Grey patches on walls

I don't have a camera no pics. 

I have dot and dab wall boards all over this house.  It is a 1900's welsh valleys terrace house, stone walls.  

Downstairs on the interior side of the external walls I have grey spots coming through. It is not black mould, it is grey, seeming to stain through the paint rather than actually growing on the interior surface.  I imagine the guy B4 painted the walls regularly before it sold to me.   I hate to think what it must be like on the other side of the plasterboard. 

What is best in the short term? Zinnser BIN ?  Do I apply it neat or dilute it with anything.  I know it is expensive I am willing to buy 10 L tin £175. 
Should I sand down the surface (wearing a mask)   and should I treat with any anti fungal  before painting?  
What is best method of application, brush,spray or roller  and is there a particular brand of applicator I should buy?

What is best in the long term? I'm thinking of changing all the uninsulated dot and dab boards for 50mm foam backed wall boards. Thinking the moisture is less likely to penetrate through the foam and it will insulate the property.   Or  go to a render and plaster skim (no wall boards).   

 Thanks

Replies

  • coffeepleasecoffeeplease Forumite
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    Just for the current state of your walls, BIN is a great solution. I've used it many times, and nothing works as well.  Zinsser has usage instructions on their website for their products.

    All surfaces to be thoroughly clean/dry no organic residue or material remaining.
    Applied with brush or roller, two coats, 45 min dry time between. 

    I would add to that that BIN is a shellac-based paint, it has a thin consistency, and stirring thoroughly is important. Stirred twice even. Stirred occasionally during use, and between uses.
    I have used brushes and rollers, no issues, but ventilation, and kids/pets removed to another area is a good idea. Brushes/rollers are cleaned with white spirit or turps.

    If mould is present their Mould Killer will resolve it before painting with BIN. Or to save work, paint with PERMA-WHITE® (INTERIOR), it actually prevents mould growth. It won't continue to prevent mould growth after time if it it's covered by a layer of other paint, but Perma-White comes in a variety of colours so a top coat of colour isn't always necessary. I use a mask/respirator and goggles because it contains a mould-inhibiting biocide that is very irritating to skin, eyes and respiratory organs; you don't want to get this in your eyes.  

    I know I sound like an advert, but this is my experience working as a painter. Doing this as a DIY is as easy as painting. And you could save a lorry load of money doing it yourself. 

    It may be that there is a vibrant mould colony thriving behind that plasterboard. Can't offer any suggestions about replacement with foam-backed boards; not familiar with them. But I would be considering having a look. As well as considering the possibility of exterior damp penetration and if it is occurring, is there is any sealant that could be applied to the exterior to reduce or eliminate moisture penetration.
  • coffeepleasecoffeeplease Forumite
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    Sorry, forgot to add, BIN it is applied neat, no diluting.
  • xxxxxxxxxxxxxxxx Forumite
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    Thank you for the reply coffeeplease.  
  • FreeBearFreeBear Forumite
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    xxxxxxxx said: I have dot and dab wall boards all over this house.  It is a 1900's welsh valleys terrace house, stone walls.  

    What is best in the long term? I'm thinking of changing all the uninsulated dot and dab boards for 50mm foam backed wall boards. Thinking the moisture is less likely to penetrate through the foam and it will insulate the property.   Or  go to a render and plaster skim (no wall boards).
    Slapping on Zinsser BIN should block the staining in the short term (you need an alcohol such as meths to clean the brushes). Over time, if the plasterboard & gypsum skim remains damp, it will turn to mush. A long term solution, especially if you want to insulate the walls, is to use woodwool or cork boards with a pure lime plaster skim - This is based on the assumption that you have solid brick/stone walls which would be typical for a turn of the century property.
    If the damp wallys have been at it with their chemical DPC & waterproof render/plaster, then you need to get as much of it off the walls as possible (including any cement render on the outside). This will enable any moisture in the walls to evaporate without causing any long term damage.
    Yes, you could use insulated plasterboard, but it will trap moisture in the wall where it can do unseen damage. The first you will know about it is when things like floor joists give way due to rot.

    Have a chat with the guys over at Ty Mawr or Mike Wye about insulating old buildings - They will be able to recommend products that are sympathetic to the construction of your home. If you don't or can't do the work yourself, they may even be able to suggest local companies that can help.

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