Does anyone out there have a good figure for coverage of lime plaster?

Specifically, how much square footage of wall could I cover with 50 lbs of hydrated lime (powder) at 1/2" and 3/4" thicknesses?

Hello DL

You know you have a very good question but being one that has wrestled with such questions in the past I will try and give you some guidance

The old text books give you formulas and coverage guides for slacked lime mixtures but unfortunately I do not have one of these texts at hand so in that regard I suggest the following:

Mix up a weighed batch of say5 lbs, and then on a flat surface apply it and you will have a close evaluaion of the coverage

You should build up the layers in stages to reach the finished thickness, putting on a base or rough coat , then a scratch coat, and then the finished coat

I suspect that you are mixing in some sand if it is a base mixture or rough coat, but if it is a finish coat then you will just be applying a lime only mixture

I personally don't not know how well hydrated lime will work so you will have to experiment

At UCV we did use hydrated lime, sand mixture to lay a stone foundation for a smoke house, and it seemed to work well

I do suggest using a very small amount of white portland cement just to ensure the proper hardness of the finished surface, there again I suggest some experimentation is in order, do not overdo this step but use caution.

hope this helps

NH

NH,

I have used it before. But just on repairs on our house. I never really bothered to measure the coverage. I also used it to make a bread oven, made of dry stacked bricks and sealed with plaster.

So I am aware of the need to build it up in layers.

But here I am making a room of certain dimensions, and for figuring costs I need to know how much plaster it will take to cover the walls and ceiling.

My plan is to have a base coat, at least one build coat with the final build coat given a wet sponge rub to make it even -this also gives it a grainy texture. It will then be finished with a lime wash to make it smooth, because this will be a comercial cheesemaking room and Indiana law requires that such facilities have smooth walls that are easily cleaned. I chose to go with lime plaster for its antibacterial properties.

I will try a test patch to estimate coverage, that is a good idea. I have some old plaster I can use. Hydrated lime works well, provided you use it quickly. It will break down over time once exposed to air and no longer make good plaster.

For Hydrated lime, I use a 3:1 ratio of sand to lime, mixed on a board with a shovel.

Have you seen/read "using natural finishes" by weismann and bryce. I've read a bit lately, and particularly like this one. Its borrowed, but worth buying. What you applying it over. I been increasingly interested in this lime and earth plasters, since with used clay finish on our walls in an addition. the book mentions:@ lime aggregate coverage- scratch 5gal. to 2.5msq thickness 10mm; straight coat-5gal. to 4msq at 6mm thick; finish 5gal. to 6msq at 3mm thick.

Brandon

The frame will be 2' OC studs (it will support no structural loads) with lath on the inside. The plaster will probably go directly on this lath, but I may have a clay base with a plaster finish instead (a lot cheaper to do myself, even if it does take more work) This mostly depends on whether or not I can dig up suitable loam nearby.

also, I have plenty of manure available, and may use such a mixture for the undercoat. BUT since this is to be a commercial cheese operation, I doubt I will go down that road...

Mortar volume equals sand volume.

An ideal mortar mix has a lime volume equal to the space between the grains of sand, so to meassure the space, place a known volume of dry sand in a bucket and add meassured water until the water level reaches the top of the sand. Then calculate sand to lime ratio.

Calculate area of walls to be plastered then multiply by thickness of plaster equals volume of mortar. Apply a fudge factor to avoid shortfall. Plaster volume equals sand volume. Apply sand/lime ratio for amount of lime needed.

To account for squeeze through and formation of the keys add at least 1/8" over plaster layer thickness.

Through a lot of figuring and searching, and with the suggestions made for figuring, I have figured that to cover 560 square feet, I need about 63 cubic feet of plaster, so about 21 cubic feet of lime...
then figuring based on a figure I found for 30 pounds per cubic foot of hydrated lime, I figured I will need 620 pounds of lime, which comes in 50 pound bags so I need to buy 13 bags of lime. By Roger's suggestion, this will yield a plaster thickness of about 5/8" (I used 3/4" for my figures)

And if I go with a clay wall with a plaster finish, then I will only need 4 bags of lime

1 50# bag of hydrated lime, according to these figures, can cover 45 square feet of wall with a finished thickness of 5/8". This seems to be pretty accurate based on past experience using this.

Hi DL

Recheck some numbers. At 3/4", 16 sq ft of coverage per cubic ft or a total of 35 cu. ft. of mortar for the project.

DL

After reading the postings on this subject, I offer the following to further cloud the picture. If you find that this is too much information ......... I apologize ahead of time. I have found that when a health department requires wall surfaces to be easily cleaned they mean that it should be smooth enough to be wiped down like a hard tile surface. I don't think the lime washed, sand float finish you are contemplating will give you that but a smooth, hard-troweled finish will.

Wood lath over studs spaced at 24" o.c. should probably be no less than 3/8" thick with a 1/4" - 3/8" gap, depending upon the size of your aggregate and the type of fiber that is in the base/scratch coat. For a lime scratch coat that would most likely be hair, hemp or even chopped straw.

I would not recommend that you use a clay based scratch coat in your plaster system. To get the best bond possible between the lime finish and the clay base requires several layers of plaster of different combinations with the clay and lime. Probably more work than the overall job warrants. I'd suggest you consider a 3-coat lime plaster with an overall thickness of 5/8" - 3/4".

Plaster work is a little different than mortar work in that the hydrated lime actually needs to be mixed with water (lime into water) and soaked for a length of time to allow it to full absorb all of the water it can. Allow it to soak in a covered container from 1 to 3 weeks. During this time the lime particles will settle to the bottom and form a putty with a consistency that approaches cream cheese. As long as you keep the putty away from air and under water it will last indefinitely. Lime putty, like wine, gets better with age. A 50 lb. bag of hydrated lime mixed with about 10 gallons of water will yield about 8 gallons of lime putty. Those 8 gallons of putty can be used in the following mixes.

Scratch Coat - 50 sf of coverage @ 3/8" - 1/2" thickness mixed at a ratio of 1 part lime putty to 2 - 2 1/2 parts aggregate and fiber added.
Brown Coat - 62 sf of coverage @ 3/8" thickness mixed at a ratio of 1:1.75 - 2
Finish Coat - 180 sf of coverage @ 1/8" thickness mixed at a ratio of 1:1 - 1.5

Aggregate gradation is based upon the thickness of the plaster coat that is being prepared. If your project will not allow the time needed for the lime to properly carbonize and cure out then gauging it with white cement is always an option.

The information here is based upon my work with both clay and lime plasters that I am called upon to provide from time to time. I hope it is helpful.

thanks, great info

the sand float won't be the topcoat. I do that on the middle coat because I found that it effectively removes any wave that may have formed, making the top coat that much easier to apply.

And I do know about soaking it too. It is not actually 100% necessary, but it is definitely worth it. The lime will work if you just mix it straight into the sand with water, but won't work as well.

Thanks for the info about clay too.

But what I was considering is more or less a clay undercoat, an outer coat with a little lime mixed in for hardness, a a limewash or whitewash finish. So it would technically be a clay wall altogether.

will there be insulation in the wall? I've been wondering how the moisture/vapor barrier issues with more conventional insulation batt or cellulose with lime or clay wall finishes. I understand (or think so) the mediating affects of these finishes, but it has been more in the context of some other clay based interior wall system/ insulation. In addition, vapor not being good for these breathable systems. any light
Brandon

the hydrated lime you speak of, is this a NHL grade, or just standard construction grade hydrated lime?
Brandon

DL

Sounds like you've got a good plan. Just to be safe though .......... I'd prepare a sample of the wall plaster with the finish you plan to use and show it to a health inspector for their approval before getting too far along with the room.

Heavy

I believe DL is referring to standard Type 'S' hydrated lime.

Yes, Type 'S' lime, manufactured and sold as a mortar reinforcer, but what it really is is partially slaked quicklime.

As far as health inspection...

In the good old State of Indiana, regulations are wonderfully loose. And Howard county inspection is all but non existent.
For example, recently in the nearby city of Kokomo we fixed up a small stand that is used as one of those drive through drink deals (drive through diabetes). It was built up on a parking lot, and so had no way of handling drainage very well. So as a result, the bottom was rotting away. So inside the bottoms of the studs and sheathing were full of rot fungus, and the bottom 2 feet of wall was colonized with good old black mold (yum).

Most places in the US would have declared this place unfit, and destroyed it. But good old Indiana laid-back policy means we could repair it instead. So the solution? We replaced the entire bottom 3 feet or so of the structure. When the city inspector came by, who is both building and health inspector, we more or less told him what we did and he said it was good. He's a great guy, we needed to move a gigantic ice machine out of our way, so he took me down underneath the city building to pick up a tool do lift and move very heavy things.

But that said, I still do want to make things to meet and exceed the standards.

The cheese that is being processed is whey cultured and raw milk. While there are no explicitly stricter requirements regarding sanitation for this I want to have a very sanitary environment for the purposes of quality control.
Cheese is cultured by bacteria, yeast, and molds. They will define its flavor. If unwanted bacteria gets into the mix, it may not be harmful to your health but it will harm the quality of your cheese.
Furthermore, my culturing method is to follow the traditional practice of holding over whey from the previous batch to introduce bacteria into the next batch. This means that if a batch is ruined by contamination, so is my culture. So you see how very important sanitation is. This method is a lot riskier than using packaged starter cultures, but it results in a richer, better and more complex cheese.

Also,

We will be aging and maturing our cheese in an unsealed basement, because the humidity and temperature are consistent year round, and are right on where they need to be (quite a bit like a natural cave, which is the ideal environment)

But for sanitation reasons, I want to coat over the 100+ year old exposed concrete blocks with a thin coat of lime plaster, to inhibit mold and make it easy to wash.

What would you suggest for this, Bruce? (and others)

would a single brown coat with a light skim coat suffice?

And also, the firebox for our vat will be built of small field stones (random round here in Central IN) mortared with lime-reinforced mud (with some chopped straw). How much lime would you recommend adding? It does not have to be waterproof, it will be inside.

Recapping, here is my plans as of now (for review)

For the shop walls: Base coat of clay mixed with chopped straw, covered with a coat of lime-reinforced clay, finished with a plaster skim and limewash. Possibly at some point I might have a tinted plaster and do some simple sgraffito work as well. I like sgraffito.

For the basement walls: Brow coat with skim coat

Firebox: random round field stone with lime and straw reinforced mortar.

For firebox and flue you would be safer to use refractory mortar instead of lime mortar, due to the high temperatures that will convert the lime to quicklime and in the end lead to mortar failure. By the same reasoning, avoid limestone in firebox construction.

Normally true, but this is a special case

The flue itself will be a stovepipe, and the actual fire does not get very hot -the rocks will never reach the 900 degrees necessary to burn lime. The fire for cooking cheese has to be very slow and controlled, and nearly all of its heat will go directly into the copper vat (this is the chief advantage of using copper)
In fact, in the Swiss Alps traditionally the cheese making huts are highly sealed, more so than any other building, because all heat needs to be retained for the cheese.

And furthermore, I will probably give the inside a thorough coating of mud with wood ash mixed in to serve as both a fire shield and to bring the casing itself to near proximity with the vat -almost touching. The vat has bulging sides, allowing it to fit snugly into such a box and retain as much heat as possible.

Hello Roger,

By that reasoning it should be possible to recharge, let's call it, opened yet unused sacks of NHL that have been sitting around for a long time by heating the powder to the required temperature. Is that so?

Greetings,

Don Wagstaff

Hi Don

I suppose so but not efficiently, if the bag spoils why not use it on acid soil?

DL

I think the brown & skim coats of lime plaster will be too much for the basement aging area. I'd suggest 2-3 coats of limewash over a clean block surface. Brush the first coat in thoroughly. Adjust the consistency of the wash coats to meet your needs. That should do it!

Your description of the firebox and how it is used leads me to believe that you will be better off with a clay/sand mortar without any straw. Just use a coarse sand aggregate with a fairly even gradation from 1/4" - down to very fine for the strength it provides. No lime or cement will be needed.