There are two tricks to
sikaflexing between strips.
Use the Sika Primer - it improves the bond strength to the
timber for a
permanent job. You can get away without it often, but it changes the
situation from a fairly strong bond to a hugely strong bond (you'll
know this if you have ever removed a window where the primer has been
used - BAAAAD idea in that application - windows have to be replaced
from time to time so don't use the primer)
The second
thing to know takes a little bit of explaining
It's quite common for teak, Australian white beech or other
oily timber strips to be left natural without varnish.
Gives good footing and looks nice, providing you clean it
from time to time.
If it is not sealed and the teak veneers are relatively thick
(4mm and
up) it is common to run a plastic or paper tape along the bottom of the
gap so the sika
will only stick to the teak and not the ply substrate (the ply deck).
The reason is that the teak will change dimensions as it
gains and
loses moisture. This will stretch and squeeze the sika during the
drying and soaking cycles of use.
Where the Sika
is stuck only to the teak strips there is perhaps a 6mm
gapa and if the Teak expands and contracts a mm the Sika is only being
asked to stretch plus or minus 15 percent - it can cope easily.
However if it
is stuck to the substrate there is much less than 6mm
between adjacent bonded surfaces. The sika bonded to the substrate is
immediatly adjacent to the sika bonded to the edge of the teak strip.
So one mm of movement down near the corner where the teak
meets the
substrate may mean you are asking the Sika to stretch 100, 200 or 300
percent.
The end result is that the sika starts tearing in the bottom
corner and
with repeated drying and wetting cycles the tear will proceed slowly up
the face of the teak until the sika tears away from the teak on one
side of the gap.
Difficult to repair too - you can only rip it all out and
start again.
So use release tape to prevent the teak sticking to the
substrate. Sika
sell "special tape - or you can just use a narrow plastic tape - it
doesn't need to be permanent - its only purpose is to make sure the
bond between the sika and substrate is not strong so the sika will tear
away from he substrate and not the sides of the teak planks/veneers
More
Use epoxy to hold
the veneers down.
Oily timbers need to have their surfaces stripped of oil
immediately
before bedding down in the epoxy. Simply brush a visible
layer of
acetone on the side that will be glued and wipe it off immediately
(before it dries) with a clean cloth.
The normal thing with filling the gaps with Sikaflex is to
slightly overfill the gaps then sand the top
surface of the whole shebang down flush when the sika is cured.. The
veneers do need to be a
minimum of about 4mm - gives you enough meat to get stuck into it.
Maybe 3mm is OK if you are careful with the sanding.