Problems with Baumit.com thin coat render system - part 3.

[ProDave]

This is part 3 of this sorry continuing story.

 

Part 1 was here where I described the problem and the total lack of interest from the manufacturer Baumit who would not even come and look at the issues to give any proper technical input into what went wrong or why. and just blamed poor workmanship.

 

 

Part 2 was here, when our plasterer out of good will, not accepting blame, re worked the failed areas, and that thread includes some pictures of what we found and some speculation of what might have happened.

 

 

So this is part 3.  Going into the first winter after the remedial work, it is clear the problems are not over, and further failures are beginning to show.  But also my understanding, or at least speculation of what might be happening is growing.

 

A couple of weeks back we had storm Arwen, which lashed the front of the house with a lot of wind driven rain blown on gale force winds for a couple of days.  Nothing leaked and all looked well.  Until a couple of days ago it got cold here, well below 0 for 3 days.  As is normal when it gets frosty, frost forms on the whole of the outside of the house (because it is so well insulated little heat is escaping)  and what I noticed were a few "bulges" in the render on that north elevation.  These bulges were solid, you could not press them in.

 

Fast forward a few more days and it turned mild, the frost has gone and so have the bulges in the render.  They look okay at the moment, but I suspect this is the start of the next failure.

 

So here is my theory about what is happening:

 

The wind driven rain from the north lashing on the rendered wall, some of it has soaked into the wall and into the base coat of render (in part 2 I posted pictures of parts of the top layer that were removed during the re work that had pinholes in them that would allow wind driven rain through)  This now wet base coat of render has frozen and expanded,  and while it appears to look okay for now after it has thawed, I believe this will fail in time now.

 

If this theory is right, then it raises 2 issues:  Why is the Silikon Top top coat of render not waterproof and allowing some water through when the rain is wind driven?  And even so, why is it soaking into the base coat of render?  The manufacturer, Baumit, say the base coat is waterproof and can be used on it's own without the top coat.  That does not appear to be my observation.

 

For the moment I can only watch and wait and see what happens, but it is not looking good.

 

If this theory is right, it will explain why most of the issues with the render have been on the west facing wall, that is the one that gets the prevailing wind and will get more wind driven rain than any other elevation.  The east facing wall which also failed, would have been lashed with wind and snow a few years back when "the beast from the east" storm hit us.  The south elevation which hardly gets any wind driven rain has been almost untouched by these issues.

 

Also worth noting, that the recent frozen bulges noted have been a little way up the wall, so I think this completely discounts Baumit's claim that the problem relates to detail at the bottom drip bead and water wicking up.  If that was the cause, why no bulges at the bottom?

 

And the new bulges are on parts of the original render that had not failed before, not on any of the re worked areas.

 

This is where I really want Baumit to man up to their responsibilities as a manufacturer and come and give some proper technical input into the issues we are having.  In the absence of that, my advice continues to be, do not consider using the Baumit.com thin coat render system.

[Gordo]

Wow that is awful ? 

 

I would put money on the problem being moisture trapped behind a waterproof thin coat render that isn’t breathing. Question is where is the moisture coming from and how to stop it. Could it be surface condensation in super cold periods maybe? A condensation risk analysis at 0 degrees and below outside would show if the risk is happening within the element or surface render. Check relative humidity indoors is it below 60%? I think this is the RH% assumed in condensation analysis and a higher figure would exaggerate problem.

 

sorry just a thought on another avenue you wish to consider.

Edited December 9, 2021 by Gordo

[ToughButterCup]

FFS Dave. I don't know how you can  be so even-tempered about it.

Ducking and Diving is a much practised art in this sector.  There's nothing to  be lost for Baumit coming out and spending some time with you. Except for f.....ing COVID   Arggggghhhh.

 

From the sound of it, the company is  German.  (Bau = build , mit = with) If that is the case and you don't get any joy with the UK crew, and you need to go German, I'll gladly help.

 

[ProDave]

I really don't see the issue is coming from within the house.  The whole inside is wrapped in an air tight membrane, and the way the mvhr has been set up the house is at a very slightly negative pressure, so even if there were a breach in the air tight membrane, nothing would pass out into the building structure.  A condensation analysis was done at design stage and showed no risk.

 

Last attempt at contacting the manufacturer got that passed to the UK agent to deal with who are the ones that fobbed me off with what looked very much like a standard reply, blaming workmanship.  They did this just by looking at some photographs, not by visiting.

 

In the past I have not been shouting the name of the manufacturer, hoping they would resolve it, but now I am not afraid to say it is BAUMIT.COM that manufactures this render system. Perhaps some bad publicity will make them take more interest?  If I do have to contact the manufacturer again, I might just go straight to the CEO in which case a German translator might come in handy, thanks for the offer Ian.

 

The issue is definitely related to water in the outer layer(s) of render and then freezing.  Yes how the water got there is a question.  My wind driven rain and pin holes in the top coat is one theory, I await others.   but you would have thought an external render system designed for houses ought to be waterproof and frost proof?  Or am I really  the first person to use it on such a well insulated house that there is little heat escaping to warm the outside of the house, and in a cold climate prone to frosts in winter?

[bassanclan]

I can't quite get my head around how the bulges can be solid. I know its flexible, but its only thin render. Are you certain that the substrate isn't moving

[Declan52]

Could you seal up an original section that is likely to get soaked in the coming months with something like Thompson's water seal. If this doesn't let any water in then it shouldn't fail. Then it's further proof that for some reason their supposedly waterproof product is actually letting water through where it settles, expands and will blow the plaster of the wall in the end.

[joe90]

I don’t like any render, period, which is why I have brick. However even at the opposite end of the country (but near the Atlantic) our west wall was soaked right through to the insulation last winter (but it did not wick ?). I coated it In a  Sealer and now the water runs off it like glass. Might be worth trying (as long as it does not invalidate any guarantee, not that they think you have one ?).

don’t be afraid to bad mouth Baumit, they won’t like bad publicity, get Ian to write/translate a letter to their head office with a link to this forum (so we can all gang up on them ?).

Edited December 9, 2021 by joe90

[ProDave]

If I knew what would stick, and not look silly (clear coating perhaps?) then I might be willing to give this a try.  But I would rather hear that from the manufacturer, or someone that has solved a similar problem by painting it with some form of sealant.

[Carrerahill]

2 hours ago, ProDave said:

I really don't see the issue is coming from within the house.  The whole inside is wrapped in an air tight membrane, and the way the mvhr has been set up the house is at a very slightly negative pressure, so even if there were a breach in the air tight membrane, nothing would pass out into the building structure.  A condensation analysis was done at design stage and showed no risk.

 

Last attempt at contacting the manufacturer got that passed to the UK agent to deal with who are the ones that fobbed me off with what looked very much like a standard reply, blaming workmanship.  They did this just by looking at some photographs, not by visiting.

 

In the past I have not been shouting the name of the manufacturer, hoping they would resolve it, but now I am not afraid to say it is BAUMIT.COM that manufactures this render system. Perhaps some bad publicity will make them take more interest?  If I do have to contact the manufacturer again, I might just go straight to the CEO in which case a German translator might come in handy, thanks for the offer Ian.

 

The issue is definitely related to water in the outer layer(s) of render and then freezing.  Yes how the water got there is a question.  My wind driven rain and pin holes in the top coat is one theory, I await others.   but you would have thought an external render system designed for houses ought to be waterproof and frost proof?  Or am I really  the first person to use it on such a well insulated house that there is little heat escaping to warm the outside of the house, and in a cold climate prone to frosts in winter?

It sounds like it just can't hack a  Northern Scottish winter! Especially given the BBA cert was pulled.

 

How certain are you the application was to the book by your chap? If this stacks up (maybe hard to prove though) then the manufacturer should really offer to get it sorted at their cost. 

Edited December 9, 2021 by Carrerahill

[ProDave]

9 minutes ago, Carrerahill said:

It sounds like it just can't hack a  Northern Scottish winter! Especially given the BBA cert was pulled.

 

How certain are you the application was to the book by your chap? If this stacks up (maybe hard to prove though) then the manufacturer should really offer to get it sorted at their cost. 

I witnessed most of the install, though not watching them like a hawk.  All the correct layers were applied in the correct order and in good dry weather.

 

What I did not check was things like were each of the layers applied to the correct thickness?

 

Yes that is my concern, that the system simply can't handle this climate.  But if it is a German system sold in many countries, I cannot believe I am the first to try it in this climate.

 

Yes I would like to know when , why and by who was the BBA certificate withdrawn.  That alone suggests somebody somewhere know there are certain issues with this system, and I would like to know that information.

[Carrerahill]

3 minutes ago, ProDave said:

I witnessed most of the install, though not watching them like a hawk.  All the correct layers were applied in the correct order and in good dry weather.

 

What I did not check was things like were each of the layers applied to the correct thickness?

 

Yes that is my concern, that the system simply can't handle this climate.  But if it is a German system sold in many countries, I cannot believe I am the first to try it in this climate.

 

Yes I would like to know when , why and by who was the BBA certificate withdrawn.  That alone suggests somebody somewhere know there are certain issues with this system, and I would like to know that information.

The BBA certified it, then pulled it, I believe they would owe it to you, as a duty of care to tell you why. I would contact them for comment and explain on the back of their cert you used it. Now have issues. Although, as I type this, I think, actually it would be advisable not to tell them you have installed it as per that cert, because, if it turns out they screwed up, they might be scared you come for them. 

 

I might play the "I proposed to install it as per the now revoked cert, what were the reasons so I can avoid issues"  - a lie but probably worth telling it!

 

Edited December 9, 2021 by Carrerahill

[ProDave]

I have just sent an enquiry to BBA

[Mr Punter]

Before Grenfell, Kingspan and Celotex were BBA certified for use on tall buildings.

[Gordo]

8 hours ago, ProDave said:

I really don't see the issue is coming from within the house.  The whole inside is wrapped in an air tight membrane, and the way the mvhr has been set up the house is at a very slightly negative pressure  
 

MVHR is usually set up to be slightly positive pressure?

 

8 hours ago, ProDave said:

The issue is definitely related to water in the outer layer(s) of render and then freezing.  Yes how the water got there is a question. 
 

yeah don’t understand where moisture is coming from. But the thin render is obviously not breathing. This is why it is blistering IMO. Someone suggested applying a breathable sealer to a patch of the wall to see if it still suffers. I would second that and maybe try a patch with the thin coat scraped back before applying the sealer. I’d say a patch about 4m2 would be about right. The manufacturer has obviously washed their hands of you so you are on your own unless you go legal route where only solicitors win. Still may be worth a solicitors letter to show you may be serious.

 

[Gordo]

I see the BBA certificate state is is only suitable for sheltered to moderate exposure without special precautions (basically manufacturers installer and advice ie do not do it). I guess this apples to you in Scotland. Very severe exposure is not covered! Alarm bells wringing. I also note there is little shelter from roof overhangs at eaves and verges to weather. 

 

The BBA certificate appears to confirm that surface condensation should not be a concern if well insulated. 
 

im pretty sure the problem lays with the breathability or lack thereof in the failure.
 

but need to work out where moisture is coming from. Condensation risk analysis are often done using the most basic model. There are more advanced full models available that will show the moisture profile through the element and show the potential dew point possibly in the external render. Just a thought if someone can do this for you, maybe a member of this forum, it would help rule it out. I think this thin render system may be inappropriate for your building in this location and it may be best to consider alternative options if you have to foot the bill

 

Edited December 9, 2021 by Gordo

[Gordo]

A large chunk of the west of Scotland is classified as very severe exposure rating!

[ProDave]

We are not West Scotland, we are 20miles north of Inverness, closer to the East coast / Black Isle.  I did see an exposure rating written down somewhere I will see if I can find it.

[SuperJohnG]

Likely a question you've answered already but was it suitable for use on a non ventilated cavity? 

 

I'm currently just getting my k rend TC15 coat applied any day (soon as we have 5 degrees and 2 dryish days in a row) onto my knauff aquapanel which is on a ventilated cavity. 

[ProDave]

7 hours ago, SuperJohnG said:

Likely a question you've answered already but was it suitable for use on a non ventilated cavity? 

 

I'm currently just getting my k rend TC15 coat applied any day (soon as we have 5 degrees and 2 dryish days in a row) onto my knauff aquapanel which is on a ventilated cavity. 

Yes that's the whole point, the BBA certificate described this particular render applied directly to wood fibre EWI.  I believe this was the only render product approved for this so it's not as though we could try K rend as an alternative.

[SimonD]

Lime Green has now developed a pure lime render for Woodfibre. One of Weber's products is also suitable for Woodfibre but with the caveat that Weber uses local aggregate so mixes do vary slightly depending on region.

 

I suspect your best long term solution may be to look at adding a rainscreen so battening, cavity, render board, render. Your problems are very similar to those experienced in Norway, Finland and west coast of Sweden with premature ETICS failures.

[ProDave]

Yes I am becoming resigned to at some point having to re think the cladding, but that is going to be a painful and expensive decision.  And just what is different with a thin coat render system applied to a render board?  How will that be totally waterproof so rain cannot get in and freeze and blow it?  If such a render applied to a render board can be resilient to wind driven rain and freezing,  why can't a render applied to wood fibre be so as well?

 

Just one little more to this trying to understand it.  My opening post showed how the front wall after being lashed with a lot of wind driven rain followed by freezing temperatures appeared to bulge in a few places suggesting water had got in, frozen and expanded.

 

Well following that it thawed, we had a few mild and dry days and now we are into the second day of sub zero temperatures, it's not been above 0 today, the wall is covered in a nice layer of frost but there are no sign of bulges.

 

So further speculation:  Water got in with the wind driven rain and when it froze it expanded.  A few mild days has dried it out and there is no longer significant moisture there to expand when frozen.

 

If, and again it is if my speculation is true, then it would tend to favour rain ingress as the problem rather than moisture from within?

[saveasteading]

On 09/12/2021 at 10:49, ProDave said:

My wind driven rain and pin holes in the top coat is one theory, I await others. 

 

I have limited experience of render but some.  When my choice we never spec'd render, because I have seen so much failed or grotty stuff.

But some projects came with it written in.

There is some crazily expensive Swiss stuff we had to use on a Mercedes dealership. 

 This was applied direct to plywood externally, and it stayed put.

 

Then our choice of render on a block wall (flats). This was high up and very exposed. The difference to yours is that the mesh was tacked to the wall first, and a base course applied. Then the finish coat went on. Again it has performed well.

The 'mesh first' ensures that any local loss of adhesion does not cause the render to bulge.

 

So I am guessing about your product and circumstances.

I agree that it is not coming from above or below,: it is failing where the water is getting in.

That is likeliest to be due to microcracking, and driven rain will get in there, then freeze and pop off.

 

It may be a local problem due to drying issues when applied, or may be everywhere.....we will hear.

 

On the other hand perhaps it is simply a poor bond locally, due to the finish of the board...dirt or oil, or too smooth.

 

I am surprised it has gone back to place..it must be very flexible.

 

How exposed is the site? From my studies your area doesn't look too severe. Anyway, how do they define severity?

 

[Gordo]

21 hours ago, ProDave said:

If, and again it is if my speculation is true, then it would tend to favour rain ingress as the problem rather than moisture from within?

Yeah I agree rain ingress is the most likely source of problem. The criteria for severe exposure zones I don't know but just refer to maps of zones. Looks like you may be in a moderate to severe exposure zone at a guess. 

 

I'm no expert on renders but have shyed away from thin coat renders but see it is getting more popular for some reason (I guess cost savings of not having to paint). I am glad I don't have to wrestle with your problem and the best solution. I Would suggest a few trials of surface coatings to see if they solve it. But think breathability of surface coating is the problem. Possiblity a product problem if applied direct from the tub? Or it is applied incorrectly maybe. I guess there is a recommend coverage rate that is key

Edited December 11, 2021 by Gordo

[ProDave]

The top coat comes pre mixed in tubs.  you just give it a mix up and spread it on.  On the original application, the quantity was bought based on advised coverage by the manufacturer, and I think we had 1 tub left over, so pretty close to the mark.

[bassanclan]

Have you tried taking a garden hose to the sheltered side?