Repairing my defective thin coat render.

[ProDave]

Earlier in the year I had a thread describing the problems I had with my Baumit.com thin coat render system on wood fibre EWI that thread is here:

 

 

This thread is to document the attempts at repairing / re working it and to show what we find as well as invite opinions as to what may have caused the problems.  As yet the cause of the problems are unknown, largely because the manufacturer and UK distributor for this render system have washed their hands of the issue, refusing to help and they have not even been prepared to come and look at the problems to give some proper technical input to what went wrong.  So we are in the dark, trying to work out what went wrong and how to rework it so it stays put next time.

 

Discussions with the plasterer suggests we have 2 separate issues, and that is how we are tackling it.  The first area we are tackling is the gable end wall of the garage where a huge area of the top coat render has delaminated.  That is where we are starting.  The other issues are small patches in other parts of the house having a similar problem.

 

Because of the large area affected the plasterer suspects either an application error or a material failure.

 

So starting on that garage gable end, the scaffold is up and today I have been busy with the scraper.  My job to start with is to remove all the loose render and the plasterer will then visit later in the week and we will formulate a plan.

 

So a picture of where I am after today's work.

 

 

What I have found is a huge area of the top coat render came off very easily, all the lower part of the wall apart from small areas either side of the door, and right up to the mvhr vents.  Higher up the roof towards the gable end it still seems solid.

 

Where the render has failed, it is clear it is the base coat that has failed.  Much of the base coat in the failed areas has turned to powder.  The red mesh you can see is a plastic mesh that was embeded into the base coat and is only visible because so much of the base coat has turned to powder and fallen off.

 

What has been exposed appears to be dry, and in a few places I have exposed the underlying wood fibre board and that too appears to be dry.

[Oz07]

I hate big manufacturers when they do that. Quickstep tried to do it to me last year but I just kept threatening the supplier with legal action. The law is so focused on the consumer that the supplier eventually buckled and paid my whole claim just by threatening action. It included cost for removal, disposal, replacement, new skirting and redecorating.

Have you tried going through supplier rather than manufacturer? Not fit for purpose? What about legal cover on house insurance. 

[joe90]

Not that I know a great deal about render, especially this newfangled stuff, if the base coat has turned to powder and is dry it must be a material failure. Can you not get an expert to inspect and give you a conclusion of fault that you can go to the supplier with to make your case?.

[ProDave]

I have not looked into legal avenues yet.  At the moment I have a commitment from the plasterers to rectify the problem, if you like the plasterers have baled out the manufacturer?

 

It is complicated. We bought the materials from the then UK supplier NBT and bought all the beads, corners, starters etc from them with the render.  They no longer exist.  A different company has taken over the UK distributor now.  the manufacturer referred our complaint to the new distributor who "answered" it with what looked like a standard letter blaming poor workmanship, wrong materials (supplied for the job by the previous supplier)

 

So now I am just telling it as it is, wharts and all.  IF that results in bad publicity for Baumit.com then so be it.  I am only publishing facts.  And you guessed it, I could not recommend this system to anyone else, mainly because I would never recommend anyone use something like this where the manufacturer has a history of not helping the customer.

 

It is all very sad, because the previous supplier had a very good and knowledgable rep, who would have visited and looked at the issue and tried to help.  He is no longer with the new company and attempts to contact him in the hope of tapping into his knowledge have failed.

[joe90]

25 minutes ago, ProDave said:

IF that results in bad publicity for Baumit.com then so be it.

That may make them sit up and take notice ?‍♂️Good for you.

[ProDave]

A small update.

 

The plasterer has seen the stripped garage wall, and has delivered some material.  His observation, there are two base coats applied (same material) and it is the top layer of that that has failed.

 

He bought some material with him, but he had not expected the issue to be the base coat so he had not ordered enough of that, so there will be a short pause while some more is ordered.

 

Now, a difference.  The base coat used originally was MC55W.  What he has bought this time is RK39.  I have not looked up the difference yet.  Anyone know?

[SimonD]

RK39 is a cement free render - lime only.It also doesn't have fibre reinforcement. Be careful here as lime only render may not be suitable for application onto wood fibre even if it has added modifiers (I've discussed this very topic with lime render manufacturers technical departments and there are multiple reasons why - thermal shock, moisture management etc.). The required thickness is also different as the base coat and topcoat on RK39 for external use is minimum 13mm, probably 15mm. The thin coat is only 9mm. Big difference in weight.

 

Why has your plasteres decided on this change of product? Has he actually gained technical advice directly from Baumit?

 

If you're dubious about MC55W, I'd question whether RK39 is a suitable alternative. You might be better off looking at the European technical assessment documents for Pavatex and see which alternative thin coat renders are available. For mine I also had a choice of using certain Weber products.

 

Edit:

If you're after a lime only render from a different manufacture, then Lime Green sell one suitable for woodfibre (although primarily developed for their woodfibre ewi system) - it's quite expensive, mind you.

 

 

Edited August 6, 2021 by SimonD

[ProDave]

Okay here is the latest.

 

The plasterer has made contact with the technical rep of another distributor of the Baumit product, where he can have an open, frank and honest discussion without them being on the defensive to defend a claim as they were not the supplier and have nothing to lose.  The plasterer has also had a pick through some of the render that has been removed in sheets and is sitting in my trailer at the moment.

 

One observation is a lot of the Silikon top top coat render appears to have a lot of pinholes in it.  And observation of some of the other areas of the house that have blisters but have not yet been removed seems to show the same.  The technical rep cannot think of any reason to do with application that would result in this happening.  Product failure?

 

Following on from that, these pinholes would allow rainwater to get through to the MC55W base coats which would become soaked and then frost over the winter would cause the breakdown we have seen.  I presently have some sample pieces of the render collected that I am going to photograph in as high resolution as possible to email to him, and I might well then package them up and physically post them to him.

 

Regards MC55W Vs RK39 base coat.  This technical rep is of the opinion RK39 is okay and has the advantage that it is rated as a sole coat i.e should be waterproof even without the Silkon top top coat, so any further moisture penetration should not cause it to fail.

 

So we are making a little understanding about what might have happened.

[ToughButterCup]

God, Dave. I'd be mighty mighty piddled off ...  Just like Jezza used to say, on every build there's always one Oh-f-f-s

[Declan52]

Would you get pin holes like when you use too much of plasterciser making motar and put too much air into the mix making it like fluff. Does anything like this get added to the render to help playability or is it premixed into it.

[dpmiller]

Silicones make fish-eye pinholes in paints...

[ProDave]

Picture of a sample of failed render.

 

From the front:

 

 

From the rear

 

 

Held up to the light to show pinholes.

 

[ProDave]

The Silikon top is a pre mixed product that comes in a plastic tub.  You just give it a miz mix and apply it.  If there was anything "wrong" about the mixture that would have been a manufacturing fault.

[joe90]

glad you appear to be getting somewhere, must be very frustrating but good on you for persuing with it ? 

[SimonD]

5 hours ago, ProDave said:

Okay here is the latest.

 

The plasterer has made contact with the technical rep of another distributor of the Baumit product, where he can have an open, frank and honest discussion without them being on the defensive to defend a claim as they were not the supplier and have nothing to lose.  The plasterer has also had a pick through some of the render that has been removed in sheets and is sitting in my trailer at the moment.

 

One observation is a lot of the Silikon top top coat render appears to have a lot of pinholes in it.  And observation of some of the other areas of the house that have blisters but have not yet been removed seems to show the same.  The technical rep cannot think of any reason to do with application that would result in this happening.  Product failure?

 

Following on from that, these pinholes would allow rainwater to get through to the MC55W base coats which would become soaked and then frost over the winter would cause the breakdown we have seen.  I presently have some sample pieces of the render collected that I am going to photograph in as high resolution as possible to email to him, and I might well then package them up and physically post them to him.

 

Regards MC55W Vs RK39 base coat.  This technical rep is of the opinion RK39 is okay and has the advantage that it is rated as a sole coat i.e should be waterproof even without the Silkon top top coat, so any further moisture penetration should not cause it to fail.

 

So we are making a little understanding about what might have happened.

 

Those pin holes are a very strange thing indeed.

 

Re the distributor and RK39, I'd have one question to ask and that is how much experience the distributor has specifically working with wood fibre. RK39 is designed for thicker application on masonry substrates and wood fibre behaves very differently, so it's not just about the waterproofing aspect. Is it designed to bond with the wood and does it have modifiers to make it lighter, for example (RK39 at recommended thickness is nearly double the weight of thin coat)? Baumit StarContact is the adhesive/basecoat used in Baumit's ewi systems.

 

If the distributor the plasterer has spoken to can reference lots of work with wood fibre, I mean years of experience and can show this render works over the long term, then fine. Otherwise treat the opinion with great care.

 

The reason I'm saying this is that I've spent over 3 years talking to people and researching woodfibre ewi and found out that there are a lot of people (including reputable suppliers) in the UK that pretend to know what they're talking about regarding suitable render on wood fibre - there's also a hell of a lot of random detailing approaches which are insufficient. In this time I've been recommended everything from lime putty to hydraulic lime to other weird and wonderful solutions, even using hemp fibre in the basecoat instead of mesh. There is, unfortunately, a lot of bs out there that stems from a lack of experience and knowledge about the product. It even goes down to the basics that suppliers and installers often don't even know they've got to measure the moisture content of the wood prior to render application. In the end, thanks to a Baumit distributor putting me in touch with them, I ended up speaking to someone who has years of experience working with the material on the European continent and they understood the product much better. Lime Green is one company who also have a good understanding and their hydraulic lime render for wood fibre has been modified to work with wood fibre.

 

Sorry to bang on in what might seem a negative way, but I remain dubious about the opinion RK39 should be fine.

 

As a side note, the guy I spoke to with loads of experience in the field suggested I add a cavity and install render board outside the wood fibre explaining that this is a safer approach in this country. If I'd known that when I was building my structure, I would have modified my designs accordingly. Unfortunately, like you I seem to be stuck with the direct render and will have to see if it lasts.

[Mr Punter]

12 hours ago, SimonD said:

I add a cavity and install render board outside the wood fibre

 

NHBC like a drained and ventilated cavity in the construction.  I can see why.