Natural wood finishes for exteriors of houses


Material Information

Natural wood finishes for exteriors of houses
Physical Description:
Mixed Material
Browne, F. L
Forest Products Laboratory (U.S.)
University of Wisconsin
USDA, Forest Service, Forest Products Laboratory ( Madison, Wis )
Publication Date:

Record Information

Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 29336146
oclc - 231625556
System ID:

Full Text


Cctobcr 1951


No. i190 |*s

Madison 5, Wisconsin
In Cooperation with the University of Wisconsin

i Tl L

k ,0E5T 5ERV|At

Digitized by the Internet Archive
in 2013

For-stL Products La.boraror,- >orest service
II. S. DeairteLcnt of r' lre

hahral f s for1 wooJ ad sidin on- the exte ritors of hou1Cs's have
becoc in"r a:inf'y o-nuar 1 "rin "." p I ye.(ars. "'Joccs tia nave a
r.c>' .r.r'. mr red color of h,,ecr c., -'ch as rcd(,mcd a! 7 es:crn rcdedar,
'd ......v.. "aticulal -,11 to at7 fns tihou n',o'ds ofo p al
c or, srch a1 c oess, ie, hnt y pine, a d ') yas-fr are oen.e tL s in 1 a L vay, Th-ose -:ho ',ave learned to use s.zitable m:at-rials
for .a aral fii. t_ ato . and. :ai-Lain -t(e, correctly have
fP.r' tr. jcasi- and s(vi:ctoI' n e']c ot* a t.r handr, sorec o -' ave
t ried ,a finse 17 1 Iri Sa 7' i ,-L tIh' r cquire ha-:( bee-
d sa'nnoint C C a .d a c. : b"'a ( c'. tc t c o -dc:i praciLce of hidinF th
uood I .c r a co. inr of !.o' "c aint.

T, first t"I2F to lea-'n abcut natxr 1 fi isi]es thai ... are
mnleh lIrs v KrbiLe a-d te r force r uCU be rkiCnre(. r-i re if, rC2eowlY C 1an
coaC v- s oe house paint, o :e 'p t srho 'i o ... ic- 1 arc before
needinpJ re:ja- ... na.0ral Si s ...n.a. rl 0 alay nee d. I, r ,ovral at least
,. .. ze r.neeal at least
nc:-e a On C arts of a house to at are fl e s -- s n and
rain na. turr inish -sualy n0c evezry 6 enons :'.iMn it,1 has
been done tlrec o0-' P.r tjj. aft' c K.c. t..e intervalc a be Lo ,at
loner, thc_71 seAdon o'"e tln I? .f or a..c '.-d r of t1e
.oluse early r-ne-al TsufficC a u: in Co ha the iervals nay bC
eve o.. Incr.

z .. a r'. lo-cs c' of o e south side of the
oSu are -"C L e/'Ie "enoo rn-.^ d -.ost- frec)(-nu eewl ^f^,ia
h c "'.ra t. ',e Iy eo-st o sLdi A c r c1 a o. (. o_ K c e th
eaves of, te. ar-, sid Ce; ..... shelt"red and can (o lr. est hcc

r n'-"''].s r or, 2 aa (IVft the locations
o0 -f :( .S ' Ce '>'2 0o r c oh. r "-l ---, 'C, 7.1d CuS

of -' *' ..'s is to Pre. Pa .. e the soi.:rfac3 g0 lo
to Sr CL, o. k.... r CL 0 o
0s (":c" ;s .. ...c .. ,e .':. :cr t.e n ;, r r ol off o+iichl ... r -'n s r Tas o.n the o :O.o

an s ,- au, rh. In d ir casn ofre appi ation o s-
C (1er rded ofeu- [.,f ,o..ish :--n<.-1 a,,` be de .l u too r.c or
.c . n or ..o.. U > a d o t f'
o7 u:.s: r'.''ot "'.s an e.:< 'ansi'n of a ar tic stnafc. ,uate ou:iso ,i;; iiat- ie'sa
or t an I ,:.. I Li i
I'F ":, (7 ao," a0 Tocni-on^ ,,is)r in c rrt zici t\t no

,C ,:co i...
)'C) 72 cI a.. U( i ,` iU11_.2 ri, 2 1 ,2 ,y P2 (
*S OnC o.

-* *c'or *, -- r -1- 12 1
r t**. l .C, 1( ^,


7 + 4 -on
Cl, 1- U111,,, -, 'L,

it is postponed unduly, the wood begins to acquire a gray color that turns
still darker gray when ore finish eventually is done. To restore
the desired color after serious grayness has developed, the surface must
be scraped or sandpapeored until the wood is bright again. If the wood is
allowed to become roughened and cupped as well as grayed by weathering,
t.e restoration of a smooth, bright surface becomes very laborious. For
thot reason tie timely rene.,wal of natural finish simply cannot be neglected.
Similar neglect of coatings of house paint is less serious.

There is no way of keeping wood very long with exactly the color and
nearly co plete absence of gloss with which it com es from the lumber yard.
. finish that could do so would enjoy a good market. But any protectivee
1ini that can be applied necessarily penetrates slig itly into the wood,
-sp1laces air from .-ood cells, and seems to deepen thie color of the wood
even if tne protective material has no color of its own. hioreover, by
filling the pores in the wr1ood, the protective material makes the surface
smoother and therefore iparts at least a moderatee degree of luster or
L;inesS. A.s time passes there is further change of color because sun-
ligit gradually darke-is the color of .lost woods by changing, yellows and
red toward brown. ,ven te weakened sunight tha.t gets through windows
eve ..tall da-es intericr woodwor,,. If in addition the protective finish
isef dar -en with age, as -ict of tihen do, still more change in color
nus be eCpected. Fortunatly at ed wood is still more attractive than
freshly cut wood.,,ral finishes !,,).y be divided into tree broad ty-es, the oil
finishes, te. wood sealer finishes, and the varnish finishes, They differ
in t r. : com ositio n of the material used, in "-e aDropriate .ethods of appli-
ca-Ution,- in +tne rsltin appearance, and in importIant characteristics of
perfor-ance. Tne u-int Lndustrv, however, has no such enerally recognized
cla sification of finishes, the arade names of commercial products do not
necessarily indicate e te tj,:j to which they belong. Thus a material m.ay
be s id as a "lo- cabin oil" and yet turn out to be either a sealer or a
var~ishc. The user must judge from such information about t.e com-position
as may be given on the label and particularly from, the way the product
behaves when he starts to apply it,

OIL ZIiSH. The natural finLish within the lowest degree of luster or
gloss is the oil finish, it also darkens the color o- the wood more than
o tler inaturai finishes do because tUe oil penetrates farther into wood.
.creu, v, tne oils are inclined to continue with age ore than
mo::t sealers or varnishes do. [ho- dala.-nlning, however, can be largely
corr cted bIr incorporating a little pi, .- L in thie oil as is described
Srtn r fon,

The simplest and oldest oil finish is ordinary linseed oil, either
raw- lin.eed oil or boiled linseed oil. Unless the work can be done in
warm, dry weoahcr it is best to use boiled oil or else to ad about one-
i of a pint of liquid paint drier to a gallon of raw oil. host painters
also li:e o aCd sso ic volat ile tninnier to lin.seed oil, thinking that it
ma:es t.-e oil -onetrate eeo er. 1'hat is not thc case but thinning the oil


hilips to avoid i .avinn- any access oil on he surface. Turntin, .inx rl
s irlts, or other tthin.r sold for "-Ln pait a usd ut d
not add 1or, Lha, a half :. lon of thinn+ r t' a 1a lon of oi.

T> oil may, be ap li..d b- brashi.-m, s ray: or rno: isj. (cr n '.
oo two re coats arc needc. Bu- it is rot. imnpor ant to se a..
of tC cil sins .nO tce surface of !`c 'cod. IfI, afer l7 s econd co-t
las Le a:licd and .as stod so 20 tcc .30 -,i's, thre aI c ;- . oss'
place'o 'vV]re excess oil stands on th sr'eC, it should be wiped off
befor it lias tl>c to hiarden. Coatil -s clfins oil arc 'isaa Lsact1
not., only bcecauso tL arc too f0osrsy but b.c'use ticy a.e inclined to run
or to ~I ..:le v:on they dry,. In a. vnt co a-s oil r so
cor .... I, -, oE. t, o so I't
tend io 1old dirt, and be come m!.2cvod In ranc-.rin: th, oil fi ih
S, i ,j, sicns of W, car one frrsh a'-,Lication should _'fice. ,'ai,
any 0acess not d. .n. into Ihc Toed shoi. xincd off. (o no fcre t
tha .t oil- ra s are a circ h.azard. Burn then promptly or : ,,.. then. in a
ih1ly4 closed metal container uti! tc,, can bc burned.)

.rad e-bra nd products ma"- be nurc.ascd at paint s.or.s. "" are
often c-"a ccd lc oils or 1o, cain" oias bc usc t nat: ural finis es- for
xt. ior -ao -'-crh frst bcca-uo popu'r for s 'r r cc "ttarc s buil of 1f
iors. TIh cosor erca. produ:cts arc usually na'c of bedie s1e oilc,
- _n o.l, o" ot,: r .... c oils an'-d I ;. o ied oils Lave :'h- heated
an: ,Lo ';( oil
or trcae ce micll to iV1creasc 1th viscosit' rr a aft "hich a
rrea r r-r' ;uien oaf inc 'cSi-e iallnncr n.u. b dKcc' tc rior sr ,-
acle vic;"' for a'l' i "ca io U ...a-oil ..i.i s d : a et'r
so dcchly in-to "'cd as ra. or boil i oil rcs a6c. Lrir t t (
t.e color of ,h -ood ss much. Tie product'ed pro. nrcrie, s of
a socd s alcr aCrc and. O: .7 cs t;;c doanre of bod C" is (incr Cas

Sarar-brand oils si_.d ap and nai.ntainc. ,jus as .as
b ccn dScricd fo te r. raw lisee Ti Lin iLs. 1incc a bcdicd oil is more
apt lae an ecs stnc I" on tch srfacc. than ra,, oil is scc.a]
cae shcol e t- to 4i-c c t. xces be- Lfore it bccor-c h.ardcncd.

oil f.=_.-oj.,s; finis ic -5 ij t:. bIst se vi in d-w, JPacOs :h.ereI c he.r
novc! arc an', roio.Lcnd a r an .. cf ar:,n< an,, such as scan.. r: Arizona.
,r. cain c a: lir for s' i. ...a t2. oils arc sb j ect to aachc
br :olds: the 2', t .row e. surfces. On fnse O cd:itio. is
.. .... 9, T. 0"s )n c cdL i :
us'ua I; ca"ledd -11"h'ar., alos vi discclcor,.tion r ayrsult
Ve cC.n C vtd -o ic suitablc: pr-srvativcs in th
nl rtis b, ..... .....
oil finish, o tho'0h ,- no an all f -he tra.d-brand oil finishes
olrn tan s r. r.. .e ain and aC.' ILI 'b s
on e la ., ...... c't, .r'e t. c: c rad t t.,se f is a re crcxc,
'10c' 1 ;, i Cs ncin: s( ('ecaus thc paat Cindus'-i us' S C a C, ,
have no su chs cc: ,.

I linsfd oil or a comnmrc'ia prodct not ccntnai'. a r'srv r ic"
Suscc, rr, arc -to 'a' s of i'cororatincr suialo pre srrv'tiv. One
.. is O b-uy oe c. th- conc'ntrat.ea s:'olions ofcn 'ctacl tor ,,.r l or
o011 r chlor'na p .rhcnols sor' a l-nbr a U'ccs ncr Cr 1s rviu -.oc:d and
te :~ % "... -LL2 i. .. ] LL: .s._.., '. J.nrS ,.C Kcfacm,.r. tr" '', :1 '' I.... r ) "can't

thinner. If the directions on the preservative say that it is to be
mixed with three times its volume of fuel oil for use as a wood preser-
vative, it a-- be mixed one volume of concentrated preservative to three
volumes of linseed oil for a linseed oil finish. The other way of
accomplishing the purpose is to buy one of the water-repellent preserva-
tives not- sold at many lumber yards and some paint stores and apply it to
the wocd before the linseed oil finish is put on. In the second case most
renrwals of the finish can be done with the linseed oil alone, for the
treatment with water-repellent preservative need not be repeated for 3 or 4

I,..c oil finishes may be further modified to advantage by incorpora-
ting a small amount of pigment in them. Usually a pigment of reddish-browm
color is desired to simulate the color of the hcart+ood of redwood or red-
cedar. The pale color of any sap.rood present in the lumber is thereby
changed to resemble the heartwood more closely and such woods as pine or
Douglas-fir arc given a richer color. Moreover, better maintenance of
color is achieved because the presence of the pigment tends to :.i:s!: the
c-radual darkening in the color of tlhe wood itself If renewal of finish
should be delayed until so'.c boards become slightly grayed from weathering,
the pigment helps to restore the desired color, provided the gr --ing has
not been allowed to go too far. Finally, presence of a little pigncment
usually adds appreciably to the durability of the finish. Of course, the
amount of .5r.,r..t must be seail, well short of the point at which it would
give a painted or even a stained appearance.

A number of the trade-brand oil finishes on the market contain pig-
ments. Such products, of course, should be stirred thoroughly before use
and should be stirred from time to tine during use. Linseed oil or pre-
pared oils without pigment can be pigmented just before use by adding a
small proportion of burnt sienna ground in oil, which is sold at paint
stores for tinting paints. The sienna-in-oil should first be stirred
thorn,.'hly with a little of the oil until it has thie consistency of a
thin paint and is free from lumps. It can then be stirred smoothly into
tVc rest of the oil. About 1/2 pint of sienna-in-oil to a gallon of oil
may be right but the exact proportions are best determined by trial by
a,-2diF the color in small amounts at a time and applying the mixture to
sample cuttings of the wood to be finished until the desired appearance
is obtained.

Unusual natural finishes can be made in similar fashion by adding
colors other than the rcdEdi' browns. Thus attractive finishes for redwood,
redcedar, cypress, or knotty pine are sometimes made by adding just a
little white, cream, or pale gray paint.
1 OOD SL l FINIKH. Like the oil finish, the wood sealer finish is
a penetrating finish that should not be rermitted to build up on the surface
into a rlosry7 coAl in,. Sealers do not penetrate wood so deeply as oils do.
For that reason the sealers usually darken the Iood less and give the surface
more luster or glossiness than the oils do. The sealers, hliowever, are less
glossT dhan varnish finishes unless too much sealer is applied and tie excess
is not wiped off.

R c *"-.


In cu:",_ r1, c ..: "'2? >.''. o l ( "...... 2 i :LLK '
th r .i.(:rr: co (tain dV.:'o 2'..% ;c il c .inc l '
*i >b ":"r, .U r~o r'r t n '::dri r :-.r .t .minrv I: to 2?' coii['i~Y i '.

c.. .. O .... ca .. il K f 22 : :
" : :(.'. r nr a co& 2 n'io.s cc lr:,
cft a-'r v .....l l'n .... over i.t, g ac vc.n-o. l- f iiSh dccc..

1 ":C.'

t:': h

1^'" '^""
in %c
for .,

S a2re ",r, ':ood s l .r 7 .(, '> 1old 27. 1a:n c tor d' C.
.C 11- r:a:"ier arEl t, rctir, fi'.''cn for

Cl r
iv;h r' : fal, cir ... .. :< td.or t (. ;nro it n d.. o tn b o c
f.. o .. ...... I*-' :. t ; . j cc s t' of :-. '.: o c:. r

,r fini.rh :'. d end{ rup, (''l., u t .. Vc~rr.Lnli fi~ ::]

c :i~r~ti; ..... o ;c '. o . o do c: 'c v.'" ,:- or
.. ......'..! so >' Ti) .' '' L 2 c d ... f

'*r" I i: h t" a": :t about an"., oqual v/olur' t of
~~~~~~ ~l ec_:,aad., ofY.' .L' %',
L4 L7o <, i ..."- : ...I '> .. i ; ''" i,

-..It O 7, 0 ': '0 (o'(d sal( 'ic arc :
o r .... .. .... "' LI O' .
-od 1iuc a rt-. ,-, " i%; rc~vcr 'ar -( a-yI}
-0.. L, c .
ad'-isc".'. c "- ..... a. T~*,:o s .-: t it. th.(
EuvyOi to fo oilJ. fi 1.....

0 .. 4 ..... O 1 :I
C ." t ( oro' Z-72 "

'"ro re.r: taat to :lld
i. t ,. ", C ... .
2 ...C. 2 .1 > -2 ,
S ..... I'1 ..

,'5 o~:'.cz Oi hk b.o

*T 'r ... 4r

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2or co*::22 rclal .-oc s,'aL';r coI' tain plf:;c--o': for t., 2aK 'c d ci(r2 ic
p'. } g'r C I .' c c cl: ... s< ](i .. ..:I I S %} . I C ,." .O_ R i p < -
:r, *,, ,...".. "`c : : : .. o :] ,n trc. iiscr ,IdC ...

, .. .... .. i.{6 3 . *

C ^.' s3(' 1 '.;7 o -- ^'.c n'" i,:'
. ... .. rt 'S. ...
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7' r -

2- 7 cih'r oi l fi n i, h oi- 0r 1 : >_ v'.2"
l. .;.,.f r-;"T [,iab.C th .chnccS coO -'-rl':" .... "ord,
r:: 7n o o' f .,:, ",. 4 d t.o i, c' "* ith2 .V 2 c2 ; 0 -or< tl
,. n \ "c of . ... ofr; ..... .....' "C" lof 1 "

.ih.Gf> : .. 4 ...... :-[.i2:.. "rr<

(.:S: o '.'"id o O V 2'"..: b'u ('2' (21r ; f r'2 .
fi-r . ... ........' 1: f ,i --!'' ~l or' 7 .- .. .. ],r .'r c ... s',';c' "'. s h

'4, C "~ ~'4' -'
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1^ art% *,:r'-r;

4.-....a .a,',r q o c ,,--de .' ..r ctr
1'i (" (' '; C a .2 ' b
'2'r -"4rnirh. .:,r:. h i":: a plie'd by-
2Cg e ".*( .C [ P- r- i" " c,,

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4. .. .. 'i

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for renewal one coat at a timc is su-ficient. On new wood the first coat
ma-y be1 tLhined moderatly _`rifh turpentine or other paint thinner. Shellac
St not be used for the first coat on exterior surfaces even over the
knots in knotLy pine. Thlie succocCdi' g coats are expected to stand out
withoutt penetrating the weed ard, of course, none of tie varnish is wiped

''hen renewing varnish finish it is difficult if not impossible to
lmit recoatil-n to the more exposed portions of a sidewall where renewval
is (ecdcd. The freshly applied varnish does not match in gloss ald color
the iderr varnish. Thus the protected areas must often be recoated even
heugh thCey do not need renewal.

Wh re here is dampness at tines varnish finishes need preservatives
against iedcw' much like sealer finishes. Unless the varnish already con-
tais a rescrvative it is advisable to apply a -irater-r)epellent preserva-
tive to the wood before staLrting to put on varnish. It is seldom practi-
calbe- to add a concentrated preservative to a varnish because varnish
cannot 7cl! stand much addition of thinner. Similarl- it is not gocd
}rac,].ce te add pim;ients to varnishi. If pignent-abion is desired, it is
st a..l- a pim-'et oil stain to the wood first and then to varnish
owvr it,

On he 5hoe, experience witih varnish finish on large areas of
01t rio ood7or> such as siding !as not proved satisfactory, Oftenlihe
v.rni's fiis d evelops millky-, opaque patches where t: coating has lost
-s adsio to te ood witho breaking open. Some varnishes craze or
crack in an unsigQtr manmncr after *.'ich rncucal of tL1e finish is difficult.
After t-:e or t rec rcnouals the ccatLng beco-Cs too thick and begins to
craclk and scale badl. t thcn becomes recessary to remove all of the
old varnis,:, vith varnish remover before hce finish can be properly restored.
Such -reoval is Oe.)pensivo and laborious.

i~ar-lwo cds

he Uethods of natural fbibrin" described so far arc suitable for
a .. soft.wods and for rerwoeds witlh pores no larger than those
i irpch. IIrdrdootds with pores larger than those in birch, however,
us-aly n S .... e e, if di, has been applied but before oil, sealer, or varunis
Sp en. e ~treat;,;ent fo-r por(c conSs) in application of a p)aste
.... fleri. ",t~ural" wood fAI' -r is a transpq)rent matrial that does
I alt,!.r' t./ aC'Kearance of ,e pes. Colored wood fillers are also
bht acccnt the pores, usually by aing then dark bra;n
S,3. a- and tereby eprshaizc ti grain -attcrn of thie ood.

To G,--)I peae w.. oocd fil.ler, thi,,n it --rith paint thiinner to a con-
V ::cictc suitable for brushing and' then a -,ly it Eik.. paint, but brushing
S.... rain c _' -c ood raeL>r tI-han Iwith uivc -rain. Then let the


7ccati nF std a I. nini'es ;u Ih nial wet, araran"c
-. ~.J~ U'~C], :.*[t [ -]LC 0'j "t.i (X:C(. I: 2 7 i *~
b'anf o dL 0.0 aspect. -7' i filOf" (,y .i d; cIanC
ras,. b''jr!a'p cotbLotn ""."rs'b,;, o. .un r n ~ n i,
firct acres: K. -ri.n to ]a c: -A ,-: pa f e ... <: e pos,
thn fial "m 1l. t af =lLeon. the rai.. to avoid. leavi s-9:t
strnl of cxccss filler crcss: L tT w: lUrn ic ifillr c-7 ..
dried( at le ct veorigt the finish'l coast of oilr, :r, or
vari-"12:. Ls- bc apliP d,

For varnish- finihes on U> <> larr pors o c.of ucocd
filler is >eccessary to avoL larger of pr.1 aure7 i.iu1r, of t fiL's.
For --oco s alxr fi.l- ,', ti se of filler is stro ,'-!r rocor= :ided,
to.' if so dsir

Docrs and ::-,n.,ou:

snug jo( ., anzl accurate s. ad d i':i'ic::s -re essential fo r LoJd
a;) T eC L .i c-s and c rocr f t,', -Lioni 7, of door ad.. 1d !. C, ] ccd doors
a a nuribcr of joi.ts ta'.t rca!di, collct ann ratai. ra': Gatr o t,:e
dotri:et of '.c 'rcod uZl ss .roe-,ctio bt coatT, .j n...t....
Pai or n cralel afcrds e..... re.l.......ilC a cir. .. ..
ncdd protection. 'or t hat aca carc:f'-i i should be ...en
to t ch oic( ofI' iint or trL". f.a ... ,or .'f .'c..s of oe
ad K.ri cws eve Thc. nat ural fining' ia s.lcctcu f:" U.c s211d>;. .a.t
o0 a color ..c.... .... of ::av,:-ra y 02i e s1'/.. ;e us'

B7"t if nax L. inish is i shed upon for doors or TrificOWS it is
Tr-,.bly be t ,,o u-ly I a, fl varni,: ficJXs cofio:; nc; of tre r fotr
L) C a "_e- 0 v a ... .' a cullb ... t r" r' ", C _Ia zIi ,C
coa-.s oeca>.rc vcarn>s fpicas better 'r Ic Lon a0'aj.nst ,S 'OCX weaO:-'unc"(i.2 .2
oil r see i'l 'd T:: .o vanicflust, ou c s' b" -s..... "
Co ..f as -2 cvcs CceC..r. 2, a ;2 ..r1n ..< coating< be'co;:s too tl.ick to ,, 2..v
crach .-, alIiraor:.., ad seao:,- us,. be strL-ppd op c "0-
y rn .... ra ' U,- f rrc rr :a ,* r c" ix... .:rc. n c .
-ai .: r o' e .....o ...a.s.. : rc ov . i.s ... l .es burd<.( sc::Y c and

crU2al c s" Y'.. C 0

Vanu>sJh ?may~ last2 lone on door 0nd Kindcvs t>ia. it.>"2 (>212 on s
bet..cau .. 0 ( 2e ...r ..d 12.>-u.<:f 0" i( ] "' : U.n1 a.. s.U. O.c ..7lE7
K ? a......... 2 7 .ox .. .. t oai .. ....(02 c: :>1." ..... O .... iL .
"bl e'rlls, receivgr nore p roteccon fro:,, roof odoarhan. : tJ,.an le focr
cours:' eh r iLL.., :'a. lbecc shltre by 7 perc orV .nry re( s en. fte
ir of' 1 Crf o (e ....' .
h'.. O cr tr r :a::- b:i~ 4' : '
... ad doo ( :;ae. f e o r t r-icre es oer r."oic
:*' i"%: 2 r-
.a. roll bei trca .t. at -:.>nLt t; -."-r .- 7 p.' 1 .h.. y .(nr'.
installed. Such trcatrlnt n', he In to pr- vent blu: s be-in i:'i SapuWOO, u;hiCli



causes discoloration even through paint coatings, and also affords some
protection against decay at v-alncrable points.

Ru-t 4- 4- ns-*

,'Joods that contain tannins, such as redwood, radcedar, oak, and
chstnut, readily produce a black color when brought in contact w-ith
ion ru-t ad a little moisture. Soluble cop ounds of iron react with
tannin to for4 a blue-black compound related to solne writing inks. Other
cxtrac tiv C npuesent in ranm, woods nay also form strong-y colored compounds
r.Lh iron Extcrior woodwork, thcreforc, should always be fastened in
place 7ri-h corrosion-resistant nails, screws, or other fastonings if it
ito rec+ a natural fini-sh, S-ch ifasenings, in fact, arc well worth
whie ,ven rh]n the wood is to be painted. Similarly har fasen, tr the L Oxt.cor surfaces of wocd should be resistant to corrosion,
or t-, c ra"n tr dppin"" fro' rust-, iron or even copper or can
discolor -.rocd an(l even paint. Vceil galvanized iron, i-latcd iron,
alminrm, zinc, and stair. ss steel do not discolor wood. Corrosion-
inhibitiv- paints will keep iron or s _el hardware from discoloring wood,
prvid'ed hie'protective coating is ma intained adequately,

Clear finish jr- materials to be applied to wood must also be free
from oluc compomunds of iron. Shellac varnish. or oticr spirit varnishes
that .v.c b.n kent in rusty- ctaL_ container: or have other',rwisc come, in
c..n.ct w.-it. iro rust will b1accn w ocds that contain tannin or other
xtractivees thatb react with iron. Tyven oil-scubl ater-repcl _Len pre-
seratives, oil finishes, and sealr finished ..ave been owaan to produce
bla.' s o on re .wood or cea w;oodCork wTih'n e naerial was ar-' id fro-D
-st- ain't pails. Similar exerior wood7rk t-a'- !,as been smothncd
... s tel -ool may develop .blac- s ec-"s after -C first rain frcm particles
Ss$eel left in h" surface of i.' woToU.

a"in_ from natu ral to paint finish

it is no, a -good plan to s2 ar out -Ti t natural finish oi a now
I _7se a n an xr'mcn-, wi-' h ideca of ca. to ,a Jnc finish later if
C .. : arl finih faCls re cac. It is much btcr to visit hoscs t hat
a .ve be( 1. in n..u. a adm in p-aint fiLniis for a ferc years to learn
ea (2 'r 'C Lc eaches a-t t hean Lo choo fi.all )Gr beforeUC ch husc is
ce ct,.d. Dfor rei al-e painting; the first or pri'ingL coat ac)liud on the
b'.i'ie ',o i' 'eC important than any coa that can be applied subsequently.
'-' -r :- .aiL for a paiin jol should be one designed speciicallc y for
*)u ro4',F :o* c of tc natural finishes comlis t coq uire(s enints
o 2a. oc, Tr 1:",i for paint t coaigs,

-I, howe"r, re arc god0CC r eso-s for paintings'; a house that
'-, vis a.d a a.......ra.l "i"."sh, ehe chance can be made roasonabl-, satis-
1.ctr' .-, r ov...'. s 'ue.. pr cautilons arc taken. If the natural ini'h
..'.. ... arnix t ,Lo or ca sealr at h's been allowed to accumulato


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3 1262 08927 3451