Monday, October 15, 2012

Building A Well House #8: Stucco

Last week we looked at wiring the well house for applying stucco to,
now let's look at the stucco process itself.

The whole series to date is:
so please take a look back to get up to speed on our project,
particularly the last post on the preparation for stucco.

I took the photo above from the previous post,
 to better be able to follow the process,
which shows the stucco netting, diamond lathe, and edge boards all in place.

Above I have applied the scratch coat, the first coat.

This is the traditional style of stucco here in northern New Mexico
 of a scratch and brown coat followed by the color coat.

Note the temporary horizontal edge stop boards 
at the bottom of the wall section on the right, above.

And above you can see the scratch a bit better;
 a little cracking is not unusual.

In this area some crews are going to using a rubber float for the scratch coat
 instead of the traditional scratching but I still prefer this way.

The 3/4" boards at the corners and doorway provide a handy guide
 to gauge the thickness of each coat and will later be covered by 3/8" x 2 1/2" trim boards.

For the scratch coat I troweled on stucco to about 1/2 the thickness of the boards (or 3/8").

Now the brown coat has been applied to the full thickness of the boards, above.

For these smaller sections I was able to use a short, straight board 
as a screed to get a uniform thickness, and a nice clean look,
before using the rubber float for the brown coat finish.

If I was not happy with the floated finish
 I would go over the area with my steel trowel and simply redo it.

The mix that I use is as follows:
+12 shovels of washed sand,
+ 3 shovels of portland cement,
+3 shovels of type S masonry cement,
(mix dry ingredients first),
+app. 3 gallons (+/-) of clean water, 
+and app. 1 cup of admix,
(add the admix after the water 
and all other ingredients are mixed 
to minimize over mixing the admix;
 be sure to read the directions).

Tips for working with stucco:

+ the masonry cement contains lime 
which makes the mix more workable and stickier, 
and extends the open time you have to work;

+ the admix does much the same
 and also makes the stucco more water resistant after drying;

+ make sure your masonry cement is a new bag 
as lime degrades from air and humidity very quickly,

+ protect your hands, skin, and lungs as lime is very caustic
 and is not to be taken lightly;

+ clean your wheelbarrow and tools before each new load 
so you do not contaminate your new load 
with left overs from the old load;

+ I like to apply the scratch and brown within a couple of days of each other 
to insure a good bond but then let everything sit a while 
to see if any cracking occurs before the color coat is added;

+ since I was working by myself I used a wheelbarrow for mixing 
which makes things go a little quicker since there is less cleaning up;

+ for larger jobs a crew of 3 or more is good 
as one person can mix and clean while the others can plaster.

The photos above and below also come from the last post
to make it easier to see the whole process.

Above the corner buildout is in as well as the block to attach the future wall hydrant...

... and the insulation, 15# asphalt paper, and wiring for the north wall is complete
 while the east wall shows the orange surface bonding cement over the cement block
and the black asphalt emulsion for waterproofing the below grade sections.

Above the east wall was insulated, wired, and the scratch coat is on.

Note the temporary board (photo above) at the bottom which is a stop for the stucco.

Above, another closeup of the scratch coat.

The scratch coat (first coat, app. 3/8" thick) is intended to to cover all the stucco netting
 and diamond lathe with little thought to smoothness or form.

Above the brown coat is on 
and the stop at the bottom has been removed giving a nice clean look.

A closeup of the brown coat having been floated with the rubber float trowel.

The brown coat is intended to bring the surface to a smooth, even, and flat finish
before the 1/8" color coat is added.

The white color probably comes from either the lime or admix used in the stucco mix and mostly disappears after a couple of days drying.

The whole series to date is: