Hi everyone. will be thankful if you help me... (sorry if my english is not good)

I am not in usa or canada to use best gfrc raw material.

I have a big trouble here and it is weight. my gfrc weight (density) and consequently the strenght is too low. My gfrc is not dence enough and when i knock on it with my finger, the sound is like knocking on empty or poke thing, while the sound should be like knoking on hard stuff like stone or porcelain tile. 

My mix design is :
100 lbs white portland cement
100 lbs silica sand 45 to 85 mesh (or 2 to 4 mm)
12 lbs liquid polymer with 50 percent water
6 lbs 3/4 inch ( 18mm) AR fiber glass
1 lbs water reducer
26 lbs water

I am not new in concrete and I did a lot of tests with my materials to solve it.

I tested with different cements and different sands and different polymers and ....
and i figured out in any case that when the glass fibers getting dispersed well , the weight and consequently the strenght suddenly comes down. 
for example:
with (.34 w/c ratio) (.5 percent water reducer) , the mortar not formed and glass fibers not dispersed well , the weight is 2100 kg/m3 or 131 lb/ft3.
but with (.38 w/c ratio) , the mortar formed and glass fibers dispersed, the weight comes down to 1600 kg/m3 or 100 lb/ft3.
why this happening? anybody could help me? could it be related to the fibers? should i change it?
right sample in the picture : with glass fiber (too many porous and voids)
left sample: without glass fiber (it is dense and strong)

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What brand of fibers and polymer?

fibers : no name pack AR glass/18mm  and made in china. 

polymer: 7 different that available in my area. Those are not specially made for gfrc because gfrc is not known here, but all of them are acrylic latex polymer base.

Please dont say use famous us brand...  I wish but its is not possible

Many things can cause this but stay away from the China fiber...find AR made in Japan.  NEGA is a good brand.  The China fiber may be breaking up in your mix and causing the air voids. 

For acrylic it has to be pure Acrylic and you need a de-foamer...hopefully built into the polymer.

I have de-foamer but when the fiber going to dispersed , weight suddenly comes down.

No matter how much de-foamer I use. 

Unfortunately we cant buy top brands easily here. 
It may take a few months.

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