Advice sought for replacing original plaster.

[Glimma]

Hi All,

New to the forum after googling for what seems like ages trying to get advice on replacing plaster.

I've been in my Victorian end of terrace for about 10 years now and have finally started redecorating the dining room. The previous owners had the room skimmed and new plaster coving installed and we thought we had nothing else to do but decorate, however its turning out to be the worst room in the house.

Basically the plaster has came away from 2 of the internal walls, if you pressed the walls the plaster moved with a ripple like effect over the whole wall. So we're back to brick on these 2 walls, most of the plaster came off without any effort at all, but the lower 30 cm had to be taken off with a SDS drill. It appeared to have been some sort of cement render, it was rock solid. When taking this off it has pulled some of the mortar with it.

Now sections of the lath & plaster ceiling are coming down.

Sections of the brick walls that had the cement render on look to be damp but the vast majority of the bricks look dry and apart from some missing/failed pointing look to be in good order. I'm assuming the damp areas are due to the cement render not allowing the wall to breathe and they'll eventually dry out now the render has been removed.

So my dilemma is how do I make good the dining room.

As the ceiling is staring to fail and there are no original features do I pull it down and sheet with plasterboard?

For the walls do I build a stud and sheet with plasterboard?

From all the posts I've read, I know I need to allow the building to breathe, so will the building still breathe behind the stud wall?

Or should I get the walls re plastered with Lime? Or is using Lime plaster pointless as the 2 remaining walls in the room are lath & plaster but with a gypsum skim and therefore not able to breathe?

Thanks

Glimma

 

[paulc]

Re: the cement render - If you have a row of holes drilled in to the bricks just above ground level outside, you have had the "chemical DPC" treatment. The cement render usually goes hand in hand.

As for the plaster, now that you have stripped more than 25% of the external wall, building regulations kick in. There is a requirement to insulate the walls (subject to cost & payback period), which is worth doing in my opinion. 75-100mm of cork or woodfibre will make a noticeable difference, and if you can wrap a layer round the window & door reveals, it will help to reduce any cold spots in those areas.

At the risk of being vilified, I'm of the opinion that gypsum plaster is "breathable" - It certainly absorbs moisture and will dry out again. However, gypsum is water solvable, and if subject to repeated & prolonged periods of damp, it will turn to mush. In this respect, lime plaster is much more tolerant. Lime also has other advantages, such as being able to add pigments (saves on painting), can be polished to a high sheen, and also waxed - Have a look at Venetian Plaster & Tadelakt if you really want to go down that rabbit hole

 

[Glimma]

Hi Paul, thanks for taking the time to read and respond to my post.

The walls with the plaster off are internal walls and I've had a look and there are no holes drilled in them that I can see, so I don't think the walls have had a Chemical DPC.

The 2 external walls still have the plaster on them, I can see the lath of one of the walls but they've both had a gypsum skim over them. So as the external walls still have the plaster on the 2 internal walls don't will building regs kick in and stipulate I insulate the walls?

I'll take a look at Venetian Plaster & Tadelakt.

As for the ceilings is plasterboard ok or should I go down the lime plaster route?

 

[fernicarry]

For internal walls and ceilings you don't need them to be breathable so you can use any material that suits.

When you say the ceiling is failing just how bad is it? My ceilings are mostly original lath and plaster and whilst they are cracked and pretty bouncy in places I don't feel like there is a danger of them coming down around my ears (touch wood). I've had some success stabilising them by raking out the cracks, filling most of the depth with a haired lime plaster and then a fine interior filler to finish. Only using lime in this case because its haired and that seems to get a good strong grip onto the adjacent areas, you might get the same effect with modern scrim tape. If you can get access to the other side of the ceiling then another stabilising trick I've used is to skim the back of the plaster to lock any dodgy bits back onto the laths, again with haired lime.

You say you can see lath on the external wall that hasn't had its plaster stripped. The normal way of doing external walls in this part of the world is to dook straps into the wall (wooden wedges are hammered into gaps in the masonry and vertical studs are nailed onto those) then lath and plaster onto that. This creates a cavity between the inner face of the wall and the plaster to stop wind driven rain getting all the way in. The cavity should be ventilated a bit at top and bottom so that the inside face of the wall can dry out i.e. to allow the masonry to breath. If you have any electrical fittings on the external walls then you can remove one and verify if this is indeed the construction.

Problems arise when debris fills the cavity and bridges the plaster to the external wall so that water can penetrate. How big a risk this is will depend on how exposed you are. I am very exposed since I overlook a sea loch and have had this problem in places. I plan to keep the finish on my external walls breathable, both the plaster and the decorative finishes, just in case. If you are less exposed and the wall cavity is working well then this might be less of a concern. Whats the condition like at the moment? Any signs of damp or mould on the existing wall finish?

Odd that your internal brick wall had the hard cement on the lower section. Is it a party wall? Could just have been a repair at some point and that was what they had to hand. Whoever last rewired this building made good the massive holes they smashed through the original plaster with something that looks much like cement.

I wouldn't worry about building control unless you are subject to a building warrant. Insulation is undoubtedly a good idea if you need to remove the finish on the external wall for any reason. Air tightness (aka draft proofing) is more important in the first instance.

 

[Glimma]

Hi Fernicarry, thanks for taking the time to respond to my post.

So basically part of the ceiling came down, it was about 2m x 1m section, all lath and plaster. My neighbour had a similar problem last year when her hallway ceiling came down during the night (she got the fright of her life!!).

At the weekend there I started taking the rest down and some of it came down without any issues and other sections required some effort to take it down.

I was originally worried about what to put back up but I really shouldn't have been as the ceiling was a patchwork of different materials. I had the lath & plaster, really thick plasterboard, 2x layers of thin plasterboard and even some thick cardboard with some sort of filler over the top.

It was a messy job but I'm glad its down.

So I'm back to the lath on the ceiling and back to brick on the 2x internal walls. One of the internal walls (the one with the cement render) is the wall between the dining room and the living room and the other is the wall between the dining room and kitchen. Both appear dry and really just need re-pointing in places.

The external gable end wall appears to be lath & plaster, see picture below of the laths poking out in the corner:


This wall had a blocked up fireplace, we're going to install a wood burner which is due to be installed at the end of November.

The plan was originally to insulate under the wooden floor and leave the walls as they were as we though they were in good order. But as I'm back to brick on 2 walls and have no ceiling, do I take the plaster off the gable end wall and insulate?

The external walls are Sandstone with no cavity, so I believe the lath is on studs which are nailed to the dooks in the Sandstone, exactly how you described your walls. The Gable end is fairly sheltered so doesn't get wet or battered by the elements. There are no signs of damp in the wall.

I was thinking of using some sort of wood fibre insulation board, mechanically fixing to the Sandstone and then plaster over the top or should I build a stud frame and insulate in between the frame? Or as this wall will have a wood burner in the fireplace does that change how I can/should insulate?

At the moment I'm thinking now is the time to insulate, I'll never be in this position again, so just do it. But could I be opening a can of worms and I'll wish I never touched it?

Thanks again

Glimma

 

[fernicarry]

I was thinking of using some sort of wood fibre insulation board, mechanically fixing to the Sandstone and then plaster over the top or should I build a stud frame and insulate in between the frame? Or as this wall will have a wood burner in the fireplace does that change how I can/should insulate?

I've done a bit of both. Where I've had the space I've built insulated studwork stood off of the wall to maintain the air gap. But around window reveals I've packed the insulation right up to the masonry since obviously there is less space. Most rooms here are in their original state though so overall its still pretty well ventilated.

If you search for "Indinature installation guide" (can't find a direct link for some reason) they have quite a good summary on retrofitting traditional builds. They recommend going straight onto the masonry without an air gap, although, as we discussed on another thread, the masonry face often isn't all that flat so its hard to avoid air pockets without adding a lot of material first. I would say that breathability of the internal finishes would be quite important if you did it that way.

I'm also in the process of insulating under the floor pretty much as described in that guide and picked up a few packs of their product yesterday to try out. Will report back once I psyche myself up for another stint crawling around in the dirt. If you do take down the external wall then you have a great opportunity to make an air tight seal between the wall and the floor to eliminate drafts around the skirting board. Where possible I'm going to lap the breather membrane from under the floor up behind the wall.

Make sure your wood burner has an external air intake so that you're not forced to undo all your good work.

 

[Glimma]

Hi Fernicarry,

The wood burner doesn't have an external air intake or at least I don't think it does.

I thought only the larger Stoves required an external air intake, the Stove we're going for is the Chesney Beaumont 5WS series with an output of 4.8kW.

Whats the implications of insulating the dining room and then using the Stove without an external air intake?

Thanks

Glimma

​

 

[fernicarry]

I thought only the larger Stoves required an external air intake, the Stove we're going for is the Chesney Beaumont 5WS series with an output of 4.8kW.

Looks like the regs say you don't need to provide permanent ventilation below 5kW. But the stove will be sucking its combustion air in from the room and that has to be replaced from somewhere so there will be increased air movement when its lit.

I think your 5WS can be connected to an external supply although their documentation isn't entirely clear but it's well worth considering if it is possible. You might be able to take the air from under the floor if you don't fancy coring through the external wall.

 

[Glimma]

So after another weekend of ripping my dining room to bits, I've got the plaster off the Gable end wall, so we're back to Stone, see picture below:


I originally started this post as I wanted to reinstate the plaster as near as I could to what was already in place (thinking it was all original), but after ripping the plaster off the wall I'd say that only 10 % was the original lath and plaster. The rest was a mix of plasterboard and whatever previous owners could get their hands on.

I've been looking into the various brands of Wood Fibre Insulation boards and their installation guides advise they need to be fitted to a flat surface. How flat does it need to be? The wall is fairly flat, but there are a few undulations and I've got the holes where the dooks were in the wall. Do you think I need to level the walls with a Lime based plaster?

As for the Stove, I've spoken with Chesneys technical team and the Hetas registered installer and they've both advised as the Stove is below 5kW I don't need external ventilation.

Thanks

Glimma

 

[paulc]

A parging coat is usually recommended to level off a wall. The brick walls that I've done here were far from flat and I didn't bother trying to level them off. But I did fill any big voids with a lime mortar (putty & sand mix).
With the fireplace there, you need to watch the minimum distance to combustible materials. Woodfibre and most other insulation materials are not rated as fireproof, even when encased in plaster. You may well need to leave 500mm of bare stone above the stove. On the plus side, this exposed stone will act as a thermal store and radiate heat long after the fire has gone out.
One observation - You appear to have some beefy cables at odd angles over the fireplace. Mains cables should run vertically or horizontally in prescribed zones. Alternatively, buried at least 50mm below the surface and/or run in (preferably) steel conduit. The wall above the stove will get extremely hot which won't do the cables any good, so I'd suggest moving them if possible. The cable to the right would also benefit from being put in conduit. A good opportunity to fit a couple more sockets to that wall too.

 

[Glimma]

Hi Paul,

What depth were the voids you were filling?

If I put a level over various parts of the wall the biggest void/indent is about 4cm but the majority is about 2cm.

I've traced both the cables, the one one the right was disconnected above the ceiling and under the floorboards so I've removed it. The 2nd one wasn't a cable but seemed to be a small pipe. It was very soft, you could bend it with no effort. Both ends were connected to nothing, so I've remove it as well. As for the 2 pipes, they've been disconnected in behind the cupboard in the corner, I've not got anything to cut them so I'll leave in place for the time being.

I'm not sure what height the opening will be for the Stove, so when I start to insulate I'll stay well clear of the fireplace. Once the guys have made the opening and installed the Stove I'll go back and insulate but keep the insulation at least 500mm from the top of the Stove. Will this be the same for the sides of the Stove?

Thanks

Glimma

 

[fernicarry]

As for the 2 pipes, they've been disconnected in behind the cupboard in the corner, I've not got anything to cut them so I'll leave in place for the time being.

Might have been for a back boiler in the fireplace.

 

[Lacan07]

So after another weekend of ripping my dining room to bits, I've got the plaster off the Gable end wall, so we're back to Stone, see picture below:
View attachment 11695

I originally started this post as I wanted to reinstate the plaster as near as I could to what was already in place (thinking it was all original), but after ripping the plaster off the wall I'd say that only 10 % was the original lath and plaster. The rest was a mix of plasterboard and whatever previous owners could get their hands on.

I've been looking into the various brands of Wood Fibre Insulation boards and their installation guides advise they need to be fitted to a flat surface. How flat does it need to be? The wall is fairly flat, but there are a few undulations and I've got the holes where the dooks were in the wall. Do you think I need to level the walls with a Lime based plaster?

As for the Stove, I've spoken with Chesneys technical team and the Hetas registered installer and they've both advised as the Stove is below 5kW I don't need external ventilation.

Thanks

Glimma

They usually advise a scratch and float coat before applying wood fibre boards, and that's with brick walls. Ideally you don't want any gaps between the stone and the boards. If you're going for 60 - 80mm depth of wood fibre board there's usually a bit of give which allows you to compensate for any minor hollows, etc.

 

[Glimma]

Hi All,

Thanks for the replies so far, very much appreciated.

I'm spoken to a neighbour who's been here for about 50 years and she advised that the all the houses did have a back boiler installed behind the fireplaces in the dining room. Not sure how big they are or how much work is involved to remove them, but guy's installing the new Stove would've come across them in the past. I'll drop them an email so they're aware of it.

I've read various product guides on the wood fibre insulation boards and they all mention not to install on damp walls. So the next stupid question is how do you know if a wall is damp and how damp can it be?

I've had a look at the wall and there is one area that looks damp:



This is the corner next to the cupboard close to the fireplace. As you can see the floorboard is rotted in the corner and the wooden dook in the wall is also crumbling/rotten. Before we started any of the works, the fireplace was covered with plasterboard and the hearth was covered with hardwood flooring which was stuck down with silicon in places. When I removed the hardwood flooring a whole load of what looked like compost fell out from behind and the back of the skirting board:


When I opened up the fireplace the plasterboard was mushy and I removed about 3 backs of debris. The debris seemed to fall down behind the skirting to the left and then down under the floor boards. I must have removed another 2 bags of debris from under the floor in the corner.

The fireplace is going to be opened up and the hearth rebuilt as under the cement screed is all rubble, so all of this will help (i think).

So before I order the wood fibre boards I just wanted to check on the damp issues? I really do think insulating this wall will help in retaining the heat in the room, but I don't want to insulate and then cause further issues down the line.

Thanks.

Glimma

 

[fernicarry]

If I put a level over various parts of the wall the biggest void/indent is about 4cm but the majority is about 2cm.

I'm using the Inditherm batts at the moment and they compress quite a bit. Down to less than 50% of their thickness if you push really hard but obviously you are wasting valuable insulating value the more you compress. They are designed to be fitted into studwork however so possibly more effort to fit on a wall.

Its a bit of a pita under the floor because you want them to sit nicely up against the bottom of the floor boards but you also don't want to hold them in place too firmly and lose too much thickness. I've settled on about 10mm compression on a 100mm batt.

So far as the damp is concerned it could have been the modern materials trapping moisture that would otherwise have left more easily. Hard to tell. The 'compost' in the second pic does look wet judging by its colour but not sure where enough wood debris would come from to create that pile.

Obvious things to check are water coming down the old fire flue if it the chimney wasn't capped. I assume your stove installers will be lining the flue so they'll be changing that situation, hopefully for the better. Also rainwater goods, external ground levels etc.

 

[Glimma]

Hi Fernicarry,

Are you using the Inditherm batts on a wall or under the floor?

I've read the Inditherm Installation guide and it advises "Current best practice guidelines advise that natural insulation be installed directly on the wall without an air gap." So I was taking this as installing rigid wood fibre boards directly onto the wall. The wall would be fairly flat as I'd fill in any voids with a Lime plaster prior to fixing the boards in place. But looking at the Inditherm install guide they show a stud wall right up against the brick/stone wall and then the Inditherm batts between each stud. Either method I'm guessing would involve any voids being filled in prior to the insulation?

The fireplace has been opened now for a few weeks and I haven't noticed water coming down but just because I haven't seen it doesn't mean its not happening! Rain is forecast for the next couple of days so I'll keep an eye on it.

The plan would be to brush/scrape down the gable wall and see how level it actually is. From there I can decide on either fixing insulation boards directly to the wall or build a stud, fix to the wall and the insulate between the studs. I'll also lift more of the floor boards and see if it looks damp under the floor.

This is turning into a far bigger job than I thought at the start, I honestly thought I'd be getting the Stove installed, redecorating and then sitting in front of the Stove with a nice glass of wine!!!

Thanks again for all the help and advice.

Glimma

 

[fernicarry]

Are you using the Inditherm batts on a wall or under the floor?

I've only used them under the floor so far. I would like to use them on the outside wall of the upstairs box room but that's kind of stalled at the moment waiting for me to fix the rest of the joist ends... I can't give up much floor space in that room so I may have to put the batts directly up against the wall rather than leaving an air gap but its a rubble wall so would take some amount of filling to get it flat enough. Still pondering that one...

I think what Indinature are getting at is using studwork to get a flat face to attach your boards onto, be that plasterboard or a breathable board. The batts probably aren't suitable for attaching directly to the wall with through fixings so the studwork helps support them too. The boards would squish the batts lightly against the wall to make sure they conform to its surface without any gaps. Your wall is probably flat enough that you could do that with just a bit of filling of any bigger depressions.

What sort of thickness are you looking to go up to, or do you have a U-value in mind?

Rain is forecast for the next couple of days so I'll keep an eye on it.

Be worth getting your stove installers to have a good look at the chimney stack and pots. I had my south chimney re-rendered a couple of years ago when the front wall was pointed and I think thats cured the problem of water running down the fire flue after very heavy rain. Its often the case that the weather needs to come from just the right direction to trigger problems like this.

Having a look under the floor is a good idea. But you might find more horrors...

This is turning into a far bigger job than I thought at the start, I honestly thought I'd be getting the Stove installed, redecorating and then sitting in front of the Stove with a nice glass of wine!!!

Pretty much everything I've done here has gone that way. Doesn't stop me enjoying a glass of something though, surrounded by the chaos...

 

[Glimma]

I was planning on using 60mm Steico Therm Dry Wood Fibre Insulation boards mechanically fixed to the walls.

To try and get the walls as flat as possible and fill the larger voids I was going to use Adaptavate Breathaplasta Universal.

The Steico Therm Dry Wood Fibre Insulation boards would then be finished with 2x coats of Adaptavate Breathaplasta Universal with a fibre mesh pushed into the first coat.

I think I could tackle the parging/leveling coat and the insulation board installation myself, but I'd need to get a plasterer to do the top/finishing coats.

I'm 100% sure that under the floor there are a few horrors waiting to be discovered.

 

[a twig]

Just in case you are interested in a cheaper alternatives to Breathaplasta, I used Reabilita Cal AC to good effect over my woodwool boards internally - post here, unfortunately the links got mangled in the forum transition but it hopefully makes sense.

Plastering question

Hello all, After nearly a year of serious unanticipated structural work we've now finished and can get on with fitting windows, plastering and everything else that we thought we'd be finished by now. I have a question regarding use of wood wool boards on an external facing brick wall. This...

www.periodproperty.co.uk

 

[Lacan07]

I was planning on using 60mm Steico Therm Dry Wood Fibre Insulation boards mechanically fixed to the walls.

To try and get the walls as flat as possible and fill the larger voids I was going to use Adaptavate Breathaplasta Universal.

The Steico Therm Dry Wood Fibre Insulation boards would then be finished with 2x coats of Adaptavate Breathaplasta Universal with a fibre mesh pushed into the first coat.

I think I could tackle the parging/leveling coat and the insulation board installation myself, but I'd need to get a plasterer to do the top/finishing coats.

I'm 100% sure that under the floor there are a few horrors waiting to be discovered.

That sounds like a plan, you can definitely do the dubbing out and insulation boards yourself.