The wetness of sand, ratios by weight or volume etc.

[Albumen]

follows on a bit from //www.diynot.com/forums/viewtopic.php?p=1662621#1662621 where I was worried I might have made a mortar mix too weak.

My sand is wet. Damp I would say, it holds it's shape, but isn't runny. Neither dry runny or wet runny.

So I took exactly 1 kg, weighed on the kitchen scales. Then dried it. Bone dry it weighed 840 grams. So 16% of the wet sand's weight was water. It's plastering sand.

On this forum people say that professionals do mixes by weight, not volume. But without buying the actual BS spec the nearest reference I can find is this:

http://www.mortar.org.uk/downloads/miadata03.pdf

Which says by volume, at least for mortar (don't know if concrete is any different). And any other ref to the BS seems to say volume.

Of course here:

http://www.mortar.org.uk/downloads/miadata03.pdf

they give dry sand and cement as similar densities, so it's going to work out the same.

Upshot seems to me to be that if you use wet sand in a mortar mix, and you measure by weight you will have a stronger mix than you think. As an example my case is:

8.5kg of cement (dry, obviously).

43kg of wet sand.

43/8.5 = 5:1 mix (oh no, I though, too weak for scratch coat).

but actually I find out that 43kg of wet sand is the same as 36kg of dry sand (43 x 84 /100)

So actually my mix is:

36/8.5 = 4.25. Just about right for scratch coat.

Whaddya mean, I should get a life?

 

[Deluks]

This is a very good question. As to whether you'll get a good answer???

Most builders and diy-ers probably still go for the 5 shovels sand to 1 cement. I try to stick to level buckets, I doubt anyone uses scales except on the big sites.

So worst to best: guesswork, volume, weight.

You'd be really unlucky to have any problems mixing by volume, and if the sand is in bulk bags then these are free draining so it's not as if the sand will be swimming in water. When mixing, if it looks right, it probably is.

 

[Albumen]

I meant to post this in plastering. Oops.

I'm sure you're right. The bags of sand were wet through when I bought them, after a while stood on end I daresay a fair bit of water has drained. Though the nature of sand seems to mean that once and water that's drained has drained, the rest stays in the sand, unless it's in the open air.

I was getting a bit nervous because I thought I'd put a weakish coat of render on first. And you're supposed to go from strong to weak. And one patch needs 3 coats, so was stressing about if I could do that without the last coat being too weak.

Worth bearing in mind, but like you said on most jobs it's not going to be critical, and when it is, like for consistency of colour in architect specified brickwork I suppose it'll be delivered or mixed on site in one of those big things.

 

[RonnyRaygun]

If you're mixing by volume, if using wet sand you might end up with slightly larger shovelfulls when the sand is wet due to its ability to hold its shape. Obviously there will be an optimum amount of water to get the most suction.
You don't really want this as the cement will obviously be bone dry so you will be getting less cement on your shovel compared to the sand resulting in a weaker mix.

So you'd probably be better off measuring level bucketfulls of sand and cement to ensure the same volume of each.

Even if you do this with an optimum amount of water the sand will compact down compared to when dry, so by weight there will be more sand in the bucket than dry cement.

So in conclusion, for that perfect mix you need bone dry sand and cement and you need to measure by weight. Don't think many people do that though.