Whitewash

[ls99]

A question for those with good understanding of chemistry.

I am planning to use whitewash on the inside and outside of a cement block building.

Having read virtually all I could find on the mixing and use of lime both hydrated and quick, in wall coatings, found dozens of mixtures and additives, to achieve whitewash.

I understand why one would use Portland cement, rice, molasses etc. in the mix.

Many mixes call for the use of salt. Nowhere could I find an explanation for what salt does to the mixture, why is it useful or beneficial.

My understanding of chemistry is dismal to non-existent. An explanation in layman's terms would be most appreciated.

 

[2B]

Why would you use whitewash?

 

[mickj]

use it because it's cheap and becomes part of the wall

Artist Articles

For example 'salt' prevents over rapid drying but leads to crystallisation damage in substrates

http://wiki.answers.com/Q/Does_salt_effect_water_evaporation

Does salt effect water evaporation?

Evaporation rate depends on the temperature of the liquid, how tightly the liquid molecules bond to each other, the surface area of the liquid, and the temperature, pressure, and air movements in the surroundings into which evaporation occurs.
...

The answer is yes, it does. Dissolved salt in water will lower the solution's vapor pressure according to Henry's Law. Evaporation rate is proportional to the difference in vapor pressure of the solution and the vapor pressure of the bulk gas phase over the water surface. I agree with the above answer as well except that the coldness of the surroundings is not a direct factor in determining the evaporation rate.

Read more: http://wiki.answers.com/Q/Does_salt_effect_water_evaporation#ixzz1wU4a6UYq

 

[samclem]

Why would you use whitewash?

+1. It's chalky and doesn't hold up well. Some sort of historical structure?

 

[ls99]

As for the why?

It is structure in my camp. It was previously owned by a biker gang. Inside it reeks of cigarette smoke, outside is just plain.

Whitewash's principle ingredient, lime is is a disinfectant and deodorant.

I just don't understand the benefit of salt in the mixture.

Whitewash is waterproof, but allows vapor to escape thus reducing moisture content of the block wall.

Oh yeah, it is cheap, highly reflective, a 50 lb bag for about $8.- covers roughly 1200 square feet. Right up my cheapskate alley.

Now about the benefit of salt in the mixture? Once dried, how does salt benefit the coating?

 

[Nodak]

Whitewash works well for concrete. When I was a kid one of my chores was to whitewash the basement walls of my Grandparents house about every 2 years.

 

[Running_Man]

Whitewash - Wikipedia, the free encyclopedia

Salt is added according to Wikipedia to prevent mold if conditions are humid, though it will attack the brick. Other sites indicated it aids in adhesion.

 

[ls99]

Thanks for the links and input.



'been internet/phone and TV free for about three days.

An F1 Tornado wreaked havoc about a mile from our house, took the utility companies a few days to to restore order.

 

[2B]

As for the why?

It is structure in my camp. It was previously owned by a biker gang. Inside it reeks of cigarette smoke, outside is just plain.

Whitewash's principle ingredient, lime is is a disinfectant and deodorant.

I just don't understand the benefit of salt in the mixture.

Whitewash is waterproof, but allows vapor to escape thus reducing moisture content of the block wall.

Oh yeah, it is cheap, highly reflective, a 50 lb bag for about $8.- covers roughly 1200 square feet. Right up my cheapskate alley.

Now about the benefit of salt in the mixture? Once dried, how does salt benefit the coating?

Consider Killz. It will seal out the smoke smell.

 

[ls99]

Having read some more, I now know that there is a difference between whitewash and limewash. Limewash is what Intended to use.


My first experiment using limewash was to give a coat of the stuff on the roof. The roof structure is 4" concrete, covered with double coverage roofing roll, then that is covered with a hot tar layer.

Water tight it is, and a splendid solar heat collector. On a typical 90 F sunny day, the inside surface was runing 110 to 120 F. Ungood.

Having read various recipes for limewash, I settled on a basic water, lime and portland cement mix.

A precise mixture was created in 5 gallon bucket using about a 1/4 bucket of lime, enough water to make it an easily stirrable mixture using a piece of tree branch. Add about a handful of portland cement, stir some more. Repeat eanough times to cover entire roof, then climb down via the ladder and wait see.

The application involved carefully sloshing some on the roof at about 2 foot distances, then spread out with a fluffy paint roller.

The results: After several severe deluges of rain storm, bad enough to wash away part of my creeks banks, the stuff is still there, intact. A few hot sunny days, using infrared thermometer to measure ceiling temperature: 85 to 87 F.

I call that a successful experiment, one that worked as intended the first time. Feynman would be smiling. One of his lines for experiments was, if the first 100 did not produce desired results, it was still successful, he now knew 100 ways that are not desirable for that particular result.