On Friday, October 11, 2002 2:30 PM, Fred Fillinger
[SMTP:fillinger@ameritech.net] wrote:
> 180-grit is probably OK, if its use doesn't show through the coating,
> but it appears that grit size bears little relationship to long-term
> adhesion. The following is from a coatings manufacturer:
>
> "Although surface roughening generally improves the adhesion,
Stits always advised that 240 was the coarsest possible without risk of
show-through on the final coat; I found that to be correct (at least for
his paints).
The improvements in adhesion probably only comes about by the increase in
surface area that the abrading generates. In which case there would be no
benefit in a coarser roughening (i.e. if, for the sake of argument, you
consider that a 90 degree saw-tooth profile is generated by the sanding
then the depth of that profile does not alter the 41.4% additional surface
area generated). Which is consistent with your comment.
Nobody has yet mentioned the appallingly high % of talc that is in Smooth
Prime. Apart from the poor adhesion of anything against talc, the presence
of this would make wet sanding very inadvisable; it would be difficult to
get it dry (and mineralogically un-hydrated(?)) afterwards, but not
impossible with the correct technique.
Personally, I added loads of Q-cell to the Smooth Prime, which makes it
much cheaper and displaces some of the disastrously heavy filler minerals
in there. My next coat was then a single-pack base coat; which is holding
on okay so far.
Duncan McF.
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