Who has a formula for stucco? are the scratch, brown and finish coats the same mix?
I have done patch jobs before, and always went 1 part portland – 3 parts sand. Today someone asked me “what about the lime?”
anyone?
also should I use the metal edges against the brickmolding on the windows, or just mud right to the trim?
Replies
Use the metal edges. Never let masonry touch trimwork if you can at all help it. One portland, one lime, and 3 sand is a good mix. Depending on the sand you will have different finishes with the stucco. Playsand or a finer sand should be used for finish coat. There is a stucco final coat premix that you can get at a good masonry supply store, it's very fine.
All of the industry publications I've read say no more than 20% lime. I don't know why.
I find that about 48 to 50 shovels sand, and 9 shovels of lime to one sack Portland gives a good mix.
The advantage to lime is it makes a stickier, smoother stucco (easier to apply) with more flexural strength.
The downside is that lime makes a softer stucco. If that doesn't bother you, then it's not a problem. Fact is, once upon a time a servicable exterior plaster was made of nothing but lime, water, and sand.
And sometimes cactus juice. <G>
[edited to comment on sand]
Sand is a very important and often overlooked component. I use only washed ASTM plaster sand. This is a clean, sharp sand of a specific size. Too much fines in the sand will mess up your water ratio and weaken the stucco, and even cause cracking. Likewise for dirt (silt, clay, contamination). Also, salts and other kinds of contamination can cause a bloom to apear on the surface of the stucco.
DRC
Edited 10/4/2004 10:47 pm ET by Dave Crosby