Coal Tar Epoxy Coating

[nicaeng]

Hi,

We need to use a Coal Tar Epoxy Coating to coat a cooling tower on a Geothermal Power Plant, the spec says we must cure the concrete for 28 days at 75°F (24°C) and 50% relative humidity. The weather here is very hot at this time of the year, around 34°C (93°F) and sometimes hotter, at night it drops to probably 28°C, the relative humidity is between 30% and 40%.

We need to start preparing the surface because we have a tight schedule, we´ll not tight schedule but we definitely want to coat the foundation before it starts to rain here which is in mid may.

Mi question is, under these weather conditions can we start to coat the foundation with the concrete walls not having 28 days in curing time?

Also, the spec says that the surface must be prepared according to ASTM D 4258 and D 4259, we plan to apply muriatic acid (hydrocloric acid) to open the pores on the concrete, it is much faster than grinding the entire surface which is over 25,000 sq ft.

Please let me know what you all think.

Thanks in advance.

 

[hokie66]

You need to get some advice from the coatings manufacturer. Obviously, you can't cure the concrete in constant atmospheric conditions. Whether acid etching is appropriate is also a coatings manufacturer issue. You will want a warranty on the coating material and application, so you need to have agreement in writing as to how to proceed.

 

[Ron]

Abrasion or acid etching are the two methods specified under ASTM D4258 and D4259. Acid etching is a common method for CTE coatings, but in my experience, the manufacturers want 28 days of curing on the concrete.

You might consider gel acid for surface prep rather than liquid acid as you likely have vertical surfaces to prepare. Gel acid cleaners are easier to work with and control in those applications.

You could use abrasive blast surface prep as outlined in D4259. That doesn't have all the issues of acid etching and can be done quickly.

Check the pH and surface moisture before applying the coating. Make sure both are within the manufacturer's standard requirements.

 

[nicaeng]

Thanks for the comments.

After speaking over the phone with the manufacturer technical assistance department, these are the answers i got:

1.- Muriatic acid is not recommended because it will not create the profile needed for the coating to properly adhere to the concrete, besides it creates hazardous waste and in my opinion it will have an adverse reaction with the coal tar coating. We´ll sand blast the surface.

2.- We should always, regardless of curing time, check for moisture according to ASTM D 4263 - Standard Test Method for Indicating Moisture in Concrete by the Plastic Sheet Method - which is a very simple procedure. He did say the surface has to be blasted and cleaned before the test is performed.

 

[hokie66]

Now you are on the right track.

 

[dik]

Some tar modified epoxies are carcinogenic.

Dik

 

[JedClampett]

As dik says Coal Tar Epoxies are nasty stuff. They're very good, when applied correctly but hard to work with.
Maybe there's an alternative that would work just as well (vinyl ester, polyamide epoxy, etc.) for your tower that wouldn't be as risky to apply. I'd ask your Tnemec or Carboline representative.
We used to use them a lot in water and wastewater treatment, but they're pretty much banned in water treatment and out of style in wastewater treatment.

 

[nicaeng]

The Coal Tar Epoxy is what the engineering company specified on the drawings, by the way it is Carboline Bitumastic 300 M.

Thanks for all the comments.

 

[dik]

From Carboline MSDS sheet... I'd sooner have my grandkids play with razors (I've already taught them the safe use of firarms where possible)...

Emergency Overview: Warning! Flammable. Harmful if inhaled. Causes eye and skin irritation.

Aspiration may cause lung damage. May cause dizziness and drowsiness. Keep away from heat, sparks, flame. Avoid breathing vapor. Avoid contact with eyes, skin and clothing. Do not swallow. Keep container closed. Use with adequate ventilation. Wash thoroughly after handling. Contains SILICA which can cause
cancer. Contains COAL TAR which can cause cancer. Risk of Cancer depends on duration and level of exposure.

Dik

 

[dik]

Should have added... you might have the other engineer suggest something else...

Dik

 

[dicksewerrat]

If you have to use this, start at the top and work down. Less fumes. May need supplied air for the guys applying this.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com