# Interior Plaster Over Adobe Repair



## ClarenceBauer (Mar 4, 2005)

oggy bleacher said:


> I'm wondering how to remove all the loose dirt and plaster from a wall that is comprised _only _of loose dirt and loose plaster? The more I dig the looser it gets.
> 
> The wall is almost 100 years old adobe brick, covered with a coarse plaster..there isn't any lath or mesh. It's just adobe covered with plaster and then a skim coat that's also crumbling at the bottom 16 inches.
> 
> ...


Your only repair mortar should be the same mortar as the existing bricks were made of. Any modern mortars will cause a very rapid failure of the original brick & mortar. Adobe brick were made of loamy soil & sand also some had dung added & dried in the sun. You can make a suitable mortar using the soil with Quick Lime added this should match the existing very close.
In the last photo I see what looks like Grey Portland or a type n mortar mix has been used if that mortar has been in place you will mostly see a failure around it. You do NOT want to use any mortar that is dense it must be sandy. Check out Rammed Earth mixture it should be a good repair mortar. Do not use any Portland in any of your mixes.


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## oggy bleacher (May 3, 2011)

Thanks for the advice. The adobe bricks are encased in the top layer of what looks like plaster and it's the plaster that I'm trying to repair. I think that grey patch is stucco but it might be quickrete...since it came out as hard as concrete. I'll look for some quicklime. Will Type S Lime work? Mixed with soil?
.
is there a method of getting the mixture to bond? I got some long wire to make long staples to hold a mesh since I suspect any mixture will just break more soil off. Or is the idea to wet the wall surface and then replicate the coat material so they dry together and bond that way?


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## ClarenceBauer (Mar 4, 2005)

oggy bleacher said:


> Thanks for the advice. The adobe bricks are encased in the top layer of what looks like plaster and it's the plaster that I'm trying to repair. I think that grey patch is stucco but it might be quickrete...since it came out as hard as concrete. I'll look for some quicklime. Will Type S Lime work? Mixed with soil?
> .
> is there a method of getting the mixture to bond? I got some long wire to make long staples to hold a mesh since I suspect any mixture will just break more soil off. Or is the idea to wet the wall surface and then replicate the coat material so they dry together and bond that way?


If the Plaster is not the same mix as the Adobe bricks are made of it can & will cause a breakdown of the Brick. Do you think the Plaster coating over the Adobe Brick is as old as the the Brick. Anything placed over the Adobe that has a different denser make up will be a problem as any moisture must migrate thru the wall at the same rate. If the moisture is slowed down by the dense coating it causes problems. I would think wetting the existing Adobe before the new mortar is placed is a very good idea. Also DO NOT let the repair mortar air dry it must be keep damp so that it re-carbonates. Limes set by absorbing CO2.
If you can not find Quick Lime you can use a type S but for the best results you should SLACK it before use. Keep in mind if you Slack the Lime and are using a dry volume mix ratio measure the lime before Slacking as the volume will change from dry to wet. I would thing the Staples would be a good idea. Have you an Archive office in your area that would have info on Adobe construction in the area?


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## oggy bleacher (May 3, 2011)

I think the coarse mortar coat is the original. it's super crumbly at the bottom 16''. the rest of the wall feels like it is still bonded (doesn't sound hollow when I knock on it) but having that bottom 16 underground has caused some problems although now the dirt berm probably helps keep monsoon rain water that runs down this alley away from the foundation. I'm not sure the alley was there when the house was built so when they made the alley it led to more run-off and the owner decided to make a berm to direct rain down the alley away from the foundation. That's one explanation, and why I'm not excavating the foundation.

the house is old and the neighborhood is on the historic register, so the city archive might have some documentation on how this was done. from what I've learned it's a 1930s Sonoran row house that never grew beyond a single small house.


I found one video that gives me an idea about how to proceed. It looks like their final product is in the ballpark of what I have. It's confusing that you refer to this as mortar but it's used as a coat for a wall, and not for a rock wall. I've always thought as mortar as a wall building material, not as a surface for a wall.

I see what you mean about a surface that dries the same rate as the adobe.
The layer of mortar coat is an inch thick.









On the topic of plaster, another interior wall has a kind of plaster on it with no lath or mesh. for instance, under the door trim. Have you seen this before? this plaster is not crumbly. it's more like concrete. none of this plaster looks like any modern plaster so I'm not sure how to repair it. so my plan is to just cover it with the trim.


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## ClarenceBauer (Mar 4, 2005)

oggy bleacher said:


> I think the coarse mortar coat is the original. it's super crumbly at the bottom 16''. the rest of the wall feels like it is still bonded (doesn't sound hollow when I knock on it) but having that bottom 16 underground has caused some problems although now the dirt berm probably helps keep monsoon rain water that runs down this alley away from the foundation. I'm not sure the alley was there when the house was built so when they made the alley it led to more run-off and the owner decided to make a berm to direct rain down the alley away from the foundation. That's one explanation, and why I'm not excavating the foundation.
> 
> the house is old and the neighborhood is on the historic register, so the city archive might have some documentation on how this was done. from what I've learned it's a 1930s Sonoran row house that never grew beyond a single small house.
> 
> ...


Mortar is a term used in the Plaster , Stucco & Masonry trade it is used to cover walls, ceilings & Jointing Materials sometimes also referred to as Mud.


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## ClarenceBauer (Mar 4, 2005)

ClarenceBauer said:


> Mortar is a term used in the Plaster , Stucco & Masonry trade it is used to cover walls, ceilings & Jointing Materials sometimes also referred to as Mud.


All of my post was not included so I will try again.
The video is a good one but I think you can do better using a dry mixing paddle & a contained to mix in.
Before you do any repairs check with this company.
ProSoCo, Inc. Kansas City, 800-255-4255 & ask about using OH Stone Strengthener I have used it on soft brick & it worked very well BUT have never used it on Adobe.
Also call the National Park Service , Preservation Assistance they will be glade to help you & can also provide you with info on who has more info on Adobe in your location. As for the hard plaster around the door it looks like someone used a Perlite Plaster which would be very hard. Yes water is your biggest problem keep in mind that water / moisture will migrate to the lowest point & cause most of the damage @ the bottom.


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## oggy bleacher (May 3, 2011)

I actually work for the NPS facility maintenance and their preservation documents are indeed good. they are all available online.

I'm going to refine this by trial and error

I made a pure lime putty, mixed in sand about 3:1 sand/lime ratio, until I had a plaster consistency and made some repairs. The area is small enough to make a few attempts if I have some failures. there are multiple videos of lime plaster on rock, brick pointing, interior walls, expanded mesh. cob, straw, etc. So, this approach looks right. 

I''ll stop at these areas and keep them damp for a day and let it dry fully to get an idea of what the final product is.

It looks like there is a final top coat that mostly is still attached, but I'm wondering if the latex paint itself isn't a good idea if I want the wall to breath. wouldn't a lime wash be more permeable? or a top coat of fine sand/lime and just leave it unpainted. I don't see how paint will be permeable.

I


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## ClarenceBauer (Mar 4, 2005)

oggy bleacher said:


> I actually work for the NPS facility maintenance and their preservation documents are indeed good. they are all available online.
> 
> I'm going to refine this by trial and error
> 
> ...


You are headed in the right direction.
Yes a Lime wash will be much better also you can tint the Lime wash.
You can also use a mineral coating which is Lime look up Cathedral Stone for info on Mineral Coatings.


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## oggy bleacher (May 3, 2011)

I had to demo part of the bathroom to expose the electrical wires. The previous method of fixing the plaster was to glue drywall to it, and when the drywall got moldy, they screwed on _another _layer of drywall. This all molded when the roof leaked and I couldn't do much except tear off the drywall and the plaster came off in a big chunk. the plaster is 3'' thick and the wall is not actually adobe brick, as much as brick sized areas of mud or dirt with a mortar joint 12'' thick. this must be an economy adobe method.








I'm not tackling this immediately since I'm replacing a wiring circuit but since the plaster has mostly detached from the wall I don't see any quick patch repairs lasting very long. The old plaster will probably fall off no matter what I do so I think I will take all the plaster off that area and try my best to replace at least 2'' of the plaster. I've struggled to patch 1'' of plaster without cracking since it is so dry right now, so I don't know what to think of rebuilding a 3'' plaster wall. Do I go in 1'' layers? The original plaster looks like a 3'' thick single layer.

as plaster tradesmen left this area the local handymen had no real strategy to deal with this wall. but they would've been better off doing nothing than gluing drywall to it.








I hurled a lime slurry on the dirt to try to keep it stable while I work on other things.









I did get some powder tint to experiment with the other wall. limewash is a little chalky to touch. I've read it can be sealed with wax but that sounds like it will trap moisture.


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## ClarenceBauer (Mar 4, 2005)

oggy bleacher said:


> I had to demo part of the bathroom to expose the electrical wires. The previous method of fixing the plaster was to glue drywall to it, and when the drywall got moldy, they screwed on _another _layer of drywall. This all molded when the roof leaked and I couldn't do much except tear off the drywall and the plaster came off in a big chunk. the plaster is 3'' thick and the wall is not actually adobe brick, as much as brick sized areas of mud or dirt with a mortar joint 12'' thick. this must be an economy adobe method.
> View attachment 630417
> 
> I'm not tackling this immediately since I'm replacing a wiring circuit but since the plaster has mostly detached from the wall I don't see any quick patch repairs lasting very long. The old plaster will probably fall off no matter what I do so I think I will take all the plaster off that area and try my best to replace at least 2'' of the plaster. I've struggled to patch 1'' of plaster without cracking since it is so dry right now, so I don't know what to think of rebuilding a 3'' plaster wall. Do I go in 1'' layers? The original plaster looks like a 3'' thick single layer.
> ...


I would try the following.
Mix the Clay & Lime mixture @ 3 parts Clay & 1 part Lime mix to a workable consistency than add about three double hand Full of USG Structo-Lite Perlite Plaster.
This should allow you to build out & have a better binder for a thicker application.


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## oggy bleacher (May 3, 2011)

I've hunted for structo-lite plaster and its only available as an order by the pallet. An old timer at a masonry supply store said my wall sample looked like an adobe scratch coat that was once sold in bags but I didn't find anything locally that was related to adobe or had perlite in it and most products looked like they had Portland cement included. I wonder if a handful of one of those Rapid Set products added to the lime/sand mixture would cause trouble or provide more strength.

looking at the one wall that I repaired I think the lime/sand mixture is good enough for the big patches and will have to be good enough to build a thick wall surface in the bathroom. I'm not really trying to "restore" the wall, although I'm curious what material they used in 1940. I'm looking for the appropriate modern material to rebuild the wall surface and it looks like the lime and sand mixture that I'm using is already the best choice. 

the sand is probably the biggest difference because I bought play sand and it is too regular compared to what was original. I think I should be using sharp sand or sand with irregular sizes and it's not really available here and my lawn is not sand.

the pictures below are the only products I could find.


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## ClarenceBauer (Mar 4, 2005)

oggy bleacher said:


> I've hunted for structo-lite plaster and its only available as an order by the pallet. An old timer at a masonry supply store said my wall sample looked like an adobe scratch coat that was once sold in bags but I didn't find anything locally that was related to adobe or had perlite in it and most products looked like they had Portland cement included. I wonder if a handful of one of those Rapid Set products added to the lime/sand mixture would cause trouble or provide more strength.
> 
> looking at the one wall that I repaired I think the lime/sand mixture is good enough for the big patches and will have to be good enough to build a thick wall surface in the bathroom. I'm not really trying to "restore" the wall, although I'm curious what material they used in 1940. I'm looking for the appropriate modern material to rebuild the wall surface and it looks like the lime and sand mixture that I'm using is already the best choice.
> 
> ...


Ok lets try another route. See if you can locate one of these products.
Crushed Oyster shells.
Bocce oyster shell mix.
Brick dust / aggregate.
Marble dust / aggregate.
Pozzolans.
By adding one of the above to your clay / sand & Lime mixture will cause it to have some what of a setting or hydrating action.
Also see if the Parex suppler in your area can get NHL (natural hyd. lime) look for NHL2 mix this with your sand or you could get it premixed & add more sand which will lower the psi.
Last yes you could use a small amount of cement along with the sand& Lime if you go this route use White Cement.


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## oggy bleacher (May 3, 2011)

one hardware store had perlite in the garden dept. Maybe I could drive my truck over the bag and create some finer material to add. I also have some quickrete Mortar mix and stucco patch and plaster powder and plaster putty. I experiment on my cinder bock wall with some combinations and the mortar mix really hardens the plaster to rock. Tucson has a Parex distributor if it comes to that.

It's funny, I went to home depot and asked for mortar options over adobe and they tell me to furr the wall out with 1x2'' and put drywall over it. 😕 I get that covering old plaster with drywall is an accepted method but the small areas I'm dealing with is manageable to just repair the plaster and try to recapture some of the old charm this house had. The entire plaster surface that I would repair is about 20' x 7'. 140 square feet of plaster that really should remain plaster since it contacts dirt. Is that excessive? The previous owner furred out every single wall and put drywall over it. two layers of drywall in the bathroom, and not drywall rated for moisture areas either. sheesh. One room probably lost 12 inches of floor space because all 4 walls are furred out 3''. Because they didn't want to repair the plaster? But covering it with drywall just hid the crumbling dirt walls! and the walls are still crumbling and now I can't get to them. puzzling. I don't even like drywall.


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## ClarenceBauer (Mar 4, 2005)

oggy bleacher said:


> one hardware store had perlite in the garden dept. Maybe I could drive my truck over the bag and create some finer material to add. I also have some quickrete Mortar mix and stucco patch and plaster powder and plaster putty. I experiment on my cinder bock wall with some combinations and the mortar mix really hardens the plaster to rock. Tucson has a Parex distributor if it comes to that.
> 
> It's funny, I went to home depot and asked for mortar options over adobe and they tell me to furr the wall out with 1x2'' and put drywall over it. 😕 I get that covering old plaster with drywall is an accepted method but the small areas I'm dealing with is manageable to just repair the plaster and try to recapture some of the old charm this house had. The entire plaster surface that I would repair is about 20' x 7'. 140 square feet of plaster that really should remain plaster since it contacts dirt. Is that excessive? The previous owner furred out every single wall and put drywall over it. two layers of drywall in the bathroom, and not drywall rated for moisture areas either. sheesh. One room probably lost 12 inches of floor space because all 4 walls are furred out 3''. Because they didn't want to repair the plaster? But covering it with drywall just hid the crumbling dirt walls! and the walls are still crumbling and now I can't get to them. puzzling. I don't even like drywall.
> View attachment 630981


Do not use the perlite from the big box store garden shop it does NOT contain GYPSUM.
As for covering the Adobe with drywall will cause failure of the Adobe over a long period of time.
Being you cannot get the materials you need local. use the shape sand with Lime mix the Lime & sand with water to a loose workability tan cover a let sit for about 3 days or longer than add the White cement. For your mix ratio one & one half 5 gallon pail = one cubic foot of material.
So use one pail of dry sharp sand & one half pail of slack lime add water than let set.
When ready to use add the White cement I would use about one double handful in each mix.


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## ClarenceBauer (Mar 4, 2005)

ClarenceBauer said:


> Do not use the perlite from the big box store garden shop it does NOT contain GYPSUM.
> As for covering the Adobe with drywall will cause failure of the Adobe over a long period of time.
> Being you cannot get the materials you need local. use the shape sand with Lime mix the Lime & sand with water to a loose workability tan cover a let sit for about 3 days or longer than add the White cement. For your mix ratio one & one half 5 gallon pail = one cubic foot of material.
> So use one pail of dry sharp sand & one half pail of slack lime add water than let set.
> When ready to use add the White cement I would use about one double handful in each mix.








HEMPCRETE – Carbon Smart Materials Palette







materialspalette.org




Just came across this material take a look at it sounds very interesting & the psi from what I found is as low as 75 psi & high of 508 psi.


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## oggy bleacher (May 3, 2011)

hempcrete. I would use that. cool product.
I embedded some rock at the bottom of the plaster. and got some expanded lath. I'm making more slack lime. I need to stabilize the plaster because with the bottom 6'' not touching the floor I don't think the plaster is held up by anything more than friction.


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## ClarenceBauer (Mar 4, 2005)

oggy bleacher said:


> hempcrete. I would use that. cool product.
> I embedded some rock at the bottom of the plaster. and got some expanded lath. I'm making more slack lime. I need to stabilize the plaster because with the bottom 6'' not touching the floor I don't think the plaster is held up by anything more than friction.
> View attachment 631051
> View attachment 631052
> View attachment 631053





oggy bleacher said:


> hempcrete. I would use that. cool product.
> I embedded some rock at the bottom of the plaster. and got some expanded lath. I'm making more slack lime. I need to stabilize the plaster because with the bottom 6'' not touching the floor I don't think the plaster is held up by anything more than friction.
> View attachment 631051
> View attachment 631052
> View attachment 631053


Question why does the mortar look pink?


oggy bleacher said:


> hempcrete. I would use that. cool product.
> I embedded some rock at the bottom of the plaster. and got some expanded lath. I'm making more slack lime. I need to stabilize the plaster because with the bottom 6'' not touching the floor I don't think the plaster is held up by anything more than friction.
> View attachment 631051
> View attachment 631052
> View attachment 631053


Question why does the mortar look pink?


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## oggy bleacher (May 3, 2011)

I tinted it. which was dumb since I want the bathroom white.


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## ClarenceBauer (Mar 4, 2005)

oggy bleacher said:


> I tinted it. which was dumb since I want the bathroom white.


You should check into this product for your finish.
American Clay
They make plaster products & they have one that is made of clay & lime. It has been about 15 years since I have used any of this product.
Also look into this product for your finish Master of Plaster & just use the base coat as a finish you can trowel this base material smoother than any drywall finish & no sanding is required.


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## oggy bleacher (May 3, 2011)

those are nice products. there's a valley nearby where dozens of santa fe style houses are being built, clay tile roofs and parapet roofs, stucco, etc. so there must be material like this for sale.


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## oggy bleacher (May 3, 2011)

Shop eco stucco



here are some other products I saw mentioned in some plaster videos.





.

I don't think Tadelakt falls into the DIY category since it involved 4 separate layers and maybe 5 coats expertly applied, but the black soap might be the approach I use instead of paint. I already have a plaster over the wall so maybe black soap applied to the existing plaster will penetrate and waterproof it.

The dream bathroom would be a walk-in tadelakt shower but the bathroom I want for the near future is a $65 glue up shower wall.


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## ClarenceBauer (Mar 4, 2005)

oggy bleacher said:


> Shop eco stucco
> 
> 
> 
> ...


Tadelakt is NOT a DIY project it is very high $$$$ also requires some high class rubbing rocks.
You could use Aqua wax in place of the black soap.


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## oggy bleacher (May 3, 2011)

I have a habit of either procrastinating forever or finishing a job as fast as possible but a little sloppy. I chose the latter for this project.
I mixed mortar with the plaster around the rocks.
then I mixed plaster of paris powder with the limewash.
I also used concrete bonding agent with both and that helped it all stick. of course scraping and washing the walls was important since there was old latex paint on the old plaster. I did experiment with car wax to see if it reduces the amount of chalk that rubs off the lime wash.
I'm going to let nature take its course before I do any more work on these walls. I need some idea of how long lime plaster really lasts. If it stays like this I will be satisfied.
I think my options for an interior earth wall are limited to custom lime plaster but I think the original plaster is some kind of structo-lite plaster basecoat with a veneer coat. I did identify lime in the original plaster by putting vinegar on it, but it looks so uniform I think it was from a bag. It might even be the same basecoat they used for the exterior.
It failed mostly because the roof leaked badly for years and the plaster is 80 years old with no lath.
I would definitely experiment with structo-lite or a stucco base coat if I didn't want to custom mix lime and sand.

thanks for the help.


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## ClarenceBauer (Mar 4, 2005)

oggy bleacher said:


> I have a habit of either procrastinating forever or finishing a job as fast as possible but a little sloppy. I chose the latter for this project.
> I mixed mortar with the plaster around the rocks.
> then I mixed plaster of paris powder with the limewash.
> I also used concrete bonding agent with both and that helped it all stick. of course scraping and washing the walls was important since there was old latex paint on the old plaster. I did experiment with car wax to see if it reduces the amount of chalk that rubs off the lime wash.
> ...


As to the question of how long Plaster will last.
There are three things that are detrimental to Plaster.
Fire it turn it back into a powder.
Water causes the Lime, Gypsum & sand to separate due to migration.
Man causes damage like demo, use of the wrong materials, neglect & improper use of materials.
Plaster is one of the oldest building materials still used to this date.
The oldest building I have worked on in relation to Plaster is 1700 still in service at this time.


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## cavenewt (Apr 25, 2021)

oggy bleacher said:


> I'm wondering if the latex paint itself isn't a good idea if I want the wall to breath. wouldn't a lime wash be more permeable? or a top coat of fine sand/lime and just leave it unpainted. I don't see how paint will be permeable.


You're right, latex paint is not a good idea. You've had a lot of good advice; another source would be the strawbale building community. I'm currently building a strawbale house with clay plaster walls and floors, so I've been researching alternative finishes.


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## ClarenceBauer (Mar 4, 2005)

cavenewt said:


> You're right, latex paint is not a good idea. You've had a lot of good advice; another source would be the strawbale building community. I'm currently building a strawbale house with clay plaster walls and floors, so I've been researching alternative finishes.


Look at the Mineral Coatings you can find them @ the following:
Keim
Beeck
Cathedral Stone
American Clay


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## sunmtnforge (4 mo ago)

ClarenceBauer said:


> Your only repair mortar should be the same mortar as the existing bricks were made of. Any modern mortars will cause a very rapid failure of the original brick & mortar. Adobe brick were made of loamy soil & sand also some had dung added & dried in the sun. You can make a suitable mortar using the soil with Quick Lime added this should match the existing very close.
> In the last photo I see what looks like Grey Portland or a type n mortar mix has been used if that mortar has been in place you will mostly see a failure around it. You do NOT want to use any mortar that is dense it must be sandy. Check out Rammed Earth mixture it should be a good repair mortar. Do not use any Portland in any of your mixes.


I am wondering How much lime to use in proportion to local dry sandy soil-I have a lot of lime putty and prefer that to the dry hot lime


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