Re-Rendering with Silicone Render?

[Bemak]

I'm planning a refurb on an old farmhouse. i've posted elsewhere about it but one part i'm curious about is the external render. the house is 2-storey and of stone construction (600mm) with sand & cement render internally and externally. the external render is in very sound condition for the most part so i've moved away from the idea of hacking it all off and replacing it with lime as doing so would blow the budget. instead i'm planning to leave the render in place, patch up any cracks and rerender the entire house to seal it up. i will install french drains around the perimeter to help reduce rising damp etc. i'll do something internally to allow the walls to dry out to the inside but that is a detail for another day.

 

i've been speaking to a few manufacturers and contractors and one approch to the external render that i'm starting to cling to is the idea of rendering the house with a silicone render as i'm told it is moisture resistant but also breathable which will allow some drying out to the outside. sounds like an ideal solution for this particular application but i'd be curious to hear thoughts on this approach in case there's something i'm missing. 

 

 

[ProDave]

All I will add is do not use the Baumit.com silicon render, you won't get any help from the supplier if it fails.  Choose a different brand and ask them about customer service before buying.

[saveasteading]

1 hour ago, Bemak said:

rerender the entire house to seal it up.

No, no no. The wall is still there because of the construction, including lime mortar and lime render allowing it to move and breathe. Any other render will likely cause problems. Don't trust the suppliers or contactors unless they are masons or can show you the successful use on masonry from more than 5 years ago.

 

What stone do you have? any pictures?

[Bemak]

the walls of the house are currently rendered with sand and cement, not lime. I wouldn't dream of sealing them up externally if they were rendered with lime. I'd probably have no problem if they were!

 

is there anything to be said for insulating the walls externally and removing the render internally to allow the walls to dry to the inside?

[Bemak]

I should have added that the external render consists of at least 3 separate layers of sand and cement render. Approximately 40mm thick overall. Pic below of my initial investigation works (with a great helper) shows the state of the wall behind the render.

 

 

[nod]

Silicone renders and sand and cement are not compatible 

If your looking to use a silicone render you will need to remove the sand and cement then stabilize the masonry 

Or patch up and paint 

[Bemak]

12 minutes ago, nod said:

Silicone renders and sand and cement are not compatible 

If your looking to use a silicone render you will need to remove the sand and cement then stabilize the masonry 

Or patch up and paint 

 

thanks - noted! That would suggest to me that the idea of externally insulating the wall might be the approach - but on the basis that I can hack of the internal render, even at ground floor level, to help dry out the wall to the inside. 

[Iceverge]

Our neighbour recently externally insulated his old stone farmhouse. The workmen often had to make a few attempts to find a stone to drill the fixings into however the end result was quite satisfactory. With this approach all the existing wall would be inside the dew point so moisture is much less of an issue.

 

I know sand and cement is considered vapour closed but in older buildings the use of cement could be so frugal that the wall might be considered vapour open. It's a case by case thing unfortunately. 

 

What exactly is the current moisture issue? 

 

Is it wind blown rain from the outside? 

Or a high water table forcing moisture up through the walls?

Or cold walls allowing the humid internal air to condense on them? 

 

 

 

 

[Bemak]

I've attached a few pics below. for the most part the house is pretty dry considering it's rarely used and has no heating. the worst case of dampness is on the eastern gable. this is primarily due to the ground being above floor level in this location, and also a defect in the existing render at chimney level which is allowing some water/dampness. the verges are also of course gravel which are also contributing. 

 

There would be good drainage in the area so ground water isn't a problem. the house is well screened by trees but persistent rain would likely be the main cause of moisture build up. the fact that the house is unoccupied doesn't help. 

 

 

 

 

Edited August 17, 2022 by Bemak

[Big Jimbo]

2 hours ago, Bemak said:

I should have added that the external render consists of at least 3 separate layers of sand and cement render. Approximately 40mm thick overall. Pic below of my initial investigation works (with a great helper) shows the state of the wall behind the render.

 

 

Fab place with a bit of land around it. I love this picture. to me it says. small hobbit person, with a huge shovel, loading a giant wheelbarrow that once full they will never be able to move. Over that low ledge is a cliff face with a sixty foot drop to the crashing waves below. Just reminds me of land of the giants. Having spent all of my summer holidays every year in Ireland, i though all of the houses were damp. All the ones i stayed in were. In the morning when there had been no fire lit, the bedclothes were always damp, and it was not because i had weed myself.

[Bemak]

oh ya we're blessed with the location. we're at a dead end as well so no through traffic or anything like that. peaceful spot. Clearly plenty of willing helpers there too! 

 

this house has only been used by relatives for a few weeks in the summer, every year since I can remember. I would imagine those early mornings were similarly damp as your experiences! 

Edited August 17, 2022 by Bemak

[nod]

4 hours ago, Bemak said:

 

thanks - noted! That would suggest to me that the idea of externally insulating the wall might be the approach - but on the basis that I can hack of the internal render, even at ground floor level, to help dry out the wall to the inside. 

If your insulating the walls 

it would save you knocking the sand and cement off

 

[Bemak]

Just now, nod said:

If your insulating the walls 

it would save you knocking the sand and cement off

 

ya that's what i'm thinking now - because I've decided to leave the external render on because of its condition it kinda makes sense to just insulate it now too. 

 

i think the house would benefit then from exposing the walls internally to let them dry out to the inside. could leave windows open for a few months to encourage airflow through. I think only then will I know what kind of heating system I'll go for etc

[Roger440]

48 minutes ago, Bemak said:

 

ya that's what i'm thinking now - because I've decided to leave the external render on because of its condition it kinda makes sense to just insulate it now too. 

 

i think the house would benefit then from exposing the walls internally to let them dry out to the inside. could leave windows open for a few months to encourage airflow through. I think only then will I know what kind of heating system I'll go for etc

 

Obviously you have an issue with water from above, which really isnt that difficult to solve. My render on the gable was the same. The easy fix was lead flashing at the top of the render.

 

But are the walls damp at floor level? If they are, thats not going to get better if you insulate externally. If they are completely dry, then maybe.

[saveasteading]

55 minutes ago, Bemak said:

I've decided to leave the external render on because of its condition

I can see that. Thanks for the pictures.

The stonework is probably difficult to make attractive, being small rocks.

Therefore I can see the attraction of keeping it, and the rain off.

My suggestions.

 

As a priority, lower the ground so that there is no rising damp, and any rain splashes are below the floor level.

(Rising damp does exist, according to me and apparently to all professors of rising damp. One website that doesn't agree seems to dominate google, so look beyond that.

 

Also deal with any other issues like chimneys and leaking gutters.

 

Then over-clad but with a rain-screen that will keep the rain off but allow the wall to breathe.

(Over-cladding creates a thickness, standing out from the all. this can be  a problem  at the eaves, as the gutters need to be moved out, involving roof extension.. Therefore I expect this has to be quite thin.)

OR

patch up the cement screed again and see how the wall behaves in a loved building.

 

[saveasteading]

See page 43 among others.

 

https://www.gov.scot/binaries/content/documents/govscot/publications/advice-and-guidance/2020/02/guide-for-practitioners-6-conversion-of-traditional-buildings/documents/guide-for-practitioners-6-conversion-of-traditional-buildings---part-one/guide-for-practitioners-6-conversion-of-traditional-buildings---part-1/guide-for-practitioners-6-conversion-of-traditional-buildings---part-1/govscot%3Adocument/Conversion%2Bof%2Btraditional%2Bbuildings%2BPart%2B1%2B.pdf

[Bemak]

42 minutes ago, Roger440 said:

But are the walls damp at floor level? If they are, thats not going to get better if you insulate externally. If they are completely dry, then maybe.

 

The walls are in surprisingly good shape at floor level. I had to replace a washing machine in the kitchen recently and when I pulled out the old one, the wall behind was perfectly dry - and this is in an area where the ground level is at its highest above the floor level. The main location for dampness at ground floor is in a bedroom on that eastern gable shown in the first image. There used to be a fireplace in that room by all accounts but there's no trace of it now - so I would wonder how it was closed up. 

 

23 minutes ago, saveasteading said:

The stonework is probably difficult to make attractive, being small rocks.

 

it was definitely never meant to be exposed!

 

23 minutes ago, saveasteading said:

As a priority, lower the ground so that there is no rising damp, and any rain splashes are below the floor level.

 

definitely - i will mark up a plan shortly to show how I intend to manage the perimeter. 

 

25 minutes ago, saveasteading said:

Also deal with any other issues like chimneys and leaking gutters.

 

Yep - I'm thinking it makes sense to reroof now when there will be scaffolding in place anyway for the works to the walls. Will completely replace the rainwater goods as well. 

 

26 minutes ago, saveasteading said:

Then over-clad but with a rain-screen that will keep the rain off but allow the wall to breathe.

(Over-cladding creates a thickness, standing out from the all. this can be  a problem  at the eaves, as the gutters need to be moved out, involving roof extension.. Therefore I expect this has to be quite thin.)

OR

patch up the cement screed again and see how the wall behaves in a loved building.

 

 

I don't think over-cladding with a rain-screen is the solution here given how well the majority of the wall is holding up. I was tempted to patch it up as you also suggest but the idea of insulating externally is starting to make more sense to me particularly as it consolidates the external envelope, improves the u-value, and in doing so moves the dew point closer to the outside.

[Bemak]

27 minutes ago, saveasteading said:

See page 43 among others.

 

https://www.gov.scot/binaries/content/documents/govscot/publications/advice-and-guidance/2020/02/guide-for-practitioners-6-conversion-of-traditional-buildings/documents/guide-for-practitioners-6-conversion-of-traditional-buildings---part-one/guide-for-practitioners-6-conversion-of-traditional-buildings---part-1/guide-for-practitioners-6-conversion-of-traditional-buildings---part-1/govscot%3Adocument/Conversion%2Bof%2Btraditional%2Bbuildings%2BPart%2B1%2B.pdf

 

Thanks for sending this through. I've come across a few scottish based publications like this on here and they're all excellent. 

 

Didn't wainscoting come about for the very purpose of covering up the lower sections of walls that would get damp?

[Bemak]

The diagram below illustrates the current context around the house. There is an existing concrete path of varying condition around the perimeter of the house. The ground level rises to the south to a maximum height of approximately 650mm above FFL at the kitchen. So the area hatched yellow would generally be above FFL. 

 

The gable pictured in the previous photos is on the left (eastern side of the house). I've shown the approximate location of the fireplace on that gable for reference. Need to open up that wall to see what's what. 

 

 

Edited August 17, 2022 by Bemak

[Bemak]

My plan is to install a french drain along the eastern and southern perimeter of the house. I'm going to dig out a patio in the south-west corner (top right) and install a new slider so that the kitchen/dining can avail of the evening sun. I will pave the patio and remaining perimeter with a permeable paving including an aco drain along the perimeter of the house. 

 

I'm thinking the remaining area at high level to the south could all be gravel with planting - like a widened french drain. I'll add a few steps for access from the patio to a small gate (not shown)

 

 

Edited August 17, 2022 by Bemak

[saveasteading]

A cross section of the wall at the higher ground would be good. You  must get below the footing, and make it easier for the water to runaway than go into your wall.

 

Do you think the ground was always higher than the wall, rendering the adjacent room very damp, or has this been filled by occupants who don't understand the issue?

It doesn't look too much work to drag a 1m strip out, below floor level. 

 

Looking  again at the damp chimney area, yes a flashing above might solve this. It would be surprising though if the constantly wet render stays put for long.

[Bemak]

There was definitely a problem in the kitchen at one point due to the higher ground. The solution was a new concrete path outside at the highest point, probably about 15-20 years ago. This appears to have worked a treat as the walls are genuinely dry on that facade. Maybe I should leave all well alone and just concentrate on the eastern wall instead?

[saveasteading]

My technique is to think of where any individual raindrop will go. Every one should have an easier route away from your wall then towards it.

Not Every raindrop obv, but a sample.