I use “standard” CA and sodium bicarbonate. ..baking powder…

sounds interesting, can think of a few unconventional uses depending on the cure time

Since calcium oxide is white, there must be additives in these powders, possibly fillers of some sort.

Geo.

Blasting soda is a free flowing baking soda, so it pours quite well. Makes for a very hard compound. Another we use as a wear strip is a combination of blasting soda and carborundum powder. I use it for a landing skid on my model planes.

Neil

As well as excluding oxygen, moisture and metal salts help CAs to go off. Humid clothes contain both, as well as large surface area in a small volume. I believe the "activator" sprays basically provide the metallic salts.

Most of these reactions are exothermic and the rate of reaction increases with temperature. Same is true of epoxy (Araldite) and car filler (MEKP?). I can tell you that if you add the hardener (or whatever it's called) neat, you can get that to burst into flames, which is presumably why it is generally supplied in a diluted form. With Araldite, if you heat it up, the reaction is quicker which can be useful, although initially it becomes more fluid – which can also be helpful.

Murray

I suggest that the 'calcium oxide' which is supplied is not actually quicklime, but slaked lime. I have three reasons:

1. Quicklime is fairly dangerous stuff, and is no doubt covered by all sorts of regulations. Slaked lime is much more friendly, even available at posh builder's merchants in lime mortar.

2. Quicklime is eager to absorb moisture, so has to be in a tightly sealed container, even in the factory where it is made. When this has occurred it turns into slaked lime (hydrated calcium oxide). So why not supply the non-noxious stuff?

3. If moisture helps c-a to polymerise, there is no advantage (in this respect) in adding a compound which absorbs moisture itself.

And it may be that the resulting set product with calcium is less soluble in water than with sodium (from bicarbonate) – thus extending the usefulness of the product.

But what do I know about it, anyway?

Cheers, Tim

This may be off topic, but lots of people here seem to know about such things – My stainless steel hot water cylinder seems to have a very small leak, in the bottom. I am thinking of draining and cleaning out as best I can, then pouring some " stuff" in. Any suggestions ? Dia. is about 400 mm, max. temp about 70 C and will be wet all the time

Your risk if you want your house flooded. The cylinder may be weak in that area and just waiting to fail in a big way! Is this a gravity system or at mains pressure?

As far as temperature is concerned, I've yet to see a hot water cylinder that is hot at the bottom. Water is a very good insulator.

Be aware that Bicarb and Calcium oxide will not form a water resistant compound with a superglue type adhesive; both dissolve in water.

If you want to try a waterproof material I'd suggest slate powder, but in the case of a domestic cylinder thats already in failure mode, I'd bin it anyway.

Eug

Over here We have "glass lined" heaters. Cut one open and try to find the glass!