Portland and Perlite

[jschadt]

To all,

HELP! I just spent the weekend pouring the oven base and insulating layer. The base went well and the rebar gave it a lot of strength. The Portland and Perlite layer is what I am worried about. I use Perlite, not Vermiculite. We mixed it in the 5:1 Ratio, five parts Perlite and one part Portland, by volume. We got it to the consistency of oatmeal. We screeded it off and it looked OK but did not trowel well. Problem is when it dried I could crush some of the screeded materials with my hand! This concerns me as to the strength of the mix.

I confess I was so concerned I took some Portland and sand and troweled on a skim coat while it was still somewhat wet. I have been standing on the top after two days cure and doing the initial layout but it is still worrying me that something is not right. I think it would be better to admit it and do it over than lose the oven later. Remember I live in Iowa! Cold Winters!

Any thoughts?? Hopefully it is OK and this is all normal, but like I say better to know now than when the dome is on top!

Thanks in advance for your help!

[PIZZAMANMIKE]

Re: Portland and Perlite

My guess is you should be OK, it will compact a little,not much. A mix of that type has no strenth like concrete and will crumble, It would be a little stronger if you added some sand and fire clay to the mix.

[jschadt]

Re: Portland and Perlite

Today I actually thought I should have put a structural concrete border around the whole thing, like I did for the front. Maybe I am overthinking??

[PIZZAMANMIKE]

Re: Portland and Perlite

That would help lock in your floor, you should be able to do that when you finish up the dome exterior.

[jschadt]

Re: Portland and Perlite

Thanks PizzaMan Mike. I am a bit more relaxed after talking to you. I also talked to some of my concrete buddies and they also use portland and a sponge to "dress up" their pours after they remove the forms. They don't know much about Perlite, but what the heck.

I think I will have my wife put some heels on and do a dance on top of the base. If it holds up we will go ahead and put in the firebricks. (No, she is not heavy!)

I think my bigger problem is being in construction I just proceed thinking everything will be great, and problems like these are quite a surprise to me!

[Dutchoven]

Re: Portland and Perlite

jschadt
Neither perlcrete or vermicrete trowel at all...you can just kind of tamp it...it will get harder with time as the perlite holds the moisture and will keep it green for quite a while...when mine was fully dry I could wlak on it no problem but it feels like cork...the edges will always be a bit crumbly...have no fear it will be fine
Best
Dutch

[PIZZAMANMIKE]

Re: Portland and Perlite

jschadt, I would keep you wife off the deck in her high heels, as you will be asking us how to add a brass pole. Ha Ha
pizzamanmike
keep us posted

[atdabch]

Re: Portland and Perlite

should be ok...slab will get harder at curing completes

[RTflorida]

Re: Portland and Perlite

Like everything else involving portland cement, perlcrete or vermicrete need time to cure. I know you want to move forward, but give it a week to set up...Dutch is spot on with his assessment - cork-like, crumbly around the edges, and it seems to stay "green" longer than one would expect. In the end, it has good compression strength.....even when set firm, your wife is going to get stuck wearing heals; but I do like the brass pole idea (maybe in my next oven)

RT

[nissanneill]

Re: Portland and Perlite

Speaking of a brass pole in the centre of the proposed oven, might be more interesting and profitable than cooking pizza. You might even be able to sell tickets, charge $5 for a stubby of beer and reap the rewards.
Build an oven later with the profits.


Neill

[jschadt]

Re: Portland and Perlite

Thanks for the thoughts. Looks like I get a time out for a few days for some cure time anyway. We will be getting 2-4 inches of leftover hurricane rain way up here for the next few days. Looking forward to Saturday!

I did find firebricks for a $1.10 apiece. They offerred to cut them in half for me for $1.00 each. As much other cutting as we will be doing I don't think it would be worth it. I did line up a bricklayer's saw for a month. Should work out fine!

[Dutchoven]

Re: Portland and Perlite

Thanks for the thoughts. Looks like I get a time out for a few days for some cure time anyway. We will be getting 2-4 inches of leftover hurricane rain way up here for the next few days. Looking forward to Saturday!



I did find firebricks for a $1.10 apiece. They offerred to cut them in half for me for $1.00 each. As much other cutting as we will be doing I don't think it would be worth it. I did line up a bricklayer's saw for a month. Should work out fine!

Keep it covered though...don't want it to get wetter
$1.10 is a pretty good price...down here in brick land I am getting them for .
.99...don't bother with the cutting service...they will not all necessarily be halves most likely...enjoy the build!a
Best
Dutch