I have high hopes. I think a talk on how to best manage hygroscopic salts in old walls and which plaster mixes are best would be key. Often, professionals vaguely advise to use 'lime' over the cement tanking option, and perhaps rightly so, but which lime and what mix? Will salt staining still occur in the new plaster and is this a 'failure', will it impact carbonation of the lime. Conversely, what actually happens when you tank the wall from salt perspective. I feel salt damp is really the main issue in older buildings due to its decay processes so would be a key topic area.
Great questions and topics, thank you. Some elements of this (the various life mixes) were covered in our Ben Kerslake episode. Dealing with salts is a great idea though so we’ll get a guest lined up to talk to that, thank you.
Hot mixed with brick dust at 1:3 dry applied hot with a minimum depth of 15-20mm, more salt requires more plaster. Finish it with a closed lime rich top coat. That plaster will trap the salt in its pores and still breathe well. It will, like any lime, needs replacing regularly as the salt builds up. For chimney breasts and/or to control sulfate staining you need to apply a hot mixed harled cow muck coat at 1:3 first. If you were to use a normal lime plaster then it will often fail as it absorbs the salt and then becomes unbreathable. The other issue to consider with this is to remember that once stone or brick has salt in it, drying it fully can cause similar spalling to frost due to the expansion of the dehydrated salt. So keeping it slightly damp can actually be beneficial and often by original design. And no salt staining will happen this way. If you want to be more thorough you'd use poultices to remove the salt first but that would be for scenarios which have a finite amount of salt, like wall bases which have absorbed the salt from concrete gauging water when floors were replaced. Basements and retaining walls which are persistently subject to water ingress you'd keep damp at the back using the method described above. I go into more detail on my website; limemason.com
I have high hopes. I think a talk on how to best manage hygroscopic salts in old walls and which plaster mixes are best would be key. Often, professionals vaguely advise to use 'lime' over the cement tanking option, and perhaps rightly so, but which lime and what mix? Will salt staining still occur in the new plaster and is this a 'failure', will it impact carbonation of the lime. Conversely, what actually happens when you tank the wall from salt perspective. I feel salt damp is really the main issue in older buildings due to its decay processes so would be a key topic area.
Great questions and topics, thank you. Some elements of this (the various life mixes) were covered in our Ben Kerslake episode. Dealing with salts is a great idea though so we’ll get a guest lined up to talk to that, thank you.
Thanks @@talkingconservation
Hot mixed with brick dust at 1:3 dry applied hot with a minimum depth of 15-20mm, more salt requires more plaster. Finish it with a closed lime rich top coat. That plaster will trap the salt in its pores and still breathe well. It will, like any lime, needs replacing regularly as the salt builds up. For chimney breasts and/or to control sulfate staining you need to apply a hot mixed harled cow muck coat at 1:3 first. If you were to use a normal lime plaster then it will often fail as it absorbs the salt and then becomes unbreathable. The other issue to consider with this is to remember that once stone or brick has salt in it, drying it fully can cause similar spalling to frost due to the expansion of the dehydrated salt. So keeping it slightly damp can actually be beneficial and often by original design. And no salt staining will happen this way. If you want to be more thorough you'd use poultices to remove the salt first but that would be for scenarios which have a finite amount of salt, like wall bases which have absorbed the salt from concrete gauging water when floors were replaced. Basements and retaining walls which are persistently subject to water ingress you'd keep damp at the back using the method described above. I go into more detail on my website; limemason.com