Permeable Observatory Flooring? <wibble>

[Macavity]

Originally I had envisaged my Observatory as a "Home from home"
with fitted carpet, TV, drinks bar etc. Sadly it didn't quite work out! ?

As a prebuilt structure, the whole thing was built on a FLAT paved
area --- The (water-proof?) chipboard floor laid onto a "tanalised"
timber lattice... and the walls attached to that! Sadly WALES is a
very wet country, and the floor *still* shows minor damp patches. ?
(I stopped most water flow under obsy with sticky flashing tape!) 

Checkout Evo Stik's "Flashband" on Amazon etc.

Retrospect is a fine thing! But with more time, I sense there are
better ways to do things. A non-permeable damp-proof course 
under the whole structure (concrete blocks?) would have helped! ?

BUT SOME THINGS I have discovered re-discovered! Like an old
fashioned (Medieval? lol) house, my observatory *can* tolerate a
certain amount of water ingress, provided it can then evaporate!  ?

http://www.oldhouse.info/ohdamp.htm  (Quite interesting tho'?!)

I am pleased to say that much of my "disappointment" has faded.
I found that much of the damp (black mold) was more... "sweating"
beneath a (nice, but impermeable) interlocking rubber tile floor! ?

For the moment I have painted the floor with "penetrating wood
preserver" (see my remarks re. potential toxicity etc. elsewhere!).

However, the idea of breathable floor coverings intrigues!?! ?

In practice, I have become a bit more realistic about "perfection"?
Many old buildings stand for centuries with a bit o' damp / rust!! ?

[Oddsocks]

1 hour ago, Macavity said:

However, the idea of breathable floor coverings intrigues!?! ?

When my GRP Pulsar dome was installed (on a solid concrete base) I had the Pulsar supplied non-permeable plastic barrier sheet laid down below interlocking non-permeable interlocking tiles. After six months the observatory began to smell of damp and lifting the floor tiles and plastic sheet the entire floor was covered by a wet black mould, not a particularly healthy environment to spend any time in.

There were no leaks around the walls or ingress from the dome roof, it seems the water source was entirely through migration and evaporation through the concrete floor and being trapped by the plastic ground-sheet. Normal concrete is not entirely waterproof unless a waterproofing additive is mixed in when it is laid and without a waterproofer admix the concrete moisture level will just balance with surrounding ground so there will always be moisture migrating through the concrete floor.

In this case the non-breathable ground sheet and solid interlocking floor tiles was a mistake, just covering up a natural phenomenon and making it worse.

To solve the problem I got rid of the ground sheet and solid tiles, painted the floor with a concrete sealer paint used for garage floors and fitted foam rubber interlocking tiles with perforations (used for the surrounds of swimming pools, paddling pools etc. Since that was done last year the floor has remained perfectly dry, no more mould. The only issue that sometimes annoys is if you drop anything small it will disappear down one of the floor tile perforations and (usually) need half the tiles lifting before finding it again.

My old observatory, A Skyshed Pod, was built on raised timber decking. That had a wooden internal floor of plywood laid directly over a 'breathable' vapour barrier used for roofs. When the Skyshed was removed and the decking taken away I found the decking timbers below the vapour barrier had rotted quite badly. Talking to a roofer just a few weeks ago about replacing the vapour barrier in my house roof he said that permeable vapour barriers don't work if they are laid directly against a solid surface, obvious really, both sides of the barrier have to have free movement of air for vapour to be able to pass through. The discussion arose because when my house roof is rebuilt in the next couple of months I was looking at adding extra Celotex type insulation between the rafters rather than mineral wool laid between the beams but the roofer said he wouldn't recommend it in an old house with a slate roof like mine as water tends to condense on the outward side of the Celotex and the slate battens rot. Adding a vapour barrier between the Celotex and battens does nothing because there is no free air circulation on either side of the barrier. So, for the house roof at least, the old system of a breathable mineral wool insulation laid between the horizontal beams and a permeable vapour barrier laid beneath the slate battens with free movement of air on both sides of the barrier gives the best results.

Certainly a complex subject.

 

[Macavity]

6 hours ago, Oddsocks said:

Certainly a complex subject.

Seemingly so! Thank you for your detailed & useful answer! ?
(Had hoped that raising this might lead to such useful ideas)

The prevailing wind drives the rain very hard against one side
of my observatory, so I have become accustomed to modest
leaks... But it surprised me to discover the black mold under
the rubber tiles on the "dry" side too. Then I noticed this got
worse toward the centre of the tiles giving large black circles
on both the floor and underside of the tiles...  everywhere! ?

So now I know (better) hopefully? I spotted some of those
interlocking *perforated* tiles and did wonder... I may well 
give them a go! After cleaning/treating the floor, I decided
to "ditch" the old tiles. A bit of a shame, but "Black Mold"
is not fun stuff. I thought I had a "cold" coming on, but it
may well have been all the brushing... or spores liberated! ?