Lime Plaster vs Woodwool board vs Plasterboard

[beetle_pete]

All advice greatfully received. I've spent ages researching and just cant figure out what to do.

We have an 1870s victorian house which all rooms need some sort of plasterwork done ranging from stripping back to brick to removing and patching 1m2 sections. What is the best method to fix?

The issue is that I've read about the importance of breathablity but can't seem to find an economically viable way of doing it. With the amount of solid brick houses around this must be a common question, do most people just use plasterboard and ignore the breathable aspect?

We have had the two front rooms professionally replastered in lime which alongside the hallway are the 'feature' rooms of the house. Unfortunately having the whole house done in lime professionally is not possible from a money or timeframe perspective.

So what are the options? I'm hoping that I've missed the right one.

1. Learn how to Lime plaster. I plan on learing to do the patching but not sure I have the time or potential skill to make a good job of a full wall.
2. Wood Wool board dot and dabbed to wall. Then coat in lime base coat with mesh put in. Lime top coat on top. Essentially a breathable plasterboard?
3. Pay professional Gypsum plaster
4. Plasterboard and skim with a Celotex style insluation liner

Thanks in advance for the help

 

[paulc]

Why patching 1m² sections ?

In answer to your questions:
1) Learn to plaster in lime, and you have a skill for life. Looking at the walls of my house, I'm pretty sure that you (and I) could do a better job than the original builders.

2) Wood wool boards would provide some valuable insulation. You would still need to learn to plaster.

3) You run the risk of being hung, drawn, and quartered by some here :shock: On solid brick walls, gypsum would not be an appropriate finish if you wanted to maintain breathability.

4) Celotex/Kingspan topped with plasterboard & skimmed with gypsum is an option, but... You would need a ventilated air gap between the brickwork and insulation and ensure a vapour control membrane is installed. The finishing detail around windows, doors, floor, and ceiling would be critical in avoiding cold spots and potential problems.

Whilst Celotex type boards are much better insulators than the equivalent thickness of wood wool boards, I would favour the latter. No need to worry about air gaps, vapour control membranes, etc... Fix the boards with mechanical fasteners, job done.

 

[TheForge]

Rarely does lime plaster ‘need’ to be stripped back to bare brick. Minor repairs can normally be sufficient. Who has suggested you need to take it back to brick? Has it completely failed? Do you have any pictures?

You mention removing and patching metre sections, why a metre? Just cut back any loose, friable material and fill that area alone. Does the existing plaster have hair/fibre in the base coat(s)? To get a good finish build the patch out in a coarse base coat and skim and trowel flat with a fine finish plaster, wetting and controlling drying to limit shrinkage at the margins with the old plaster. Straight on to well brushed and wetted brick will be fine.

If cost is an issue repair will be more affordable. Pre mixed putty based lime plasters are available from about £7-9 a bag and can be used with no further mixing required. Mixing your own will be even cheaper but you need to select suitable aggregates and the standard unwashed cheap sands available from DIY sheds won’t give best results.

An 1870 brick built house may have a slate damp proof course, are the walls single skin brick? Most likely around 9” thick?

Is penetrating damp an issue? If the walls are dry it will have little impact (other than historical authenticity and the final look) what method or material you choose. If water is penetrating the wall there is a right way (breathable/permeable coating) or a bodge.

If walls are very damp gypsum is hygroscopic and will fail if plastered directly onto them.

The paint finish is just as important in terms of permeability, all too often people invest time and effort to lime plaster and then coat it with modern petrochemical paints which negates the ability for water vapour to evaporate.

Wood wool board is very easy to plaster on to, you could get away with a single coat of lime plaster. I wouldn’t even use mesh unless you predict excessive movement, just scrim the joints.

 

[88v8]

As TheForge said, if the house has an effective dpc then you can use gypsum.
I presume you're wallpapering, so the texture is not of importance anyway.

In our previous house, there was some badly blown plaster. Bits of it were redone, but much of it I papered over with a scrim paper underlayer, and it was still there 20/30 years later.
Yes, it sounded hollow if tapped, but that always put me in mind of Tommy Cooper's joke:

"Doctor doctor if I do this it hurts."
"Well, don't do it."

Ivor

 

[beetle_pete]

Thanks for the replies.

The walls dont have a cavity but are double brick on the outside walls and single on interior walls. I haven't spotted a DPC but that isn't to say there isn't one. What should I look for? I have suspended floors in the two front rooms so can look underneath. There is only one bit of damp in the house in the kitchen which I haven't investigated yet.

The original plaster in the house has a brilliantly smooth finish, far better than the professional job that we have had done in the two front rooms which is still a good finish. When we stipped the walls I didn't spot any hair just very dusty sand. I think this is the main issue as below the skim nothing will stick to it without potnetially a PVA film. Is there a product to use for this?

The house has been patched in the past with Gypsum which is still solid around 30 years later and doesn't appear to have had any ill effects.

I wasn't planning to strip 1m2 sections more that the walls that could be fixed need patching up to about 1m2. Time is more important than the money as we have a 8 week old baby and I work away alot. Sounds like the premixed lime putty might be a good option.

I'll try to get a few pictures up

 

[beetle_pete]

This is the current room in progress. Apologies for the poor pictures, its a small room.

Both these walls are external and the Gypsum on the left is right across the room. All the plaster above the window is loose and needs to come off. Due to the condition, my plan was to remove all the plaster off both walls and start from scratch potentially using wood wool boards with a lime skim.

These are the opposite walls both internal. I was planning to leave and fix with filler / one coat lime plaster dependent on size.

This shows the very dusty sandy base coat. What would be the best method to fix as nothing will stick to it?

Thanks for all the help.

 

[MikeG]

Don't introduce an unnecessary complication. Forget the render carrier board, and plaster direct to the masonry. Having said that, I doubt there is any need to strip back that far, and if there is it will be because of a damp issue. If you have a damp issue, then I certainly wouldn't be advocating adhering a render carrier board to the wall!

 

[Feltwell]

An easier option - have you thought about not taking the plaster off & using lining paper? Works a treat if the plaster is still well attached. My walls are mostly original plaster, generally not bad condition but certainly not good enough for a direct paint finish.

I use "Vario Plus" non-woven lining paper - much tougher than standard papers. Use ready mix adhesive with it, the sachet stuff you mix yourself isn't strong enough I've found. Gives a good smooth surface to paint on, so long as you make sure no high spots underneath, will certainly help mask any patching.

https://www.decoratingdirect.co.uk/viewprod/m/MAVNWLPV/

 

[MatthewC]

Your house does look pretty dry, in which case you might be able to do anything with the plaster really (according to money supply and any desire to keep original). However, I would say that breathable walls are only one part of the solution - poor rain water goods and high ground level outside are far more liable to cause you a damp problem if they are not OK now.

The ground level outside must be below the floor level inside, preferably by 6 inches, but 2 or 3 inches is a lot better than level; my house had concrete at floor level against the wall, and then some stones retaining some earth on top of the concrete! Also, people often don't realise that any concrete or paving up to the wall causes the base of the wall to eventually lose its lime pointing and/or the brick/stone base of the wall starts to recede, due to splashback when it rains; cutting a small gully with gravel is a fairly easy and effective solution, or else a French drain if you are keen.

Moreover, if the base of the wall is dry then you don't need a dpc at all, in my view. I have lost count of the number of folks who assumed that in restoring the house I had installed some form of dpc, and they always look astonished when I say that I didn't.

I recommend that you make sure the outside is OK first!