adding frostproofer to postcrete

[nick9one1]

I need to replace e couple of fence posts and with it being cold at the moment (2C daytime and -3C night) I planned to add a bit of Sika Frostproofer to the postmix.

I have hanson postmix which requires two litres of water. I plan to quickly mix in a flexibucket then chuck it in the hole around the post.
But I cant quite work out how much frostproofer to use...

The directions have some calculations for concrete mixes. Then further down it says 1.25 - 2.5litres per 25kg of cement.

Assuming postcrete is a 123 mix, my 20kg bag would contain 3.3kg of cement.
at 1.25 litres per 25kg, this would work out at 170ml for 3.3 kg cement, so I roughly need to mix 1.8l water and 0.2l of frostproofer. Then add the postcrete.
Does that sound right?

 

[nick9one1]

I've just noticed it also says Do not use with high alumina cement

but Sika make another product called wintermix that doesn't have this limitation..
It has the same dosage rate so the question is still valid.

at 2.5 litres per 50kg, this would work out at 170ml for 3.3 kg cement, so I roughly need to mix 1.8l water and 0.2l of wintermix. Then add the postcrete.

Does that sound right?

 

[noseall]

I've just noticed it also says Do not use with high alumina cement

but Sika make another product called wintermix that doesn't have this limitation..
It has the same dosage rate so the question is still valid.

at 2.5 litres per 50kg, this would work out at 170ml for 3.3 kg cement, so I roughly need to mix 1.8l water and 0.2l of wintermix. Then add the postcrete.

Does that sound right?

View attachment 403637

Postcrete is already loaded with accelerators. Don't put any other additives in.

 

[^woody^]

Frost layer is up to 6" below the surface.

Don't over think it, these are fence posts.

 

[nick9one1]

Thanks for the replies.

The additive was only £5 and the postcrete instructions said min 5 degrees C.
When I bought it I thought I could just throw a bit in for extra protection.

 

[foxhole]

Use warm water , will be solid before any frost can affect it .

 

[Ivor Windybottom]

Postmix will set in about ten minutes anyway.

Perhaps just bung the scrunched up bag on top with a brick over as a precaution, but it's definitely not going to explode overnight with a bit of frost.

 

[nick9one1]

Thanks for the replies.

I phoned Hanson and they told me they produce two types of postmix - fastset and postfix. Both go hard in under 10 mins.

fastset contains high alumina cement, postfix doesnt. I have the postmix which is fine to use with the frostproofer.

I added 250ml to the water, mixed in a flexibicket then chucked it in the hole.

This is probably overkill for fenceposts but cement is vulnerable to frost even when hard.
Although it feels solid after 10 mins it is very weak and there is still moisture present that can freeze, expand and crack the cement before it has reached full strength.

Key Frost Vulnerability Periods:

• Critical (First 24-48 Hours): Maximum risk; freezing water destroys hydration and can cause up to 50% strength loss.
• High (Up to 7 Days): Still gaining significant strength, but vulnerable; protect with insulation or blankets.
• Moderate (7-14 Days): Stronger, but still needs care in severe conditions.
• Low (After 14+ Days): Near full strength achieved, but strength development slows significantly in cold.

For the sake of five quid it's worth adding a splash of frostproofer.

 

[noseall]

T

Key Frost Vulnerability Periods:

• Critical (First 24-48 Hours): Maximum risk; freezing water destroys hydration and can cause up to 50% strength loss.
• High (Up to 7 Days): Still gaining significant strength, but vulnerable; protect with insulation or blankets.
• Moderate (7-14 Days): Stronger, but still needs care in severe conditions.
• Low (After 14+ Days): Near full strength achieved, but strength development slows significantly in cold.

I doubt any of those numbers apply to postcrete.

 

[nick9one1]

Like I said, possibly overkill for a fence post. But while moisture is present and full strength hasn't been achieved there is a risk of cracking. The bag says minimum 10C for a reason.

 

[noseall]

Like I said, possibly overkill for a fence post. But while moisture is present and full strength hasn't been achieved there is a risk of cracking. The bag says minimum 10C for a reason.

I get that. But you are in the ground and the gear will be self insulating apart from the top 10-15mm.

 

[nick9one1]

this is ground temp on a farm in yorkshire at 10cm.