Silane and siloxane masonry sealants - thoughts?

[jsmac]

We have removed the old render from two elevations of our property, replaced a couple hundred perished bricks, repointed one elevation completely and repaired the pointing where necessary on the other elevation. We found that it has been necessary to make a call on where to stop removing damaged bricks. When you're up close and looking at them one by one many of them look a bit knackered compared to a new wall so we have had to decide where to stop replacing them or reversing them as we have have fortunately been able to do for many of the original bricks. The walls are solid now and in better structural condition than they have been in probably many decades. However, there will no doubt be some bricks that will have lost some of their outer face and so be more porous than they would have been originally. The wall that suffered the most and was in worse condition by far is made of softer red bricks so I would expect those bricks to absorb moisture more readily.

I am wondering if anyone has opinions or experience with using silicone-based masonry sealants. We collected some render from Best of Lime last week and were speaking with them about a sealant they sell which claims to be breathable but allows the masonry to more effectively shed water. (ie. water vapour passes through but liquid water is repelled). Beeck manufacture a similar product and Mike Wye also sell something similar. I presume they all consist of a similar chemical composition. The data sheets suggest that it is only slightly less vapour permeable than lime wash but I really don't know what to think of that.

I guess what I'm wondering is if using a sealant like this on the masonry is a sensible or terrible idea. They make bold claims but I have no idea how long they've been available for so if there is in actuality any long term real world testing.

Has anyone come across these treatments?

Thank you!

 

[Flyfisher]

"We have removed the old render from two elevations of our property . . . "

Is it possible that the render was the problem? I only ask because there are hundreds of thousands (if not millions) of buildings with bare brick walls that have no problems, even those with 'soft' bricks.

There seems to be a general view that rain is a bad thing that will quickly destroy any structure unless it is somehow waterproofed to within an inch of its life, yet we've all experienced how quickly a paved surface can dry after a rain storm and that's a horizontal surface that catches the full effect of the rain, unlike a vertical wall that will only catch a proportion of the falling rain. Yes, the wall will get wet but it will also dry out pretty quickly if left alone.

We have a length of 6-foot brick garden wall with concrete coping stones that was cement rendered and over the years the render had cracked and started to come away from the wall. To tidy it up I decided to remove the render rather than watch it slowly fall apart on its own. The bricks behind the render were all soaking wet, though thankfully not badly damaged. Rather than re-render the wall, I simply left it as bare brick. It dried out and 15-ish years on shows no sign of degredation despite now being fully exposed to the weather.

So I wonder if rushing to 'waterproof' everything is always the best thing to do.

 

[Cubist]

I would very much echo @Flyfisher and would add that the whole idea of stripping off a cement render only to then 'seal' a newly breathable external wall is to my mind counter-intuitive and perhaps bordering on the non-sensical. I appreciate that some of these compounds are reckoned to be 'smart' enough to reject water in its liquid rather than gaseous state but I cannot bring myself to believe that it could be so discerning that it would not also severely inhibit and constrain the walls ability to expel unwanted moisture from indoors.

Right now I would be putting that 'sealant' very much on the 'Up-sellers' Snake Oil products list.

 

[jsmac]

Thank you both.

Right now I would be putting that 'sealant' very much on the 'Up-sellers' Snake Oil products list.

So I wonder if rushing to 'waterproof' everything is always the best thing to do.

That's pretty much what I was wondering about. But then I saw that Beeck supply a similar silicone-based product and they've been making breathable mineral paints for over 100 years so I couldn't help but think there was something to it.

It wasn't a cement render that was removed - it was a softer (but still quite hard) stucco render on the front elevation and a similar looking render on the side elevation. We're confident that the render pre-dates 1887 because it is behind the timbers of the bay windows which were added on or around that date (we found a dated signature and a coin on the underside of a section of the cill that needed replacing). It's a shame that the building was rendered at all - it would have been quite handsome and held up a whole lot better if the brick walls had simply been left as is. In the end however, I think that it was the layers and layers of conventional masonry paint that had been applied over the past 50 or so years that created the conditions for much of the damage to occur.

And there were also some small sections that had more modern repairs with cement. This, unsurprisingly, is where some of the worst damage has been found. The parapet wall in particular was a real mess. About 2 sqm area had been rendered in a seriously hard cement so it required a lot of careful repairs. The bricks were soaking wet behind this rendered section. We'll have to re-render this area because even after the repairs it looks really knackered, which is why we visited Best Of Lime. Their Rendercote is supposedly designed precisely for highly exposed areas such as this.

I agree with both of your conclusions though and will be steering clear of the silicone-based products.

 

[a twig]

There was someone on here years ago who used one of those types of products after driving rain was still coming through - I’ll see if I can find the thread

 

[a twig]

Ah yes - @CliffordPope almost a decade ago - god I’m sad that I remember this stuff:

C

Thread 'Lime mortar pointing - water penetration'

Jan 4, 2016

A few years ago our house was suffering from damp, clearly resulting from faulty cement rendering, which was bowing away from the walls and falling off in sheets.
So at some expense we had all that hacked off, and the stone walls repointed using lime mortar. It looked lovely, now highlighting the contrast between the pale stone/mortar and the red brickwork, previously all hidden in decaying mouldy rendering. Everyone said this was the correct thing to do. The walls could now breathe again as intended.

That was until the autumn storms, and weeks of constant driving rain. Water poured...

• CliffordPope
• Replies: 29
• Forum: Period Property Discussion Forum

 

[Aurelius]

I'm putting my tin hat on as I type this! I too have a property in an exposed/elevated location and in Wales (read wet). My cottage takes the brunt on the weather to the front elevation which I'm assuming is why it had been covered in a cement based render. Although the render was in good condition, I didn't like the appearance nor did I relish the thought of painting it every 2-3 years and I was conscious it wasn't doing the wall any favours. I did have reservations of what lay beneath such as repairs with ill matching bricks/blocks etc. but in the event it was just a case of replacing circa 200 damaged bricks, albeit acid cleaning the cement stains off the entire wall brick by brick was arduous! I'd already noted the back boxes to the internal sockets were completed rotted out so clearly the wall had been damp at some time and yes, maybe the render was a factor, the render was in good condition with no cracking . I initially intended to repair and repoint the wall and be done but during the spraying down process prior to pointing, I realised just how porous the bricks were, partly I suspect due to the original kiln face of the bricks having eroded. It seemed to me that the walls ability to dry naturally is somewhat limited when it can rain here for days on end! So after some research I opted to use a product called Stormdry masonry cream, which claimed to leave the brickwork vapour permeable (chinstrap of mentioned tin hat now tightened). There are a few videos on the SkillBuilder YouTube channel showing demonstrations of how the product works and at the time I could only find positive reviews online. This is obviously not a silicon based product which I would stay clear of as silicon will trap moisture inside the wall as effectively as it keeps the rain out. So far the results appear all good and having bare brick walls throughout last winter (in readiness for IWI), no damp was evident whether from inside or outside. Time will tell. Possibly I'd have made a different decision if I was located in a more sheltered location.
Before the incoming artillery arrives, I'm going outside to dig a trench !

 

[Flyfisher]

That's pretty much what I was wondering about. But then I saw that Beeck supply a similar silicone-based product and they've been making breathable mineral paints for over 100 years so I couldn't help but think there was something to it.

I'm at my limits of A-level chemistry knowledge here but I'm pretty sure that the Beeck product you're referring to is a silicate-based paint, not silicone.

Silicate-based paints are indeed very old and well established as a breathable 'paint' similar in many ways to limewash but with the advantage of being far more durable. Think in terms of many decades rather than many years. From what I've read, including many discussions here, silicate paints are more expensive to buy and need more careful application compared to 'cheap-as-chips' limewash but their longevity should pay off in the long run, especially if the cost of scaffolding every 5, 6, 7 years for limewashing is taken into account.

Silicone, on the other hand, is highly impermeable and resistant to water, hence it's widespread use as a bathroom sealant etc where it is expressly intended to prevent any seepage of moisture - liquid or vapour. I've little doubt that coating brickwork with a silicone-based water repellant will indeed prevent rain water from seeping into the brickwork, but it will also hinder those same bricks from 'breathing out' any internal moisture they might accumulate.

It's another example of a trade-off, similar in many respects to the insulation-vs-ventilation issue when trying to make our homes more energy efficient.

 

[stuart45]

If you want to strengthen the face of your bricks, ethyl silicate is used in the trade as a stone or brick consolidator, but it comes with a price.

 

[jsmac]

Thank you everyone.

I'm at my limits of A-level chemistry knowledge here but I'm pretty sure that the Beeck product you're referring to is a silicate-based paint, not silicone.

I was hoping that was the case but when I read the technical data sheet I was disappointed to see its composition described as a 'combination of silane-siloxane based active organosilicon components dissolved in isoaliphatic hydrocarbons.' So silicone-based penetrating sealants dissolved in an organic solvent. A shame really. If Beeck did a clear silicate paint I would be interested.

I've little doubt that coating brickwork with a silicone-based water repellant will indeed prevent rain water from seeping into the brickwork, but it will also hinder those same bricks from 'breathing out' any internal moisture they might accumulate

That's what I thought, which is why I was hoping there would be some more comprehensive information in the data sheets, but all they say is mainly 'it keeps water out, maintains breathability, and allows water vapour to pass through'. I'm sure there are aspects of the chemistry and physics that are far beyond my knowledge but anecdotally I agree that this doesn't make much sense.

I opted to use a product called Stormdry masonry cream

I wonder if that was the cream the brickwork repair team were referring to. They mentioned that they have used a product in the past to some positive effect but couldn't remember the product's name when we were talking about it.

If you want to strengthen the face of your bricks, ethyl silicate is used in the trade as a stone or brick consolidator, but it comes with a price.

Thank you. I'll look into it. This is why this forum is such a valuable resource!

I think that in the end I will replace as many bricks as is viable and then hope for the best. At its worst the internal walls weren't actually wet as far as I could see (well not these walls, the timber frame walls were an entirely different problem!). And now that we've removed all of the knackered, spalled and perished render and impermeable old masonry paint the walls should certainly be in much better shape to withstand the next winter.

 

[jsmac]

Ah yes - @CliffordPope almost a decade ago

A very interesting thread. And one that I didn't see when I searched the forum.

It will of course be deeply ironic if we discover to our misfortune in 8 months time that the reason the property was rendered originally over 150 years ago was because driving rain was penetrating the double skin brick walls! We are after all only about 500m from the North Sea

 

[Cubist]

Before the incoming artillery arrives, I'm going outside to dig a trench !

Make that a Zebcolm Trench and all will be forgiven - if not then make it a foxhole instead and stand-by for incoming.

 

[stuart45]

"We have removed the old render from two elevations of our property . . . "

Is it possible that the render was the problem? I only ask because there are hundreds of thousands (if not millions) of buildings with bare brick walls that have no problems, even those with 'soft' bricks.

There seems to be a general view that rain is a bad thing that will quickly destroy any structure unless it is somehow waterproofed to within an inch of its life, yet we've all experienced how quickly a paved surface can dry after a rain storm and that's a horizontal surface that catches the full effect of the rain, unlike a vertical wall that will only catch a proportion of the falling rain. Yes, the wall will get wet but it will also dry out pretty quickly if left alone.

We have a length of 6-foot brick garden wall with concrete coping stones that was cement rendered and over the years the render had cracked and started to come away from the wall. To tidy it up I decided to remove the render rather than watch it slowly fall apart on its own. The bricks behind the render were all soaking wet, though thankfully not badly damaged. Rather than re-render the wall, I simply left it as bare brick. It dried out and 15-ish years on shows no sign of degredation despite now being fully exposed to the weather.

So I wonder if rushing to 'waterproof' everything is always the best thing to do.

A very interesting thread. And one that I didn't see when I searched the forum.

It will of course be deeply ironic if we discover to our misfortune in 8 months time that the reason the property was rendered originally over 150 years ago was because driving rain was penetrating the double skin brick walls! We are after all only about 500m from the North Sea

The additional problem near the coast is the salt driven into the walls.
This comes back to the surface and crystallizes which tends to break up the the masonry units and mortar.

 

[Aurelius]

Make that a Zebcolm Trench and all will be forgiven - if not then make it a foxhole instead and stand-by for incoming.

Zebcolm eh
I may have some infill work to do.........