How do I know my mortar is strong enough?

[nordita]

First time building anything with mortar. I put up a block wall and used a ratio of 4:1 sand:cement with a splash of plasticiser. The mortar had a smooth texture, kept it's form, stayed on the trowel and was easy to apply if I wet the blocks a bit.

The following morning it seemed to set and the wall felt sturdy but if I shook the block vigorously enough I could pry it loose. I put it up in 13 degrees. But overnight the temperature was 4 degrees since midnight dropping to 0 degrees at 06:00 for an hour.

I tore it down because of a different reason but this time I want to make sure its right.

I put up another corner (picture 2) trying making to make sure I used the precise ratio but this time I feel it was a bit too wet? It definitely felt a bit soupy when pointing.

 

[Koolpc]

Surely you got to give it more time before you start stressing it?

 

[nordita]

That's my hunch. I just thought I asked as I had the opportunity to start again due to a different reason.

 

[23vc]

Totally normal and expected

 

[robinbanks]

I'd use 5:1 or 6:1 as a ratio and wait around 3 weeks before I started beating the s**t out of it.

Mortar can't cure overnight; it's nothing to do with drying or looking dry, it's about crystals growing in the mortar and locking everything together. That takes time and requires moisture to be present for effective crystal growth. In very hot working conditions you might need to wet the work again if it's drying out too fast

When newbies are mixing, their overbearing temptation is to put too much water in and not mix for long enough. Use the amount of plasticiser as per the instructions on the bottle. Add water gradually until the mix looks like apple crumble topping and then stop. Let it roll round the mixer for another 10 minutes. It should be more like angel delight when it's done, it should pile up in the barrow like a whippy ice cream and if you drag a deep line in it with your finger it should retain the trench and not collapse on itself. It got to this workable state not my addition of water, but by the plasticiser and mixer working together to aerate the mix. Too much water impedes that and makes it awful to work with

Wetting the blocks down some will help but don't go so crazy with it that water is running out of the block again. Damping them down if they're very dry will stop them pulling so much water out of the mix, as the mix needs the water to cure well

As you lay, use the trowel to scrape off anything that has splurged out but otherwise leave it alone. Keep a check on it through the day; when it's reached the point where it's more dry and it flakes and crumbles when you run a trowel over it, that's the time to do your pointing. If you're planning on rendering it that doesn't need to be an involved process, just a sweep with a stiff yard brush will be fine. Watch for flicking mortar in your eyes if you're doing this. Pointing when it's too wet makes a mess

 

[jeds]

Indeed, if you can lift a block off in three weeks time you might have a problem, otherwise crack on. Most people make mortar too hard. 1:4 is probably ok but, as robin said, 1:5 would be better. Hard mortar makes joints prone to cracking and can even crack blocks in half. There's an old saying; mortar doesn't so much stick blocks together as hold them apart.

 

[DiyNutJob]

Most people make mortar too hard.

Guilty as charged. I did 1:1. Luckily, only for patching.