Do you get Amine Blush under Peel Ply

I am just building a large model boat - and was faithfully cleaning the surface of recently cured epoxy for another coat -

then - I remembered that someone mentioned applying extra coats of epoxy over surfaces that had been covered in peel ply - without mentioning cleaning.

Does the use of PeelPly prevent Amine Blush ?

 

It is supposed to.

 

Waxy deposits on the surface of a freshly cured epoxy are the result of insufficient chemical reaction between the glycols and amines. This is caused by a few things, but most commonly are humidity and hardener formulation. Some epoxy formulations are worse then others, but most of the common marine epoxies will blush given the right set of conditions.

If the surface is covered with a moisture vapor proof barrier, such as plastic sheeting, Mylar, etc. the humidity portion of the equation is removed as the moisture vapor can't get at the surface. Since peel ply permits some breathing, it's possible to get a blush, but you'd have to be working in pretty humid conditions with a hardener that is prone to blush.

Over coating peel ply will seal the surface under it, though I think this is a waste of epoxy. Another option is to over coat the peel ply with plastic sheeting. In most cases, using blush resistant formulations, you can eliminate blush issues, by using peel ply. I have an industrial epoxy that will blush no matter what you do, then again I have another that doesn't blush unless you're laminating in the rain.

In most back yard shops, conditions don't warrant the use of peel ply. This is simply because they don't have sufficient environmental control, to prevent the usual suspects from rearing up. The average shop has so much dust and dirt floating around, that any surface that is going to get any type of coating, needs to be cleaned and prepped before hand. Since this is the case, save yourself the bother and cost of peel ply, as you know full well you'll have to clean and prep the surface anyway. I now have an air conditioned shop which has changed the way I do everything. I can lay perfect coatings, not a drop of dust, temperature and humidity controlled to requirements, etc. This is a far cry from the average shop where if you place a glass plate down after cleaning it, and can expect a layer of dirt and dust in 30 minutes. Something as simple as using long tube florescent lights can generate dust. Without dust extraction and climate control, you'll have to prep the surface, just to be sure you don't have contamination or other issues, like blush.

 

G'day bloke.
With great respect - oh YES I do wish I had your work-shop (sounds SUPA) however I do think you should consult an Industrial Epoxy chemist . Your first paragraph is very misleading & may well be considered to be a tad incorrect. Think you might clear this up for all of the people in this place - that are not in the know. With respect, Ciao, james

 

Unless you have perfect mixing ratios (never a complete certainty, particularly in an average shop) you will always have some unreacted glycol or amine groups in the mix (depending on which is in excess). These are left in suspension within the cured matrix, but on the surface the amine groups in the hardener will react with moisture in the air (moisture vapor) and carbon dioxide (also in the air), which forms an ammonium carbonate skin (salts of amine) on the surface. An asymmetric reactive amine molecule can be employed, which can dramatically lower blush problems, but this usually comes at the cost of physical properties depreciation, typically reducing strength of the cured product and also slowing the reaction time down too.

 

My epoxy does blush.
However I learned a long time ago to work VERY clean
I ALWAYS use peelply because the blush comes off with it and the surface is ready for painting as is
Peelply saves a heck of a lot of work

Do the experiment
one without peelply
and one with peelply
it is a huge difference

I have never had blush problems under peelply

 

The air conditioner does make a huge difference in tropical climates (as does infusion, which I now do on all large parts, as environmental conditions make no difference under 29" of vacuum).

I have successfully used MAS Infucure, System Three SilverTip and System Three General Purpose without any blush from any of them. Some of that time was actually in fairly humid conditions, before I got my air conditioner in the shop.

I guess you get what you pay for with epoxy.

 

Thanks everyone for the submissions, especially Pars detailed explanation.

Obviously, a model boat isn't that critical in its construction, but for any bigger project, this is a big consideration.

Also, in using Peelply, you would never see any blush, as the surface is matte. But, at a microscopic level, would there be a chance of contaminants forming that would create adhesion problems ?

Should we be washing even peelply surfaces before re-applying epoxy ?

 

The local fiberglass gang never washes after peel ply when working in the shop...and always washes after peel ply when working outside in the temperature change.

I also note that the local gang always sands the surface after peel ply. Its a combination of bonding tooth and removing bump and blobs. The peel ply simply makes this sanding operation go much much faster.

The local shop doesnt build boats...they build boat components...consoles, flybridge roofs, furniture.

 

On a model, don't worry about it, if using peel ply, but on critical structural elements and surface coatings that you want maximum adhesion from subsequent mechanical bonds, yep, better the be safe then sorry. Again, peel ply is a fine weave nylon fabric that permits moisture vapor to penetrate, abet at a much reduced rate then open air exposure. A high percentage of blush will come off with the peel ply, but in all those little valleys, you can bet there's some still in there. As to a percentage of total area, who knows, but how much of a reduction in bond are you willing to accept.

 

more than I need to know-

http://www.huntsman.com/performance_products/Media/Blushing_of_Amine-cured_Epoxy_Resins.pdf

 

Keep the peelply on as long as possible.

 

Phil the PDF you list is fairly dated, about a decade and some of the conclusion and speculation have now been attended to.

There's really no advantage to leaving peel ply on once the tack is well gone. Some surface absorption is possible, but in very small amounts. Most of the chemical reaction has occurred and if the coating is stiff enough the peel ply can be removed. Some level of reaction will continue for a few weeks, but the surface can be treated with chemical or secondary bonds directly after.

 

Peelply is perfect for protecting the laminate against foot traffic, resin spills and other disasters that occur when building boats. I prefer only removing it at locations where bonding takes place, then remove it only when the final coating is applied.

 

The peel ply shields the laminate from workshop contamination. I observe that the glass gang leaves the ply on for weeks....and even "repairs" exposed laminate to shield from shop contamination.