Browse Forums Owner Builder Forum Re: Non-standard (acrylic) 22Nov 03, 2020 5:44 pm alexp79 Mirrmu83 Thats incorrect, acrylic paint will form a film and not breathe. According to the laws of physics, every single substance can be vapour permeable (as it is just about allowing water vapour molecules to pass through the structure via diffusion, this is mainly what you refer as "breathable", although there are some other properties affecting overall breathability too). Even with exteremely resistant waterproof epoxy coatings, the process is still (slowly) taking place. The thinner the structure is, the more chances for water molecules to pass through. At only 120 microns of thickness, the vapour resistivity (literally defining the amount of water vapour passing through the material over certain amount of time) of a thin layer of outdoor emulsion paint will be MORE THAN TWICE lower than vapour resistivity of 100 mm of brick. For indoor emulsion paints it will be virtually insignificant as indoor paints have 5-10 times lower vapour resistivity than outdoor paints. What is more important is the point at where the vapour permeability becomes lower (such as installing OSB sheet to the outside of frame, so the framing remains exposed to the water vapour for extended periods while it is passing through OSB) and at some stage under certain conditions the frame timber starts to rot. If it is simply passing through brick, layer of render and paint (as it is doing anyway), it is certainly much less concern. How does this work for polyurethane coatings people put on timbers etc to repel water? It's basically adding a thin layer of plastic, and water won't get through. Similarly with solvent based paints, they are like putting glad wrap on the surface... Re: Non-standard (acrylic) 23Nov 03, 2020 6:19 pm Debunk alexp79 Mirrmu83 Thats incorrect, acrylic paint will form a film and not breathe. According to the laws of physics, every single substance can be vapour permeable (as it is just about allowing water vapour molecules to pass through the structure via diffusion, this is mainly what you refer as "breathable", although there are some other properties affecting overall breathability too). Even with exteremely resistant waterproof epoxy coatings, the process is still (slowly) taking place. The thinner the structure is, the more chances for water molecules to pass through. At only 120 microns of thickness, the vapour resistivity (literally defining the amount of water vapour passing through the material over certain amount of time) of a thin layer of outdoor emulsion paint will be MORE THAN TWICE lower than vapour resistivity of 100 mm of brick. For indoor emulsion paints it will be virtually insignificant as indoor paints have 5-10 times lower vapour resistivity than outdoor paints. What is more important is the point at where the vapour permeability becomes lower (such as installing OSB sheet to the outside of frame, so the framing remains exposed to the water vapour for extended periods while it is passing through OSB) and at some stage under certain conditions the frame timber starts to rot. If it is simply passing through brick, layer of render and paint (as it is doing anyway), it is certainly much less concern. How does this work for polyurethane coatings people put on timbers etc to repel water? It's basically adding a thin layer of plastic, and water won't get through. Similarly with solvent based paints, they are like putting glad wrap on the surface... Epoxy and rubber based coatings indeed have very high level of vapour resistivity (like 250,000-350,000 MNs/gm), although still finite. 120 micron layer of such coatings will be roughly 10-20 times more vapour resistant than outdoor emulsion paints and 4-8 times more water resistant than brick. Still not infinitely resistant, but more than enough to provide protection for the life of the building. Comparable vapour resistivity or even higher can be also provided with 50 mm of XPS, as well as any foil based insulations. Infinite resistivity can only be provided by metals, some plastics and asphalts. See below for reference. What is important in the end of a day is the Construction resistance. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Re: Non-standard (acrylic) "breathable" paints 24Dec 29, 2020 11:46 am Mirrmu83 Murobond has <10% acrylic polymer. See safety sheet. Film forming. Are you suggesting the lime mix as a basecoat or finish coat? Rockcote Lime Plaster is a finishing coat. long time between replies, I didn't get notifications of your comments theoretically lime (NHL2) can be used for all layers of your wall system - difference is based on the granular size of the prpduct you mix it with, and proportions. So base coat is a coarse sand, with lime. Main wall coat is a finer washed sand, with lime (forget the proportions). I managed to match - exactly - the original lime render of my 1927 house using local washed river sand. Skim coat should be - lime - mixed with a very very fine sand. OR gypsum. Problem is getting info on gypsum. CSR product is I believe not pure and their technical department cannot answer questions about it. Western Australia use this more regularly, they do double brick houses, but here in nsw its difficult to get good clear info Re: Non-standard (acrylic) "breathable" paints 25Dec 29, 2020 11:48 am Mirrmu83 I don't believe so. The problem is customers want to be able to choose from 3000+ colours like if selecting a Dulux or Taubmans colour. It just doesn't happen with "mineral" based products. So they introduce an acrylic system which can utilise typical paint tints. To achieve a breathable wall is very easy. Use sand, cement and lime renders. An admixture of boncrete at 1:10 can be used for water. Oxide is added for colour. If polystyrene blocks/cladding is used then breathability will reduce as more polymers are added to render to make it stick to polystyrene. Straw bale industry would be a good place to investigate. adding cement and bondcrete to your wall system will not make it breathable. Bondcrete is essentially plastic, and cement is not breathable Re: Non-standard (acrylic) "breathable" paints 26Dec 29, 2020 11:49 am Debunk Mirrmu83 I don't believe so. The problem is customers want to be able to choose from 3000+ colours like if selecting a Dulux or Taubmans colour. It just doesn't happen with "mineral" based products. So they introduce an acrylic system which can utilise typical paint tints. To achieve a breathable wall is very easy. Use sand, cement and lime renders. An admixture of boncrete at 1:10 can be used for water. Oxide is added for colour. If polystyrene blocks/cladding is used then breathability will reduce as more polymers are added to render to make it stick to polystyrene. Straw bale industry would be a good place to investigate. adding cement and bondcrete to your wall system will not make it breathable. Bondcrete is essentially plastic, and cement is not breathable agree strawbale industry is excellent place to go - the walls have to be 100% breathable The yellowing mainly occurs to white or very light colours. 1 2949 Hi Alex, Thanks for the reply again. I had a chat with the builder, he said he will use primer, then hydrotec which comes with colour and sealer as well. A Renderer I… 12 18099 Suggestions please for acrylic rendering Color to match austral brick urban one pepper. Pic for reference. Thanks 0 5071 |