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TWO PART LINEAR ALIPHATIC POLYURETHANE
"Two Part Poly"
URETHANE PAINT - COATINGS
Your Host and Tour Guide:
Paul Oman, MS, MBA - Progressive Epoxy Polymers,
marine epoxies, underwater epoxies, repair epoxies)
Member: NACE (National Assoc. of
Corrosion Engineers), SSPC (Soc. of Protective Coatings)
Friends of the Suncook River
- 501(c)(3) non profit ----- Founder: Friday
Night Paddlers .
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"Professionals helping Professionals"
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or by telephone, shall constitute acceptance and knowledge of all such terms.
CLICK HERE (www.epoxyproducts.com/legal.html) to access these terms.
LPU Urethane Paints (polyurethane)
The following is an introduction into 2-part urethanes and 2 part urethane clear-coats. These two-part LPU paints
are perhaps the best performing coatings (low yellowing, high gloss, durable and tough physically and chemically)
available for brush, roller or conventional spray application.
Most, of not all, 2-part urethane paints are either acrylic polyurethane paints or polyester polyurethanes paints.
Sometimes the prefix “poly” is left off. These are also called linear (or aliphatic) urethanes, or LPUs (linear
poly-urethanes). In any case, lots of ‘keywords’ for generally two kinds of 2-part
Polyester (poly) urethanes are considered the ‘best’. Compared to acrylic (poly) urethanes the polyesters are more
abrasion resistant, stain resistant, and more chemical resistant. You’ll find polyester urethanes on jet airplanes,
and on the floors of the hangers these airplanes live in. Boat owners should
note that operating a boat in water, especially seawater, is very much a chemical environment. Two very well known
2-part marine paints, (we will not say their names) are polyester urethanes.or acrylic/polyester urethane blends.
Acrylic urethane coatings are a bit cheaper and generally one notch down from the polyester urethane paints in
terms of toughness and chemical resistance, but still above ‘regular’ paints. Acrylic urethanes are found in clear-coats
used in the automobile industry and ‘city water towers’ that grace many
small towns in America. Boat owners should note that Awlcraft 2000 (tm) is an acrylic urethane, as probably are
most of the 2 part urethanes sold in marine catalogs that don’t specify if they are polyester urethanes or acrylic
APPLICATION PROPERTIES: Both kinds of urethanes contain large amounts of solvents and thus have a strong solvent
smell. That said, additional solvents are often added during application. In the urethane world solvents are called
reducers. There are ‘fast reducers’ for spray application. These speed up the time it takes for the urethane to
‘gel’ on the surface. “Slow reducers” slow down the gel time for more working time when applying by brush.
Brushing on a two-part urethane is not like brushing on a varnish or oil based enamel. The thin, almost watery
urethane (you’ll probably need two coats or more to cover) starts to ‘gel’ on the surface quickly. Unlike varnish,
you’ll get 2 or 3 brush strokes and then, like it or not, it’s time to move on. An application method called ‘tip
and roll’ gets almost sprayer like results by applying the urethane with a roller and then gently removing the
roller marks with the tip of a brush. If is likely you will not be happy with the results of a brushed on application
on such things as boat hulls, epoxy table tops,etc...
In my experience, both the acrylic and polyester urethane coatings go on about the same, but the general view is
that the acrylics are slightly easier and friendlier to apply and, perhaps, repair.
Urethane’s weakest link is their adhesion. Because of that they are often applied over an epoxy primer. Besides
priming the surface the epoxies tend to ‘level the surface’ too, important because the high gloss urethanes will
show every flaw in the subsurface.
Recoat window for two-part urethanes is about 6 to 16 hours. Beyond that, sand lightly. Apply only in good, dry
weather, as urethanes are moisture sensitive during application and curing. The coating will become dry overnight,
hard in about 3 days, with maximum hardness in 7-10 days.
EVALUATING YOUR TWO-PART URETHANE: Obviously, the first question is, is it an unmodified polyester polyurethane
or an acrylic urethane? Next, what is the price (two part urethanes sold in marine catalogs are priced sinfully
high)? Finally, look at percent solids.
Percent Solids: these coats, like most other coatings, consist of some amount of solvents which evaporate away
(called VOCs - volatile organic compounds) and what is left behind is the ‘solids’ of the coating. A coating with
40% VOC has 60% solids. Apply a 10 mil (1/1000 times 10 in inch units) coating of this product and when dry you
will have 6 mils on the surface. Some manufacturers describe it in terms of coverage for 1 dry mil of their product.
A coating with 0% VOC (most epoxies) will have a dry 1 mil coverage amount of 1604 square feet. A coating with
50% VOC will have a 1 mil dry thickness coverage rate of 802 square feet ( you applied 2 mils over the 800 square
feet and 50% of it evaporated
The higher the solids (the lower the VOC) the more paint you are actually getting on your surface. One of the leading
vendors of ‘boat hull’ 2-part urethanes does a wonderful job of providing their technical product information on
their web site. Their web site reports 1 mil dry film thickness of 570 square feet for their original polyester
urethane and 846 square feet for their version 2 polyester polyurethane. Their acrylic urethane product (introduced
around 2000) reports 512 square feet at 1 mil dry coverage.
NOTE OUR PIGMENTED 2 PART POLYS CANNOT BE SOLD IN CALIFORNIA
AND ARE ONLY APPROVED FOR APPLICATION ON MOBILE EQUIPMENT SUCH AS CARS, BOATS AND PLANES. SEE OUR VOC PAGE FOR DETAILS.
Urethane Clear-coats are almost a different topic from pigmented urethanes and much of that is due to UV blocking.
UV rays damage and fade coatings. It yellows and damages epoxies. One of the best blockers of UV rays is pigmented
paint. The pigments block the UV, limiting their affect to the very surface only. Clear coatings, of course, have
no pigments to block UV, hence, while they add additional gloss and ‘depth’ to a fine paint job, they are generally
considered to be performance inferior to the pigment coatings they commonly go over.
There are UV blockers that can be added to clear 2-part urethanes, but surprisingly a very minimal ‘UV Package”
is generally added to these clear urethanes (I’ve heard that automobile Clear-coats are an exception). The additives
are expensive (about $8 per gallon) and since most clear urethanes are applied over pigmented urethanes the manufacturers
tend to let the pigments in the bottom coating perform the UV blocking.
The Acrylic Poly UV Plus™ offered by Progressive Epoxy Polymers (mentioned above) is also an exception. This clear-coat
acrylic polyurethane has the maximum amount of UV blockers that can be added. Progressive Epoxy also sells both
‘fast’ and ‘slow’ urethane reducers, as well as moisture cured urethanes and, of course, all kinds of epoxies!
SEE LINKS BELOW.
THIS PRODUCT IS CONSIDERED A WATERPROOFING
SEALER. IT CANNOT BE SOLD IN SOUTHERN CALIFORNIA.
The Polyester Poly™ offered by Progressive Epoxy Polymers (mentioned above)
is a polyester LPU coating, the best 'LPU Flavor' in terms of toughness and
chemical resistance. It doesn't have the UV blockers that the Acrylic Poly UV
Plus contains. This is the best clear topcoat you can apply to a newly applied
epoxy floor (but it lacks the UV blockers). Best is the acrylic poly over the
epoxy or epoxy and chips, then the Polyester Poly over that.
THIS PRODUCT IS CONSIDERED A WATERPROOFING
SEALER. IT CANNOT BE SOLD IN SOUTHERN CALIFORNIA.
WHY ALMOST NO UV PROTECTING
CLEAR COAT PRODUCTS:
Two reasons why there are few clear coat
products available with UV blockers. One is cost. These additives for clear
coats are expensive. Second, most clear coat products go over pigments coatings
that are not epoxy and do not yellow (but might still fade a little bit). Simply
the top coating of epoxies with a clear coat is a small market, that few address
(except for our Acyrlic Poly UV plus mentioned above.). So, if some vendor tells
you they have an special clear top coat for epoxy surfaces and it doesn't really
mention special additional uv blockers etc. added to it (don't think there are
any), they you already know they are stretching the truth because the product
wasn't designed with epoxies in mind. Some vendors just 'forget' to mention
epoxy yellowing entirely. LET THE BUYER BEWARE.
URETHANE COLORED COATS:
We offer polyester polyurethane (50% VOC) available in white only (LPU
Marine) - for use on boat hulls, cars, planes. Not for sale in Southern California.
NOTES: 2 part poly paints are really sensitive to surface contamination
problems etc. Guys that paint cars use 2 part poly paints. They use a product made by Du Pont and sold at auto
part stores called 259S Paint Additive (quote: an additive for topcoats and clears to eliminate fisheyes, craters
and other surface defects). I paid $22 for a pint of it in 2003.
LPU coatings like to go on thin (multi thin coats!) - many folks sand between all or some of the coats. The coats
are very thin so here is a link to a site that sells 'sandpaper' in the 400 - 12,000 super/super fine range (thanks
for this info from one of our customers!) https://www.micro-surface.com/
The 2009 West Marine Catalog lists 1 quart units of Perfection™
two part LPU (page 200) at $77.99 a quart!!!! They don't say if it is an acrylic poly or the better polyester poly,
which usually means it is an acrylic poly... They also sell an LPU 'varnish' (page 203 - $77.99 per quart) which
I assume is akin to our Acrylic Poly UV plus clear coat. Our products are about 66% less in price.
Find the Polyester or Acrylic Polyurethane in our Marine Catalog - click here
Find the Polyester or Acrylic Polyurethane in our Industrial Catalog
- click here
Products have low viscosity, but if thinning (reducing) is still desired use our:
SU 93 REDUCER (Thinner) - slow - used mostly for brush/roll application
SU 94 REDUCER (Thinner) - fast - for spray applications
Progressive Epoxy Polymers, Inc.
Frog Pond Hollow
48 Wildwood Drive
Pittsfield, NH 03263
lpu, 2 part polyurethane, two part poly,