From: macrakis@osf.org (Stavros Macrakis)
Subject: Re: Exterior House Trim Painting
Organization: OSF Research Institute
Distribution: usa
Date: 2 Sep 92 15:14:53

In article <24480@oasys.dt.navy.mil> odell@oasys.dt.navy.mil (Bernard O'Dell) writes:

   In painting the exterior trim on a house, some of which
   is badly weathered, what is the best way to go?
   Some say-caulk first, wire brush, scrape, sandpaper, then a
   quality oil base primer, then a quality gloss latex.
   Any particular brand recommendations for the paint?

Here is the painting specification I've put together for my old house.
I have looked into this pretty extensively, since I will soon be
repainting my 120-year-old house.  It hasn't been painted for a long
time (30 years?) and the old (lead) paint is in very poor condition.

It turns out that almost all the experts nowadays, from the paint
companies, to our local historical commission, to the Society for the
Preservation of New England Antiquities conservation department, agree
that 100% acrylic latex is a better product than alkyd or oil paints.
It is said to last as long, but to keep its color and sheen better.
However, local contractors are split: some recommend alkyd, others
recommend latex.  The experts are split about alkyd vs. latex primer,
and all contractors recommend alkyd primer.

Here is the complete paint specification for our house, as I defined
it based on the information I collected:

0) (not painting, but a prerequisite) Inspect roof, gutters, flashing
   (especially over windows), etc.  and repair or replace as
   necessary.  Be sure you don't have excess humidity in your house
   (e.g. vent bathrooms and clothes dryers to the exterior) -- such
   humidity is a major cause of paint failure.  Be sure you have
   effective vapor barriers, especially if the house is insulated.  In
   the absence of a continuous poly film under the wallboard or
   plaster, consider painting with a vapor-barrier paint (Pratt &
   Lambert Lyt-All Double Duty Primer is one such).

1) Scrape thoroughly.  Bag and dispose of scrapings properly (lead
   scrapings are hazardous waste).  It's a good idea to dispose of the
   dry scrapings before you power wash, so they won't be weighed down
   by the water.

2) Power wash with detergent (TSP).  For a deluxe job, scrub with a
   hard brush.  Bag and dispose of scrapings properly.  (If it is lead
   paint, it needs to go into a low-level hazardous waste dump.)

(steps 1 and 2 can be done in the opposite order, but that leaves you
   with a lot more wet paint scraps, which are much heavier than dry
   paint scraps)

3) Rinse with clear water.

4) Let dry for at least three days of warm, dry weather.

5) Kill any mildew by scrubbing with chlorine bleach.  Rinse.

6) (carpentry work) Replace any split clapboard, or cupped clapboard
   which cannot be nailed back (using hot-dipped galvanized nails).
   (This step is done after scrape and strip because you can see the
   condition of the wood better.)  Replace popped nails with slightly
   larger ring-shank nails.

7) Caulk all vertical joints between clapboard and trim.  Polysulfide
   caulk is the most highly recommended, but hardest to use.
   Silicone-reinforced acrylic latex caulk (e.g. DAP) is next-best.
   Paintable silicone is excellent caulk, but apparently doesn't paint
   up all that well.  You can use clear non-paintable silicone AFTER
   painting.  Although silicone has the longest life, you will
   certainly repaint (and recaulk) before any of these caulks breaks
   down.  Some painters caulk under each clapboard, others consider
   that the paint film suffices, or that `breathing' is desirable.

8) (optional) For best results, use exterior spackle to smooth the
   surface.  This is only worth doing on the most visible parts of the
   house.  A deluxe job uses set finish nails and fills the nail holes
   with spackle.

9) Now, inspect the wood.  If there are places where it is heavily
   weathered (2 years or more without paint) it will have turned from
   brown to grey.  Such areas need reinforcement to accept paint
   properly.  SPNEA recommends using an oil product called Kyanize
   Kyanoil 21 as a pre-primer on such areas.  This is the modern
   equivalent of boiled linseed oil.  Use enough to pentrate the wood,
   and brush off any excess -- the goal is NOT to create a film over
   the wood, but to soak into the wood itself.  Let this dry.

   In places where the trim is split or cracked, either replace the
   trim or fill it with an epoxy filler, which is expensive, but very
   effective.

10) Now, prime.  Alkyd primer and acrylic latex primer are considered
   equally good by the experts (as long as you always stick to the
   top-quality product of the good brands), but to be conservative,
   use a breathable alkyd primer.  You only need to prime where wood
   is exposed, not over intact paint (remember, you have already taken
   off any loose paint).  Many painters add Penetrol (a brand name) to
   the primer.

11) Two coats of paint.  Use 100% acrylic latex.  Be sure it is really
   100% acrylic and not vinyl acrylic.  Benjamin Moore is a
   universally respected brand.  Pratt and Lambert and California also
   have excellent reputations.  Stay away from house-brand paint.
   Some painters tint the primer and use one coat of paint, but two
   coats should last considerably longer.

12) For highly exposed trim, such as sash and sill, you might try a
   polyurethane-reinforced latex such as California AllFlor (a floor
   paint), although high-quality enamels such as Pratt and Lambert
   Effecto (alkyd) also have excellent reputations.

General notes:

Never paint wet wood (except with certain special products formulated
specifically for this).  Never paint when it threatens to rain.  Let
wood dry at least a day after rainfall before continuing to paint.

Do not paint in the sun; this dries the paint too fast.  In the
morning, paint the west or north side, in midday, the east, etc.

Box your paint, i.e. if you have multiple containers of paint, mix
them together so that the color is uniform.  As a general rule, it is
best to do a "surface" in a single session.  If you have to break, do
it where there is some natural boundary, such as vertical trim or
between clapboards.  Do not paint the left side of a well, then a few
weeks later the right side -- you will see a line down the middle.

High-gloss paint is somewhat stronger than semi-gloss or flat, as a
general rule.  Experienced painters claim that high-gloss does NOT
have the effect of showing up defects on exteriors as it does on
interiors.  I do not understand this claim, and am not sure I believe
it.

I would appreciate comments on the above.

	-s
Newsgroups: misc.consumers.house