Using cement frostproofer

Unique joe · 9 Feb 2021

This week is getting frosty and I'm in the middle of building a wall that really needs to be done and waiting for the cold weather to pass is far from ideal. I bought some febmix winter additive to lay blocks down to -4c. It never gets colder than that here. It says on the tub to mix it 2.5ltr per 50kgs of cement. I worked out that's 50ml per kg. I'm mixing at 3 to 1 and I'm making small loads(24kgs). So that's roughly 1.2ltrs of additive.
That's didnt seem right but I went on anyway. The mix was way too runny. Even with no water added the mix is still way to runny. Am I doing something wrong?
Is the ratio 2.5ltrs per 50kgs of cement powder or per fully mixed load. Just cant get this right. Any help would be appreciated.

^woody^ · 9 Feb 2021

Is the sand saturated?

Unique joe · 9 Feb 2021

Bone dry on top and a little darker under the surface. I would barely call it damp.

Oj01 · 9 Feb 2021

Just checking, you're making a batch of total weight 24kg? Sand and cement?

Because at 3:1 that's 6kg of cement, so 300ml of additive, not 1200ml?

Oj01 · 9 Feb 2021

Also just be aware that stuff is 20% Nitric acid, its not particularly nice stuff to get on skin or in eyes

Unique joe · 9 Feb 2021

This is what I'm not sure. Is the ammount added based on the cement I add(6kg) or the total weight of the mix(24kg)? I tried 300ml and it didnt set at all. Had to pull the work down and restart. Not something I want to keep repeating to learn the correct mix. The instructions on the tub dont make it clear.

Oj01 · 9 Feb 2021

It states per kg of cement. So 300ml for 6kg of cement in a 24kg batch. 3:1 is quite a strong mix, standard would be 5:1 which would reduce it to 4kg cement and 200ml additive. How long did you leave this to go off...?

Also some other add-mixes state 1.5-2.5L per 50kg, so you can reduced it slightly if its still too wet.

Unique joe · 9 Feb 2021

I left it 24 hours and when I pulled the blocks down the mortar just crumbled like sand. I had a feeling i did it right the first time. When I did the last mix it just didnt seem right to use so much. Now I just need to work out why it didnt set. It was almost as soft as fresh mortar after 24hrs. Even with the admix will it still take longer to set in colder conditions? It barely gets below -1 here.

^woody^ · 9 Feb 2021

Are you following the usage instructions? It seems like your mortar froze

These additives work by accelerating the setting time to make the mix set before it freezes, and should not be used if the temperature is less than 3-4° when mixed or if temperatures are likely to drop suddenly near to zero son after use. These products are not the saviour you think they are.

As for the sloppy mix, a 24kg mix would normally take at least a 1/4-1/2 bucket of water, so your 1.2ltrs off additive would not make it sloppy unless the sand is already soaking wet. However the additive is also a plasticiser so that's not helping.

And you are better off gauging by volume not weight.

KenGMac · 9 Feb 2021

Additives can be a nightmare?

I have seen on 2 occasions historically where the concrete we were placing failed, meaning it simply did not set, in Summer, no frost or anything like that.

What we found was that the Additive we were using as a water reducing agent was inadvertently over dosed in a pan mill mixer, the Additive was Coremix P7 the walls we were casting were over 1.0. m thick 8+ m high in what was a "Blast Resistant Structure" in a MoD [establishment]

OK moral of the story, Additives are fine but do not get the proportions and ratios screwed up.

On several occasions when in tight contractual situations and placing [say] a floor slab I have used a thin thermal mat placed on top of finished but unset concrete, arrive on site early next day, shove your hand under the insulation material and it was warm, overnight temperature was below 0

Ken.

Unique joe · 9 Feb 2021

Thanks for the tips. I will try again tomorrow. If it fails again I will have to wait for things to warm up next week.

catlad · 10 Feb 2021

Just not the time of year for laying bricks, you may as well keep banging your head against the wall.

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Using cement frostproofer

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