40" pompeii, first time builder

[totalnewbie]

Is this a burnout fiber?

Polypropylene Fiber for Cement Concrete Fiber Additive, Impact Resistant Anti Seepage Fiber Reinforcement Concrete Mix for Building Wall Garden Anti Cracking, White (19 mm, 3.6 LB)

About this item

• Solved Crack Trouble: Mixing Polypropylene fiber and mortar to make the mortar stronger, increase the vibration resistance of the cement, so to reduce the cracking problem, which can suitable for strengthening cement projects
• Material: Polypropylene Fiber is different from ordinary fiberglass fiber, polypropylene fiber has the same length and standard, smooth overall, ordinary fiber is rough and varying standards.
• Widely Application: Anti seepage polypropylene fiber for cement for concrete reinforcement are good at increasing cement density, so they can reduce infiltration to some extent, can be widely applied to countertop, fireplace surrounds, basement, pond, exterior wall and other wet places.
• Easy to Use: you will get 1 packs of polypropylene fiber , just blend sand, cement and fibers for concrete, then add the right amount of water, and stir evenly, Add more for high impact or severe freeze or thaw areas.
• Friendly Customer Service: If you have any issue during using Polypropylene Fiber, pls contact us at any time, we will reply u in first time while we have received your message.

[david s]

The poor English is not exactly helpful. They sound like the right ones, but don’t give any sizes. They should be finer than human hair and around 19mm long. They do not provide any flexural strength being so fine, but do increase compression strength a bit. Their use in concrete is primarily to hold the wet mix together better which reduces slump and shrinkage cracks from developing
For our purposes, because they melt at 160C they act as burnout fibres leaving behind a network of fine pipes through which moisture can pass. They do not increase density as your unclear description days. Being so fine on melting and burning away you’d expect a slight decrease in density, but because they are so fine there’s no change.
They must be dispersed well in the wet mix by extended mixing. Pull the fibres apart and adding them to the wet mix after the water is added. Attempting to add them to an unwetted mix results in them clumping like a fur ball.

[totalnewbie]

Welcome to US Amazon.com. :-)

I guess I'll just order them and see if they are finer than human hair. And thanks for the tip on mixing. I'll let you know what they look like.

[totalnewbie]

I've been meaning to ask this for a long time. Do burnout fibers help decrease cracking primarily during the curing process, in the early fires where I am trying to get rid of the water from the casting process, or do they help all the time -- long after the oven is cured. Each time the oven is fired.

Thanks again.

[totalnewbie]

David. One other thing. What are you recommending these days?

5:1:1:1 (fine masons's sand, Portland, fireclay, hydrated lime)
5:1:1:0.5 (fine masons's sand, Portland, fireclay, hydrated lime)
3:1:1:1 (fine masons's sand, Portland, fireclay, hydrated lime)

[david s]

Yes, I halve the clay.
Once the fibres have melted then burnt away they cannot contribute to strength. For that you need a fibre that can withstand higher temperatures., like basalt, glass or stainless.

[totalnewbie]

Thanks. Which do you recommend:

- 5:1:1:0.5 (sand, Portland, lime, clay)

or

- 3:1:1:0.5 (sand, Portland, lime, clay)

[totalnewbie]

I'm also curious about this.

I've been meaning to ask this for a long time. Do burnout fibers help decrease cracking primarily during the curing process, in the early fires where I am trying to get rid of the water from the casting process, or do they help all the time -- long after the oven is cured. Each time the oven is fired.

[WaterDog]

david s advised me to use the 3:1:1:0.5 ratio and that's what I did. Along with 2% AR fiber by weight, and 8 oz Poly burnout fibers per 10.3 qts of dry mix by volume.

[totalnewbie]

that's great. Thanks.

i asked on your thread. Did you get both the AR fiberglass and poly fibers from Glob Marble?

[david s]

Thanks. Which do you recommend:

- 5:1:1:0.5 (sand, Portland, lime, clay)

or

- 3:1:1:0.5 (sand, Portland, lime, clay)

A 3:1:1:0.5 mix sounds extremely rich in cementious material so logic would suggest a 5:1:1 0.5.
But if the Portland becomes exhausted it would be then considered just a fine aggregate. As the clay is also not a cementious material and only becomes permanent at higher temperature than the oven reaches it too should be considered an aggregate. In this case only the lime would be the cementious material left so the aggregate proportion in the 3:1:1:0.5 would be 4.5:1 and for the 5:1:1:0.5 mix it would be 6.5:1 which I think is too weak.

[totalnewbie]

Well darn. I just built a massive pizza oven incorrectly because of poor communications. These community sites are so problematic, and this one is unusual because it is hosted by a commercial company that provides no input.

"Is the right number 3 or 5?"

"Logic would suggest 5. Words, words. words, words, words. But the real answer is 3."

I'm checking out now.

[david s]

You will probably be ok. It may turn out that your mix is the ideal one for ovens in this temperature range. I’ve never attempted making a weaker mix so I’m not really sure. Only by trying something different and seeing how I works, can you tell if it’s successful. You’ve actually done the forum community a great service so long as you share your results through careful observation and experience.