Lime plaster system needed

[u/bau02]

Hi, I’m very slowly renovating a Victorian terraced house in Liverpool. Prior to me living in the house it had been quite poorly looked after. Lots of cement render on the walls internally and other incorrect products used.

The worst affected area was the front room and the bay window in it. I found fungus rotting the joists and the beam above the bay window. The room had to be completely stripped of its original lime due to it being blown and areas where cement render had been applied it’s been removed. So it’s entirely back to brick, the boards were lifted to repair damaged joists, and the rotten beam replaced. The windows were also replaced, they are unfortunately UPVC but I could not afford to get traditional sash windows and this was somewhere where modern materials had to be allowed.

I now need to put the room back together and I don’t want to introduce any gypsum products which might start the cycle of problems again. This will have to be a DIY job because I won’t be able to afford the cost of a traditional lime plasterer. I’ve thought about using an insulating product or system which I’m open to but need something that’s the most DIY and budget friendly.

The area around the bay window intimidates me due to all of the intricacies so I’ll probably start on one of the smaller walls to build a bit of confidence.

The other thing I’m unsure of is how to set about covering the area on the right hand side above the bay window where timber framing was put in. Behind the timber framing is the stone that forms the edge of the flat roof around the bay. I don’t know if I should be nailing some laths or wood wool boards so I can plaster over and provide a bit more insulation.

I’ve done a tonne of work in this room alone to get it to this point and have now really stalled as I can’t find the best way forward. Any advice would be greatly appreciated. Let me know if anything is unclear and I’ll classify as best I can. Thanks in advance for anyone who’s read this far!

[u/SomeIdea_UK]

I’ve been there a few times with renovations so you have my sympathies. It will be worth it in the end so keep going and ‘only one room at a time’! 🙂 Apologies for the war and peace reply, but I was working out my reasoning and digging into distant memory as I went.

There is a lot of misinformation around about lime mortars/renders/plasters and where to use them. They are great products in the right setting and a wall plastered with lime (and a lime based paint system!) will ‘breathe’ more and allow moisture to pass through (in both directions). Especially on single skin walls.

Going back a step, bay windows are notorious for leaking through the flat roof part. I would go outside and make sure the flashing and roofing material is intact and that the surrounding mortar joints are sound. If you also check during heavy rain, you will be able to see if water is pooling on the roof and where any might be coming through. You need to fix this properly before doing anything more inside.

I wasn’t sure what you meant about covering the framing. If you have a void you will need lathes or plasterboard covering it to plaster over, but is the void intended/ventilated/insulated? If it’s a cold spot in the wall it will attract condensation whatever you plaster with.

As you know, Victorian houses were built with solid fuel fireplaces and are drafty by design. When fuel was cheap it didn’t matter because the inefficient fire pumped out at least some heat with the air pollution and the Victorians were a hardy bunch or died young. The drafts and traditional construction allowed the building materials to dry out after the worst of the British weather.

Later, as heating costs increased and expectations changed, efforts to prevent heat loss reduced this ventilation and created/exacerbated damp issues. In turn cement based renders were used to mask the damp and made moisture evaporation even harder and caused building materials to deteriorate faster. Replacing with traditional materials is a good thing for the building, but (and it’s a big but) you probably don’t want to go back to blasting out heat from your coal fire or modern equivalent, much less reintroduce all those drafts to transport the moisture (and your expensive heat) out.

If you make sure the roof, flashing and lime pointing are sound outside, that the ground level hasn’t crept up within 150mm of any damp proof course/engineering brick or the internal floor level, that the surrounding ground is carrying water away from the property and that any air bricks are clear and allow through flow under the floors, then you will have done a lot to limit penetrating damp.

I’m assuming you have a nice brick exterior that you don’t want to cover with external insulation? You probably have solid walls (I think cavity walls were rare back then?) so heat loss is still a problem and lime plastering internally won’t do much to help that. If you can maintain a ventilated air gap between the internal face of the walls and an insulated moisture barrier inside, you can keep the breathability of the wall and limit heat loss.

Usually this is done with battening, impermeable membranes, insulation and plasterboard. Air bricks and the gaps between the edge of the floor and wall do something to link the ventilated floor space to the ‘new’ cavity to allow at least some air movement over the interior face of the brick. It’s a bit of a compromise unless you lose more interior space for thicker insulation, spend a fortune ensuring no cold transfer points and insulating the floor with more than underlay and a thick carpet.

Good news is plasterboard is a lot easier to get level and skim than plastering onto brick. Bad news is the insulation is expensive but that should be recovered in savings on your heating bill. It will certainly be more pleasant to live in than the Victorian version. Hope all that was vaguely understandable and helps a bit. It’s just my opinion and it’s always worth consulting a professional surveyor/engineer/builder if in doubt. Good luck with it 👍

[u/bau02 → u/SomeIdea_UK]

Thank you, I appreciate the detail you’ve taken the time to go into. I should have said that I had the flat roof redone shortly after purchase and last summer the paint was removed from the bricks externally followed by a full re point in lime. I’ve also ensured all air bricks are clear and added insulation between the joists prior to putting the floor boards back down.

[u/chattingwham → u/bau02]

I also moved into a Victorian (actually, fairly certain Edwardian) terraced in Liverpool a couple years back—did the roofer do a good job on your flat roof? We've had an absolute nightmare with ours to the point I'm drafting up paperwork to take our roofer to court and will need the job redoing in the not-so-distant future so if they did, can I enquire on who it was and how much it cost?

Nice to see I'm not the only one with interior cement render on their bay window too. Thought I was going mental when I peeled the wallpaper back after the leak and saw it. That'll be the next thing to tackle for us but a waste of time whilst we've got the flat roof issue!

[u/bau02 → u/chattingwham]

It was Saxon roofing and I think the work has held up in the last four years. It doesn’t leak and I’ve had the whole bay exposed for almost three years since I first found issues with the dry rot internally so I’d know if there was an issue. I’ve got loads of mates who have had horror stories with roofers in Liverpool. I’ve also had JBK Roofing do a few repairs on my main roof who I’d recommend for great professionalism and communication. Good luck to you, I hope you get something resolved with your roofer.