Help with Stucco Cracks

[Bacterium]

thanks Neill
.........if anything made me nervous building the oven it was this bit. I'm a sparky (electrician) & I.T. guy not a bricke etc..

Its all fun though.....thanks for starting the post Balty

[Unofornaio]

Originally Posted by Bacterium

thanks all....recapping I think this is how I'll do it:

-First (scratch) coat will be a 3:1 mix (plaster sand/portland), slighly drier mix, laid on thick - and I'll scratch up surface once on

- Next coat (on top of first) will be same ratio, thinner coat, slightly wetter. I'll mix in the oxide (by weight) to get the desired colour. I'll do this coat either same/next day to first.....its winter here so I guess it will be 2 days cure at least.

Once its all cured/dried I'll get some clear surface coating to maintain the look......but the actual waterproofness will really be from the 3:1 mix

If we are talking stucco here the "color coat" (very last coat) need only be around 1/8" thick and of a consistency you can almost paint on, professionally it is mixed like soup and put on with a stiff sponge float. It takes A LOT of color to change the color of Portland, unless you are using white cement which I don't think you are.
As far as lime goes it is still a very valuable component of masonry work now and will be in the future.It is not out dated by any means, adding lime to mortar for (lime, cement, sand) is the only way I lay bricks,block or stone it was the way I was taught and it works much better than a chemical plasticize additive. Lime helps the mortar sick, makes it more easily trowlable and keeps its board life up. As far as mixing it with the re-factory stuff defiantly do not.
Thick is something you want to avoid at this step much better to do 3 steps
Scratch,brown, finish (color) too thick a coating will give you cracks every time.
You already have the scratch coat (although its not scratched) get a pint of "concrete bonding adhesive" about 6 or 7 dollars this is a glue (I swear its just Elmer's glue) if you get it smell it and see what you think. we use this all the time for bonding old and new cement it works very,very good.
Paint this on, wait a bit put your brown coat on about 1/2" with a sponge float make it nice and smooth. Its consistency should be a little wetter than the mortar used to lay brick but no where near dry.. brown coats are mixed at 1 part cement to 3 to 5 parts sand.
finish coats are 1 part cement to 1-1/2 to 3 parts sand. If you choose to add lime count it as cement.
J.P.


F.Y.I. you said in another post "Maybe I'll swap the lime for some oxide instead" actually the oxide is a form of lime, Calcium oxide (CaO) this is different that hydrated lime (masons lime) Ca(OH)2

[Bacterium]

Hi Uno,

yeah I'm using Portland cement (not white). When I mean oxide its the stuff we use as a colouring agent. Say for 5kg (11 pounds) of cement you would use approx. 0.5kg(1.1pound) of oxide.
Interesting how oxide is just another form of lime

The original scratch coating on my oven is now covered by a thermal blanket and vermiculite. But I get your point to go for the 3 coat approach.....and changind the sand cement ratio as the coats go on.

Think I'll print this thread and have it on hand