Structural Slab for new WFO

[mikku]

Re: Structural Slab for new WFO

About 350 liters perlite, give or take, but no vermiculite. The ratio to water came out to be about 30% by volume perlite. A little more volume than you estimated but your statistics are dead on as usual. Portland cement--just a tad over a 25kg bag. I had a bag that had a few chunks in it--first batch, then I tossed it. Did not want more variables to screw up the mixture!

As mentioned, I did leave an area maybe 40 cm diameter open at apex, but nothing compared to total surface area. Am having thoughts on a permanent vent at top of dome once everything is dry and enclosed.

There has been a lot of chatter about completed WFO's that have been gotten wet and had to go through the drying process again. Maybe not the amount of water I am dealing with right now. I think that firebrick really absorbs water as well.. I noticed that when doing the few cuts I had.

(Maybe a good new thread-" Design considerations to prevent water migration into WFO igloo design")- Do's and Don'ts

Just a lot of things racing through my mind... builders with counters up to the WFO's where rain might hit-- a real entry point for water!

Today was the first day that the sun shone with any intensity and the temperatures were higher. When I can, I will open the garage doors and get some sun/wind action--but the drying will be much decreased because of surface area..

Need to get the chimney attached and some heat inside. That basically means a move outdoors. At least I have some protection in place for that move. Will have to see how things work out. Still have overnight freezing temperatures to deal with!

Thank you for your input, technical leads, and non-judgemental advice. This is just a work in progress--learn as I go.

[david s]

Re: Structural Slab for new WFO

So you did the insulation about a week ago, then plastered over it. Seeing as it's indoors then very little water will have evaporated. Don't know how much vermiculite and perlite you used, but if it was about one 100 L bag of each then you will have about 70 L of water in that layer. A small amount of that will have been taken up by hydration with the cement, but you have still trapped a large amount of water there. You will find that the insulation layer will expand a bit on heating too. 70 L water makes 70,000 L steam. Ask yourself how much fire you would need to boil dry a 70 L drum of water? (That's why I advocate doing a thick layer of vermicrete dome insulation in layers with a week to dry in between). This might give you an idea of what you're up against. Folk who use blanket don't have to worry so much because if they use any vermicrete it is a thinner layer and their vermicrete won't get so suddenly heated because of the blanket between it and the hot dome.
leaving open an area at the top of the dome might be helpful, but it is the moisture around the base of the dome and under the floor that is the most difficult to remove. Steam will condense on the inside of your stucco and run down to the base where you have dammed it up. That reminds me, if you want to get good adhesion between the base of the outer shell and the supporting slab, cut some grooves into the supporting slab with an angle grinder fitted with a diamond blade. It's a good solution as often it is a place where a crack will develop.

[mikku]

Re: Structural Slab for new WFO

Just did an msds search on "Plaster grade Lime"!

A real eye opener!

I think that the mixing of my render is going to be outdoors, at least until after the water is added. I was doing a light sweep up, then vacuum cleaning today.. Maybe sweeping not such a good idea! Vacuuming maybe better, but now thinking of really being careful with cleaning the filter... Also, some thoughts of diluted solution of vinegar to mop the floor surfaces..

Maybe a little more careful on how the mixing is performed and any materials not getting into the mix that may be floating around!

Thank you for the heads up!

Gets you thinking about the dangerous things you get used to having around.

As a kid, my father always had a box of dynamite upstairs the garage--its use was for blasting out stumps.. I remember that when it got old, it used to weap an amber colored fluid... sometimes would use cut-off pieces and blow them off over the 4th of July because possessing fireworks was illegal! Go figure?

Same goes for "carbide"... had that around to produce "acetylene" for welding torch.. Old type of carbide-acetylene-generator. We would put a couple of grains of carbide in the bottom of a Hershey chocolate can, make a little hole in the bottom to run a fuse into, spit into the can; put on the cover; light the fuse and run! Big Boom and do it over again! Crazy thing kids do --growing up in the northwoods--for entertainment!

Always had a dog around for company!

[mikku]

Re: Structural Slab for new WFO

Is there an MSDS for my upside down render?

[david s]

Re: Structural Slab for new WFO

If you have a concern about any material there is a MSDS (materials safety data sheet) on everything.Easy to look it up on the net.

[mikku]

Re: Structural Slab for new WFO

Thanks, I did!

Read it from start to finish and added my 2 cents as usual!

That thread should be at the beginning of every page...so we do not forget!

The lime I purchased only had drawings of peoples' faces with masks, goggles, and hands wearing gloves.

Never saw those pictures on the bags of lime we used in the outhouse!

Probably MORE hazardous substances there than lime! But both requiring respirators at times!

[david s]

Re: Structural Slab for new WFO

Search "safety issues"

[mikku]

Re: Structural Slab for new WFO

I don't know if there is a thread or not.. Haven't looked but there should be one on the dangers of some of the materials we are handling.

I am thinking that lime, glass fibers, portland cement, perlite, vermiculite,.....all have to be handled carefully--stay away from breathing any of it... Only thing not dangerous is possibly the water! And a great pizza or loaf of bread when the build is done!

[mikku]

Re: Structural Slab for new WFO

Against all the good advice offered, I put the render coat on today.
However, I left the apex open, and area around the chimney.
The 4:1:1 mixture along with fiber reinforcement render was a pleasure to work with. I have seen guys with the tool that looks like a graduation hat--that they put plaster on...so I knocked a few pieces of wood together and a thin piece of plywood on top.. That mixture stuck to that board no matter which position (except upside down) without sliding! Also stuck to the face of the trowel without budging... Great mixture! But it spread like creamy peanut butter.

This first layer is only about 1/2" thick, but it should give the stability I am looking for! Reverse reasoning is: if this stuff sets up as quick as experienced today, then it has to be sucking water like crazy! Maybe it is good to apply it now..chemically sucking the water out!

Other thought-- "What is the (WORST) that can happen?"
next to last thought- "a person does not learn without making some mistakes!" so --it is a learning experience here...if something really crazy happens..then I have learned and do it differently on the second oven build!

lastly- "I do not accept something as a mistake -- unless it CANNOT be fixed!" --and I have the McGuiver mentality, that most things I can fix!

So the future will tell-- next step--chimney, sometype of oven entrance surround to close off insulation--the "Burn!!!!!!!!!!!"

[mikku]

Re: Structural Slab for new WFO

Another "good advisor" stopped by to check on my build. While explaining my plastering plan to him, he told me that I am "over spec. ing"!

He said that I should concentrate on getting a good bond between the structural base and my render coat. Tapering it away from the dome -allowing for a thicker surrounding base. He felt that the fibers in conjunction with a strong bond to base is vastly superior than trying to wire mesh things together.

Further, he said--if the mesh is not enclosed in the render coat, it is useless!

This guy is a good friend and does not mince words. He has been around building for a very long time and I need to think over what he said carefully!
A little cheaper, less complicated, he is probably right!

Advice seems amazingly like a guy from OZ tropics, David s!

[mikku]

Re: Structural Slab for new WFO

I found some of the illusive components for rendering.

Pure silica sand (ka tsuna) can be purchased for $8.50/30 kg, compared to $24.00/ton-washed river sand. (typical component for plaster contractors).

Portland cement is just a commodity- everywhere available!

Hydrated lime- in its pure form (Shosekkai) must be special ordered at $16/25kg bag + $10 delivery fee.

Another type of lime- the component used in plasters for stucco, is a blend but also a commodity- sells for $16/25kg bag.

Reinforcing fiber- comes in a small vinyl bag--sells for $2.50/bag.

A premix-plaster containing lime/micro fibers/blend... top coating (maximum thickness) 2mm sells for $24/25kg bag.

What I am considering now is to do a scratch coat this coming week-but leaving a larger area toward the apex open.

To anchor the dome to the structural slab, I have stainless wires already cast into the slab. I am considering using a 1" grid stainless chicken wire, cut and twisted to conform to the shape and then additional stainless wires criss-crossing the dome connected to my embedded wires. Once the scratch coat gets applied, this net will be completely covered.

The scratch coat would probably be 4:1:1, using standard washed river sand, portland, lime and fibers.

I can load up on the fibers for crack resistance.

I am trying to avoid damages that could be caused by jolting. I.E. a forklift bumping into the slab in the moving process and the whole dome shifts on the firebrick!!! What a sad day that would be!

I am thinking that a partial render coat will protect what I have and an opening will leave an exit for water vapor.. I think vapors under pressure seek the weakest course- like a typical wall assembly.

Those are my thoughts, please pick them apart and point out faulty thinking--I am just trying to chart a course to get from one point to another without messing things up too much!

[david s]

Re: Structural Slab for new WFO

.

Here are the questions:

1) Does this pericrete reach an "ultimate strength" after a certain number of days?

2) If so--by experience, how many? Like concrete approx. 28 days?

3) Will it develop a structure where I do not have to be careful about bumping it without fear of it crumbling to powder?

4) Given the fact that this material is extremely porous, and that a render coat will re-introduce a significant amount of water... and the strength of the render will be dependant upon a slower dry (for hydration)... would it not make sense to do the render sooner, rather than later BUT leave a significant opening...like Gulf describes for venting moisture?

5) I am dealing with a slightly mobile build--I worry about jacking up the slab to install the wheels--and any vibration to the slab by moving... I really don't want a chunk of this insulation to fall off like an egg shell!

6) The other upcoming event will be a curing fire--so far "done outdoors" unless I use the "propane fire ring" technique or "heat beads" with the garage doors open. Both techniques, however, require a final burn using wood to get the high temps. This would involve moving everything outdoors via forklift and possible-bumping, twisting, etc. forces---that a render might protect!

My structural slab is quite rigid--visibly at least, if the base is not supported equally, it will rock rather than flex.. But this pericrete seems very brittle!

Only someone who has worked with pericrete can answer these questions because they have actually observed the characteristics of a 10:1 mix as it is installed and as it ages!

I can see no reason for anyone to build up pericrete in 1" layers over a dome!
I saw on another website, someone advocating the use of lime with portland & vermiculite/perlite --only reason I can see would for it to adhere easier in thin coats...But this would also decrease the insulative properties?

Sorry for the "longwindedness" but a lot of questions requiring answers.
Also must evaluate risks vs advantages in the build!

1.Because perlcrete or vermicrete is made with portland cement it continues to increase in strength over time. One week is generally sufficient. A vermicrete mix contains about double the water needed for hydration so there is plenty of moisture there for this stage.

2. Only if you are making a ferrocement boat or high strength concrete would you require 28 days. the difference is minimal (look at a strength vs time graph of concrete strength)

3.No it will always be weak. But it only needs to be strong enough to stand up vertically and be firm enough to render over. The more cement you put into the mix the stronger it will be, but you drastically reduce its insulating value if you do.

4.There is some sense in this , but water left in this layer presents problems in removal. I take the view that it is better to dry the insuation layer completely, render over it ,then seal the render layer for a week using cling wrap.

5. If any falls off it's easy enough to patch it up.

6.The reason I advocate doing the vermicrete in 1" layers is so it has a better chance to dry. If you do it all in one layer it is much slower to dry the stuff that is buried deeper.

[mikku]

Re: Structural Slab for new WFO

Question time again:

1) I have been warned about getting all the water out of the insulation prior to rendering.

2) Today, the insulated pericrete dome when tapped returns a hollow type sound.

3) I did not clean out the wheelbarrow used for mixing yesterday--but the dry stuff left from yesterday shows no properties of firmness--simply crumbles if you roll it around in your hand. But that material was not pressed into place or tamped in any fashion.

4) Yesterday, when adding the second level to the dome, I wet the dome--and you could visibly see it absorbed into the refractory... the water placed on the previous days pericrete--simply disappeared with no sign of color change from absorption.

Here are the questions:

1) Does this pericrete reach an "ultimate strength" after a certain number of days?

2) If so--by experience, how many? Like concrete approx. 28 days?

3) Will it develop a structure where I do not have to be careful about bumping it without fear of it crumbling to powder?

4) Given the fact that this material is extremely porous, and that a render coat will re-introduce a significant amount of water... and the strength of the render will be dependant upon a slower dry (for hydration)... would it not make sense to do the render sooner, rather than later BUT leave a significant opening...like Gulf describes for venting moisture?

5) I am dealing with a slightly mobile build--I worry about jacking up the slab to install the wheels--and any vibration to the slab by moving... I really don't want a chunk of this insulation to fall off like an egg shell!

6) The other upcoming event will be a curing fire--so far "done outdoors" unless I use the "propane fire ring" technique or "heat beads" with the garage doors open. Both techniques, however, require a final burn using wood to get the high temps. This would involve moving everything outdoors via forklift and possible-bumping, twisting, etc. forces---that a render might protect!

My structural slab is quite rigid--visibly at least, if the base is not supported equally, it will rock rather than flex.. But this pericrete seems very brittle!

Only someone who has worked with pericrete can answer these questions because they have actually observed the characteristics of a 10:1 mix as it is installed and as it ages!

I can see no reason for anyone to build up pericrete in 1" layers over a dome!
I saw on another website, someone advocating the use of lime with portland & vermiculite/perlite --only reason I can see would for it to adhere easier in thin coats...But this would also decrease the insulative properties?

Sorry for the "longwindedness" but a lot of questions requiring answers.
Also must evaluate risks vs advantages in the build!

[mikku]

Re: Structural Slab for new WFO

Progress on insulation.



That is far as I can go without a chimney!
Tried to make the top of the dome insulation thicker- but now it looks like one of the "cone heads"! A few bumps and dips--but better than I expected from eye-balling it only.
Just have to call it character!

I was surprised, this morning I was able to shave some of the edges using an OLFA cutter. The insulation is still very fragile, but it cut like styrofoam.

There are places where this stuff is over 6" thick--(near the inner door opening), lots of water to dry out!

[mikku]

Re: Structural Slab for new WFO

That is worth a good chuckle!