Crépi problem - 'Sick-Stone'

[nemltd]

Hi

I have a dark red/purple rash on the south elevations of our exterior walls, the walls are covered with white crépi.

The rash is only on the elevations that are exposed to the southern sun and not the shaded areas or the north elevations, which get far less sun.

Also, the rash does not cover the parts where I assume there are lintels above the windows and what looks to be the concrete beams that run horizontally along the elevations. Behind the crépi is a red brick.

The French builder we have been using regularly is not familiar with the problem. One of his specialities is applying crépi, so I am surprised he has not seen theproblem before.

The temptation is to say it is a lichen of some sort. If I scrape it with a key, it reveals the bright, white crépi underneath.

It has been suggested that I have a problem called 'Sick-Stone'. Apparently this is where the acid from the bricks bleeds through the crépi render and manifests itself as this rash on the surface. They said the only cure would be to remove the crépi render and then seal the brickwork underneath. And then re-crépi and paint, if required.

Any thoughts or knowledge of this anybody?

Kindest regards.

Tony

 

[NuBeginnings]

Can't help with the diagnosis, but it may be a good idea to take some pictures and load them up so people can get a good idea of what they are dealing with. I will ask my mason tomorrow for you.

[pachapapa]

http://www.sdap-poitou-charentes.culture.gouv.fr/conseils/restauration/index.php?dep=17&dossier=restauration&Id=RA05_31&NumSr=403

Sounds dubious; Are the bricks fired?

Seen plenty of HLMs with the crépi showing a reddish tinge after a couple of years.

[nemltd]

Thank you, I hope he has seen it.

Probably quite simple, but I cannot work out how to get a picture on my post? I have tried just copy and paste but it won't let me..............help please

[nemltd]

http://www.completefrance.com/cs/forums/2439130/ShowPost.aspx

I did ask this question awhile ago without any real conclusions, I can't remember how I got the picture on the post! But you can follow this link.

Thanks again

[Alex H]

[quote user="nemltd"]

http://www.completefrance.com/cs/forums/2439130/ShowPost.aspx

I can't remember how I got the picture on the post![/quote]

Its in your link :-)

[Val_2]

Its extremely common here in Bretagne. Most houses around here have it somewhere on the walls and its caused by a small algae microbe which thrives here in the maritime climate. There are lots of firms and the manouches who come round offering ravalément, high pressure washing with a bleach agent and it works for a certain time and then the algae comes back again. If it is the same thing it is nothing to do with the construction although some people thought it was to do with the sand being used but its not, its a climate thing which encourages the stain and often or not it starts up high andlooks like it is running downwards. Try a pressure washer after washing with some strong bleach, we do that chimneys that are crepied before repointing them.

[pachapapa]

[quote user="Val_2"]Its extremely common here in Bretagne. Most houses around here have it somewhere on the walls and its caused by a small algae microbe which thrives here in the maritime climate. There are lots of firms and the manouches who come round offering ravalément, high pressure washing with a bleach agent and it works for a certain time and then the algae comes back again. If it is the same thing it is nothing to do with the construction although some people thought it was to do with the sand being used but its not, its a climate thing which encourages the stain and often or not it starts up high andlooks like it is running downwards. Try a pressure washer after washing with some strong bleach, we do that chimneys that are crepied before repointing them.[/quote]

Thanks for the authorative explanation.

I had previously thought that it was triggered by H2S drifting in on the wind rom the green algae fields.[:D]

[mint]

I have my own theory, for what it's worth.

I think it's some sort of efflorescence leaking out of the "bricks" that they use.  The leakage is from the "perps" and I will expect it to occur on the gable end walls.  Of course, I do not KNOW....it's just what I would expect from my albeit limited knowledge of these things.

Alas, I didn't finish my building surveyors course in Reading but I won't bore you with all of that here.

[Val_2]

99% of all new houses built here are in grey concrete block construction (parpaigns) with rendering and then crépi finish.Very very few have the terracotta block construction. Most of these and the lotissement next to us built this way in 98 are covered in the red stain on certain fasçades and even my own 450year old stone longère which had the front rendered in the 1950's when they elevated it to take a first floor on the front has this stain too.

[Val_2]

From the thread on algae in 2008 I wrote that the cause is known as Trentepholias.

[Val_2]

If you google trentepholia sur bâtiment it shows some photos of the stain.

[Jay]

[quote user="Val_2"]If you google trentepholia sur bâtiment it shows some photos of the stain.[/quote]

It's "trentepohlia". This is an interesting site - look at the 30minutes after picture. Pretty hard to believe! http://www.mtpeintures.fr/traitement-algor.php

[suein56]

[quote user="nemltd"]

I have a dark red/purple rash on the south elevations of our exterior walls, the walls are covered with white crépi.

The rash is only on the elevations that are exposed to the southern sun and not the shaded areas or the north elevations, which get far less sun.

[/quote]

It is common here in Brittany, as Val says in her reply. As our prevailing winds are from the west this is usually where 'les champignons' are first to show, but, gradually, they spread. We treat it ourselves with a pressure spray containing a diluted bleach solution - which doesn't damage the crépi.

Our spray doesn't give miracle results in 1/2 hour as it usually takes 24 hours or so to take full effect, but it does cost cents and not 000s of euros!

Sue

[nomoss]

[quote user="Jay"][quote user="Val_2"]If you google trentepholia sur bâtiment it shows some photos of the stain.[/quote]

It's "trentepohlia". This is an interesting site - look at the 30minutes after picture. Pretty hard to believe! http://www.mtpeintures.fr/traitement-algor.php
[/quote]

Interesting how it also changed the colour of the shutters!

[mint]

[quote user="Jay"][quote user="Val_2"]If you google trentepholia sur bâtiment it shows some photos of the stain.[/quote]

It's "trentepohlia". This is an interesting site - look at the 30minutes after picture. Pretty hard to believe! http://www.mtpeintures.fr/traitement-algor.php
[/quote]

Yes, right, so I won't believe it!

I am not convinced it is trentepholia...I googled it and read it up and looked at pictures and I don't think this lichen, whatever, is what's on the walls of houses I see around me.

I still think it's to do with leakage of salts from the "bricks" when rain and moisture penetrate the crepi and dissolve these salts.  However, I will have a good look round when I walk the dog later.  Just to see if it's on other elevations than gable ends where I have found the staining most noticeable.

 

 

[nemltd]

Hi Pachapapa

The bricks are the standard red style with the holes in them and the fluted edges. I don't know if they are fired, I assumed all bricks were. The link you posted shows problems with stone, so I guess the point is that I don't have stone! Sounds logical, I guess I just thought the translation 'Sick Stone' was a loose one. So probably not 'Sick Stone' then!

This does point toward the other suggestions of a fungus of some type.

Thanks, funny how when you hear things out-loud, they sound different!

Tony

[nemltd]

Pachapapa

HLMs? & H2S?

I bet it turns out to be obvious!

Tony

[nemltd]

Hi Val_2

Thanks for your posts, you seem very sure about this problem which is very encouraging for me. Do you have any idea why the rash seems to not like settling on the areas with the lintels behind the rendering, and the concrete beams, you can just make it out on the photo in my earlier post link.

Our house is a concrete frame on the south elevations filled in by the red brick that seems pretty standard (in the south west). You can see where the concrete frame is, by where the pattern of the red stains are, also the window lintels are apparent by the same means.

I just wonder why the algae would not form on the parts of the render where the concrete is behind, and only where the red brick is behind? This is my only reservation, if you like, as to the algae theory. If indeed something is bleeding through from the brickwork, it would make sense that is doesn't bleed through where the concrete is, does that make any sense?

I have tried scraping the rash with a key, it just shows solid white crepi underneath, this supports the fact that it isn't bleeding through from the brickwork.

I would value your feed back.

Kindest regards.

Tony

[nemltd]

Hi Jay

Thanks for the link. It does almost convince me that I have 'trentepholia', just a couple of questions I need answering to be 100%, please see my latest post.

 

[nemltd]

Thanks Sue

Do you wash the walls first, only our crepi is the rough finish, the hose with the pressure/trigger attachment won't touch it. Or do you just spray and leave it to work? Oh, what formula do you use, bleach to water?

Thanks for your help

Tony

[nemltd]

Nubeginings

Did you have any luck with your mason?

Thanks

Tony

[nomoss]

Return of the red spider thingies [:D]

http://www.completefrance.com/cs/forums/2519635/ShowPost.aspx

[suein56]

[quote user="nemltd"]

Do you wash the walls first, only our crepi is the rough finish, the hose with the pressure/trigger attachment won't touch it. Or do you just spray and leave it to work? Oh, what formula do you use, bleach to water?[/quote]

No pre-washing at all. The bleach/water mix depends on the intensity of the champignons colour. For example on our house, which is treated every 3 or so years, then we use Lidl bleach, which is about 6%, diluted down to 1 part bleach to 1 part water. On the balcony west-facing wall of a friend's newly acquired appartment my husband used our normal 50% dilution to little effect. He repeated using undiluted 6% bleach to huge success. This wall had not been treated before and the block is 5 years old. He uses just an ordinary pressure spray ie a pulvérisateur, not a high pressure spray. We work on the principle of gently does it. When we walk or even drive past houses in the course of being treated the strong bleach smell can be overpowering, IMHO this doesn't do the crepi any good - but I could be wrong.

Sue

[pitway]

Most supermarkets have a product B NET Gros travaux, it has a picture of a house in red and blue on it, normally it is next to the bleach, costs about 5 euros for a 5 litre container, spray it on lightly with a garden sprayer (seems to work better on a dampish day but not raining) very effective on patios too.

Tim