Blown Plaster advice

[blackcat]

Hi Everyone,

Our house is a solid wall Victorian cottage, a section of a wall in our lounge looks to have a damp issue as there are patches of blown plaster about 50cm up the wall.

I guess water has got trapped between the cement render on the outside and modern Gypsum plaster on the interior.

From my understanding of period buildings ideally we would strip the walls of Gypsum and re-plaster in Lime to allow the wall to breath. However this not an option because I have 2 small children and I feel this would cause too much dust and disruption to our main living area. We are also currently looking to sell our house so I am looking for a more affordable alternative to resolve the issue.

One solution I can think of would be to remove the gypsum plaster at the bottom of the wall up to around 50cm to allow the wall to dry and breath. Then dry line by battening and plasterboard (maybe also add some vent bricks)

Does this sound like a good solution? I guess it would also have the added benefit of making the room a little warmer as we would be able to include insulation.

Any advice would be greatly appreciated

 

[Penners]

Hi David

If your damp is about 50cm up the wall, I think you should consider hacking off the plaster up a bit higher than that, just to ensure that you've exposed all of the damp substrate.

Yes, you could batten and plasterboard over the hacked-off plaster, but given the age of your property don't you think that waist-high wainscoting would be more in keeping? There are many styles to choose from, as the link below will show you (scroll down the page a bit).

http://faq.elitecrownmoldings.com/wainscoting/

Mount your panelling on to treated timber battens attached to the wall, so that there's an air-gap behind the panelling. Make sure that there's plenty of provision for air circulation in this void. You can arrange this in a number of ways, by leaving gaps behind/beneath dado and skirting, or by incorporating grilles in the system.

 

[blackcat]

Hi Penners

Thank you for taking the time to help.

Fitting wainscoting certainly feels like it would make the job more manageable (no replatering needed), I guess I would have fit to every wall in the room so that it matches.

When fitting wainscoting what size battens would you suggest, also I wondered if it would be best to have the vents internal or should I fit an air brick ?

 

[Penners]

It's a moot point, which depends on your own taste, but I don't think the wainscot would necessarily need to be on every wall.

The size of battens isn't critical, but you'd need them thick enough to leave a respectable air-gap behind - say 32mm thick.

As regards ventilation, you raise an interesting point in questioning whether internal or external air would be better. My gut feeling is that internal air circulation would be better than external, because it will be warmer and therefore able to carry away more water vapour. However, if there's a risk that the internal air will already have a high moisture content itself, such as in a bathroom or kitchen, then drier, external air might be better.

Anyone else have a view on this?

 

[Flyfisher]

A view, yes, although no particular expertise.

It seems like the classic ventilation-vs-insulation dilemma. Allowing internal (warm) air behind the wainscoting might result in condensation if the wall itself is much cooler than the other parts of the house - quite likely, I would think, because of the insulating nature of the wainscoting itself.

On that basis, ventilating the gap behind the wainscoting with external (cold) air might be more effective - although this would probably result in more heat-loss through the wall.

My general feeling is that external ventilation is the answer to damp problems, i.e. allowing fresh, low-humidity air, waft over damp materials and thus drying them out over time. That seems to be the basis of effective roof-space design. But what's practical for a roof may not translate very well for a wall.

Perhaps if the wainscoting itself is well insulated then the thermal loss would be minimised anyway - the equivalent of insulating the attic floor, leaving the air-space nicely ventilated but with little heat lost.

But, as I say, not an expert view by any means.

 

[timinder]

It seems to me that if you're going to hack off plaster from the lower parts of the walls anyway, and are thinking about drylining, wainscoting and possibly adding air bricks, you're going to be making quite a bit of mess and disruption anyway.
Why not just hack off the plaster from the problem wall and get it replastered in lime? You say that the plaster is blown, so it really wants to come off anyway.
doing it that way is more likely to give the most successful outcome and you won't be putting-off potential purchasers who will see the new airbricks etc. and wonder what problems you're trying to hide!
You may well find that even with the render on the outside damaged, the lime plaster on the inside allows the wall to breathe sufficiently well to remove the damp patches. Just make sure whatever finish you use on the wall is also breathable.

Edit: Oops - I was reading through old posts on the forum as well as the new ones, and didn't check the age of this before I replied

 

[vicky whitworth]

How funny! I wonder what happened next? Is the plaster still blown? Did the kids get lost in the dust or misplaced behind the wainscotting?

 

[DJH]

My own solution to overcome damp and cold walls is to panel the lower part of affected walls has been to batten the wall with treated 2" x 1" treated timber using stainless steel screws with staggered gaps between each row to allow some circulation in that space.I've then used foam with a foil backed insulated plasterboard and wood panelling as a finish, in some cases painted and others sealed/stained depending on the decor in that particular rooms finish.

The idea behind this method is to keep the wall cool by insulating it from the warm moist temperature in the room thus preventing condensation from forming on the cold wall surface. The wall, then can in effect, can stay damp and cold in the case of it not having a dampcourse and, where they ground outside is too high making the wall damp, that can be rectified at another time. The house can be occupied in those particular rooms that are suffering from damp without it affecting furnishings and floor coverings etc.

I haven't ventilated the gap between the wall and foil backed plasterboard from the outside but fitted ventilators at floor level in the panelling to allow evaporation in that space to vent out. Being at floor level minimal warm moist air will enter the ventilator if at all except maybe some if underfloor heating is used as we all know that hot air rises and cold air falls and evaporates in my case through the venti;lators which are fitted about 4ft apart and close to the corners of the room.

This method has worked for me and after ten years or so and there has not been a problem with any of the walls so far!

Doug