Change angle of decoration or pattern along a path independently

Question

I want to give the impression of a wall, but the diagnals i drew cross each other. I just want them to follow around the corner like pictured on the left

    \begin{tikzpicture}[
    media/.style={font={\footnotesize\sffamily}},
    wave/.style={
    decorate,decoration={snake,post length=1.4mm,amplitude=2mm,
    segment length=2mm},thick},
    interface/.style={
% The border decoration is a path replacing decorator. 
% For the interface style we want to draw the original path.
% The postaction option is therefore used to ensure that the
% border decoration is drawn *after* the original path.
       postaction={draw,decorate,decoration={border,angle=-135,
        amplitude=0.2cm,segment length=2mm}}},
    ]
          \draw[black,line width=.5pt,interface,rotate=180](-11,-2)--(0,-2);
    \draw[black,line width=.5pt,interface](0,0)--++(1,0)--++(0,-1)--++          (1,0)--++        (0,1)--++(1,0);

    \end{tikzpicture}

Answer 1

Here's one approach based on \fill rather than using decorate.

\documentclass[margin=5mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{patterns} 
\begin{document}
\begin{tikzpicture}
    \fill[pattern=north east lines] (0,0) -- (1,0) -- (1,-1) -- (2,-1) -- (2,0) -- (3,0) 
    -- (3,-0.12) -- (2.12,-0.12) -- (2.12, -1.12) -- (0.88,-1.12) -- (0.88, -0.12) -- (0,-0.12) -- cycle;
    \draw (0,0) -- (1,0) -- (1,-1) -- (2,-1) -- (2,0) -- (3,0);
\end{tikzpicture}
\end{document}

I am sure there is a more efficient way to do the coordinates of the paths, but at least this gives you the general idea.

Answer 2

I think that Thruston's filling answer above gives a neater result and it is faster to compile, and probably easier to construct. However, you can use the border decoration if you wish:

I used 2 tricks. First, I drew the path 'backwards'. Second, I clipped it.

\documentclass[border=10pt,tikz,multi]{standalone}
\usetikzlibrary{decorations.pathreplacing}
\begin{document}
\begin{tikzpicture}
  \clip  ([yshift=.2pt]0,0) -| ([xshift=.2pt]1,-1) -| ([yshift=.2pt,xshift=-.2pt]2,0) -| (3,-1.2) -| cycle;
  \draw [preaction={decorate, draw}, decoration={border, angle=45, amplitude=1mm, segment length=.5mm}](3,0) -- (2,0) |- (1,-1) |- (0,0);
\end{tikzpicture}
\end{document}