| What is a
Can I apply stucco mortar over durock ?
The durock system was a synthetic stucco system made by United States
in the 1990's and was discontinued by USG due to water infiltration.
falls off durock when
durock is lifted up. This is a sample board made by
An acronym for this method is DEFS, of Direct Applied Finish System.
I have heard there are people still using durock with a
synthetic basecoat and a synthetic finish coat. This method isn't
recommended by USG
and should be stopped. USG is the manufacturer of durock.
Cement mortar or conventional stucco basecoats won't bond to
(cement board, also wonderboard, hardie backer, etc.) A synthetic
or EIFS basecoat will bond, because synthetic basecoat is an adhesive.
Only a synthetic finish will bond to a synthetic basecoat. This is the
same synthetic finish that traps water against the wall on EIFS
I spoke to a USG representative about durock synthetic stucco
after it was discontinued. The main reason was water infiltration and
water against the wall. Also, the rep told me, it was specified by USG
to use felt paper over wood studs or sheathing prior to installing the
durock board. This practice was rarely used.
Durock is a good crack resisting substrate for stucco,
lath is applied over the durock, attaching to the wood through the
with nails or screws.