Bricks, Masonry, Asphalt and Concrete - Firebox repair

I'm looking for additional advice concerning repair of a firebox. I had two ceramic bricks that were cracked down the center due to age. I couldn't find bricks that size anymore, so I bought the biggest I could find along with some fire-clay and portland.

I haven't done much masonry, but after getting lots of advice and reading two books on masonry, I gave it a go. Well, the mortar has thin cracks now that it's had time to cure. One of the guys I've been consulting told me that it's bad news and I need to start over; that my mortar was too dry.

I have photos and I need advice to continue. Just how wet should the mortar be? Is an extra bit to a mortar joint bad news for a firebox? If I screw this up, is my chimney in danger?

First, don't use portland cement in your fire clay. Here is how you use fire clay:

put the clay in a bucket and cover with water. Do not stir it. Let that sit for a while (overnight is best), then pour off the excess water and gently stir it to an even consistancy. To use the fireclay, dip the brick into the bucket and scrape off excess material. You do not want a joint; you want just enough to chink the gaps.

If you have an old fireplace with actual jointed firebrick (3/8 to 1/2" joint), then you should use refactory cement, not fireclay.

Your chimney is probably not in danger, but your house could be.

Thank you for the advice. I talked with one guy who looked at the pictures and said my mortar was too dry. The other guy said that it was too wet. The books that I read said I should have minimal mortar joint.

As it is, I do have an older home with a 3/8" to 1/2" joint. The brick I have is labeled ceramic (stamped right into the block). So when I talked to the guys at the brick-yard, they were not helpful at all. They convinced me I had to buy fire clay and the only fire brick they had. I read about refractory mortar, but wasn't able to find it in stores.

Does anyone know where I might find refractory mortar?

This is an eBay listing, but has what you need: the product and a source. It seems not to be common.

http://cgi.ebay.com/Firebrick-Refractory-Mortar-Air-Set-3000-degree-50-pail_W0QQitemZ8280031674QQihZ020QQcategoryZ3090QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

Hope this helps.

That is the product, but you don't need that much. You can get it in a caulk tube, named Fire-Pak by Wesco Refactories in Ft Worth, TX