Most suitable grog granularity

[di11on]

Hi folks,

I have found grog with two different granularities - 0/3mm and 4/8mm

Given that I am going for a dome of around 8cm(3") thickness, which would be more suitable. Someone kindly suggested that I should shoot for an eighth of the total thickness which would point to the 4/8mm grade but is there a disadvantage or problem with going for finer than is required?

[Tscarborough]

Re: Most suitable grog granularity

Both, actually. What you want is a a range from dust to the largest size required. 0/3 means dust to 3mm, 4/8 means 4mm to 8mm, so a blend would work well.

The idea of an concrete material is a thin matrix of cementious material surrounding graded aggregate. The aggregate is graded such that the interstitial spaces are as small as possible.

[di11on]

Re: Most suitable grog granularity

Thanks TS... and if I had to choose one or the other (not that I will have to, but if I did?)

[Tscarborough]

Re: Most suitable grog granularity

The larger.

[leetheldc]

Re: Most suitable grog granularity

You really need 0 to 1 grade as fine as possible for a dome as the joint tamper from nothing to around 10 ml on outside of dome any granular larger than 3 ml and your brick would "rock" ie ground out on the gravel making for a nightmare to lay

[leetheldc]

Re: Most suitable grog granularity

Sorry not gravel but ground firebrick grog size

[Tscarborough]

Re: Most suitable grog granularity

He is not laying brick, he is making refractory concrete, the fines are already covered in the other aggregates he is using.

[di11on]

Re: Most suitable grog granularity

And what about the sand? I've heard builder's sharp sand being mentioned. I'm not sure how I would identify that here in France - what distinguishes it? Can I use regular builder's sand? Is the granularity important?

[Tscarborough]

Re: Most suitable grog granularity

Cleaned washed sand, it may be called concrete sand, torpedo sand, stucco sand, or sharp sand.

[di11on]

Re: Most suitable grog granularity

Thanks - appreciate all the help

[di11on]

Re: Most suitable grog granularity

Hmmm... I have an interesting dilemma... I was told there were three grades of grog, namely:

Extra fine: 002
Fine: 005
Coarse: 015

I assumed that was 0 to 2mm, 0 to 5mm and 0 to 15mm

I bought a bag of "Fine" and a bag of "Coarse".

I'm now looking at my sacks of grog and they say 0.5mm and 1.5mm!!!

Arrrgggg...

Is there anything I can do with these? What could I add as a coarse aggregate? I really don't want to lug those 50kg sacks back and start my search all over again!

I would be grateful for any suggestions!

[Tscarborough]

Re: Most suitable grog granularity

Get a canvas bag and some brick and start pounding.

[di11on]

Re: Most suitable grog granularity

Get a canvas bag and some brick and start pounding.

Does it need to be firebrick that I pound?

I was originally going to go for a mix something like:

48% Grog 0-15mm
30% Sand
22% Refractory cement

Any suggestions as to what ratio I would then mix the following components:

Grog 0-0.5mm
Grog 0-1.5mm
Pounded Brick
Sand
Refractory cement

[Tscarborough]

Re: Most suitable grog granularity

The fine grog should replace a portion of the sand.

[di11on]

Re: Most suitable grog granularity

Thanks TS,

I'm guess there really isn't any benefit to having the two grades of fine grog, but I assume there will be some benefit to using one of them to replace the sand as you say?

Putting the question another way, if I'm going to have to pound brick now anyway - will the fact that I have a bag of 0-1.5mm grog mean that I will have to crush less brick than I otherwise would have had to (if I had no grog)?

Can I get away with non-refractory brick?