Hello,

I'm about to install some T&G poplar beadboard as a ceiling on my
exterior porch. Now the boards are inside @ 68 F and 30% RH, where
I've primed both faces and put the first finish coat on one face.
Outside we're been having an unusual cold spell for California, lows
30-35 F, highs 45-55 F, about 60% RH.

So two questions: do I want to let the board acclimate to the exterior
conditions prior to installation, and/or do I need to leave a small
gap between each board for future expansion? Obviously what I want to
avoid is installing the boards tightly when they are at the low end of
their expansion range, as then they may buckle when conditions bring
them to the high end of their expansion range.

Thanks, Wayne

On 2007-01-16, Wayne Whitney wrote:

Obviously what I want to avoid is installing the boards tightly when
they are at the low end of their expansion range, as then they may
buckle when conditions bring them to the high end of their expansion
range.

OK, I think I have a partial answer to the question: the thermal
expansion of wood is dwarfed by its expansion due to changes in
moisture content with changes in relative humidity. So I definitely
want to move the boards outside where the relative humidity is 60%.
The only remaining question is whether it is OK to install them
tightly at 60% RH, or if I need to leave a small gap to allow for
expansion at 99% RH.

Cheers, Wayne

On Tue, 16 Jan 2007 20:42:23 GMT, Wayne Whitney
wrote:

Hello,

I'm about to install some T&G poplar beadboard as a ceiling on my
exterior porch. Now the boards are inside @ 68 F and 30% RH, where
I've primed both faces and put the first finish coat on one face.
Outside we're been having an unusual cold spell for California, lows
30-35 F, highs 45-55 F, about 60% RH.

So two questions: do I want to let the board acclimate to the exterior
conditions prior to installation, and/or do I need to leave a small
gap between each board for future expansion? Obviously what I want to
avoid is installing the boards tightly when they are at the low end of
their expansion range, as then they may buckle when conditions bring
them to the high end of their expansion range.

Thanks, Wayne

I thought that the tongue in T&G was oversized to produce the
proper spacing, by force..

On 2007-01-16, Goedjn wrote:

I thought that the tongue in T&G was oversized to produce the
proper spacing, by force..

At least in the boards I am using, the groove is slightly wider than
the tongue and noticeably deeper. So the boards do butt together
tightly if I wish--I'm just trying to figure out in what weather
conditions (if any) it is OK to install that tightly.

Cheers, Wayne

How about leaving a gap around the outer edges and cover that with some
coving or quarter-round? Kind of like is done with a wood floor.
I've hung/finished exterior Sheetrock under a Bank drive-up
canopy..The Architect specified 3'x3' panels separated by 1/2" gaps all
around each panel..I'm sure this was for expansion and looks both..
Dean

Wayne Whitney wrote:
On 2007-01-16, Wayne Whitney wrote:

Obviously what I want to avoid is installing the boards tightly when
they are at the low end of their expansion range, as then they may
buckle when conditions bring them to the high end of their expansion
range.

OK, I think I have a partial answer to the question: the thermal
expansion of wood is dwarfed by its expansion due to changes in
moisture content with changes in relative humidity. So I definitely
want to move the boards outside where the relative humidity is 60%.
The only remaining question is whether it is OK to install them
tightly at 60% RH, or if I need to leave a small gap to allow for
expansion at 99% RH.

Cheers, Wayne