Home brew with airset alumina mortar

[Diswal]

I have the problem that I cannot get my oven hot enough to get the mortar to cure. This is not a problem in the dome, but in the chimney where a bit of water comes in the mortar just turn to clay again. Just as described on this link.
Refractory Mortar

I would therefore like to mix a home brew with the alumina mortar which I have available. (42% Alumina, 52% Silica) with the recipe shown below:

2 Parts AirSet Refractory Mortar
2 Parts Fine Washed Sand
1 Part Portland cement Cement
1 Part Hydrated Lime (would NHL 3.5 be a good enough lime?)

Has anyone had the same problem or tried the recipe?

And/or would you suggest to use the standard home brew suggested on FB?

Thank you in advance

Br. J?rgen

[Tscarborough]

Re: Home brew with airset alumina mortar

Do not use airset refractory cement at all in the mix.

[Diswal]

Re: Home brew with airset alumina mortar

So the best mix would just be to use the standard home brew mix recommended on this site?

What happens with using the mix with the alumina mortar?

And would the lime NHL 3.5 be okay to use (Natural Hydrated Lime)?

Br. J?rgen

[Tscarborough]

Re: Home brew with airset alumina mortar

NHL would be superior. Why use something that serves no purpose?

[david s]

Re: Home brew with airset alumina mortar

Lime added to calcium aluminate based cements, which is the usual active ingredient in high temp mortars, has the effect of accelerating the workability of the mortar to such an extent that only small amounts can be mixed at a time. This can be adjusted by adding certain additives (proprietary products and homemade additions like citric acid or sugar), but without a fair amount of testing it's hard to get it right. Calcium aluminate cements are also very much more temperature dependent than calcium silicate cements and are way more expensive.

The Homebrew, 3:1:1:1 sand, Portland cement, builders lime and clay has proved time and again to be cheap, workable and serviceable for the temp range of WFO's. Why try and invent a mortar that is fraught with workability problems and is way more expensive?

[wotavidone]

Re: Home brew with airset alumina mortar

I find that mix confusing - it looks like it has more binders than aggregates.

I envy you the Natural Hydraulic Lime. I think it would be superior to the ordinary hydrated lime available to us in Australia.

[Diswal]

Re: Home brew with airset alumina mortar

NHL would be superior. Why use something that serves no purpose?

This is what we have available here in Denmark - But sounds good that it is superior :-)

The cost is also not that high for it, 16 USD for 25 KG

[Diswal]

Re: Home brew with airset alumina mortar

Lime added to calcium aluminate based cements, which is the usual active ingredient in high temp mortars, has the effect of accelerating the workability of the mortar to such an extent that only small amounts can be mixed at a time. This can be adjusted by adding certain additives (proprietary products and homemade additions like citric acid or sugar), but without a fair amount of testing it's hard to get it right. Calcium aluminate cements are also very much more temperature dependent than calcium silicate cements and are way more expensive.

The Homebrew, 3:1:1:1 sand, Portland cement, builders lime and clay has proved time and again to be cheap, workable and serviceable for the temp range of WFO's. Why try and invent a mortar that is fraught with workability problems and is way more expensive?

Hi David,

Thank you for the feedback and explanation.

The reason for trying the mix with alumina was that I have some available all ready. I will try to make a mix of both mixes just to test it, but I will probably go with the standard mix without the alumina.

[Diswal]

Re: Home brew with airset alumina mortar

I find that mix confusing - it looks like it has more binders than aggregates.

I envy you the Natural Hydraulic Lime. I think it would be superior to the ordinary hydrated lime available to us in Australia.

But then you have many other things I envy even more ;-)

After living in Sydney for 6 months it is tough coming back to the Danish "summer"

[Diswal]

Re: Home brew with airset alumina mortar

I have now tried out the two recipes to compare them.

Both of them worked very well and seem to hold equally well after using the oven twice.

The mix containing alumina silica was easy to work with and did not set so fast that it was a problem to work with. It was workable for several hours and did not set hard until the day after. Of course the temperature was also only around 10 degrees Celsius but still I must say it felt very nice to work with.

All in all I must say I could not see or fell the big difference between the two.

But as you said, for most people the normal home brew is probably the cheapest and easiest available option. The only reason I wanted to try it out was that I had some available and that testing new things are always fun :-)