What's the trick to everlasting mortar for outdoor fireplace

[Thor]

I've noticed that numerous outdoor fireplaces don't seem to last. The mortar seems to deteriorate and yet I have seen some that have been around since the early and mid 1900's that are still as solid as the day they were built.
I'll be constructing an outdoor fireplace/pool heater combination that I want to last for many years , so I'm curious if there is a special method or additive involved for a long life expectancy of mortar that will be exposed to extreme elements.

[Rich]

Read this article on Refractory Mortar (http://www.construction-resource.com/firebox_mortar.php). It may help you to understand a few things.

[Thor]

It's all so clear now , thanks for the article Rich.
Now I understand why regular mortar deteriorates in a fire place.

[Thor]

Oh oh...... :( just finished reading another article on refractory mortar that stated it is not recommended for outdoor installations because it is water soluable. Any ideas :?

[Rich]

There is non-water soluble refractory mortar available.
http://www.alsey.com/flueset.htm

[Thor]

I knew that..... :o
Thanks again Rich.

[Shanley]

Also keep the joints tight no more than 1/4 inch