Use of cement and gypsum on victorian houses

[Robert harvey]

Am I right in saying my house that was built in 1898 should only be repaired with lime mortar and lime plaster? Is this to allow the building to breathe as opposed to cement based products which can trap moisture in the wall and eventually damage the wall

 

[Tigercubrider]

I am no expert but 1898 wasn't that long ago.
Portland cement had been around for 50 years by then

 

[skenk]

What is the wall construction? Typically here (in the many ~1898 buildings) it is either plaster on laths, over timber studs fixed back-to-back for interior walls and to stone/exterior wall lining or; 'float and skim' plaster (about 20mm thick) onto brick. In either case it's fine to use plasterboard.. no problems over brick, and the exterior stone wall can still breathe (or whatever it does) behind the stud cavity. What you don't want to be doing though is using cement on products on the exterior sandstone (and probably other stone of that era?).

If it's a listed building you may only allowed to use traditional/lime products, depending on the grading.

 

[opps]

Most of the houses that I work in (west London, as a decorator) were constructed around that period. The bricks used are a combination of red rubbers and yellow stock bricks.

The internal plastering on the external walls would originally have been the crumbly horse hair base coat and then a skim coat. As you are probably aware the plaster has a finite life and eventually needs to be ripped off and replastered. To the best of my knowledge, none of those properties has been replastered with lime.

The moisture in the bricks following rain is supposed to evaporate outwards.

I guess that lime plaster is more forgiving of condensation but most people use wallpapers or emulsions that are fairly waterproof anyway.

 

[gasbanni]

You are absolutely correct forget a cement base mortar.

The info you need ~
http://www.limestuff.co.uk/pages/using-traditional-building-products-help-and-advice.html

Cement rich mortar means you wouldn't have to re point very often but the bricks would spall,

Lime rich mortar ....the evaporation takes place from the mortar preserving the brickwork.

No brainer.

 

[opps]

You are absolutely correct forget a cement base mortar.

The info you need ~
http://www.limestuff.co.uk/pages/using-traditional-building-products-help-and-advice.html

Cement rich mortar means you wouldn't have to re point very often but the bricks would spall,

Lime rich mortar ....the evaporation takes place from the mortar preserving the brickwork.

No brainer.

I can't see anything on the site that you linked to that say that cement based pointing will definitely cause the brick faces to blow. I am also at a loss to understand why a wet brickface would greatly benefit from pointing that absorbs more moisture. Sorry I am not trying to be confrontational, but it seems counter intuitive.

Can you provide any specific links?

Thanks.

 

[gasbanni]

I can't see anything on the site that you linked to that say that cement based pointing will definitely cause the brick faces to blow. I am also at a loss to understand why a wet brickface would greatly benefit from pointing that absorbs more moisture. Sorry I am not trying to be confrontational, but it seems counter intuitive.

Can you provide any specific links?

Thanks.

Ok the link may not have illustrated the point, originally I read about this in a spabs publication many years ago.
I've seen it time and time again ...sad but I see it on old walls when I'm looking at old masonry. Start looking at old walls and you can't mistake that cement rich mortar damages the masonry be it brick or stone.

Question three is what you need to see

https://www.spab.org.uk/advice/technical-qas/technical-qa-11-repointing/

This is the point cement rich mortar is impervious, so evaporation from a wall then takes place from the brick or stone and it erodes whereas the mortar is in perfect uneroded condition. You can actually see where the mortar was in contact with the masonry but it's eroded away leaving sharp edges on the mortar where it was in contact with the masonry when it was pointed up. Now its gone ....I've seen this on historic houses too, ignorance has caused very bad damage.

With a lime mortar the evaporation takes place from the mortar bed and it's sacrificed but protects the masonry, but yes you have to re point more often.

I have my own theory that in a lot of cases it's purely the evaporation and not always spalling due to frost damage, you can see it a lot more from walls maybe waist height and higher not usually at ground level. The wind dries the walls out a bit higher up hence the increased erosion lower down the wall the wind is not as effective in drying it out do less erosion. These are my thoughts at pondering what I've seen loads of times. I'll post some images .

The damp in old buildings leaflet explains the point in detail.
https://www.spab.org.uk/publications/the-bookshop/

Based on this info and what I've observed I think just evaporation not necessarily frost and salts cause a lot of damage,

 

[Gerrydelasel]

Use lime mortar; yes cement mortar will spall your bricks.
You can use gypsum plaster on internal walls. Whether you should use lime plaster on external walls depend on whether they are solid and get a lot of moisture hanging around (weather facing & in shade etc). You'll probably be OK with gypsum though.