Movement of Nails in Floor Joists

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N A T I O N A L R E S E A R C H C O U N C I L CANADA D I V I S I O N O F B U I L D I N G R E S E A R C H THE MOVEMENT O F N A I L S I N F L O O R J O I S T S by G.O.P. H a n d e g o r d R e p o r t No,

105

of t h e D i v i s i o n o f B u i l d i n g R e s e a r c h O t t a w a A u g u s t

1956

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THE

MOVEMENT OF NAILS I N FLOOR JOISTS

by

G. 0. P. Handegord INTRODUCTION The u s e o f r e s i l i e n t f l o o r c o v e r i n g s i n house c o n s t r u c t i o n h a s proven q u i t e p o p u l a r i n r e c e n t y e a r s . O c c a s i o n a l l y r e p o r t s a r e r e c e i v e d o f t h e a p p a r e n t "movement" of n a i l h e a d s upward under s u c h m a t e r i a l s , r e s u l t i n g i n t h e f o r m a t i o n o f " b u t t o n s H which may l a t e r d e v e l o p i n t o l o c a l i z e d f a i l u r e s of t h e s u r f a c e m a t e r i a l . T h i s phenomenon i s a p p a r e n t l y a s s o c i a t e d w i t h plywood s u b f l o o r i n g o r h a r d b o a r d

u n d e r l a y p l a c e d o v e r s t a n d a r d t o n g u e and groove o r s h i p l a p s u b f l o o r s ,

.

_{The r a i s i n g of n a i l heads may, i n most c a s e s , be due t o m e c h a n i c a l}

f o r c e s which r e s u l t when w a r p i n g of j o i s t s o r warping of b o a r d sub- f l o o r i n g o c c u r s . Some p o s s i b i l i t i e s a r e i l l u s t r a t e d i n F i g o 1.

There i s y e t a n o t h e r p o s s i b i l i t y i n t h a t t h e changes i n mois- t u r e c o n t e n t of f l o o r i n g j o i s t s might c o n t r i b u t e t o n a i l movement,

p a r t i c u l a r l y s i n c e a good p e r c e n t a g e of t h e lumber s u p p l i e d f o r house c o n s t r u c t i o n i n t h e West h a s a n i n i t i a l l y h i g h m o i s t u r e c o n t e n t . With the' d r y i n g o u t of t h e s e j o i s t s t h e i n i t i a l l y t i g h t j o i n t between sub- f l o o r i n g and j o i s t s i s l o o s e n e d due t o s h r i n k a g e i n t h e d e p t h of j o i s t from t h e u n d e r s i d e of t h e f l o o r i n g t o t h e p o i n t of t h e n a i l , Such s h r i n k a g e would have

t

he e f f e c t of a l l o w i n g t h e n a i l t o p r o j e c t above t h e t o p s u r f a c e of t h e f l o o r i n g and e x e r t a f o r c e depending on t h e l o a d a p p l i e d t o t h e p a r t i c u l a r s e c t i o n of t h e f l o o r .

An a p p r o x i m a t i o n o f t h e e x t e n t of s u c h n a i l p r o j e c t i o n may be e s t i m a t e d from t h e s h r i n k a g e c h a r a c t e r i s t i c s o f t h e wood u s e d i n t h e

j o i s t s , Fbr Douglas

Fir

( C o a s t ) , average r a d i a l s h r i n k a g e i n d r y i n g from t h e g r e e n t o oven d r y c o n d i t i o n i s 5.0 p e r c e n t w i t h a v e r a g e t a n - g e n t i a l s h r i n k a g e of

7.9

p e r c e n t , Assuming t h e p o i n t of t h e n a i l r e m a i n s s t a t i o n a r y w i t h r e s p e c t t o t h e wood and t h e n a i l i s d r i v e n t o a 2 - i n c h d e p t h , t h e s h r i n k a g e i n t h i s p o r t i o n of t h e j o i s t s h o u l d amount t o 0.10 t o 0.15 I n c h . The n a i l head might t h u s p r o j e c t 0 , 1 0 t o 0.15 ' i n c h h i g h e r i f d r i v e n i n t o a wet j o i s t which l a t e r d r i e d t o 0 p e r c e n t m o i s t u r e c o n t e n t . I t i s n o t u n u s u a l f o r lumber s u p p l i e d f o r r e s i d e n t i a l con- s t r u c t i o n t o have a m o i s t u r e c o n t e n t of

25

t o

35

p e r c e n t . I t i s un- l i k e l y t h a t i t w i l l d r y t o 0 p e r c e n t a f t e r c o n s t r u c t i o n , b u t c o u l d d r o p t o

5

p e r c e n t i n a h e a t e d house i n w i n t e r . Under s u c h c o n d i t i o n s n a i l movements of t h e o r d e r of 1/10th i n c h might o c c u r i n h o u s e s i n Western Canada, The e f f e c t of s o a s o n a l v a r i a t i o n s i n m o i s t u r e c o n t e n t p r e - s e n t s y e t a n o t h e r problem. If t h e wood p e r i o d i c a l l y s h r i n k s and s w e l l s i n t h e d e p t h t o which t h e n a i l i s embedded, t h e q u e s t i o n a r i s e s a s t o

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w h e t h e r t h e n a i l w i l l r e m a i n a t t h e same r e l a t i v e p o s i t i o n w i t h r e s - p e c t t o t h e j o i s t , o r w h e t h e r i t w i l l p r o g r e s s i v e l y move i n t o , o r o u t o f , t h e wood. A _{p r e l i m i n a r y s e r i e s o f t e s t s}_{was u n d e r t a k e n t o i n v e s t i g a t e} t h e change of n a i l p r o j e c t i o n w i t h m o i s t u r e c o n t e n t u s i n g t h r e e t y p e s of n a i l s common t o b u i l d i n g c o n s t r u c t i o n . T h i s r e p o r t d e s c r i b e s t h e work c o n d u c t e d t o d a t e on t h i s phenomenon. TEST PROCEDURE S t a n d a r d 2- b y 4 - i n c h d i a m e t e r f i r lumber w a s u s e d i n t h e s t u d y , c o n s i s t i n g of s a m p l e s a p p r o x i m a t e l y one f o o t i n l e n g t h . Three 2 s - i n c h n a i l s , one a c o a t e d box n a i l , one a b l u e d s p i r a . 1 n a i l , end t h e o t h e r a common s t e e l w i r e n a i l , were d r i v e n i n t o t h e edge of e a c h sam- p l e a t t h e q u a r t e r y o i n t s t o a d e p t h of 2 i n c h e s .

S i x of t h e samples were o b t a i n e d f r o m lumber which had b e e n a i r - s e a s o n e d t o a m o i n t u r e c o n t e n t of a p p r o x i m a t e l y

5

p e r c e n t . T h r e e of t h e s e specimens were p l a c e d i n a h i g h h u m i d i t y c a b i n e t s o t h a t t h e y r e a c h e d a m o i s t u r e c o n t e n t of a p p r o x i m a t e l y 18 p e r c e n t p r i o r t o n a i l 7 i n g , The o t h e r t h r e e had a m o i s t u r e c o n t e n t of

5

p e r c e n t a t t h e t i m e of n a i l i n g . The f i r s t t h r e e s p e c i m e n s were a l l o w e d t o d r y t o a l m o s t t h e i r o r i g i n a l m o i s t u r e c o n t e n t , t h e n p l a c e d i n t h e h i g h h u m i d i t y cab- i n e t u n t i l t h e y o b t a i n e d a m o i s t u r e c o n t e n t of 2 1 p e r c e n t , and were s u b s e q u e n t l y d r i e d t o 0 p e r c e n t m o i s t u r e c o n t e n t i n a l a b o r a t o r y oven. The second s e t of s a m p l e s w a s p l a c e d i n t h e h i g h h u m i d i t y c a b i n e t a f t e r r l a i l i r l g u n t i l i t r e a c h e d a m o i s t u r e c o n t e n t of a p p r o x i m a t e l y 1 9 p e r c e n t and w a s t h e n d r i e d t o t h e oven-dry s t a t e , Measurements o f t h e h e i g h t of n a i l p r o j e c t i o n were made a t f r e q u e n t i n t e r v a l s , u s i n g an Ames d i a l i n d i c a t o ~ lnounted on a _{1 - i n c h d i a m e t e r , t h i c k w a l l b r a s s p i p e ,}

The s a r r q l e s were a l s o weighed a t t h e same tirue as a measure of m o i s t u r e c o n t e n t ,

T h e e a d - ? L t i o n a l sai?:ples u e r e p r e p a r e d u s i n g lumber o b t a i n e d f r o m a l o c a l d e a l e r which \ad an o r i g i n a l m o i s t u r e c o n t e n t of a p p r o x i - m a t e l y 30 t o

35

p e r c e n t , \Freight and n a i l p r o j e c t i o n were d e t e r m i n e d f o r e a c h of t h e s e s a m ~ l e s 2s t h e y d r i e d t o e q u i l i b r i u m condlt-i-ons p r e - s e n t i n t h e l a b o r a t o r y , a s t h e y i n c r e a s e d t o

1 7

p e r c e n t m o i s t u r e con- t e n t i n t h e t e s t c a b i n e t , and a s t h e y were s u b s e q u e n t l y d r i e d i n a n oven a t 2 1 2 ' ~ ~ RESULTS The r e s u l t s a r e silown g r a p h i c a l l y i n F i g s . 2 t o 9, i n c l . u s i v e , i n which t h e n a i l p r o j e c t i o n h a s been p l o t t e d a p a i n s t e s t i m a t e d mois- t u r e e n r ~ t e n l ; . The direc-[;ion of m o i s t u r e c o n t e n t change i s i n d i c a t e d on e a c h f ' i g u r e , a s w e l l a s t h e c r o s s - s e c t i o n a l wood g r a i n p a t t e r n , The n a i l s i n samples A,B,C,E, and F were d r i v e n a p p r o x i m a t e l y p e r p e n d i c u l a r

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t o t h e g r a i n d i r e c t i o n and t h e wood s h r i n k a g e c h a r a c t e r i s t i c s o b s e r v e d might be c o n s i d e r e d a s t h o s e c o r r e s p o n d i n g t o t h e r a d i a l d i r e c t i o n . The n a i l s i n s a m p l e s G and I were d r i v e n t a n g e n t i a l l y t o t h e g r a i n . The g r a i n i n sample H was s u c h t h a t t h e n a i l e x t e n d e d p e r p e n d i c u l a r t o t h e g r z i n f o r p a r t of i t s d e p t h , and t a n g e n t i a l t o t h e g r a i n f o r t h e r e m a i n d e r *

Evidence o f h y s t e r e s i s i s shown i n a l l c a s e s e x c e p t f o r t h e c o a t e d n a i l i n samples C , F and

H,

and f o r t h e s p i r a l n a i l i n sample

E o

The magnitude of t h i s h y s t e r e s i s was s m a l l compared w i t h t h e maximum '

d i f f e r e n t i a l n a i l p r o j e c t i o n i n most c a s e s .

A summary of t h e p l o t t e d d a t a p e r t a i n i n g t o t h e p r o b l e m i s g i v e n i n T a b l e I , where t h e maximum n a i l p r o j e c t i o n f o r e a c h n a i l i n e a c h sample i s l i s t e d , t o g e t h e r w i t h t h e p o s s i b l e r a n g e which might b e e x p e c t e d u n d e r c o n d i t i o n s of s e a s o n a l m o i s t u r e change and m o i s t u r e c h a n g e s f o l l o w i n g t h e i n i t i a l c o n s t r u c t i o n o f a house.

The l a r g e s t d i f f e r e n t i a l movement was.065 i n c h f o r t h e c o a t e d n a i l i n sample G . _{The a v e r a g e p r o j e c t i o n r e s u l t i n g from t h e change i n} m o i s t u r e c o n t e n t f r o m t h e s a t u r a t e d c o n d i t i o n t o oven d r y c o n d i t i o n f o r a l l samples was o f t h e o r d e r o f 0.04 t o 0.05 i n c h . T h i s would seem t o b e i n c a p a b l e of p r o d u c i n g b u t t o n s i n t h e c o m p o s i t i o n f l o o r i n g , p a r t i c u - l a r l y i f p a p e r u n d e r l a y was u s e d i n c o n s t r u c t i o n . The d i f f e r e n t i a l movement t o be e x p e c t e d , i f t h e p o i n t of t h e n a i l r e m a i n e d f i x e d , would be of t h e o r d e r o f 0.10 i n c h f o r r a d i a l s h r i n k a g e , arid 0.15 i n c h f o r t a n g e n t i a l s h r i n k a g e , a s p r e v i o u s l y men- t i o n e d . The r e s u l t s of t h i s s t u d y would s u g g e s t t h a t , s i n c e p r o j e c t i o n s of o n l y one-half t h i s amount were measured, t h e n a i l may have r e m a i n e d s t a t i o n a r y r e l a t i v e t o t h e wood a t some p o i n t midway of i t s embedded l e n g t k . I n o t h e r words i t would a p p e a r t h a t t h e p o i n t of t h e n a i l ec- t u a l l y moved i n t o t h e wood a s t h e m o i s t u r e c o n t e n t was r e d u c e d ,

The d i f f e r e n t i a l movement of n a i l s t o be e x p e c t e d f o l l o w i n g i n i t l a l c o n s t r u c t i o n w l t h t h e wood d r y i n g from t h e f i b r e s a t u r a t i o n p o i n t t o t h e m o i s t u r e c o n t e n t of

5

p e r c e n t a p p e a r s t o be i n t h e o r d e r of 1/32 i n c h , T h i s would b e t h e maximum movement t o be e x p e c t e d i n house c o n s t r u c t i o n and would b e i n s u f f i c i e n t t o c a u s e f a i l u r e o f com- p o s i t i o n f l o o r c o v e r i n g i f p a p e r u n d e r l a y m e n t was s e l e c t e d s o a s t o a b s o r b a t l e a s t t h i s amoilnt of movement. D a t a on s e a s o n a l m o i s t u r e c o n t e n t v a r i a t i o n i n h o u s e s i n J e s t e r n Canada a r e n o t a v a i l a b l e , b u t f o r D u l u t h , Minnesota, i n t h e U n i t e d S t a t e s , t h e e s t i m a t e d m o i s t u r e c o n t e n t v a r i a t i o n i s f r o m 1 0 , s Lo

5

p e r c e n t , and t h i s would b e f a i r l y r e p r e s e n t a t i v e of S o u t h e r n Canada. The d e g r e e of movement e x p e r i e n c e d t h r o u g h t h i s r a n g e i s a l m o s t i n s i g n i f i c a n t i n r e l a t i o n t o t h e problem of f l o o r i n g f a i l u r e .

Another a s p e c t of t h i s phenomenon i s i t s r e l a t i o n t o t h e problem of popping of p l a s t e r o v e r n a i l h e a d s i n " d r y w a l l " c o n s t r u c - t i o n , I t i s n o t i n c o n c e i v a b l e t h a t t h e s e a s o n a l change i n m o i s t u r e c o n t e n t of wood s t u d . d i n g ' m i g h t b e a s h i g h a s f r o m

5

p e r c e n t t o

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s a t u r a t i o n due t o t h e a c c u m u l a t i o n of m o i s t u r e i n t h e i n t e r i o r of t h e w a l l under w i n t e r c o n d i t i o n s . It i s a l s o p o s s i b l e I n t h i s p a r t i c u l a l a c a s e t h a t much s m a l l e r movements c a n be t o l e r a t e d a n d i t h a s been sug- g e s t e d by one a u t h o r i t y t h a t t h e p r o j e c t i o n of' n a i l hadds 1/64 i n c h might c a u s e f a i l u r e of t h i n p l a s t e r c o a t i n g s , If s u c h i s h e _{c a s e , Lhe}

movement of n a i l h e a d s produced by c y c l i c a l m o i s t u r e c o n t e n t c h a n g e s may be a prime c o n t r i b u t i n g f a c t o r .

CONCLUSIONS

The r e s u l t s o b t a i n e d from t h i s p r e l i m i n a r y s t u d y would i n d i - c a t e t h a t t h e movement of n a i l s b r o u g h t a b o u t by m o i s t u r e c o n t e n t c h a n g e s i n f l o o r j o i s t s w i l l n o t produce s e r i o u s " b u t t o n i n g n i n r e s i l - i e n t f l o o r c o v e r i n g s , p a r t i c u l a r l y i f p a p e r u n d e r l a y i s s e l e c t e d t o ab- s o r b t h e s m a l l movements i n v o l v e d . The i n c r e a s e i n n a i l p r o j e c t i o n r e s u l t i n g from d r y i n g of t h e wood f r o m s a t u r a t i o n t o oven d r y a p p e a r s t o be a p p r o x i m a t e l y o n e - h a l f of t h a t e s t i m a t e d from a v a i l a b l e wood s h r i n k a g e d a t a ,

The measured n a i l movements, w h i l e n o t s i g n i f i c a n t f r o m t h e s t a n d p o i n t of f l o o r i n g f a i l u r e , may b e of a magnitude s u f f i c i e n t t o c a u s e popping of p l a s t e r o v e r n a i l s i n i n t e r m e d i a t e s t u d s of " d r y w a l l " c o n s t r u c t i o n s ,

The a s s i s t a n c e of Miss V,L, Magwood and t h e s t a f f of t h e P r a i r i e R e g i o n a l S t a t i o n i n c a r r y i n g o u t t h i s work was v e r y much a p p r e c i a t e d ,

REFERENCE

1, Canadian Woods, T h e i r P r o p e r t i e s and U s e s , F o r e s t r y Branch, F o r e s t P r o d u c t s L a b o r a t o r i e s , ~ 9 5 1 ,

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SUMMARY OF DATA

SAMPLE

NAIL TYPE

G R A I N CHANGd I N N A I L PROJECTION ( i n c h e s ) DIRECTION _{i l o i s t u r e Content Range}

S a t .

-

0% 10.5

-

5.0%

S a t .

-

5,0$

Coated S p i r a l Common R a d i a l R a d i a l R a d i a l Coated S p i r a l Common R a d i a l R a d i a l R a d i a l Coated S p i r a l Common R a d i a l R a d i a l R a d i a l Coated S p i r a l Common R a d i a l Rad i a 1 R a d i a l Coated S p i r a l Common R a d i a l Ra.dial R a d i a l Coated S p i r a l Common T a n g e n t i a 1 T a n g e n t i a l T a n g e n t i a l Tang. & Rad, Tang. & _Rad, Tang. & Rad, Coated S p i r a l Common Coated Spil.al Common T a n g e n t i a l T a n g e n t i a l T a n g e n t i a l

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WARPAGE OR M I S A L I G N M E N T O F J O I S T S

D E F L E C T I O N O F F L O O R I N G UNDER LOAD

WARP I NG O F BOARD SUB- F L O O R 1 NG

F I G U R E

1 P O S S I B L E C A U S E S O F N A I L P R O J E C T

I

O N

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(11)

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