Can you use Wedi/Marmox/Jackoboard instead of plasterboard?

Hi all,

I'm looking for advice regarding using cement XPS foam core boards as an insulating wall finish.

I'm currently refurbishing my kitchen (1930's bungalow with an insulated cavity wall) and after removing the units off a cold external wall, found lots of black mould presumably due to poor air circulation, the plaster/render was also in poor condition so I've stripped the wall back to brick and was thinking as I'm fed up of being cold and rising fuel bills it would be good to add some sort of internal insulation but I'm restricted on what I can use due to having a window on the adjacent wall that only allows me the depth (660mm to the bricks) of a standard worktop/kitchen units.

A plumber friend suggested using the XPS foam core boards and plastering that instead, he said he's seen it done a number of times outside bathrooms.

I looked further into it and this stuff is Euroclass E with regards to fire safety which has unsettled me somewhat but seeing as it will be plastered and mostly behind timber cabinets does it matter? All the manufacturers advertise the insulating properties and the ability to plaster it as a wall finish but can't find any info on whether this is advisable or even allowed outside a bathroom? I've looked at the Part L building regs on the Planning portal but seem to be no wiser.

If this a non starter could anyone suggest an alternative slimline product? I realise it'll probably be a minor improvement regarding the insulation but any improvement will help.

I would really appreciate any input anyone can give.

If youve got mold because of lack of air circulation will insulating help? Youve got a filled cavity wall, so insulation-wise it ought to be OK anyway. Have you looked into other possible causes for the damp?

Many thanks for the reply

I'd thought the wall was cold because warm air wasn't able to warm it to the same degree as other walls in the kitchen. I really am struggling to work out what is the best solution I pretty much get one chance to sort this now and don't know what's best? DPC seems good - damp brick below & dry above, external wall is rendered, again in good order.

Further reading suggests that with CWI then adding internal insulation will trap moisture in the masonry and cause more issues down the line?

Probably best for me to stick with render of some sort? Does anyone know if it would cause issues on a property of this age to use sand & cement render and skim with gypsum? Existing mortar is black ash.

Thanks again, much appreciated