“Waterglass” for protection & paint
Waterglass has become my preferred binder in places where it’s needed. The chemical name is sodium or potassium silicate. It’s an inert mineral compound similar to window glass, but under heat and pressure, it’s soluble in water. I get it from a ceramic supplier for $9 a gallon. It’s clear, viscous, and pours like heavy cream. It dries into a clear, brittle substance that crushes to a fine powder, but it has significant binding power, and is used in some refractory cements, as well as numerous other industrial applications.
I’ve only discovered it in the past few years, so I’m still learning, but it has made murals possible in less protected areas where I might not have risked it before. It does interesting things with color. And it’s cheap!
Mixed at least 50:50 with water and sprayed (or brushed) onto dry mud and allowed to dry again slowly, waterglass will bind the mud to a significant depth, preventing damage from rain, hoses, and curious fingers (but not hostile ones). Brushed on, it soaks in deeper, binds more, and may darken colors.
Mixed with pigment, it produces wonderfully varied mottling: more opaque in deep areas, where the pigment settles thicker, and more transparent on raised surfaces.
A 50:50 mix will treat approximately 30 sq ft per gallon — more if you spray, less if you use a brush and really saturate the mud. More saturation provides more strength and water-resistance. If you want to stretch your supplies a bit more, you can dilute it with a little more water.
Make sure to really fill every nook and cranny, otherwise, you end up with uncemented areas which will be fragile. When applying it, especially over deeply textured mud, it's almost as if you're pouring it on with the brush. As you'll see, it soaks in so fast you don't really have time to brush it. Strange stuff.
Spray bottles are a good way to apply it, especially if you want a thinner application. Coarse rather than fine spray is less of an inhalation hazard.
• Waterglass is mildly caustic, so gloves or regular hand-washing is indicated.
• While it’s liquid, it is still silica, and bad for the lungs; if you decide to spray it, wear a mask.
• Be careful of overspray and drips, as the stuff will mar glass surfaces, and can be hard to clean off of other surfaces as well.
1. Mud should be thoroughly dry before applying waterglass.
Waterglass, clay, sand, and water make a gel before drying out completely. Perhaps because of the very binding properties that make it useful, it can take some time for that final drying to occur. If additional moisture is still moving out from deep in the wall, applying waterglass too soon may further slow drying.
So a thick mud wall may just appear to be dry. If you apply waterglass too soon, and then get rain, you may end up with soft, jelly-like patches that can even slough off completely. If you’re not sure, better to let an earthen wall dry completely – a year, if need be – before waterglassing.
2. Let the waterglassed surface dry slowly.
Say you waterglass a dry wall on a sunny day. The next day you find it covered with white powder. Some of it brushes off easily, but some sticks and gives your final color an annoying dusty finish.
I’ve heard two explanations: one is that fast drying pulls both water and waterglass out at such a rate that the mineral ends up drying on the surface where it turns into powder; the other explanation is that the waterglass displaces other salts that may be present, and those get deposited on the surface. Either way, the problem seems to be exacerbated by overly quick drying. I waterglass late in the day after the sun is low and the heat has dropped.