Painting Hardness

Not likely, but maybe conceivable. If they applied the paint in too cool of an ambient condition, it would cure slowly and might be able to catch up later. But it would be chancy to rely on this. Also possible, the mix proportions could have been off, in which case the paint may never harden satisfactorily. One thing to try would be to put the pipe into a warmer place for a while, and see what happens.

Any handling will compromise the coating if it is not properly mixed (if a two part system) and cured.

Lack of meaningful information prevents further help from me.

I have noticed on some occasions that "good" paint on well prepared steel pipe has shown the conditiont hat you described.

The condition never provided a satisfactory outcome (compared to "normal painting" that hardened per normal.) and while it eventually dried to a firm surface, the adhesion was unsatisfactory and eventually peeled away.

I suspect that the situations that I've seen were not the fault of the paint, or even the method of application, but rather related to the metalic substrate. [When the same pieces of pipe were stripped, buffed, cleaned with MEK and re-painted, some still exhibited the same outcome. That is a "tacky" non-dried surface that even when it did dry still felt "rubbery".]

It might "dry" but it will probably never be equivalent to what the paint manufacturer would expect of their product. You will be dissappointed if you don't have it remedied.

Hi Just an Engineer,

You have to change supplier of epoxy coatings. I personally make epoxy coatings and adhesives for over 35 years. When the 2-pack epoxy coating doesn't cure within 12 to 24 hours in normal conditions (15 to 20*C temperature) and well prepared substrate (degreased or/and sand-blasted or scarified as concrete) there is a chemical reaction problem we have between the epoxy resin and the hardener. Summer and winter type formulations are futile. The application conditions need to be right to obtain what we want. DMP-30 accelerator use transforms the coating to too rigid, brittle, and can delaminate from rigid substrates like metal, plus it accelerate yellowing or colour change of the film. For colder temperatures, around 5*C but not less, conditions use amine adducts as hardener without DMP-30 but mix small amounts because pot-life could be very short. When we use solventbourne epoxy/polyamide coatings, we need induction time around 30 to 60 minutes and mix every 15 minutes for at least 2 minutes.

To buy and use epoxy coatings, applicators need a technically well equipped company as supplier. Any soso company will drive applicators in trouble.

Good luck and let me know the results, Gil.

I think it is not necessary to change supplier or even the product.

We were painting handrails and structural steelwork. Some part painted stayed tacky for days, while others cured within the day. (Same can of paint consecutive painted parts.)

Also it wasn't poor mixing as some of the later parts also remained tacky. That's why I drew conclusion (in my specific case) that it was the substrate rather than the paint or the prep.

I'm now out of that game but was just passing observations.

Ask the contractor for the Product Data Sheet (PDS) for the specific paint that was applied (all layers) and the paint records / environment data. The PDS will give you cure time (ex Manufacturer) at the specified environmental conditions. check that v the records and you can tell is the contractor is giving you the correct information. If they do not have the pds - then you can ask for the paint spec and download from the manufacturers web site - but then if they do not have the paint spec sheets, how did they apply in accordance with the manufactures tolerances. If it was extremely cold, they may be correct. some epoxies may be moisture cured, again if it was very dry weather, there may not be enough humidity to cure the paint.

Some epoxies are "temperature cured", most are not.

If the paint was applied as per spec sheet, then as previously suggested the surface preparation was faulty.

You could have a problem. If the primer was not dry before, topcoating the pipes or if the primer is not of a compatible chemistry, If in cold weather fast dry reducer should have been used in your E-poxy paint, as long as proper mixing ratio was correct, the product you used needs to achive a set temp before to reaction starts to take place. some products will be ok at around 60 degress, but the paint will be soft or it may just skin over and as the layer underneath dry the top will crack because of the un-even heat to the product used

The contractor should have known better then to paint under cool conditions. I still have a concern about the primer if it was used, soom thinners and cross linkers are not compatible and will NEVER dry.

Keep an eye on this problem

Happy New Year Mckenty1963,

You are perfectly right! The applicator must have the knowledge to apply a coating or a system with or without specifications. First, temperature and humidity conditions are the major part of the success or failure of a painting job. Second, mixing ratio and induction time if needed must be followed, which isn't many occasions and let a few hundred square feets trouble on 25,000 square feet floor.

Also, without criticizing people in epoxy business, they buy resins and many hardeners and make coatings and adhesives. Trouble is that hardener manufacturers can make small mistakes too. Thet buy or produce amines with certain variation in their composition. The small variation of a hardener composition creates off grade finished products without malice of the coating manufacturer. They think one adducted or mixed hardener is exactly the same because they call H199. Most of commercial amines, amidoamines are mixtures with certain variations batch after batch which can influence the final results. More variations are created when the amine in particular is modified by mixing with other ingredients or reacted with another compounds. The best control a manufacturer of epoxy products has on the quality of finished goods when they mix and/or react themselves to make their own hardeners. Resins are close enough.

Epoxy doesn't create hard skin, based on chemical reaction. It becomes hard or stay soft for eternity at normal conditions.

The inspector must get all information about the application and its conditions to make further recommendations. My another note told how eventually to correct the soft epoxy coated pipes. By heating at different temperatures and establish the good answer for corrective actions.

I think we said everything about epoxy problems, which is with us from the 1940s, Gil.

From your description, it appears that there was insufficient heat when catalyzed to cure the mixture. Try an infra red heat lamp far enough away to not burn the epoxy but close enough to apply the heat needed. If you can put your hand on the pipe and leave it there for 2 minutes before it gets uncomfortable, that should be enough to find out.

Leave it there for about 2 to 3 hours, then take a scribe or awl and scratch the paint. If it powders or chips and makes a distinct scratching sound, then it's cured. If it puddles up like glazing putty and makes no sound then it's not cured.

When I make composite parts, I make it a point to pour a sample of the remaining epoxy into one of those small catsup cups you see next to the condiment dispensers at fast-food places. I leave the cup next to the parts made and later do the above scratch test. If the sample is cured odds are the parts are too.

L.J.

Your best course of action depends on how personally involved you plan to get with this problem. You could ask the painter to mix some epoxy to demonstrate its performance on a piece of optimally prepared and cured test surface. The paint may have have been improperly mixed, the catalyst may be no good, the pipe surface may have not been properly prepared, or the proper cure conditions not satisfied. I would discuss this with the contractor. If he can't resolve the problem, I would send a sample to the paint manufacturer for analysis.

Was this a green colored epoxy used to coat boiler tubes for the reduction of ash build-up?

Happy New Year ZIZO10,

The answer is: Absolutely no!!! Thermoplastic resins indiquate the need of heating at a certain temperature or use a hardener. In this case, we have the resin and the hardener. The type and quantity of resin and hardener is variable. Can low or high molecular weight resins. The hardener can be polyamid or amine or blend of them or modified for each resin type. However, the 2-pack system is made to be blended in a certain ratio, mostly by volume or by the container, established by the manufacturer.

Single resin need heating to cure. How much, depending of the resin type.

The problem with epoxies are the following: First, the manufacturer don't deliver the right mixing ratio of resin and hardener in the containers but it's very rare. Second, the most offen, the applicator, this is not an accusation, it's noticed, don't respect the mixing ratio for some reasons. When the film, at room temperature conditions stay soft after 24 hours, will never get hard and perform. One solution can be tested but need technical competance. Cut the pipe, 6 or 12 inch long, and heat this piece in an oven to a temperature around 55*C and maintain for 30 minutes, another at 105*C, and another at 155*C. Check the hardness of each film after a reasonable, 30 minutes, cooling time. Heat is the only solution for soft epoxy coatings. If nothing get satisfactory, sand-blast or solvent wash and start over again with proven mixing ratio. The inspector need to have specification of the coating from the manufacturer before application, Gil.

4 days is a long time for the epoxy to set, but you indicated it had not set up, yet. It must have been 60 F or less. If it was a polyamide hardener, the mix ratio is not critical. For lower temperature uses, epoxy manufacturers often use (or increase amount of) an industry-wide catalyst in their formula called DPM-30 tm (or other brand). Sounds like the 'winter grade' version was not used in your case. Consider using a hot air gun to a minute or three, to start kicking the reaction along. Be careful not to heat much about 120 F or so, otherwise the paint mixture may drip off. If you indeed, get a small portion of the pipe coating to cure OK, perhaps you can feel confident that in-use heat will cure the rest up. Good luck. Joe M

Pl check ohan time and temp duration during painting.

What kind of EPOXY? Tar Epoxy?

TEMP. Among coats Cured end for dip

16 ºC 36 hrs. 30 días

24 ºC 18 hrs. 15 días

32 ºC 8 hrs. 7 días

Epoxy metal adhesives are best set under heat cured conditions

*if the contractor uses two component mixer based epoxy, the hardener part is kept low to maintain paint life. In such cases the epoxy part under the solvent influence will be highly tacky and takes longer hardening hours.

* If other P.F resin based hardeners are used also such a problem may arise.

* Just check up the literature of the paint manufacturer on curing conditions.

*If you want improved cold condition results you may try with addition of Hexamine for quick hardening.

* I think the paint stability aspect had been in operation.

* if the contractor is correct let him demonstrate the workability by some sampling curing.

*If not found as per his promise you got to work out the hardener part.

Thermoset resins like Epoxies fix well after heat curing to get rid of condensation products like water or methanol etc. Paint manufacturers keep the formulation inactive by suitable conditioning so as to become reactive after application, Possible catalysts or pH adjustments if necessary. End users should get proper technical information on usage. You may veryfy the contractor's statement by a hand dryer or blower drying test which is very simple exercise. In automotive industries I have observed the chasis beams getting spray painted and being Hot cured to thermoset the resin.