Lime plaster versus gypsum plaster

housebuyer7

Hello

I have a Victorian home and every external wall has had a stud wall created with a large space between the stud wall and brick wall, with a timber frame built and polysterne filled in between. 

I want to have all these stud walls removed and then have the brick walls plastered. There are six walls in total and I've been quoted £14,000. This is for lime plastering with insulating materials mixed into the lime, removal and disposal of the existing plasterboard.

I think it would be good to do with lime but this cost is really high. Would it be really detrimental to instead go with a standard plasterer using gypsum? Could this lead to damp problems? At the same time we are getting our cement external render removed from the rear and will definitely be re-rendering in lime.

grumbler

housebuyer7 said:

I have a Victorian home and every external wall has had a stud wall created with a large space between the stud wall and brick wall, with a timber frame built and polysterne filled in between.

Well done by the previous owner, although I don't understand why this large space.

I want to have all these stud walls removed and then have the brick walls plastered.

Very unwise IMHO, unless your are either a very wealthy or a cold-resistant person.

  for lime plastering with insulating materials mixed into the lime

I don't buy this nonsense and, I think, neither will the building control if you get them involved. Most likely you have to.

ETA: you can save some space by replacing the stud wall with insulated plasterboard (with 5cm insulation), but will this really be a good value for the money you'll spend?

Apodemus

While I understand your wish to replace the polystyrene with a breathable internal finish to match the new external render, you will struggle to get anything like the same level of insulation from an insulating lime mix.  You could get costs for something like external or internal wood fibre batts, finished with lime render/plaster, but I suspect that would cost a lot more than your current quote of £14k.

housebuyer7

OK so what about just replastering in gypsum?

housebuyer7

@FreeBear any thoughts?

FreeBear

housebuyer7 said:

@FreeBear any thoughts?

Hemp and cork filled lime plaster does provide some degree of insulation, but you need a very thick layer to get anything useful. A work colleague used hemp plaster in her Victorian cottage. She wasn't impressed...

I'd be reluctant to recommend Celotex/Kingspan stuck to the walls. Woodfibre or cork topped off with a lime plaster would be the most breathable solution. But it isn't going to be cheap. The insulation boards would cost some 20% more than Celotex, and then there is the lime plaster on top..

If you can afford to lose the floor space, you could use Celotex and leave an air gap of ~25mm between the brick & insulation. This would need ventilating to the outside both top and bottom. You would also need a vapour control membrane incorporated in to the wall. Here is how one blogger tackled it - https://jack-kelly.com/insulating_our_victorian_living_room - Might be worth dropping him an email to see how it is working out 12 years on.

If you can do much of the grunt work yourself, that will help to keep costs down.

Apodemus

FreeBear said:

housebuyer7 said:

@FreeBear any thoughts?

Hemp and cork filled lime plaster does provide some degree of insulation, but you need a very thick layer to get anything useful...

...Woodfibre or cork topped off with a lime plaster would be the most breathable solution. But it isn't going to be cheap. The insulation boards would cost some 20% more than Celotex, and then there is the lime plaster on top...

This is what I was suggesting above, but I would still suggest that if the OP is removing an external concrete render and wants to gain interior space, it is worth looking at whether an external breathable insulation is feasible or desirable - this will in part be down to aesthetics as well as practicality. It would be hugely expensive.

FreeBear said:

housebuyer7 said:

@FreeBear any thoughts?

If you can afford to lose the floor space, you could use Celotex and leave an air gap of ~25mm between the brick & insulation.

That was my understanding of the OP's description of the existing insulation, although they would need to check on whether it is properly ventilated.

housebuyer7 said:

Hello

I have a Victorian home and every external wall has had a stud wall created with a large space between the stud wall and brick wall, with a timber frame built and polysterne filled in between. 

housebuyer7, can you tell us what the problem is that you are trying to solve? Is it simply to gain more space (in which case external insulation is your only real option), to solve a damp problem in your outer brick wall (ventilation of the air gap and removing the cement render might be sufficient) or an interior damp problem (some form interior fresh-air ventilation/humidity control needed)?

billy2shots

I can't comment on the insulation side of things but from a breathable damp point if view I made a mistake years ago. 

I bought an older property (built before central heating). When renovating I had every wall and ceiling (lowered) plastered. This was about the only trade I had in, preferring to do most of the work myself. 

The mistake I made was not having the house lime plastered. I just had the regular modern day method carried out. 

The result was creating an air tight box that didn't allow internal moisture to get out. With central heating in a home not designed for it, it caused internal damp that we were forever fighting against. 

Time again, I should have done my homework, paid a bit more and gone lime based. 

housebuyer7

I guess I just wanted to create a bit more space and make the wall solid rather than have a stud wall. I'm hoping I might hang a radiator off one of the stud walls.

The insulating material that would be put in the lime plaster or render is perlite.

grumbler

billy2shots said:

The mistake I made was not having the house lime plastered. I just had the regular modern day method carried out. 

The result was creating an air tight box that didn't allow internal moisture to get out. With central heating in a home not designed for it, it caused internal damp that we were forever fighting against. 

Your explanation makes no sense to me. Central heating heats the house, not ventilates/dehumidifies it. And modern houses are drier than old ones.

billy2shots

grumbler said:

billy2shots said:

The mistake I made was not having the house lime plastered. I just had the regular modern day method carried out. 

The result was creating an air tight box that didn't allow internal moisture to get out. With central heating in a home not designed for it, it caused internal damp that we were forever fighting against. 

Your explanation makes no sense to me. Central heating heats the house, not ventilates/dehumidifies it. And modern houses are drier than old ones.

Modern houses are designed to breath, vents in brickwork and on windows. 

Older houses were built to keep the cold out ie let the least amount of air in which also acts the opposite way by not letting air out. 

Central heating and a sealed box equals internal condensation (inside windows warmer than outside) and with nowhere to go that moisture then leaves the windows as the day warms and finds its way to the colder parts of the house/walls. 

The same way clearing your windscreen in you car is cleared but that moisture is still in your car unless you open a window and let air out/in. 

Lime plaster is breathable and does a better job of relieving the issue.