Different coloured plasters?

Hi all,

Maybe this is a post for the cob forum, buuuut...

I am trying to achieve a black and cream finish to my cob bench and was wondering if the appropriate plasters can achieve those colors? My cob is already nearly black and i have a bunch of little blue pool tiles left over from a friend and thought how bad-ass it would look with a black bench lined wth blue tiles. I even have a name for the bench, ha!

Please advise as im itching to make this dream a reality..

There should be plenty of help down the tile aisle of you local home improvement store. Either that or the stucco aisle. Colored grout and colored stucco is well developed technology and there's no reason why you can't add those colorants to your cob/plaster. It may not set up exactly the same shade as if it's mixed according to directions though, so it may take a little trial and error on your part to get it exactly where you want it to be.

Thanks John. Just one question, as its cob i obviously want any colorant to allow breathing, right? So is there a type of stucco/colorant whose nature/behaviour is more compatible with cob than others? Or at thi spoint would all types work well?

All ceramics "breathe" to some extent and that is more a function of pore size than it is color. The only real way to make ceramics (and I mean that in the most general sense that any metal oxide can be used as the starting material to make a ceramic) non-porous is to vitrify them. That's what happens when you put pottery in a kiln, the surface gets hot enough for it to start to melt and it glassifies. Now it may get hot enough on the inside of your rocket stove, but it probably won't unless you coat it with a special slip. Slips and glazes are surface coating for pottery that have a glass transition temperature significantly lower than the rest of the pot so that only the surface glassifies.

I wouldn't worry about it being able to breathe. The problem with cob/adobe is usually on the other side, they are too porous. Think about saltillo tiles used for floors. One big problem there is to seal them so that spills of liquid will clean up and not leave the surface permanently discolored.