Crack Control and fiber addmixtures

[Fairview WFO]

Re: Crack Control and fiber addmixtures

I ended up using glass fiber reinforcing in this top coat. High melting point, Alkali resistant and easy workability in a thin coat. Glass fibers have been used for years in concrete applications. I got mine for about $5/pound at NYCON.com A pound is typically enough to reinforce a cubic yard of concrete. Not sure if that helps you overseas though.

[david s]

Re: Crack Control and fiber addmixtures

Mixing some stainless needles in with your cladding mix is much faster than embedding bits of mesh in the cladding layer and has the added benefit of not having a corrosion problem.

[wlively]

Re: Crack Control and fiber addmixtures

I don't know how effective the needles would be in cladding. I used them there because I had some left over and thought it wouldn't be a bad idea. There weren't too hard to work with or obvious in finish, but you do need to be careful as they are sharp. Can't say if it would be worth it if they were very expensive or allot of trouble to get. Casting is a different story.

I think it is best to resign yourself to having small cracks, and then plan to minimize their effect with barrier layers.

[dmun]

Re: Crack Control and fiber addmixtures

Stainless steel needles are reinforcement for castable refractory, I haven't heard of them being used in oven coating. I think they might be a little ungainly in a troweled layer.

You can get stainless steel mesh if you're concerned about corrosion, but i'm sure it's not cheap.

[phipham]

Re: Crack Control and fiber addmixtures

Minimizing cracking is more important for me than thermal mass, so I am happy to add an extra layer of reinforced mortar if this leads to less cracking.

The reason why I put in chicken mesh is because this is available in the Netherlands (tiny spot on the worldmap). So I have to figure out where I can get stainless needles overhere ..

Phi

[david s]

Re: Crack Control and fiber addmixtures

The thickness of your refractory mortar over your bricks depends on how thick you want your dome to be. It's purpose is to add thermal mass and added strength. I think chicken wire that is galvanized could be a problem because zinc's melting point is around 420 C and the oven dome could well exceed this at times. Heat will accelerate any reaction. I think that is why stainless needles are recommended. The curing before or after insulating has been addressed on another thread somewhere, the consensus seemed to be that either way was ok but there are advantages and disadvantages for both.

[phipham]

Re: Crack Control and fiber addmixtures

I have some questions I need your help:
- I just have finished the dome and have added a layer of mortar to the outside of the firebricks (so no insulation on the outside yet). Then I came across with this subject. What is the best next step ? a) Add another layer of mortar mixed with stainless needles. b) add another layer of mortar on a chicken mesh. c) or just leave it this way (no extra layer of mortar with reinforcement).

- And should I start curing the oven before applying insulation of after insulation ?

Btw, just curious, I don't understand why stainless is used here. Does this have anything to do with rust ?

thanks.
Phi

[wlively]

Re: Crack Control and fiber addmixtures

It is hard to remember. I bought around 2 lbs I think. I told him what I was doing and he recommended the amount, there is a recommended ratio depending on product used.

I mainly used mine for my dome plug and vent transition which I cast. What needles I had left over went into the cladding coat on the dome. My castings are holding up well so far. Can't say about the cladding because I added a layer of perlcrete over the top.

[Fairview WFO]

Re: Crack Control and fiber addmixtures

thanks Wade, did you use this to parge the outside of your dome? How much did you use and did it work well?

[wlively]

Re: Crack Control and fiber addmixtures

Where did you get your needles? Wlively

I bought them from this supplier. Look up the contact info and call him, he can sell by the pound. I also bought my Insblock 19 here for $1.00 sq ft.

http://stores.ebay.com/HIGH-TEMP-REFRACTORY-STORE

[david s]

Re: Crack Control and fiber addmixtures

I've had trouble with the outside cracking, but since going to fibres, problems gone. There is considerable expansion with the heat and steam pressure build up. A render mixture that has lime in it is apparently more elastic. Try a 4:1:1 sand ,cement, lime mix for the outer shell, only needs to be thin, after all it's only a weather coating.

[Fairview WFO]

Re: Crack Control and fiber addmixtures

Thanks David, I've found a supplier of Alkali resistant fibers and I can get relitively cheep ($32) delivered for 4 - 1# bags (way more than I need). I think this would be the preferable way to go from a cost and workability standpoint.

What I really want to know if this is a good idea, or does it cause more problems?

Ordinarily on any concrete, stucco, or motar work its alway a benifit to add fiber reinforcement. But with this high temp application I wonder if everything will move together and still be contained?

Is the cooefficient of thermal expansion of the glass fibers the same as the firebrick and mortar? Does this really matter?

Just trying to work it arround in my head....cost isn't much and I only want to do this once....not that it hasn't been fun so far. (I'm actually on the last row now and its not fun at this point!)

For those who have done this, did it work out ok?

[david s]

Re: Crack Control and fiber addmixtures

Glass has a melting point around 900 C which is way out of our range, but ordinary glass fibers react with the material. You need to get alkaline resistant fiberglass.

[Cypress]

Re: Crack Control and fiber addmixtures

Where did you get your needles? Wlively

[Fairview WFO]

Re: Crack Control and fiber addmixtures

I would think fiberglass fibers would stand the heat? Wade, where did you source the stainless needles by the pound?