I'm installing a floating mantel on a brick fireplace. The mantel is 3.75" thick X 8" deep X 68" long (cedar). I was looking at a YouTube video which suggested placing .5" x 10" lag screws in a grout line, one every 16", with lead anchors. Then, cut off the heads. Drill the back of the mantel to fit over the half-inch rods. Someone at Lowes told me 5 half-inch rods to hold a mantel is overkill. Any thoughts? PS: I've never found any resolution to the debate about drilling into the grout vs. into the brick itself.
That is exactly the way that I do it. Five anchor points over 68" is not overkill, especially if you are lagging into anchors. Now, if you can figure out where the framing is behind the brick and can anchor your 1/2" lags through the brick or mortar and into the studs, then you could drop down to four or even three anchors. But I would stay at 16" OC if you are just going into the lead anchors.
I haven't found any strength advantages of going through the mortar vs through the brick other than it's usually easier (and thus, more accurate) to drill through the mortar line. With a typical mortar joint of about 3/8" and an outside diameter of a 1/2" lead anchor of almost 3/4", the lead anchor will be gripping the sides of two bricks anyway.
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