From: macrakis@osf.org (Stavros Macrakis)
Newsgroups: misc.consumers.house
Subject: Re: 89 Re: Exterior House Trim Painting
Date: 4 Sep 92 20:29:35 GMT
Organization: OSF Research Institute

In article <1992Sep4.143137.19095@msuinfo.cl.msu.edu> 21329JMK@MSU writes:

   Any changes when painting aluminum siding? Also thanks for your input.

I have not studied this issue because I don't like imitation
clapboard, whether aluminum or vinyl, especially not on old houses.
On the other hand, I have looked into removal and repainting, and my
newly revised painting FAQ incorporates the appropriate instructions
(see below).  If you want to keep the aluminum, the paint
manufacturers should be able to recommend materials and procedures.

	-s

----------------

As I was preparing to repaint the clapboard and trim of my
120-year-old house, I looked into paint specifications rather
extensively.  Here are my conclusions.

I cover the following subjects:

A) painting a house that has been badly maintained (like mine) for a
   long time;

B) adjustments to the specification for houses in better condition;

C) painting foundations

D) general notes on painting

E) houses which currently have asphalt, asbestos, or other siding on
   top of the original clapboard siding;

F) maintaining a painted house.

--- (A) Re-painting a badly maintained house

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.
The only advantage of alkyd is that window sash won't stick (this is
called `blocking', a typical problem with latex paint; the best brands
don't have too much of a problem with this).  However, local
contractors are split: some recommend alkyd, others recommend latex.
As for primer, the experts are split about alkyd vs. latex, 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.  Under each step, I give the
rationale for it.

0) (not painting, but a prerequisite) Inspect roof, gutters,
   downspouts, flashing (especially over windows), etc. and clean,
   repair, or replace as necessary.  Often roof leaks appear as
   alligatored paint several feet down the side of the house (where
   some cross-piece keeps the water from continuing downwards).  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).  Trim any shrubs or trees to a few feet
   away from the house, so that they not only don't touch, but allow a
   free flow of air.

   Rationale: humidity from behind is a major cause of paint failure.
   It is a waste of time and money to paint before you fix any sources
   of humidity.

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.  Keep doors and windows closed during this step to
   avoid filling your house with lead dust (and wash off your shoes
   before entering the house).  Also, be sure to have wide, solid drop
   cloths.

   Rationale: The goal is to get rid of badly-adhering paint, which
   will sooner or later come up.  In fact, new paint may actually pull
   badly-adhering paint off the surface -- this is especially true of
   latex paint.  Some people recommend stripping a house if it is
   painted with lead paint, but lead paint is only a hazard if
   ingested.

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.)  The
   power wash not only cleans, it also removes whatever loose paint
   you missed in step (1).  Try to avoid forcing water up between
   clapboards or other joints.

   Since most old houses will have lead paint, it is NOT advisable to
   dry-sand, because this will create lead dust, a health hazard
   (especially for children), illegal in some states (e.g.
   Massachusetts).  You could wet-sand, but it is a paint.  It might
   be worthwhile to feather rough edges where scraped areas meet paint
   by wet-sanding.

   If the paint is _very_ thick, it may be necessary to completely
   remove it before painting.  This is because subsequent layers
   (especially of latex) will have a tendency to lift it off the
   substrate.

   (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)

   Rationale: paint will not adhere properly to dirty or greasy
   surfaces.

3) Rinse with clear water.

   Rationale: paint will not adhere properly to detergent, either.

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

   Rationale: paint will not adhere properly to wet surfaces (except
   certain latexes).

5) Kill any mildew (dark, dusty-looking spots) by scrubbing with
   chlorine bleach.  Rinse well.

   Rationale: mildew prevents adhesion, and can sometimes grow through
   new layers of paint.

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, but you can also do it with other
   preparation in step (0).)  Replace popped nails with slightly
   larger nails.

   Rationale: see (0).

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, but this is
   probably a bad idea, as it holds moisture in.  If you _do_ caulk
   under clapboards, be sure that (1) you have zero leakage into the
   wall (from the roof, gutters, etc.); (2) you have at least a
   moderately effective vapor barrier (e.g. vapor barrier paint on
   interiors; and (3) that you haven't missed any spots (where water
   could creep in under areas which _are_ caulked and cause mischief).

   Rationale: see (0).

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.

   Rationale: aesthetic.

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--where lignin has been leached out, and
   you can dent the wood with a fingernail--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.  I do not know what the equivalent is in other brands.

   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.  Epoxy filler is a superior material for such patching,
   because it doesn't hurt the wood, and can be cut and sanded like
   wood.

   Clean and oil your gutters while you're at it.  Wooden gutters
   should be oiled with boiled linseed oil annually (on the inside).
   If you've bought Kyanoil 21 for the clapboard, use it for oiling
   the gutters, too: it should be better than linseed oil.

   Rationale: paint won't adhere well to weathered wood.  Also, the
   Kyanoil actually strengthens the wood.

10) Now, prime with a brush, being sure to get it into all nooks and
   crannies.  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 or oil 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; Penetrol increases penetration of primer by
   thinning it a bit, while not destroying its properties (as straight
   thinning would).  I don't know why manufacturers don't use such
   additives themselves.

   Rationale: primer is designed to bind well both to the substrate
   beneath it and the paint over it.

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.  If you spray, be sure your
   coats are thin enough that they don't drip and sag; you may well
   need three sprayed coats instead of two brushed coats.

   Rationale: paint protects the wood against moisture, and of course
   gives the color you want.

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

--- (B) Houses in better condition

For houses in better condition, many of the steps go faster, but the
procedure is basically the same; even if you're just changing the
color on intact paint, it can't hurt to inspect thoroughly and treat
incipient problems.  Step 0 is essential in any case (inspection and
repair of potential leak sites).  Step 1, scraping, need only be done
where you see flaking or peeling paint.  Step 2, washing, is always a
good idea, but you could wash by hand instead of by power washer
(still, you do want to get rid of accumulations of dirt, soot, etc.,
which inhibit paint adhesion).  Step 3, rinsing, is essential.  Step
4, drying, can go faster if you haven't exposed bare wood during
scraping.  Steps 5 and 6 (mildew removal and clapboard repair) will go
fast -- but do make sure to inspect your clapboard and nail it back as
necessary.  Step 7 (caulking) is important; do check all the caulk,
pull out deteriorating caulk if any, and replace with fresh caulk.
Step 8 probably won't be necessary.  Step 9 will surely not be
necessary (except for wood gutter oiling).  Step 10 (priming) is only
necessary where you've gotten down to bare wood.  Steps 11 and 12
(paint) are of course necessary.

--- (C) General notes on painting

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.

--- (D) Painting foundations:

My house has a fieldstone foundation below grade, and a brick
foundation above grade.  The brick has been painted.  There is a good
chance, in fact, that it was always painted, since paint protects
brick against moisture, and thus allows the use of lower-grade brick
without spalling.

Next year (probably), I'll be working on the foundation.  First step
is repointing the mortar where it's deteriorated.  This involves
digging out mortar with a special tool, and replacing it.  The main
tricks here seem to be (1) not hurting the brick (2) using the right
mortar and (3) finishing the mortar correctly.  To avoid hurting the
brick, do _not_ use the trick of running a circular saw along the
mortar tracks.  There is a good chance that you'll cut into bricks
(note that the exterior skin of bricks is much tougher than the
inside).  Also, NEVER sandblast brick, especially exterior brick.  The
right mortar should not be too strong, or it will break the brick over
time.  Modern mixes are too strong, and need more sand.  I don't have
the formulas with me.  Finally, the finished pointing of the mortar
should be such that water runs out of the joint, and ice doesn't crack
it.  There are many kinds of point, but the simplest sound ones are
either completely flush (probably best if you intend to paint anyway)
or beveled outwards, that is, set in at the top of the joint, and
flush at the bottom.

To take off peeling paint, use a wire brush.  Then get special masonry
paint.  Color will make a difference in the final effect.  Don't make
the mistake of using too-bright a red, which will look garish and
unnatural.  A very earthy red is probably a good choice, as are shades
of dark brown or grey.  If you want to make it look like brick, you
could take a sample of unpainted brick to a paint store with a
color-matching computer (but you presumably won't be painting the
joints a different color...).  Another color to match might be the
color of the bark of any shrubs planted in front of the foundation.

--- (E) Dealing with asphalt, asbestos, etc. siding

Many old houses were covered with asphalt or asbestos shingle in the
40's and 50's.  (Some houses newly built at that time used this as
their primary siding.)  This was done for the same reason that more
recently many old houses are covered with vinyl or aluminum imitation
clapboards, namely the promise of lower maintenance.  Although it is
true that all these products last longer than a coat of paint, they
have other problems, the most serious of which is that they tend to
hold moisture in, and therefore accelerate the degradation of the
underlying wood (some of the newer imitation clapboards are better
vented than older varieties).  The other serious problem is that they
look awful, and usually destroy any character the house originally
had.

It is perfectly feasible to remove these products and restore the
original clapboard.  This is done in three steps: 1) removal; 2)
repair; 3) repainting.  Removal is easy--you just yank it off with
(e.g.) a flat crowbar or roofer's tool ("Wonderbar").  It takes time,
but is easy.  Don't be shocked if the paint is in bad shape
underneath: that's why they put up the siding!

Repair is the hard part.  You need to identify bad clapboard and trim
and replace it.  This should be done by a competent carpenter (which
you may well become yourself, of course).  The sad thing is that
original trim was often torn or sawn off to make installing the crummy
siding easier (this is especially true of vinyl and aluminum, which
are easier to install if all the vertical edges are straight, and the
horizontal runs are long).  If possible, you should try to restore
this trim.  Now you should let the house `rest' for several months of
warm, dry weather.  This is important, because the siding has held
moisture in over time.  You want to let the wood breathe and return to
a more normal level of humidity.  Thus the usual recommendation is to
remove the old siding in the spring, and re-paint in the fall.

The very worst case is if there has been water leaking into the wall
over a long period of time (bad gutters, bad roof) and the framing is
damaged.  If this is the case, you will probably see water stains on
the inside of the house.  Of course, if the inside walls are covered
with paneling or something, you may not be able to tell.  But you
should be suspicious, because maybe they were covered with panelling
precisely to hide water damage.

Now follow the specification in section (A), being particularly sure
step (0) has been done thoroughly.  You will probably want to spackle
all the nail holes left by the installation of the siding.

Remember, the usual cause of paint failure is not the paint, but the
underlying surface.  And the usual problem with the underlying surface
is moisture.

--- (F) Paint maintenance

Now that you've painted the house, you shouldn't ignore maintenance
until the next complete repainting.  Don't forget to oil wood gutters
every fall.  Be on the lookout for leaks, and repair them.  And
whenever you get flaking or peeling, scrape, prime, and repaint.  If
there are patterns of flaking or peeling, the problem is not the
paint, but the substrate.  You probably have a source of moisture,
either leaking water, or vapor (from, e.g., a bathroom).

----------------
Copyright 1992 by Stavros Macrakis
Usenet distribution authorized when I post it.
Redistribution to Usenet or other networks forbidden.
Newsgroups: misc.consumers.house