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 (it was $9 a gallon when I first published this, now it’s $20!). 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.
There’s a lot more to learn about it, 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 (still, relatively) 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 — less 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.
SAFETY
• Waterglass is mildly caustic, so gloves or regular hand-washing is indicated.
• While it is a liquid, it is also 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 permanently mar glass surfaces, and can be hard to clean off of other surfaces as well.
APPLICATION
1. Mud should be thoroughly dry before applying waterglass.
Waterglass, clay, sand, and water go thru a gel phase 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.
sir, have any solution about two storied earth building toilet or bath area?
Can you say more about the problem and/or situation? There are many options for compost toilets. Here’s one that’s worked well for me: http://www.appropedia.org/Ersson_vermicomposting_toilet_(original). And a basic sawdust toilet (includes link to online version of Jos. Jenkins’ Humanure Handbook): http://www.appropedia.org/Original:How_to_make_and_use_a_sawdust_toilet
I am going to waterglass my cob bench (which also has a good roof but needs some durability for the public). I am confused on the dilution ratio.
The sodium silicate that I bought from my local ceramic supplier indicates that is a solution of 37.5%. I have seen that you can also buy it to seal cement (Rutland brand), and it is 100% sodium silicate solution with a 4:1 dilution ratio recommended (4 parts water, 1 part sodium silicate).
You recommend “at least 50:50” but I am unclear of the amount of sodium silicate in the product that you are using. Recommendations?
apologies for late reply; for some reason, I don’t seem to be getting notifications when people comment! I assume that most/all sodium silicate sold by ceramic suppliers is the same, and that is what I typically mix 50:50 with water. Waterglass itself is a solution, so that is how I make sense of the information on what you got from your supplier. Visually, the stuff I use, when undiluted, looks more like light cream as you pour. Diluted, it pours like water. Hope this helps (if not you, maybe the next person!)
— Kiko
i got some sodium silicate from a ceramic supplier, and it is a solution of 37.5%. the website says to mix it 50:50 with water, so i would imagine that your solution would be the same (and that it is the same as what the author of the article uses).
I suspect any liquid sodium silicate is a solution. The stuff I buy is also liquid, but thicker than heavy cream when you pour it. I call that 100%, and mix it half and half with water. Whatever you do, you want the liquid to absorb deeply so it binds the plaster well below the surface. When in doubt, test!
I am in process of rebuilding the oven. The ceiling keeps falling and leaving dirt on my pizza. Will adding waterglass directly into my first layer mix be effective in keeping my ceiling together and free from falling? If so, from your experience with water glass, is there a ratio that you could recommend for the first clay layer? Example 20% waterglass solution (50 water:50 water glass) to 80% clay/sand mixture?
While waterglass in the mix will help, you might also want to re-evaluate your source of clay subsoil, or your mix — lack of bonding suggests poor quality — or lack of — clay. It is also possible that your mix simply wasn’t tamped hard enough to bond clay to sand. (Many variables make many possible sources for a single problem!) On the waterglass and mix ratios, please look up the post on DIY castable refractory (now at the top of the “hot from the oven” blog). Good luck!
So this year we ended up moving the oven and building again, mixing some water glass into our first base layer of mud. After firing for the first time, was disappointed that the dirt is falling on our pizza again. Is it possible to add a slip coat of pure clay and water glass (or several slip coats, drying in between each layer) to the inside of our oven, particularly over the roof area to form a more solid ceiling? In your experience, will it adhere or will it worsen the problem. Right now I’m tenting my pizza with foil. Any advice would be appreciated!
Hello Kiko, I purchased your book and built an earth oven last year. We love it, but sadly haven’t been able to use this year. The ceiling at the entrance of the oven is starting to loosen and dirt keeps falling which makes for icky pizzas. How does one go about repairing a loose dirt ceiling? We’ve tried adding a slip, but it doesn’t seem to adhere. I’m wondering if spraying a coat of the waterglass would work, and whether it is safe to use on the inside of the oven? Any advice would be appreciated. Thank you!
yes yes waterglass is safe to use on the inside of the oven — just re-read the precautions above. (It was reportedly used to preserve eggs, so ingestion is apparently not a worry.)
I just finished building my first oven and am trying to come up with a finish plaster that will give some weather protection, although I am planning on building a roof for it. Can waterglass be used as a top coat to help with rain protection? How does this compare with using lime plaster? Should I do a basic clay plaster and then just brush it on? Thanks!
yes, it does give some weather protection — comparable, in some (but not all) ways to a lime plaster. But a roof will be best. Yes, brush it on per the directions in the article.
Does this process/finish leave the earthen wall ‘breathable’?
Unless you use many coats, the wall should remain breathable after waterglass application
Hello Kiko !
Built my own oven following instructions in your book – great book,easy to read and follow.
Thank you!
One question : it is a little flakey inside and I get grit on the food. I am thinking of trying to use waterglass to seal the inside of the oven. What do you think/suggest ?
Kind regards
Bruce
Hi Bruce, I am also experiencing the same difficiulty. Did you ever try the waterglass?