Adhesive for wood fibre boards

[Stickworm]

Hi

I'm looking for an alternative to seciltek isovit lime or Gutex Thermoroom Adhesive for bonding wood fibre boards to the wall. Ideally from ecomerchant as I'm already making an order there (I've emailed them but they've not got back to me). I'm not super knowledgeable about these products, so any help would be appreciated.

Cheers

 

[a twig]

Ordinarily you fix them mechanically with screws and large insulation washers

 

[Stickworm]

Yes I'll be doing that also, but I contacted the manufacturer and they said it should also be bonded and recommended the seciltek (for steico). A number of the suppliers weren't bothered but I thought it best to go with the manufacturers instructions.

 

[a twig]

Ah you mean bonding between the edges of adjacent panels?

 

[Kearn]

They don’t need bonding - I’m confused or missing something here?!

Assuming you’re talking about the T&G 30-60mm fibre insulation boards to plaster onto?

Mechanical fixing is all they require, unless you believe you can’t get a decent fix into the wall.
The reason for chucking something onto the wall first is to deal with any uneven surface and remove air gaps between wall and board. Just a nice sticky putty mix is fine.

The joins in boards have the (delicate) T&G to align them, but you will want to use some plastic mesh over, ideally 10mm gap, to minimise any cracking in the plaster due to future movement.

 

[Kearn]

Ah you mean bonding between the edges of adjacent panels?

They do recommend a plastic glue product. It’s not needed really

 

[Stickworm]

Heya

So I'll be levelling the wall first. I'm using steico wood fibreboards without T&G and I am referring to sticking them to the wall not their edges to each other. I've included a document here with reference to bonding on page 7.

This video refers to the bonding coat:

Mikewye.co.uk suggests using 3mm Isovit Lime and fixings (they reached out to me after I contacted Steico directly on their behalf), ecomerchant says only fixings, ecologicalbuildingsystems suggests both.

I appreciate there's some differences of opinion here.

 

[Kearn]

The T&G is largely irrelevant anyway, I usually cut them off as they’re so flimsy.

You say levelling the wall - how?

Because if you do that the usual way with an initial coat of lime, then that will ‘bond’ them to the wall as you pull them into the plaster with the mechanical fixings.

Seems like you may be overthinking it a bit - what’s your actual concern to avoid / goal?

 

[Jahouli]

I went with the system recommended by Mike Wye (isovit lime + mechanical fixings) for the reasons quoted in your linked video , but also because I'm a belt and braces sort of guy, and wanted to minimise the risk of hairline movement cracks: Internal wall insulation spec

The isovit on the back of the boards was in addition to using it as a levelling coat on the wall first, as my walls had too many low spots that needed evening out.

Additionally I used solvent free gripfill to glue the flat edges to each other (solvent free is much more spreadable than the regular!).

I assume any regular lime plaster could be substituted for the isovit as it can be used as a base coat for the final plaster finish. The key thing is to plaster to the back of the boards and get good contact with the wall.

 

[Stickworm]

I'm levelling with prooftherm. It might be overkill, I'm not sure - that's the thing, I haven't done it before. Was just following the manufacturers instructions so I'm happy to hear other suggestions/experiences etc. If people think that can be skipped or substituted for something else etc.

 

[Stickworm]

Following on from this I cancelled the Prooftherm order this morning as it's stated as not having capillary action (though is very breathable), nothing else had been ordered yet. I'm a bit lost now. I've received plenty of advice from merchants but obviously they're keen on their own products. Could people please recommend to me what approach and product they'd take to levelling the walls pre boarding? Mike Wyes delivery costs are very high so would probably prefer to avoid them. I had looked at Breathaplaster this morning as I could get it at ecomerchant and the drying time would help speed things up, but I've not come accross many people singing it's praises. Any help would be really appreciated, thanks

 

[Lacan07]

If your walls are flat no bonding required, just use mechanical fixing. 40 - 60mm wood fibre board has a certain amount of give to it anyway.

 

[Stickworm]

If your walls are flat no bonding required, just use mechanical fixing. 40 - 60mm wood fibre board has a certain amount of give to it anyway.

The brick sections are reasonably flat, the stone sections are very much not flat.

 

[Lacan07]

The brick sections are reasonably flat, the stone sections are very much not flat.

If you have uneven walls you need to make good with a layer of lime plaster, as you would as if normally plastering a wall.

 

[a twig]

Time for my customary post on all wood wool and wood fibre threads:

Lists of useful information in this thread covering both wood wool and wood fibre insulation options and installation methods

 

[Kearn]

Following on from this I cancelled the Prooftherm order this morning as it's stated as not having capillary action (though is very breathable), nothing else had been ordered yet. I'm a bit lost now. I've received plenty of advice from merchants but obviously they're keen on their own products. Could people please recommend to me what approach and product they'd take to levelling the walls pre boarding? Mike Wyes delivery costs are very high so would probably prefer to avoid them. I had looked at Breathaplaster this morning as I could get it at ecomerchant and the drying time would help speed things up, but I've not come accross many people singing it's praises. Any help would be really appreciated, thanks

Don’t go near it.

 

[Stickworm]

Thanks for all your input, that thread was a really nice read thanks twig, really good to see peoples processes and results. I've not done this before hence the huge number of questions and hand holding. As a bit of a sanity check:

1. If I need to do a bit of repointing internally (with a NHL3.5 mix) do I need to wait for this to fully cure before working on top of it?
2. How about this for levelling out any uneven sections? (I can get it locally) https://ewistore.co.uk/wp-content/uploads/2024/02/EWI-747-Lime-Render-3.5.pdf
3. That same company suggested I used this as an accompanying adhesive but it seems inappropriate to me https://ewistore.co.uk/wp-content/uploads/2021/10/ewi225-4-1.pdf and I guess I'd just go without.
4. Then mechanically fix the boards, and plaster later etc

Then hopefully I can get out of everyones hair

 

[Kearn]

Pretty sure most of the simplest, cheapest, most appropriate approach has been covered already… but to answer your Qs briefly
1 - NHL, and particularly 3.5 has no place indoors. And very little externally, maybe hard stone walls. You may as well use sand and cement - will probably cure softer. Buy pre mixed lime putty form any of the usual suspects, if you’re buying other stuff then add a few tubs to the pallet you’re already paying for. Yes you need to give it a couple of weeks at least, 4 ideally before pushing boards over as it needs to cure.
2. No. Just use lime, pure and simple. Cheaper and without chemical additives, same as you’ll use for the scratch coat.
3. You’ve already answered, this is a cement product. No place near your building. You’re taking advice from retailers who sell incorrect products and are just pushing sales - try any of the usuals, Eden Hot Lime - great service and pricing, Ty Mawr - good advice too, but pricier, Mike Wye, similar, Cornish Lime… they will all talk you through at length and answer all the questions you still have about how to approach this, options and products to achieve your goal.
4. That’s the easy bit, but you’ll need to buy the washers from one of the suppliers, and ensure you use stainless screws. Hopefully it goes without saying, just a putty based lime on top - I’m pretty sure I’ve commented before on another of your posts my personal preferences for what I’m currently using into internal wood fibre boards.

 

[a twig]

As per other threads, Kearn and I “agree to disagree” on the interior NHL side of things.

I used NHL2 and NHL3.5 as a base for a variety of internal finishes and repointing without issue, no problems with cracking or movement over several years and a noticeable improvement in damp etc. NHL2 in particular in my experience was certainly a lot less hard than a cement based mix.

 

[Kearn]

As per other threads, Kearn and I “agree to disagree” on the interior NHL side of things.

I used NHL2 and NHL3.5 as a base for a variety of internal finishes and repointing without issue, no problems with cracking or movement over several years and a noticeable improvement in damp etc. NHL2 in particular in my experience was certainly a lot less hard than a cement based mix.

A week 2 mix is the lesser of the evils indeed - especially if a decent brand with good free lime content. Don’t get me wrong, I’ve got quite a bit of St A on site at the moment …. But it is all for external use. Much of the stuff from builders yards is far less ideal - there is no spec on the ingredients, which is why NHL can be unpredictable.

I was chatting with our lime plasterer the other day about it - he made a fair comment regarding its use on wood wool boards, given how rigid they are anyway. But that doesn’t allow for the building moving around them…!