Breathability of clay paints questioned.

[Flyfisher]

I think we're both saying the same basic things. I didn't think you were suggesting using "any old modern plastic emulsion on the inside walls or cover the external walls with cement" and I agree with your point about some modern paints being "good enough" in terms of breathability. I was just suggesting that we have more choices today and some of them are definitely not appropriate, so there is more chance of mistakes being made - as we frequently read about here. I also agree with you that 18th century builders would have used our modern materials had they been available at the time. I don't really subscribe to the view that the historic builders and craftsmen were somehow generally more knowledgeable and/or skillful than those of today and I'm sure if they had access to, say, cement then they'd have made exactly the same mistakes.

As for damp, I also agree with you. Perhaps I should have said that old houses were inherently susceptible to damp but it was managed by copious ventilation, as you describe. This of course is generally unacceptable today, for the reasons I mentioned among others, and presents another cause of conflict between the old and the new. Fact is, 'the good old days' might have been old but they were rarely as good as today (in the round) and except for the very privileged few the vast majority of people led very hard and uncomfortable lives. Nostalgia is a funny old thing.

 

[MikeG]

........ a combination of better ventilation (or poorer insulation depending on your point of view).........

This is a simple misunderstanding of the relationship between insulation and ventilation. It is perfectly possible to have great insulation and great ventilation, and indeed this is the basis of design decisions for modern buildings. This applies just as well to ancient buildings too. Insulation does not in any way restrict ventilation, with the one exception of through a timber suspended ground floor. In terms of air circulation, there is no reason not to insulate, and insulate well. I say again...insulation has no effect on ventilation.

 

[MatthewC]

I've got a wall where the original plaster had to be taken off before it fell off and I have used EPS insulation and gypsum plasterboard in its place. I know some people will react in horror at this, but EPS is breathable and so is gypsum

Is gypsum really breathable (whther plaster or plasterboard)?

 

[Lithgae]

Is gypsum really breathable (whther plaster or plasterboard)?

I've seen figures before that suggest gypsum is more breathable than lime plaster. I suspect that there is a misconception that gypsum is not breathable, because it so often goes hand in hand with modern impermeable paints. I think the real advantage that lime plaster has is that it seems to have the ability to soak up moisture, then release it without impact to its structure. Gypsum gets wet and it falls apart.

Like the discussion on paints, all of these building materials are breathable along a continuum. EPS is breathable but not as breathable as say wood fibre. Gypsum is more breathable than lime, but maybe not so much if it has been stuck together with PVA, and if you cover it all with impermeable paint it doesn't really matter whats underneath.

 

[Lithgae]

Insulation does not in any way restrict ventilation

Not sure that's completely true. In the sense that putting wall insulation on an already sealed wall then yes it wouldn't have any effect, but most of the time fitting insulation properly will result in sealing unwanted ventilation for example where the wall meets the floor. In fact if insulation is not sealed against air leakage it can defeat the purpose of insulation.

Air leakage and excessive ventilation are probably a bigger issue in old houses than insulation, and its usually a bigger win to seal against draughts than it is to insulate. Modern homes are designed with ventilation in mind, but thats because they are so airtight that the need to be deliberately ventilated. Most old houses will never be that airtight.

 

[Flyfisher]

........ a combination of better ventilation (or poorer insulation depending on your point of view).........

This is a simple misunderstanding of the relationship between insulation and ventilation. It is perfectly possible to have great insulation and great ventilation, and indeed this is the basis of design decisions for modern buildings. This applies just as well to ancient buildings too. Insulation does not in any way restrict ventilation, with the one exception of through a timber suspended ground floor. In terms of air circulation, there is no reason not to insulate, and insulate well. I say again...insulation has no effect on ventilation.

Quoted out of context (again?) :roll:

 

[MikeG]

The context doesn't alter the meaning in this case. At least, it doesn't as far as the reader is concerned. If I have misconstrued your meaning, then I apologise, but if I am commenting on a single simple point there seems little point quoting the entire post.

Incidentally, I take the rolly-eyed emoticon as the snidest and most unpleasant of them all. Again, if this wasn't your intended implication, you might want to have a look at what is perceived by the reader rather than what you think you're saying.

 

[Flyfisher]

If I have misconstrued your meaning, then I apologise

Accepted