Help with Stucco Cracks

[Balty Knowles]

Thanks for the advice Jim.

No, not a bricky but I did serve a 5 year apprenticeship in engineering. I think I got my admiration for craftsmen & their skills then. I've had several accolades in the many years since but it's my indenture papers I'm most proud of. They hang on my office wall in a more prominent position than my degree.

There's an honesty in hand skills & hard work that's very rare elsewhere. I live in Silicon Valley which is quite a cut throat work place & many of the higher ups here obsess over woodworking projects on the weekend. I think thats why.

I placed this thread in the wrong place so I'm starting a new one for the insulation.

Best Regards

Balty

[Bacterium]

Neil.....or others
just back on the stucco/render

using a mix of 3:1 (plaster sand, cement).....
what would lime do to the mix eg
3:1:1 (plaster sand, cememt, lime)

reduce cracking?

I bought some with the last lot of gear to stucco/render the outside of my dome (final weatherproof coat)......but I forgot why its been a few pizzas since then

[nissanneill]

Damon,
By reducing the cement ratio, you will reduce the water proofing characteristics. This will in fact be the case with the addition of other ingredients such as lime.
Today, we use lime I think to make the mortar a little lighter in colour and more workable, but also because it was used years ago in preference to cement. Let's face it, our pioneers used materials that were found locally to build with and limestone burned in a kiln or oven was easy to produce. Today, cement is easy to source and is easily (although expensive in some instances) to transport and it is also superior to lime in strength and water resistance when used in the correct proportions.
I recall some thread on the forum with reference to a specialist who said that lime has no part in refractory materials, (even though I used it in my mortar for the dome).

Neill

[Bacterium]

ok.... I'll stick with the 3:1

Maybe I'll swap the lime for some oxide instead. I suppose I can then correctly colour match the oven coating (final outer coat) with the general area of my pergola. I've just been looking through the Diggers range of oxide:
http://www.diggersaust.com.au/catalogue/index.html

It talks about putting some sort of "Raincoat" stuff of theirs onto the surface after it all - to seal it - as they say "to protect against fungus decay". I'm guessing this is more about keeping the natural look of the surface......whereas the real water resistance comes from the 3:1 mix.

.....any thoughts?

[Archena]

The sealant doesn't so much increase water resistance as make the surface water repellent. It's basically keeping the water from seeping into the surface (which happens normally in concrete) so that fungus, mildew etc cannot grow and salt won't leech (one surface has to take in water for that to happen - think concrete retaining walls).

At least, that's how I understand it.

[maver]

Originally Posted by Bacterium

Neil.....or others
just back on the stucco/render

using a mix of 3:1 (plaster sand, cement).....
what would lime do to the mix eg
3:1:1 (plaster sand, cememt, lime)

reduce cracking?

I bought some with the last lot of gear to stucco/render the outside of my dome (final weatherproof coat)......but I forgot why its been a few pizzas since then

I'm certainly no expert, but I used a scratch coat with portland cement and sand and finished with white sand and lime. I found the lime coat much easier to work with - it was significantly more sticky, and it did not crack at all, which my scratch coat did. It is not likely as weather resistant or durable as the portland, but it looks good, and I have a roof overhang to protect the sides of the oven (the stucco). I may still paint the oven after the move - new house, new colors.

[Balty Knowles]

Originally Posted by nissanneill

Damon,

I recall some thread on the forum with reference to a specialist who said that lime has no part in refractory materials, (even though I used it in my mortar for the dome).

Neill

See the thread on refractory mortar question. I was having problems with the formula in the plans & called the chemist at Lumnite. He told me that lime is used as an accelerator for portland cement but calcium aluminate goes off very fast & lime would exacerbate this. Said to omit it all together for his product.

[james]

Hey Balty,
I have moved this thread to Design and Finish. This seems to be the right place for a very valuable posting.
James

[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

[nissanneill]

Bacterium,
Now your talking. I wouldn't mix the render too dry, but on the other hand not too wet either.
You need it wet enought to be able to trowel it easily and if you are going to put a "final" waterproofing top coat, a wooden trowel will give you a better surface for the last one to bond to. Steel floats bring the water to the surface and give you a smooth shiny surface which is what you do not want on sub coats. Add enough water for the thinner (rather than a thick layer say 1/2 to 3/4" thick) for the mortar to stick and readily hold together.
Your last or top coat can be at the same wetness consistency but use a steel trowel to provide your smooth water proofed surface.

Neill