Hello folks!

I have been using Lime Green ready mixed products: Duro, Solo and Board Adhesive (lime based), which you only mix in the water. 2 out of the 3 walls went really well if I say so, but the third one is crumbly to a point that I can use a pencil to scratch the plaster off without breaking the tip!

The walls that worked:
internal bare brick < 10mm of Duro < another 10mm of Duro < 5mm of Solo
party wall existing lime render < 3 to 5mm of Solo

The issue:
external bare brick < 10mm of Duro < 5mm board adhesive < 60mm hard wood fibre < 8mm of Solo (two passes in the same day with mesh in the middle

The base coat of Duro was very strong as the others, and I was also happy with how the wood fibre bonded with the adhesive and mechanical fixings. However, a month after applying the top coat of Solo, it still feels crumbly (please see pics)

This is how I applied the plaster:

1. Added 5mm of Solo across the whole wall, pushing the sections of mesh as I plastered
2. Added 3mm of Solo on top of the mesh (around 4h after the coat above)
3. Sponge floated and used a smooth steel trowel for a smooth finish (about 2h after the second coat, it came out smoother than the other walls).

At the end of the same day I noticed some small bubbles coming out of the plaster, then also noticed it being a bit wet on the surface (like condensation), even though I left the window a touch open.

Would anybody be able to point what I did wrong? I followed the product guidelines to the best of my knowledge, especially when they say the first and second coats around the mesh should be applied within 24h, so I am a bit puzzled and scared to carry on plastering the other external walls the same way.

Any ideas are welcome and hope you are all having a wonderful week!

I've no idea what went wrong but......

Why not ask Lime Green Products Ltd via their web site.

Posted By: djh
I'm confused whether this is really external, or is it the internal side of an external wall?

Sorry, this is the internal side of an external wall! We have no heating on there at the moment but the minimum temperature it reached was 9C, but 12C for most of the day.

I didn't use any primers but sprayed the wood fibre to dampen it before plastering. I also dampened the wall slightly for around 3 days after installation, but stopped when I noticed the "condensation" like build up on it. When you say it is likely moisture-related, do you think it lacks moisture or got saturated?

I will check their website again, but Solo seemed to be their top recommendation for wood fibre (on the website, datasheeet, videos etc).

I also filled the contact form on their website asking for some advice and will keep you posted, but all ideas are sitll welcome!

I have used Baumit lime plasters for over 10 years and never had any problems with the materials. RK 38 for any dubbing-out required, RK70 as adhesive coat and base coat and (if you want a rougher finish) top coat too. I use Kalkin Glatt for the top coat, giving a very thin and very smooth finish. I have never used Solo, but then the Baumit plasters have done exactly what I want, so why change?

Posted By: bgasparottoGood point about a possible out of date bag, but I used 4 bags on the wall and the problem appears everywhere on that wall. Moreover, I used bags from the same delivery batch on the other walls and it worked wonders.

I am a bit committed with Solo now since I purchased half a pallet, so I am keen on making it work for financial reasons, but will definitely consider other materials in the future.

I read in another topic that somebody else applied the second pass after the mesh 17 hours later (assuming next morning). I also read in another forum that using a steel trowel too much would bring the lime to the surface and leave a sand rich mixture on the back, hence weakening it. Could that be the reason? I am considering applying the second pass on the morning after on my next walls, then barely do any steel troweling and settle for a rougher finish.

How much water are you using when you knock it up? The instructions on the back leave the mix woefully dry and there's a tendency for people to add a lot more water, I wonder if it was too wet?

Did you float before flattening? I've never had any issue with overworking the wall, just a few light cracks.

Is all of the plaster coming away when you scratch it or just the surface?

<blockquote><cite>Posted By: bgasparotto</cite>I just keep slowly adding water and mixing until it looks creamy and doesn't fall from the trowel. I did favour a bit of a wetter mix once I realised it was setting too quickly given I had to do two passes.</blockquote>

I ended up doing this also. My first try went off in the bucket, as Kristeva said previously. I don't find Solo to be user- friendly in that respect, and may one day try Baumit instead. I have used lime putty before for plastering and it was a doddle, but that was when we could collect tubs from Bleaklow in Hassop, who seems to have ceased trading.

Posted By: bgasparotto

Posted By: kristeva
How much water are you using when you knock it up? The instructions on the back leave the mix woefully dry and there's a tendency for people to add a lot more water, I wonder if it was too wet?

I didn't measure how much water I added, I just keep slowly adding water and mixing until it looks creamy and doesn't fall from the trowel. I did favour a bit of a wetter mix once I realised it was setting too quickly given I had to do two passes.

Did you float before flattening? I've never had any issue with overworking the wall, just a few light cracks.

For the floating, I usually apply the plaster on a 1sqrm of wall, flatten it with the speedskim, repeat this twice so I reach the whole height of the wall then push the mesh in with the trowel so it ever so slightly hides from the surface. On the second pass, I flatten first with the speed skim then wait until it is harder to the touch before I sponge float. I do remember finding the right side of the wall a bit softer for the sponge float, but I had to it anyway (quite gently) as it was 9pm already!

Is all of the plaster coming away when you scratch it or just the surface?

No, I need to keep going in millimetre by millimetre to take it all out. It feels like sanding a surface with almost no effort. This won't happen on the other walls though, the pencil will simply not go in.

It doesn't sound to me like you've done anything wrong, on the contrary it sounds like you've been handling a difficult product really well. As I said before I've abused Solo in the past and never had it not set, I mean this is NHL we're talking about here and not the fussier lime putty based mortars. NHL products usually go off rock hard!

Actually, a couple of weeks ago I was using up some really old bags of Solo that have been around for 2+ years. I needed to level up a wall to the window reveal in prep for some wood fibre I was given for free. Lets just say I'm keeping a beedy eye on it, some areas had to be applied quite thick but I'm a tad surprised and how long its taken to dry. I can't dent it with my finger nail but the slightly darker off white colour tells me its obviously still drying.

Your wood fibre board being the strata upon which the plaster has been applied is the outlier here compared to your other walls. If the plaster is soft or sandy and coming away it sounds like the lime hasn't set. The board sucking out all the moisture not allowing it too react perhaps, and yet you had this condensation effect. Just a thought, with the wood fibre board I was generously given the 2 sides seem slightly different, I don't suppose with the brand you purchased there is a right and a wrong side to plaster?

Posted By: bgasparottoI used the LG's Warmshell boards, and according to their datasheet (and to my memory from when I installed) it apparently can be installed either way:

Application
Only apply to dry backgrounds. Consult with your supplier for fixing advice. Before rendering or plastering do not allow to become saturated and ensure the absolute moisture content is no more than 13%. Render within 4 weeks of installation. When used as a sarking board ensure the Warm-shell Woodfibre is covered with ADB membrane immediately after installation. Compatible renders and plasters are available from Lime Green.

I don't know how to measure this but I don't think I went over 13% moisture, but I say that only having dampened the boards in a similar fashion I did with the other substrates.

Another thought too, the problematic wall has a smoother finish than the other walls where it worked. I am not saying that this is the cause, but on the next walls I feel like trying:
1. Not having a smooth finish (not close the lime with the steel trowel, only sponge it)
2. Maybe do the second pass over the mesh on the morning after to give a better chance of the first pass starting to set quicker? Hope this won't make the bond of the first pass and the second pass weaker around the mesh though.

Do you guys think it is worth trying or it possibly it won't make any difference? I just don't feel doing exactly the same process that failed on me before, so I need some hope!

I assume LG recommend you dampen down the wood fibre first?

I don't think the type of finish will make a difference tbh, if the plaster fails the lime hasn't reacted or set. You could try the 2nd pass the next day, the plaster will still be green and won't need a key, just make sure the first pass isn't ultra smooth.

I think maybe a test is in order to get your confidence back, have you got a spare bit of wood fibre board? Do 2 or 3 at the same time slightly differently. And have you contacted Lime Green, I'm sure they could cast fresh light on this.

Posted By: Nick Parsons'I assume LG recommend you dampen down the wood fibre first?'

Interesting, this. I was writing a series of 'how to' guides for a client, including IWI. They added wetting of the boards to my draft, having had a practical session from a trainer who used Lime Green products.

I have been using Baumit products for over 10 years and did training with (the late) NBT for IWI and with Baumit for EWI. In neither case was wetting suggested and I have never wetted a WF board. Equally I have never used any plasters or renders than Baumit on WF. I wonder why it helps with LG.

I might try some LG sometime as an experiment.

Its been some time since I've referred to the wood fibre board installation instructions i have filed away from various manufacturers including Steico but I can't remember any mentioning of wetting the boards either. LG Solo is a common recommendation for WFB.

I did wonder if it was to do with dry lumps in the mix that didn't get mixed properly. I seem to recall something like this when I used it, but it was about 2 years ago now since I used it and my memory fades... sorry I can't be more specific!

Thanks for all the responses and encouragement! It is really appreciated especially as I am just a keen DIYer :)

I got a response from LG regarding the dampening of the WF, and they said I actually didn't need to, so they recommended to only brush off any dust/debris next time, without any water. They didn't say this could have caused the issue though :(

I am considering trying the Baumit plaster instead of Solo for the lounge, or perhaps adding a bit of NHL 3.5 onto solo already just so I don't hit the wall with exactly the same mix that failed last time. For the Baumit plaster, would I use RK70 instead of Solo with a similar technique?

https://www.mikewye.co.uk/product/baumit-rk70/