Wet mix, or dry?

[hpmer]

Other than less drying time, is there some reason for working with a dry mix? I know with cement mixes there is a specified amount of water to use, but I'm thinking more along the lines of a home made refractory.

I like to work with them more on the wet side than dry, say a peanut butter texture, since the materials seem to morph together better, but I've usually see recommendations to keep the mix dry-ish and wondered what the reasons would be.

[matt walker]

It's a great question Hpmer, and one I ponder all the time. I cast a core on Thursday and that question was running through my head a lot. Here's why: Just like with concrete, too much water is said/known to weaken the overall product, even after curing. I'm no expert, I can only guess why that is, but every concrete mix instructions, and every refractory mixing guide I've ever read has said the same thing. Don't make it too wet.

So, the first refractory mixes I made, I followed the recommended ratios exactly. Measured out my water exactly, mixed carefully, etc. They are exceptionally dry, and if you work them enough you can get them to liquefy with vibration and working, but man, it's really, really tough. And getting it all to wet out when you use the minimum water is really difficult as well.

So, I, like you, tend to add too much water. If you look at the ratios, I add WAY too much water. It's just so much easier to work with. And the reason it's always on my mind is that when I am doing it I am fully aware I am not following the instructions and I of course worry that I'm doing it wrong and wrecking everything. It's just like the dry out procedure with refractory. You'll never be able to do it right without a huge kiln and whole lot of equipment, so I just say screw it, and light the damn thing on fire after a day.

My feeling with the mix is that whatever downside there is to too much water is far outweighed by the fact that I don't have big air pockets, dry spots, and mealy mix. I can only imagine that is way weaker than a monolithic cast that was too wet and dried wrong. I'm sure I'm wrong, and somewhere and engineer is shaking his head at me, but that's how I do it, and so far so good.

[brocken]

The local refractory store here has premixed wet rammable refractory that is like modeling clay, you actually hammer it into the mold with a small jackhammer. One type dries out by heating it the other dries with contact with air. The only problem is that it is expensive.

Dave