Finishes (Part 2): Sand Finish and Texture
Photos #2 and #3 shows the use of a very sturdy barrel. Marvin Newman, my father-in-law, is mixing up some sand finish that will be used both for the sand finish on the ceiling and also the texturing that will be done on the walls. Water is always put in the barrel first, then the lime and Keene's cement is added at about the same time. The sand is added at the end. Mixing is done for about five minutes and then the mix is allowed to set another five minutes, then mixed again. Because there is so much lime mixed with this type of finish, a lot of water is used in comparison to basecoat mixes. For large mixes, the Milwaukee drill pictured is used by Marv, which mixes at one speed. He likes the variable slower-speed drill the company has which helps control the mess.
The difference between texturesSand finish is different from smooth coat mixes in that there is a lot of time to work with it. It won't set up hard for about 24 hours in the bucket. And even if it does, it's the one type of plaster that can be re-tempered and used again. Some more Keene's cement can be added when it's re-mixed and it's ready to go again. If it is left over, we usually will add some water to thin it down and this makes using again easier, as the thinning keeps it from setting up hard (using a scoop of sand finish will help accelerate a batch of basecoat very effectively and adding molding plaster to sand finish will make it set-up quickly).
If you find the plaster is skipping where there's plaster that's bare or thin, just go back and fill these in. It's better to get into the habit of using long strokes right from the start.
Other peopleSome crews I've visited double coat everything. They run a tight coat of sand finish over the ceilings, then go back over them with a second coat. Then the person floating the ceiling does a preliminary pre-float. He goes over the entire ceiling or perhaps just part of it, maybe 5 or 10 feet, roughing up the sand finish that brings the sand to the surface of the finish. Depending on how wet or dry the ceiling conditions are, he will then finish the ceiling out with a sand finish swirl pattern. Other crews like the random float look, where no particular pattern is put on the ceiling, just a roughed up look. One other crew I met had a really neat look they added to their ceilings. They took a rectangle yellow sponge that was about 8 or 9 inches long and swirled tight, complete circles all over the ceilings. This left a distinct and unique look and it was kind of their signature they left on the ceilings they did.
If the ceiling is not going to be painted, it is very important for the person floating the ceiling to complete the job as quickly he can. It's vital to keep a wet edge, meaning he should keep floating the ceiling back and forth, not leaving any edge more then five minutes at a time. The reason is that if part of a ceiling is swirled and left for too long, when swirling is started up again, a definite line will appear. It's not that the plaster will be any higher or lower, it's just that in the overall ceiling you will notice a definite line or difference in the way the plaster dries out, so that the finished product will not have a nice consistent look overall. This is especially critical if color is ever added to the sand finish. A difference in the actual coloring will be noticeable where the floating is started and stopped, so once the floating starts on a wall, it's highly recommended to go for the finish line!
When using sand finish texture, a few things should be kept in mind that will prove helpful.
If the conditions are very dry in a house, there is a danger of the texture checking. This is where the moisture is pulled out and the texture does not have enough time to cure properly and grab onto the basecoat. Small crack marks will occur and the affected texture will have to be scraped off and redone. There are several things that can be done to avoid this tragedy. One is to fog down the basecoated walls with a hose or pump sprayer. A pump sprayer is easier to control and to get a consistent fogging accomplished. This will slow the drawing of moisture out of the sand finish.
Something else that will help is adding a dash or two of molding plaster to the thinned down texture. This will help the texture set up faster when its put on the wall. Another good idea is to add some additional Keene's cement which will make for a stronger finish coat.
If the texture is to be knocked down, an indication that it's ready is a dulling of the surface. It will appear wet for a while, then slowly take on a flat look. If the texture is being applied over fresh basecoat that's been done the same day, the danger of checking is greatly reduced. It's pretty safe to help the texture along by putting a fan to a wall that needs some help getting rid of some of the moisture. Keep in mind with dry walls that it is good to drop back and check the surface now and then if it's going to be knocked down. This is especially important if the walls are not going to be painted. If the walls are dry and the texture gets to the stage where it's pretty hard, the troweling needed to knock it down can make some areas look darker or dirty. So check it frequently and this will be avoided.