Gunite Cure time?

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zach5150

0
May 22, 2013
70
Austin, TX
Hey all,
Quick question on gunite. I've heard from someone that gunite should cure 30 days before plaster. My PB is definitely NOT on that schedule. He's moving much faster. I see lots of pools built here in TFP in less than 60 days, so it seems like if a 30 day cure was required, I'd have heard about it. I suspect my 'source' is wrong, but I thought I'd bounce the idea here for feedback.

Thanks!
 
http://www.cement.org/basics/concretebasics_faqs.asp

What does 28 -day strength mean?

Concrete hardens and gains strength as it hydrates. The hydration process continues over a long period of time. It happens rapidly at first and slows down as time goes by. To measure the ultimate strength of concrete would require a wait of several years. This would be impractical, so a time period of 28 days was selected by specification writing authorities as the age that all concrete should be tested. At this age, a substantial percentage of the hydration has taken place.

What is 3,000 pound concrete?

It is concrete that is strong enough to carry a compressive stress of 3,000 psi (20.7 MPa) at 28 days. Concrete may be specified at other strengths as well. Conventional concrete has strengths of 7,000 psi or less; concrete with strengths between 7,000 and 14,500 psi is considered high-strength concrete.

Up to you and PB on how long you want it to sit. Keep in mind that the concrete is curing in that 30 days, whether the PB is doing other things around it or not.

My PB said to keep it wet (water it 4 to 5 times/day) for 14 days. It's still curing after 14 days but the water doesn't penetrate as much and now the curing is going on inside under the hardened outer parts.
 
Given, those charts, I wouldn't think it would take very long at all for the concrete to become hard enough to handle water. The pressure at the bottom of an 8' pool is less than 4 PSI which is less than 0.03 MPa so there is very little load on the concrete. That load level isn't even discernible on the charts and much less than 7 days.
 
Thanks for all the replies and info! Very educational! I also spoke to a gunite company and between what I learned there and here, I definitely think a 5-7 day cure for gunite is adequate for construction to continue. This is a great forum! Thanks again!
 

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IIRC, 30 was an OK range but I assume (incorrectly possibly) that tenting and cooling the work area with some water could improve the curing process of the plaster.

This is all assuming the article is accurate.
 
techguy said:
IIRC, 30 was an OK range but I assume (incorrectly possibly) that tenting and cooling the work area with some water could improve the curing process of the plaster.

This is all assuming the article is accurate.
Click to expand...

Well, it's something I can look into, so thanks for pointing it out! Yeah, I'm sure the workers would LOVE a humidity tent. :)
 
There are numerous tower cranes around Austin and I can promise you they are not waiting 28-days to go vertical. Gunite is porous, the plaster seals everything up. I expect you will have plaster the week before labor day.
 
TAMC93 said:
There are numerous tower cranes around Austin and I can promise you they are not waiting 28-days to go vertical. Gunite is porous, the plaster seals everything up. I expect you will have plaster the week before labor day.
Click to expand...

I hope so! I think we'll be shooting gunite this week assuming we get these little issues taken care of early in the week. I'm ready!
 
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