добавить setListCollection('grid')
в app\design\frontend\base\default\template\catalogsearch\advanced\result.phtml
* Docs 1006 *
или заменить
<action method="setColumnCount"><count>4</count></action>
с (комментарий) в catalogsearch.xml из папки макета
<action method="addColumnCountLayoutDepend"><layout>empty</layout><count>6</count></action>
<action method="addColumnCountLayoutDepend"><layout>one_column</layout><count>5</count></action>
<action method="addColumnCountLayoutDepend"><layout>two_columns_left</layout><count>4</count></action>
<action method="addColumnCountLayoutDepend"><layout>two_columns_right</layout><count>4</count></action>
<action method="addColumnCountLayoutDepend"><layout>three_columns</layout><count>3</count></action>