Fast concrete curing

I want to make a few special coving bricks to replace broken ones on a chimney. I shall make a wooden mould first. Is it practical to speed curing by gentle baking in an electric oven or even in a microwave?

Reply to
peejos
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Concrete cures better when wet, lots of people have the mistaken notion that 'dry' means hard, but it's the opposite that is true, the longer it stays wet, the harder it becomes, drying out too quickly causes cracks and stops the cement from hardening properly, resulting in a crumbly texture

Reply to
Phil L

Agreed!

Tanner-'op

Reply to
Tanner-'op

Heat dramatically speeds up setting and curing, so yes as long as its at low enough power that it doesnt raise it too near boiling and dry it out. Maybe plastic wrap it to prevent drying, and heat several bricks at once on 10% nuke, or 60C oven.

NT

Reply to
meow2222

No, all that will do is result in excessive shrinkage and a very weak product.

You could cure them underwater in warm water, which would help, but personally I would use high alumina cement or "ciment fondu". This cures much more quickly than Portland cement and should be perfectly satisfactory for your application.

High alumina cement was a controversial material because designers omitted to allow for the fact that concrete made with HAC suffers a loss of strength if its environment is damp. School swimming pool roofs were an example of improper use of the material, and several failed because the designers worked on the basis of the "unconverted" strength. But that won't affect you because the "converted" strength should still be more than sufficient for your needs.

You can get high alumina cement on special order from good builders' merchants. They will probably warn you about the "conversion" issue, but if you tell them what you will be using it for, there shouldn't be a problem.

Reply to
Bruce

Agreed: years ago when I laid a 6" thick self-mixed concrete slab for a new 'kit' garage, I covered the freshly poured concrete with plastic sheeting and kept it moist for about a week. Result, one very hard tough slab.

Reply to
A.Clews

You are correct. Many people believe it goes hard by drying. It does not. There is a chemical reaction that requires water. Too little and it will not cure properly, too wet and little bubbles of water form in the mix which will never be absorbed so become little holes in the mix. Not so strong.

Reply to
Chewbacca

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