Discussion in 'The Pit Stop - General Paint Trade Discussion.' started by Pars Painter, Jul 20, 2017.
Does anyone know if 123 is microporous?
Was speaking quite some years ago to a chap in Zin tech and he was firmly of the opinion that microporous was as much use to real life as rocking horse shxt
I Would probably agree with you there Barry, but I'm doing a spec for a big sash and case job and it all needs to be microporous so I just want to make sure. The zinsser website lists 123 plus as microporous but doesn't say whether the normal 123 is or not. I've used 123 as an exterior undercoat for ages and it's always been superb.
Would like to point out as this thread re-opened, microporous is not the same as moisture vapour permeable. It is often mis-interpretated.
Microporous acts as a liquid barrier but still allowing air to travel through, while permeable let's both gas and liquid through.. Is that correct..
Microporous allows moisture etc.. to pass both ways. Mvp only allows vapour out from substrate ( not excessive moisture). Not sure about gases etc as i wouldn't use a full mvp system over plastic, mdf etc. internally. Mvp systems are developed for external paints.
I'm 99% sure on this. May need a bit of a tweek from a paint tech.
As with all written comments, please do research before quoting me.
I am pretty much 100% sure the source you used or your memory of the source is not quite right. If water vapour can go one way it can go the other. The original source might have indicated that water in its liquid phase cannot go through to the wood whilst water vapour can be released from the wood in the right conditions.
Interestingly if you can make a material which allows water vapour to just pass one way you can break the first law of thermodynamics. A balloon coated in that vapour barrier will inflate in a damp environment with water vapour which can go in but cannot leave. You can use the inflation of the balloon to do work such as lift a weight placed on the top of the balloon, and then you can use the raised weight to generate heat by numerous means as it falls back to earth such as rope friction. So you have created heat out of a stable closed system which is not allowed. Hence I am pretty much 100% sure your source or memory of the one way water vapour barrier is wrong as it would be quite famous in the world of science.
@Puma. You may well be correct. I was working from memory, hence the reason that my quote should be researched before quoting. Microporous coatings will allow moisture to pass in liquid state sometimes in excessive amounts leading to possible premature decay. Mvp will allow moisture in its gaseous state (vapour) to pass through.
I am no paint chemist but from what I have been told in the past microporous paint only lets a very very very small amount of water vapour through and it seems to be a marketing ploy for paint systems to last over damp wood!