I have an open wall above a cabinet in my kitchen and would like to mount an open shelf to hold the Microwave above the counter top. House was built in early 40's and has plaster walls. Microwave weighs 38 pounds! I see some not too stylish heavy metal brackets at the big box stores that look strong enough. I could attach wood to the brackets to hold the microwave. What do I use to attach the brackets to the wall? When I try to use a stud finder on my walls - it seems unreliable.