saveasteading

See if you can keep the wood structure completely dry . as @JohnMo , but also with clear space underneath (not boxed in) so that it can have draughts and dry Unless you use very special timber it will start to go mouldy and rot immediately, and a 10 year max life should be expected for the wooden surface.

More questions. How recently was this built? The plaster looks damp still, and perhaps the floor too. How thick do you think the celotex is? Is there a space between concrete on the ground, and the timber floor? Is there any heating in the room? For an immediate benefit, stuff the draughty hole with rags: it will be a good test before doing it permanently.

Accepted. I can see that bigger gaps would fill substantially as you say, and the microscopic ones are the least issue anyway. and it is filling from the inside so the weather shouldn't be any issue.

Do we know that this stuff will stay in place / not detetiorate as a permanent seal? I'm wondering if some/ most of the seals are just a few fibres, because as soon as they cover a hole, the draught ceases and no more fibres will adhere. What happens when there is air pressure in the other direction (out to in)?

There will be specialist local roofing merchants who will know what is the local preference.

And what was mortar called in your area? Frog up or frog down? Did they request... Mr Flanagaj, would you awfully mind making us another batch of your excellent mortar whenever it suits?

Great. And what about sourcing the sand to be suitable and all the same? That's a huge advantage having been there and done that. Were you instructed on accurate mixing? What else did you learn about tricks of the trade?

They will have regular gangs too, not just picking up whoever is available or cheap. They probably aren't working on mass production sites. I think you would best put a query up on your local social media.... brilliant brickie wanted.

it will be fitting the space exactly, including any lumps and bumps, eg mortar courses, so will require a hefty tug. it will then start to expand again as it has been released, so won't go back in.

What @Russell griffiths says. This will take a bit of research and a lot of management. And you will have to pay a bit more for the materials and a very professional bricklayer. The typical bricklayer will engage a ' trowel' (another bricky) or two, and a labourer. He may understand your requirements but not convey that properly, or they don't understand or don't care. The labourer especially is unlikely to make much effort and will be under constant pressure for 'more bricks, or more pug/muck/mortar ' acc to region. Then next day it is a different labourer. Most just shovel in sand and cement and add some water. The same shovel holds different volumes of cement / dry sand/ damp sand. I have never witnessed the use of a gauge box. Even getting them to use buckets rather than shovels is a pain. Explaining is likely to be met with a smirk implying 'what do you know?' they dont know what they dont know. And then you must only use one brand of cement...fairly easy. And one source of sand. This week's big bags may be completely different from last week's as they come from a different sand pit or a different layer of the same one. The BM has little to no control over this. Some sand is remarkably orange and will never look like your pics. But I don't want to discourage you as the right mortar makes the wall right too. Perhaps you have to be cheeky and knock on the door of a house that has achieved what you want. a few compliments will excuse the intrusion and you might get the info you need. To me the answer is a professional and proud bricklayer or builder who knows how to achieve this, and will want an extra 20%. They exist. You will choose your sand and get it all delivered in one hit. Why's this? Again because of getting the mix exactly the same for every single mixer load. No chance really other than black.

In case this is relevant or of interest. From my experience, limited to non-glazing uses. 1. The Compriband I knew in structures was close celled and fully closed on the outer surfaces. 2. In constructing hundreds of steel buildings, every one had lots of profiled foam fillers to close off the ends where there were crowns in the cladding. It came from a single source from our cladding supplier. One of our clients happened to be a manufacturer of foam sheet and board for packaging. The owner examined a piece of the roofing material and expressed huge satisfaction that it was closed cell, saying it was a superb product and he was pleased to have it in his building. He added that it was an unusually high quality and relatively expensive. Thereafter I took more interest and looked at all foam fillers from other sources, and the difference in quality was clear. I suppose I am saying that there will be all sorts of similar products out there, with differing performances. The wrong one may save the installer £30 on your house, but you will pay many times that in heat loss and deterioration.

I have no doubt you are reputable and have a proven solution. I've had badly used foam cause extensive damage and leave a bodge behind.

The reputable ones anyway. Aerosol expanding foam is banned on my projects without express permission. It (esp the cheap varieties) is the preferred solution of the bodgers. Even the more flexible varieties should be used with knowledge and skill.

It appears to be that the Illbruck product is Compriband and other manufacturers are adapting the name as a generic.

@craigmay correct me. I only know Compriband from major Civil Engineering works, eg bridges, basements and sea defences and long ago. The band had to be compressed using a special machine exerting huge pressure, was inserted or cast in, and then would return to shape over many hours and continue to exert pressure indefinitely. It was intended to seal joints and cope with future movement. By hand it barely compressed under a thumb. From what I understand there are umpteen products for different situations thus for every case it can be the appropriate strength to not crush. Ie it will keep pressure on both sides of the gap. BUT I've a suspicion that many installers use cheap and quite flimsy foam strips. I came across a supplier who seemed to have a wide range of products for the window industry, which was encouraging. I asked what was the difference between theirs and Compriband, and they insisted theirs "is Compriband". I suspect the trade name was being abused as a generic term.