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Roller - Brush Application of Solvent Free Epoxies On Smooth Surfaces

Progressive Epoxy Polymers, Inc.

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Paul Oman, MS, MBA - Progressive Epoxy Polymers, Inc.

Member: NACE (National Assoc. of Corrosion Engineers), SSPC (Soc. of Protective Coatings)

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There is a big difference in the coverage and appearance of coatings when applied by roller vs. brush. Even common interior latex wall paint has a ‘dimple' pattern when applied by roller and a smooth finish if applied by brush. With much thicker, solvent free epoxies the difference is even more pronounced.

Roller Nap

Roller basics: ‘regular' paint rollers have a 3/8 inch nap. Epoxy and adhesive rollers generally use a 3/16 inch nap. The nap is better attached and sheds little or no lint into the coating while the 3/8 nap rollers generally release a lot of lint into the sticky epoxy during the first few minutes of use. "Phenalic" paint rollers are basically rollers with absolutely no nap. You can make your own phenalic roller using 1.75 inch PVC pipe. We sell 3/8 inch low lint epoxy rollers in addition to our many different epoxies.

Roller Performance

When being applied to rough or semi-rough surfaces (wood, pitted metal, concrete) the roller transfers the epoxy to the surface nicely. However, when applying sticky coatings, like epoxy, to a smooth surface (fiberglass hulls, smooth metal, etc.) the roller nap tends not to want to give-up, or transfer the epoxy from the fuzzy nap to the smoother surface. The result is a very thin coating of epoxy applied to the surface (perhaps 6 - 8 mils resulting in a coverage rate of about 200 square feet instead of 100 square feet on a rough surface or with a brush). Most of the epoxy remains in/on the roller.

Surprisingly the shorter the roller nap the more epoxy gets transferred from the roller to the smoother surface. Usually the most epoxy gets transferred by using the phenalic (napless) roller. Unfortunately there is a downside to applying a greater volume of epoxy with a roller. The backside of the roller tends to lift the epoxy into little spikes as it rotates. That's how/why those little dimples appear when you roll on interior house paint. Well, with the thicker epoxy those ‘dimples' become ridges and the shorter the nap (which means more epoxy on the surface) the larger and more pronounced the ridges. Fortunately, to a more or lesser degree, all or most of those product ridges will flow out and smooth away. A paint brush used ‘behind' the roller can also add additional epoxy to the surface and/or smooth out any ‘ridges'.

Brush Application on Smooth Surfaces

There is no ‘lift' on the back side of an epoxy loaded paintbrush, hence no ‘lift' ridges. THEREFORE MAXIMUM AMOUNT OF COATING CAN BE APPLIED BY BRUSH. Generally the upper limit of coating thickness applied by brush (or roller on a rough surface) is about 25 mils (yielding a spread rate of about 65 square feet per gallon). Any thicker than that and the coating is usually applied by trowel or plastic spreader.

Progressive Epoxy Polymers offers several solvent-free, medium viscosity epoxy coatings used as barrier coats in the marine industry and as general purpose containment and wall coatings in non-marine commercial projects. These epoxies are from different formulators but address the same niche. Never-the-less there are very slight differences between them, differences that might affect which one you select. The ‘rollability' of these different epoxies is compared later in this document.

UPDATE 9/15/02

WE RECENTLY TESTED THOSE 'PAINT PADS' AVAILABLE AT ALL PAINT STORES. THEY ARE OFTEN USED TO PAINT AROUND EDGES ETC. BUT CAN ALSO BE USED ON LARGE SURFACES VERY SUCCESSFULLY. THE PADS HAVE A SHORT LINTLESS NAP AND SINCE THE GLIDE ALONG THE SURFACE INSTEAD OF ROLL, THEY DON'T HAVE ANY 'REAR-END ROLLER PICKUP' AND THEY HOLD A LOT MORE PRODUCT THAN A BRUSH.

IN OUR TESTS WE FOUND WE COULD EASILY PUT DOWN A SINGLE THICK COAT OF EPOXY RATHER THAN THE THIN, BUMPY LAYER MOST ROLLERS PUT DOWN. WHEN IT COMES TO EPOXIES THESE PADS SEEM TO HAVE THE BEST OF BRUSHING (I.E. THICK COAT) PLUS LOTS OF THE ADVANTAGES OF A ROLLER.

IT IS TOO EARLY TO MAKE A POSITIVE RECOMMENDATION, BUT WE URGE YOU TO TRY THESE PADS AND REPORT BACK TO US. THEY WOULD/SHOULD/COULD BE IDEAL FOR THE APPLICATION OF A MARINE BARRIER COAT ON A BOAT HULL, FOR EXAMPLE.

Other application/selection factors - click here


Water Gard 300 / NSP 120: pretty good - perhaps a just a wee bit of 'ridging' that doesn't flow out

Corro Coat FC 2100: With internal kevlar (tm) and ceramic this no/low sag epoxies leaves behind bumps and ridges after it cures.

Hi Flex 3: Thinner than the rest so it applies nicely with ‘ridges' flowing out, but tends to sag or drip more than the other products.

Knowledge is Power - We like informed consumers!

Learn the basics of epoxy at our educational EPOXY 101 page - Click Here.

Finally, email us back with your questions or comments before you buy - EMAIL HERE

Note: the differences between these products is minor - we're comparing apples to apples. The biggest and most obvious difference is simply color.

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