has very little to do with mould growth within the wall structure. Interstitial condensation just requires some cavity where moisture will condense from any air which pretty much always has a certain amount of moisture in it. With that in mind, a safer approach is to simply allow the moisture to escape. Lime is also alkaline and anti microbial. If anyone is interested in Diaphonite or other insulating Lime plasters, I would recommend contacting Carrington Lime in Gloucestershire who run practical and online courses/seminars on the specific products.

[abescheele]

Great video Charlie. There’s an interesting EU project called Ri Build. It’s essentially research being done into the best approaches for internally insulating historical buildings. They have a calc that helps determine the recommended maximum amount of insulation for a given type as too much can introduce potential issues with timber rotting and cracks forming due to frost.

[unknownmale]

Interested in the route you go down, I'm about to undertake this, by using 3x2 CLS stud work to the wall, filled with wood fibre, vapour barrier taped over followed by butyl tape along the studs and noggins so when the plasterboard is attached the barrier isn't compromised. My reason for this route is so that I have good fixings for shelves, radiators etc. It also allows me to get the wall level and plumb which is currently is not

[philipdeacon]

The lime plasterers will hate you, but as somebody who wants a warm family house think you doing a sensible and well researched refurb .