Home Brew Mortar Sand

[SirClutzz]

Quick question on home brew mortar. I am having trouble finding specifics around the sand to know.

I know it should be silica (quartz) sand, but I am having issues determine the grain size.

I'm in Australia, which is probably what is complicating the process. I've seen that pool filter sand is ideal, and at 20/40 grade is what I should be trying to find. I THINK that is 0.8 to to 0.4mm grain size.
I can find 16/30 here, which I think is a larger, 1.1 to 0.6 grain.
I can also get c3 (which is 3mm) and c1 (which is 1mm).
I'm unsure if these sands are classed as sharp sands or not.

I can also get sand from a coatings supplier, and there sizes are SF2, F4, F6 and F8, but once again, I don't know what that means, or if they are sharp sands (I've reached out to the them, but don't have a response as yet).


So the questions are..
Would c1 pool filter sand do the job?
Is pool filter sand normally sharp sand? I thought I read somewhere that sharp sand doesn't allow for good water flow so they DON'T use it for filter sand?

I'm just a bit lost on this point, any help and advice would be awesome

Thanks

[SirClutzz]

Actually looks like filter sand is sharp sand, so ignore that part of the question

[david s]

The general rule with any aggregate is not to exceed more than 1/3 of the thickness.

eg. for a 30mm concrete slab do not exceed 10mm aggregate. Or for a 3mm mortar joint do not exceed 1mm sand grain size
I use silica sand and pass it through a 2mm sieve which takes out any foreign material, breaks ups lumps and removes around 5% of the given volume in larger grains. It's then suitable for mortar, castable or render mixes.

[SirClutzz]

Thanks david s , I was thinking the 1mm (c1) sand would probably do the job, and it's the closet supply to me. The other company got back to me about an hour ago, and could only really send me pics of the sands beside a ruler, and they are smaller then 1mm, so I'm not sure if the small the better for these mortars, but they are also an hours drive each way to pick up.

[Pizzarotic]

I can also get sand from a coatings supplier, and there sizes are SF2, F4, F6 and F8, but once again, I don't know what that means, or if they are sharp sands (I've reached out to the them, but don't have a response as yet).
So the questions are..
Would c1 pool filter sand do the job?

Pool filter sand is silica sand and quality is excellent due to it being washed and graded. C1 as you know is 1mm grain size so might be a little course for mortar if you're doing very fine joints. SF2, F4, F6 and F8 are finer grades, I think SF2 & F4 are the same same and very fine. F6 might be a foundary sand, F6 & F8 would probably be ideal size for Verry fine mortar but pool filter sand is readily available at any pool shop and should work just fine. If you had the choice I would blend pool filter sand with a fine sand for the ultimate mortar.

[SirClutzz]

I grabbed some of the 1mm filter sand, I think it's too course. Gave it a go to mortar the insulation bricks down to the slab, this joint was a bit thicker then I'll want for the higher levels, but none of this bit will be seen, so figured it was worth a go. Worked under the bricks ok, but way to course for between. I had a small 5kg bag of a high heat mortar that I ended up using between the brick, so that was a bi of a pain running to mortars at once..

here is a pic of the mortared down bricks

[SirClutzz]

following is some close up pics of the sand. The first is the c1 filter sand that I used in the previous posts pic.


the next 4 are from the other supplier. I think I'll have to go for a drive during the week.

[david s]

Apparently a range of grain sizes provides superior strength. For mortar large grains only become a problem if they interfere with the joint size or reduce workability. Our local blocklayers just use silica sand as supplied through landscape suppliers. I do run it through a 2mm sieve to remove some larger grains and to break up lumps. The addition of lime and/or powdered clay increases any mortar workability as do fine pp fibres. As clay is not a cementious material like lime or cement, it should be considered an aggregate, although it’s extremely fine particle size makes the particles want to cling together. A good analogy is that fine sand makes sandcastle building way easier than coarse sand. Therefore too high a proportion of clay induces excessive shrinkage, so don’t overdo it’s addition.

[Pizzarotic]

What mix are you using for your mortar?

[SirClutzz]

I tried sieving the silica sand with a seive I had, and it didn't anything out of it, looking closer at is the grain size is very consistant. i.e. there's not alog of smaller stuff in there.From the pics previously, I think the f12 sand looks a better option. I am trying to get as tight of joints as possible.

The mix I'm using is just the 3:1:1:1 mix I've seen on here as the standard.

[david s]

Your sand should be quite ok to use as is. The thickness of the joints varies enormously because as the bricks are laid on an angle the joint is very thick on the outside while the exposed joint on the inside is usually very thin or even nonexistent.. Many builders use some of the wedge shaped off cuts to jam in the thick joints on the outside.

[Pizzarotic]

The mix I'm using is just the 3:1:1:1 mix I've seen on here as the standard.

The 3:1:1:1 mix works well for casting.
in your application I would try a richer mix with more clay as your fine aggregate.

Give 10 : 6 : 2 : 3 (Sand, Fire Clay, Portland cement and Lime) a go and see it that works better with your finer joints.

[david s]

The 3:1:1:1 mix works well for casting.
in your application I would try a richer mix with more clay as your fine aggregate.

Give 10 : 6 : 2 : 3 (Sand, Fire Clay, Portland cement and Lime) a go and see it that works better with your finer joints.

No, this is not advisable. As previously advised "too high a proportion of clay induces excessive shrinkage, so don’t overdo its addition."

The proportion of clay in the homebrew is already at the max IMO. It's high proportion is designed to make the homebrew more refractory and does a pretty good job, as discovered by the many builders on this forum. Try a test yourself if you want. I'm sure you'll discover that you'll end up with shrinkage cracking by departing from the tried and true 3:1:1;1

[SirClutzz]

ok, thanks for all the input. I think I'll go a get some finer sand to mix with what I have, that should give me the finer aggregate without as much risk of shrinking. I am intending to have tight joints on each course (the verticals), but probably wedge between each course, so that will be a larger joint.

I need to start a build log thread, should I do that in the newbies or the pompeii oven construction thread?