vermiculite finishing problem

[litecrete]

Greetings,

I found your website some time ago and appreciate the discussions on vermiculite though we are not in the pizza oven business.

We are using vermiculite, portland cement mix for ornamental objects including planter boxes. We love the lightweight nature of this product but we are struggling with one major issue.

The 3 sides against the melamine board look great - it's the open side that comes out dry and crumbly, like there wasn't enough cement in the mix.

Do any of you have thoughts on what can be done about this? I'm including a couple of pictures for reference.

We are mixing 2 coarse grade vermiculite: 2 fine grade vermiculite: 1 portland cement.

Any thoughts appreciated!

[Gulf]

Stop about 3/8" to 1/2" from filling your form. Finish the pour with only fine vermiculite in your (if my math is right) 4 to 1 Mix. The fine will finish as smooth as cement.

[david s]

If you want to use it to make things like planter boxes then you probably need more strength. You can do this by adding sand and a higher proportion of cement. Lots of people end up using too much water in the mix. This tends to wash all the cement to the bottom leaving crumbly vermiculite on top. I've found about 3 -4 parts water for every part vermiculite works well (the finer the vermiculite the more water you need)

PHYSICAL PROPERTIES
MIX PROPORTIONS BY VOLUME

DENSITY
PCF COMPRESSIVE
STRENGTH
28 DAYS PSI

cement verm sand wet density dry density comp. strength 28 days
1 8 0 40-48 19-22 70-125
1 7 0 42-47 20-24 125-140
1 6 0 44-52 23-27 135-175
1 5 0 49-55 25-31 175-125
1 4 0 55-62 30-35 225-325
1 3 2 85-91 75-80 600-620


Sorry about the table but it doesn't like the format, but as an example the compressive strength of 1:3:2 cement, verm. sand is 600-620 whereas the 1:8:0 mix is only 70-125

[mrchipster]

Originally Posted by david s

PHYSICAL PROPERTIES
MIX PROPORTIONS BY VOLUME

DENSITY
PCF COMPRESSIVE
STRENGTH
28 DAYS PSI

cement verm sand wet density dry density comp. strength 28 days
1 8 0 40-48 19-22 70-125
1 7 0 42-47 20-24 125-140
1 6 0 44-52 23-27 135-175
1 5 0 49-55 25-31 175-125
1 4 0 55-62 30-35 225-325
1 3 2 85-91 75-80 600-620

I resaved your chart as a jpg file and I think it is easier to read.

Chip

[david s]

Thanks Chip,you little computer guru. Why didn't I think of that? It is actually a pretty useful chart.