Brian,
Sorry I have been late in responding but here goes...
I have a few concerns and questions about sealant at the "bottom" of a
section of tongue and groove woodwork. If I understand the detail, water
will find its way into the t&g's and then be trapped behind the sealant. I
think a sheet metal counter flashing that extends up behind the t&g's and
then extends out over the top of the trim below would be more historically
accurate and functional. Water trapped behind the sealant will lead to paint
failure and wood rot.
As far as choosing sealant, you need to first consider the long term
performance of the sealant. Urethanes last a long time, are relatively easy
to use and easy to replace when the time comes. Sonneborn NP-1 has a good
amount of movement capacity and Sikaflex 15-LM has even more but it is not
necessary to go overboard just estimate the amount of movement and then
check the allowance for the sealant you have selected. There are also 2-part
sealants that you mix on site but these are really a pain and have had
projects "go south" by poor mixing. I don't know anything about SW sealants
so I wonder if they are high performance or painter's caulks. There are also
various types of silicones, some supposedly are paintable.
Paintability of sealants can be problematic. Usually high performance
sealants are much more elastic than paint. If the sealant is pushed through
its allowed elastic "range" most paints will fail. Leading to cracking and
peeling and possibly place unanticipated stress on the sealant. I don't know
if this is a concern on your project though. Frankly, I suggest getting a
sealant colored to match your paint. Sonneborn has a ton of colors and can
customize to match. Also there are 3-part systems that include a color pack.
I have not used these in years but recall being able to really customize
these.
Hope this helps and is not too late!
Eric Hammarberg
Vice President
Thornton Tomasetti
51 Madison Avenue
New York, NY 10010
T 917.661.7800 F 917.661.7801
D 917.661.8160
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-----Original Message-----
From: Brian Robinson [mailto:[log in to unmask]]
Sent: Monday, May 15, 2006 10:39 AM
To: [log in to unmask]
Subject: [BP] Caulking question
BP'ers,
Here is a caulking question from a friend of mine in Savannah. Since you
guys knocked the ball out of the park on the Ceramic Paint question I posted
last week I thought I would give y'all a swing at this one.
Thanks,
Brian
Brian,
While at Jekyll Island, were there specific caulking products that you liked
to use on historic materials, such as historic wood. The question stems
from choosing a caulk/sealant to use on the Coach & Paint Shop "barn" doors
at the Roundhouse. Historically, caulking (which included asbestos) was
applied to the tops of horizontal and diagonal elements of the doors'
structure where they meet with the tongue and groove boards of the doors.
This mainly was a seal to prevent water from going behind the structural
elements.
I have been getting advice from too many ends at this point. We want the
caulk to be paintable. I have restoration companies and architects (and
others - did you know that there is a Sealant & Waterproofing Institute?)
most highly suggesting Sonneborn NP-1 which is a urethane based product. I
am considering going with a Sherwin Williams product b/c we are using the SW
A-100 paint system. Urethanes would have better adhesion and durabilty than
most latex-based caulks, but we are concerned about reversability.
Therefore I am looking for good latex options. I am considering Sherwin
williams 1100A, but are there some other good choices out there. I am going
to call DAP on Monday and see what the comparable product are to SW, but any
advice you can give would be wonderful.
I have to talk to Stewart about this, but my understanding is that the main
protection of the caulk would be to divert water/moisture from behind the
wood element, and not to create a weatherseal to the interior of the
building. I believe that, with the current proposal for museum use, we
would be looking into a secondary interior door/barrier system that would
insulate/weatherize the door openings. Can you think of anybody with APT or
NPS that may have advice??
Thanks,
Tracy Bakic
Preservation Planner/Project Manager
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