Reinstate lime plaster if external render cement&tyrolea

[paulbandler]

I've read with interest the extensive advice on this forum and elsewhere about the merits of reinstating lime plaster in old properties.

I am in the midst of renovating a 1920's modest cottage and have removed quite a lot of blown lime plaster on ground and first floor and have been considering reinstating with lime. There was some rising damp on the ground floor that I hope have addressed by removing external render where it breached the DPC. However it is not feasible to remove the remainder of the render that I think it cement based and has been coated with tyrolean to give it a rough-cast finish. From what I've read this this outer coating would prevent the walls from 'breathing' as it was originally designed to before the render was applied right?

My question is then is given the 'cement/tyrolean' jacket on the outside of the property, is there any real merit in reinstating with lime plaster internally?

Thanks in advance for any advice.

 

[Lime]

Well, you've got problems of damp if you do or if you don't use lime plaster.
If the wall is damp the water will damage the decoration and plaster somewhere.
I'm sure you appreciate that there is no easy answer.
Perhaps with lime plaster and a lime based paint applied the wall would be allowed to breath.
The trouble with that solution is that the building was designed to breath on the outside not solely on the inside.

 

[middi]

Put in another way, it is definetely better than cement or other harder renders, and will not make the situation worse.

Your concern should be that whatever you use do not bridge any damp proof slates which may be in the base wall, make sure that there is a good water shed from the exterior render away from the base wall and that the ext. render is not cracked.

 

[Moreteyne]

Hi
I can give you an example from my place without you having to suffer the slings and arrows of outrages fortune.
My place was built in 1787 , lime rendered externally. The place was renovated in 1989 , the lime render was removed and a wonderful coating of quick drying ultra smooth cement was applied. ( I imagine it looked fantastic ) Lovely crisp edges , all those years of pitting restored to a clean new render.
Zip in time to 2004 when we bought the place. The cement render had cracked in places leaving lovely gaps for water to run in. Mold was growing on the inside because it only had a one way breathable skin.
It may seem like a big job , and even a waste of time , but to remove the outer cement render will allow the place to breath. When we removed ours, no joke , the walls were glistening with water. Now a year and a half later the walls are almost dry and the mold and fluff are beginning to clear.
Go on , take the plunge , it will save the building and yourself in the long run.

 

[paulbandler]

Thanks for the suggestion Moreteyne but I suspect your 18th century place is something of a different proposition that the very modest early 20th century house I have. In particular I think the render was probably added a couple of decades ago at least and has mostly done quite well (although I do wonder if has contributed to the decline of the internal plaster even on the first floor).

Also, the limited experience of removing the lower render where it bridges the DPC does not encourage me to remove loads more due to the damage it does to the brick faces.

 

[Moo]

Are you absolutely certain that the render is relatively recent, or just recently painted? A local resident (try a retirement home) may remember what the original finish was like.

 

[Moreteyne]

My concern would be related to the fabric of the building. If left as is , in time it will crack, it will let water in , it will cause huge expensive problems.

The nature of the material is that it is hard and fantastic at keeping water at bay. But if the water gets in , it wont let it out either, hence it will come through the wall.

Go on , join the looney limeys !

 

[paulbandler]

Thanks again, but I don't think removal of all the render is a practical option. So again, my question is, given that fact, is there any merit in reinstating internally with Lime.

I am also considering reinstating internally with insulating board to improve insulation and avoiding the plaster type question altogether. Any (additional) breathability issues with this approach?

 

[Lime]

Thanks again, but I don't think removal of all the render is a practical option. So again, my question is, given that fact, is there any merit in reinstating internally with Lime.

I am also considering reinstating internally with insulating board to improve insulation and avoiding the plaster type question altogether. Any (additional) breathability issues with this approach?

The question that comes to my mind is where does the moisture in the wall go if both sides of the wall are made impervious?
Your damp problem will go on and on.

The ideal dream situation is to remove the render and find perfect brickwork underneath.
The reality is that the removal of the render would probably reveal damage.
The only long-term solution to your damp problem is replacing the cement render with lime based render.

 

[NT]

In this case it is even more important to use lime inside, since this will give you one surface for evaporation to occur, which is clearly needed. And porous paint on it, not emulsion. Allowing this evporation makes a big difference to wall water content in the long run.

I would agree with not removing the cement if it causes brick damage, as once the bricks are damaged its downhill from there.

The real question is where is the water getting in? Theres very little likelihood of it being rising damp. If your ground levels and rainwater goods are ok, and any exterior pointing is sound, condensation would be the most probable cause. This implies interior RH too high, and again you need to find out why.

Forget rising damp, its a rare beast pressed into service by salesmen up and down the country for the sake of keeping their businesses going.


NT

 

[paulbandler]

"The real question is where is the water getting in?"

Well I am hopeful that the water isn't getting in any longer as I've removed flagstones that were adjoining walls that would have caused splash, reduced external ground height by digging a french drain all round the property and removed bridging cement render.

I appreciate that the hard external render is more likely to crack as and when the lime mortared walls move and therefore become vulnerable to ingress that would be better able to escape if the internal walls were lime plastered, but against that I need to weigh the benefits of energy savings from significantly improving the insulation of the property by reinstating with an insulated board. The house only has 9" non-cavity walls and of a 'thin-oblong' design that presents 3 external walls to both bedrooms and reception rooms. As someone else on this forum said, we do need to be responsible to both our heating bills and the environment do we not...?

So would I be right in then concluding that it comes down to weighing the practicality of vigilantly maintaining the water-proofness of the external render/gutters etc forever against the benefit of a much better insulated property and nothing else?

 

[NT]

> So would I be right in then concluding that it comes down to weighing the practicality of vigilantly maintaining the water-proofness of the external render/gutters etc forever against the benefit of a much better insulated property and nothing else?

Not really, no. Creating a damp problem isnt a solution. Its wiser to get the walls working ok before applying insulation. Otherwise you'll just have to rip the whole lot off later when its got wet.


NT

 

[paulbandler]

"Its wiser to get the walls working ok before applying insulation. "

How would one do that? I mean, if I reinstated with a lime plaster internally then added insulation board atop of that, would that be any better? I can't see how...

I understand that these insulation boards are fixed with dab's of adhesive and leave an air gap between the brick and the board - could I address the concern by inserting a ventilation grill at the top of the insulation to allow some cirulation of air? It would be somewhat unsightly and would presumably undermine some of its insulating properties, but if needs must...

BTW. my sister put insulation board all round a 1930's bungalow that is rendered on the outside 20 years ago and hasn't had any damp issues...

 

[Gervase]

By working properly, that means getting the external face breathable as well. It sounds from your gables as if the render is already starting to crack and trap wter, so the rest of the walls must be considered at risk if you leave the stuff on.
And, If you're going to dry-line the interior, leaving an air gap, you don't need to plaster the walls under the boarding - leaving them bare would be far better.
And yes, you would need some form of ventilation at skirting level and at the top.
It's best to fix the board to battens rather than dabs of glue - screw the battens to the wall and fix the board to those.
If you're going to use a reflective insulation (one of the controversial foils or the cheaper 'bacofoil and bubble-wrap' versions) you would need to counterbatten - a layer of battens, the insulation foil, andother layer of battens and then the board - and that would lose you quite a bit of floor space and make your window reveals very deep.

By far the easiest solution would be to remove the concrete and re-render in lime. Get a couple of quotes - I don't think there'll be an enormous difference between the two jobs if you want to do the interior properly and make good afterwards.

 

[paulbandler]

Yes, the walls will be left bare where the render has already come away and yes, the builder proposed creating some vent holes into the floor and ceiling spaces behind the board to address concerns of trapped moisture behind the board.

"I don't think there'll be an enormous difference between the two jobs"

Um, as far as I understand it, adding insulation internally doesn't preclude or require any particular approach externally so there's nothing to compare here is there...?

 

[Nemesis]

Re the 1930's bungalow - had it cavity walls?

 

[paulbandler]

"Re the 1930's bungalow - had it cavity walls? "

It has cavity up to the window sill, which is not rendered, then solid cinder-block above rendered externally. It does however have wide soffits and good guttering so rarely is there water on the higher parts of the wall so maybe not such a valid reference after all...

 

[Gervase]

Um, as far as I understand it, adding insulation internally doesn't preclude or require any particular approach externally so there's nothing to compare here is there...?

Sorry, I meant in terms of cost.

 

[NT]

I understand that these insulation boards are fixed with dab's of adhesive and leave an air gap between the brick and the board - could I address the concern by inserting a ventilation grill at the top of the insulation to allow some cirulation of air? It would be somewhat unsightly and would

sounds ideal, if you want condensation and black fungus.

Its as simple as this. Putting 2 impermeable layers onto a porous external wall with cracked cement render is a recipe for trouble. It doesnt mean it always happens, but it certainly isnt a great idea.

You can of course do whatever you want, if its not listed. With my own I try not to cause further problems, as it seems the sensible way to go.


NT

 

[paulbandler]

sounds ideal, if you want condensation and black fungus

I'm a bit unclear why that would result. Is it a question of whether the ventilation provided is adquate for the level of anticipated water ingress?

Is this not similar to venting of a disused chimney?

Putting 2 impermeable layers

The insulating board planned is one integrated layer of insulation and plasterboard.