Dot and Dab Insulated Plasterboard Condensation

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Reunat

New Member
Hi all,

Need some urgent advise thanks. I wanted to create a home office so had the outhouse in my garden fitted with 6 double power outlets (back boxes to the brickwork) then dot and dabbed directly to the brick with, on advice of the builder, Knauf 27mm XPS plus insulated plasterboard after applying PVA to the brickwork. The plasterboard was then skimmed.

Bitumen paint was applied to the concrete floor, then self leveling concrete then laminate laid.

Once all was dry, they painted initially with a mist coat of emulsion paint then with Dulux Easycare. This dried then immediately crumbled and flaked. They claimed it was the Easycare being kept in the cold outhouse but believe it or not, this is the least of my worries!

I have noticed that the power outlets get quite a bit of condensation forming on and around them every night which is quite worrying (I have now turned off power to the outhouse at the fusebox).

They assured me when I initially noticed it, that it was the plaster drying but its been weeks since it was plastered and I am still noticing the condensation. I have read a little and suspect the condensation is forming as the warm air is travelling through the plasterboard, hitting the colder brickwork which is forming condensation on the Backboxes as they are attached to the brickwork

Am I on the right track in anyones more experienced opinion, or is it a bigger issue? Most importantly, how do I rectify this?

Its getting colder and I have noticed rust forming on the brand new power outlet screw today!

I just want to make it safe and avoid condensation ruining the whole structure - ideally without having to rip everything down but worse case, I will have to do this. The structure was in place before just as a brick shed and never had condensation issues before.

I currently have a dehumidifier running in the room and was told maybe a condensation sensing vent fitted would help but I am not sure. I have also been told that the power outlets should be surface mounted to the plasterboard. My worry is that the cabling between the outlets are on the brickwork so cable would still have to be presented through the XPS. At this point, I have no idea.

Your advice is welcomed and appreciated. Thanks

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is welcomedx
 

raggles

Private Member
Loads of questions
1. Is the out house single skin brick or blocks or timber ?
2. Is it a flat roof or pitched and how is it insulated. ?
3. What is the heat source in the room. ?
4. Is there a water source in the room i.e. Sink, toilet ?
5. Is there any kind of insulation in the floor ?
6. Is it attached to the house ?
7. Do the Windows have Trickle vents ?
8. Were building control involved ?
 

Brimstone

Well-Known Member
Lots of good points from Ray and Raggles. Your builder is a t**t.
Essentially you have a single skin un-insulated outhouse with nothing like enough insulation or sheer bulk, including especially the floor and the roof. It didn't get wet before because there was no warmth inside to hold moisture.
That's why your house is made with 9inch brickwork or cavity brickwork. Somehow you will have to increase the thickness and insulation all round - walls, floor and roof, to move the dew point (where the water condenses) to a point where it can do no harm e.g. inside the brick, other side of a vapour barrier etc.
It is possible to build an internal skin of studwork, insulation vapour barrier etc inside but you may end up with something the size of a generous Khazi, not an office.
Presuming you don't have ther sort of job where you want to sit on a khazi all day, ( who knows?) the other option is to insulate and thicken up on the outside.
But for either option you need a proper builder.....and more money.
 

Reunat

New Member
Loads of questions
1. Is the out house single skin brick or blocks or timber ?
2. Is it a flat roof or pitched and how is it insulated. ?
3. What is the heat source in the room. ?
4. Is there a water source in the room i.e. Sink, toilet ?
5. Is there any kind of insulation in the floor ?
6. Is it attached to the house ?
7. Do the Windows have Trickle vents ?
8. Were building control involved ?
Hi @raggles - Ill try to answer as best as possible.

1. Single skin brick.
2. Flat roof. I think the builder put in wool insulation then plasterboard on the rafters.
3. No permanent heat source in the room. I have a plug in Electrical oil heater.
4. No water source - no sink or toilet.
5. Floor was concrete on a membrane which he painted with bitumen, covered in self levelling concrete, Arbiton acoustic and thermal underlay, then laminate.
6. It is not attached to the house.
7. Windows does trickle vents which I have tried to leave open.
8. Building control were not involved per se. The outhouse was an existing building (A brick shed - no insulation / plaster but power already ran.) when I bought the house last year. I therefore contacted building control to confirm the insulation, flooring and additional plugs were permissible which they confirmed was fine.
 

ChrispyUK

Well-Known Member
Hi all,

Need some urgent advise thanks. I wanted to create a home office so had the outhouse in my garden fitted with 6 double power outlets (back boxes to the brickwork) then dot and dabbed directly to the brick with, on advice of the builder, Knauf 27mm XPS plus insulated plasterboard after applying PVA to the brickwork. The plasterboard was then skimmed.

Bitumen paint was applied to the concrete floor, then self leveling concrete then laminate laid.

Once all was dry, they painted initially with a mist coat of emulsion paint then with Dulux Easycare. This dried then immediately crumbled and flaked. They claimed it was the Easycare being kept in the cold outhouse but believe it or not, this is the least of my worries!

I have noticed that the power outlets get quite a bit of condensation forming on and around them every night which is quite worrying (I have now turned off power to the outhouse at the fusebox).

They assured me when I initially noticed it, that it was the plaster drying but its been weeks since it was plastered and I am still noticing the condensation. I have read a little and suspect the condensation is forming as the warm air is travelling through the plasterboard, hitting the colder brickwork which is forming condensation on the Backboxes as they are attached to the brickwork

Am I on the right track in anyones more experienced opinion, or is it a bigger issue? Most importantly, how do I rectify this?

Its getting colder and I have noticed rust forming on the brand new power outlet screw today!

I just want to make it safe and avoid condensation ruining the whole structure - ideally without having to rip everything down but worse case, I will have to do this. The structure was in place before just as a brick shed and never had condensation issues before.

I currently have a dehumidifier running in the room and was told maybe a condensation sensing vent fitted would help but I am not sure. I have also been told that the power outlets should be surface mounted to the plasterboard. My worry is that the cabling between the outlets are on the brickwork so cable would still have to be presented through the XPS. At this point, I have no idea.

Your advice is welcomed and appreciated. Thanks

View attachment 57806 View attachment 57807 is welcomedx

As per above. XP boards not up to this kind of job as probably single skin of bricks. They are not a miracle cure.
They’ve basically strapped a desk fan to the back of the cross channel hovercraft and expected it to go twice as fast.
 

Reunat

New Member
Lots of good points from Ray and Raggles. Your builder is a t**t.
Essentially you have a single skin un-insulated outhouse with nothing like enough insulation or sheer bulk, including especially the floor and the roof. It didn't get wet before because there was no warmth inside to hold moisture.
That's why your house is made with 9inch brickwork or cavity brickwork. Somehow you will have to increase the thickness and insulation all round - walls, floor and roof, to move the dew point (where the water condenses) to a point where it can do no harm e.g. inside the brick, other side of a vapour barrier etc.
It is possible to build an internal skin of studwork, insulation vapour barrier etc inside but you may end up with something the size of a generous Khazi, not an office.
Presuming you don't have ther sort of job where you want to sit on a khazi all day, ( who knows?) the other option is to insulate and thicken up on the outside.
But for either option you need a proper builder.....and more money.
Hi @Brimstone,

thank you so much for the feedback. Does not sound very good for me. At this point, I just want to ensure that the condensation does not ruin the main structure. Insulating externally sounds expensive :-(

How would you remedy this? I guess I need to know what is less hassle - some sort of fix that would stop the Interstitial condensation (my extensive reading has pointed to this being the issue - please confirm?) ideally not ripping all the plasterboard out and undoing all the work?
Every day that passes I feel like is doing damage. What a stressful situation.

I do appreciate your advice.
 

raytheplasterer

Well-Known Member
Hi @raytheplasterer - no Airbricks or vents outside the building. I had someone else suggesting a humidity activated vent installed but I am guessing the problem is bigger than that?

They definately shouldn't have dot/dabbed the insulated board onto the single skin brick wall, there is probably a very minimal gap between the wall and the board to let it breathe causing the excessive moisture, also pva'ing the bricks is going to trap the moisture in the gap between the cold surface of the bricks and the warm air in the room. the un pva'd bricks could have soaked up some of that moisture. The boards are eventually going to pop off the wall, boards should have been fitted onto battens with fixings to allow a gap and the only way to do it properly is to rip it all off and start again. and put the electrics on the outside of the board, and also maybe a vent and airbrick.
They couldn't have done a worse job of it unfortunately.
 

raggles

Private Member
Hi @raggles - Ill try to answer as best as possible.

1. Single skin brick.
2. Flat roof. I think the builder put in wool insulation then plasterboard on the rafters.
3. No permanent heat source in the room. I have a plug in Electrical oil heater.
4. No water source - no sink or toilet.
5. Floor was concrete on a membrane which he painted with bitumen, covered in self levelling concrete, Arbiton acoustic and thermal underlay, then laminate.
6. It is not attached to the house.
7. Windows does trickle vents which I have tried to leave open.
8. Building control were not involved per se. The outhouse was an existing building (A brick shed - no insulation / plaster but power already ran.) when I bought the house last year. I therefore contacted building control to confirm the insulation, flooring and additional plugs were permissible which they confirmed was fine.
 

raggles

Private Member
Hi @raggles - Ill try to answer as best as possible.

1. Single skin brick.
2. Flat roof. I think the builder put in wool insulation then plasterboard on the rafters.
3. No permanent heat source in the room. I have a plug in Electrical oil heater.
4. No water source - no sink or toilet.
5. Floor was concrete on a membrane which he painted with bitumen, covered in self levelling concrete, Arbiton acoustic and thermal underlay, then laminate.
6. It is not attached to the house.
7. Windows does trickle vents which I have tried to leave open.
8. Building control were not involved per se. The outhouse was an existing building (A brick shed - no insulation / plaster but power already ran.) when I bought the house last year. I therefore contacted building control to confirm the insulation, flooring and additional plugs were permissible which they confirmed was fine.
Unfortunately the work completed is not up to par as already stated, other than keep it well ventilated there isn't a lot you can do without major works.
If you are still in contact with the electrician he may be able to surface mount those sockets and at least remove concerns you may have about them.
 

worthwords

Member
What you have is a unventilated box. Any moisture from within the room /occupancy will increase the relative humidity. Get a cheap logging humidity sensor to see what you are dealing wittps://www.amazon.co.uk/Govee-Thermometer-Hygrometer-Temperature-Greenhouse/dp/B086YYL439/ref=asc_df_B086YYL439/?tag=googshopuk-21&linkCode=df0&hvadid=463159373478&hvpos=&hvnetw=g&hvrand=3772017238124657463&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9045858&hvtargid=pla-966670669177&psc=1

That humid air is essentially a gas and will get through any gaps and settle on cold surfaces and to a lesser extent will diffuse through the plasterboard. The electrics are just holes/bridges to the cold area and so surface mounting them may have helped.

When you put insulation on, unless your vapor barrier is tight you are exacerbating the problem by making the brick wall colder - so likely to get dripping condensation between the plaster and cold wall.
Single brick will have moisture passage across to the void, particularly with wind driven rain. So need to really understand the building before slapping some insulation on.

It sounds as if the building will be cold between uses. This can't help as any moisture in the air from occupancy might be ok while the temperature is 19 degrees but as soon as you leave and temp falls, the amount of moisture the air can hold will drastically and all that moisture deposited the first surfaces to reach the dew point, windows, dot and dab patches.
If you ventilate it properly, any moisture from occupancy but ideally would want to keep a low level of heating throughout the colder months.
 

Brimstone

Well-Known Member
Sorry Reunat but as others say, think you have to rip it out and start again. find a decent builder who knows what they're doing, which isn't easy - ask around and all ways follow up references.
I suspect it might be easiest to put a second skin/blockwork on the outside and a new roof (warm roof design), but your builder is the one to advise & price it.
 

Reunat

New Member
Sorry Reunat but as others say, think you have to rip it out and start again. find a decent builder who knows what they're doing, which isn't easy - ask around and all ways follow up references.
I suspect it might be easiest to put a second skin/blockwork on the outside and a new roof (warm roof design), but your builder is the one to advise & price it.
Thank for ALL your feedback and advice. Sounds like unfortunately I have to get everything pulled down. Seemed like such a straight forward job. Very disappointed. I am hoping that the builder is willing to take all down for me and soon before this causes any permanent damage.
 

Zanzibar26

Member
Not only as mentioned above, also consider that for an air tight vapour barrier you cannot be having sockets buried in the insulation. This creates a huge gap where warm(er) air is entering and going behind the insulation, causing condensation. Same with spot lights. “Steve roofer” on youtube has decent videos explaining real situations like yours.
 
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