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curing compound
03-22-2011, 01:34 PM
Post: #1
curing compound
what effect does the use of an acrylic curing compound have on the time it takes for the rh to get to acceptable level (75%)?
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03-22-2011, 02:01 PM
Post: #2
RE: curing compound
I advise clients the best thing you can do is to do a wet / burlap cure to decrease your drying time and don't spend too much time finishing/burning your concrete. http://www.concreteconstruction.net/conc...loors.aspx

There is a reason why Europeans invented topical concrete screeds a long time ago. American concrete contractors are just lazy.
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03-22-2011, 03:34 PM
Post: #3
RE: curing compound
(03-22-2011 02:01 PM)eaadams Wrote:  I advise clients the best thing you can do is to do a wet / burlap cure to decrease your drying time and don't spend too much time finishing/burning your concrete. http://www.concreteconstruction.net/conc...loors.aspx

There is a reason why Europeans invented topical concrete screeds a long time ago. American concrete contractors are just lazy.

Thats an interesting link there eaadams. I've always heard hard troweled/steel troweled glass like finish on slabs retards mve. Not much likes to stick to them however.

You'll note lots of patching or slc's want a broom trowled finish.

Out here in the old parts of town we have some steel troweled colored concrete finishes. The put down the slab first, rough, and then used a fine grit colored finish last. Hard as diamonds too.

Stephen Perrera dba
Top Floor Installation Co.
http://www.tucsonazflooring.com
http://www.floorsavior.com
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03-22-2011, 04:11 PM
Post: #4
RE: curing compound
A curing compound by definition is for curing, whereas a cure-n-seal cures and ----- wait for it------ seals!!! Big Grin

Ha ha... But seriously, I have been asked to approve a self-dissipating curing compound and checked into this issue. Of course adhesive manufacturers will tell you that there can be NO contaminants on the slab, including sealers and curing compounds, but what about the dissipating kind of curing products?

A contractor can save a lot of money using a curing compound verses wet curing, but I advise against it for several reasons. First of all, the cure continues on much longer than it needs to. Excessive curing ( I recommend 3 days) makes the surface harder and less porous which leads to a slower overall drying process. Until this cure dissipates, it is sealing the concrete.

Another reason to not use self-dissipating cures is they just may not dissipate! The SD cures rely on UV and traffic to breakdown and rub off. When you call and ask the manufacturer if they guarantee the SD cure will be completely gone within X number of days or even if they guarantee it will EVER be completely gone, the answer is no..... The manufacturer will NOT guarantee these chemicals will not be found on the concrete no matter how long you wait, or even if you pressure wash the surface.

Now what happens if you have a problem with the flooring? The flooring manufacturer comes in and asks if you have ever sealed the floor. You tell them you used a SD cure and they pull a few cores and have them tested. If they find any trace of a curing compound who ends up holding the bag?

So I advise a wet cure (misters, burlap, plastic, soaking) and then immediately remove the water and begin drying the slab.

As for how long a slab takes to dry to 75% RH, well that is a good question. Under ideal conditions a slab will take about a month for each inch of thickness. That means a 4" slab poured at 50% water/cement ratio will dry to 75% RH in 4 months at 70* and 50% RH. This amount of time can depend on the aggregate used, the length of cure, the airflow over the surface, the quality of finishing, the porosity of the slab, the anxiousness of the flooring contractor to start and almost any other reason under the sun. Rewetting by tracking in water and snow, working on sprinkler pipes, mixing mud and grout on the floor and being sloppy with the water, covering the slab with cardboard and mats while you work on it, etc. etc. can all make predicting slab drying time impossible.

Another point before I forget: Steel trowels are used because they seal the concrete, keeping the water in the slab and creating a denser surface through slow drying and cement paste reaction. You want to keep steel trowels off any floor that will be getting floor finishes. Have the concrete sub quit with his magnesium trowel, or at worst case use a combo blade. The floor will get plenty hard and dry much faster, it just won't give that glass smooth easy to sweep finish.

JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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03-22-2011, 05:34 PM
Post: #5
RE: curing compound
"As for how long a slab takes to dry to 75% RH, well that is a good question. Under ideal conditions a slab will take about a month for each inch of thickness. That means a 4" slab poured at 50% water/cement ratio will dry to 75% RH in 4 months at 70* and 50% RH. This amount of time can depend on the aggregate used, the length of cure, the airflow over the surface, the quality of finishing, the porosity of the slab, the anxiousness of the flooring contractor to start and almost any other reason under the sun. Rewetting by tracking in water and snow, working on sprinkler pipes, mixing mud and grout on the floor and being sloppy with the water, covering the slab with cardboard and mats while you work on it, etc. etc. can all make predicting slab drying time impossible. "

Also covered (w/ roof on) and no sub slab granular fill. Yes, ideal. It is helpful to look at concrete constructions field test (which BTW, Wagner helped sponsor). That slab was done in ideal conditions and the latest update (#3) the slab is still wet @ > 90%. 3 years later!! http://www.concreteconstruction.net/conc...sults.aspx
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03-22-2011, 07:35 PM (This post was last modified: 03-22-2011 07:39 PM by Ernesto.)
Post: #6
RE: curing compound
Those large slabs are going to dry slower just due to the fact of their enourmous size (new word Smile . Just like setting 24 inch tiles on a slab vs a 12 inch tile, it takes the thinset three times as long to set up and cure. Throw a roof over it real quick or pour inside then double it.

I've only seen people using burlap out here maybe twice in my lifetime. Some guys like to use sprinklers on it. Rolleyes and the surface gets all sandy and pitted. I had one that virtually sucked the water out of the patch before my very eyes.....go away run for your lives!

Stephen Perrera dba
Top Floor Installation Co.
http://www.tucsonazflooring.com
http://www.floorsavior.com
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03-23-2011, 06:04 AM (This post was last modified: 03-23-2011 06:10 AM by CC Solutions.)
Post: #7
RE: curing compound
(03-22-2011 05:34 PM)eaadams Wrote:  It is helpful to look at concrete constructions field test (which BTW, Wagner helped sponsor). That slab was done in ideal conditions and the latest update (#3) the slab is still wet @ > 90%. 3 years later!! http://www.concreteconstruction.net/conc...sults.aspx

If you look at the drying conditions they are far from ideal. The slab has been kept at up to 80% RH and as low as 40 degrees. The surface has also been sealed by steel trowels until it is almost black. Much of the concrete is covered and in use.

I bet if I blasted that surface the slab would dry out in 3 to 4 months.

We get 4" slabs to dry to 75% in less than 5 months more often than not by following our own advice. I know it is possible because I have done it many times.


(03-22-2011 07:35 PM)Ernesto Wrote:  I've only seen people using burlap out here maybe twice in my lifetime. Some guys like to use sprinklers on it. Rolleyes and the surface gets all sandy and pitted.

Sprinklers work but make a mess of a job site and waste a lot of water. They cannot be used until the surface has hardened sufficiently and will not be damaged, i.e. 'sandy and pitted'.

While burlap and plastic may seem like a pain in the tush to maintain (and it is!) when it means the difference between having your concrete ready for flooring in time or spending half a million $$$$ for mitigation, GC's are more willing to try the burlap.

JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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03-23-2011, 09:25 AM
Post: #8
RE: curing compound
"I bet if I blasted that surface the slab would dry out in 3 to 4 months."

This is absolutely true. A light blast can really help. Even an aggressive sanding with a rock/diamond enforced pad has been shown to help over 6 months.

However, for us where 90% of revenue comes from public bid contracts, we can't afford to build that cost into the bid. Thus, a better cure and less finishing I think would be the better standard to shoot for. Rather than adding another costly (and financially unrealistic) service to a bid.

Also of note from the article is a closest that just has a broom finish that has shown quite different curing characteristics.
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03-23-2011, 10:00 AM
Post: #9
RE: curing compound
(03-23-2011 09:25 AM)eaadams Wrote:  This is absolutely true. A light blast can really help. Even an aggressive sanding with a rock/diamond enforced pad has been shown to help over 6 months.

However, for us where 90% of revenue comes from public bid contracts, we can't afford to build that cost into the bid. Rather than adding another costly (and financially unrealistic) service to a bid.

Well you do have a clause in your bid that if conditions are not proper you cannot continue and all that jazz right?

I blast every day so it's not a big deal to me. For some reason concrete guys love to polish that slab, even when you tell them not to and explain why....

Blasting will add about $1 / sf to a job.

JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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03-24-2011, 09:30 PM
Post: #10
RE: curing compound
I find the GC doesn't ever listen to clauses considering the bid specs govern.

But yes I agree.

When I sub out blasting in CA, it goes for WAY over $1 s/f.
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