Using strong magnets for hanging window blinds

Question

I have a wide window a touch less than 6' across and I want to install a blind with 2" deep horizontals. The blind that was within my price range comes with five support brackets, which can either attach to a vertical, or a horizontal surface. The kit comes with two screws per bracket, (although the end "cap" brackets appear to be more load bearing, with the center 3 for stability).

I don't know the exact weight, but likely between 30 and 50 lb. [Edit: actually 20 lb.] That's before I've stripped out the unneeded horizontals from the bottom of the blind.

I cannot drill into the vertical surface, because that's the plastic window frame, and doesn't really have enough "meat" on it for supporting something this heavy.

The horizontal surface above is a thin (1/4") cake of old plasterwork, over a steel joist; possibly an I-beam.

The walls are adobe brick.

I've considered building a minimal plywood support frame, with a piece of steel angle to match the window frame. That's not outside my skill, but it's still a lot of work.

I found some magnets about 2" long, pack of 10, which say the breakaway force is 60 lb each. They have two screwholes each. I'm looking at using two magnets per bracket, with a piece of 3/8" plywood in between the magnet and bracket for their respective screws to attach. I'd check how strong they are before hanging, and possibly clean away the old plasterwork to achieve a direct contact between the magnet and the steel beam.

Does this sound reasonable? Other suggestions?

Answer 1

You need to worry about not just the weight of the blinds, but also a weight slightly greater than the blinds focused at the string when the blinds are pulled up. I'm going to make up some numbers, but if you had a blind that was 10lbs, you would see maybe 7lbs on the left bracket and probably upwards of 20lbs on the right bracket (assuming string on the right) when they are lifted. The weight of the blinds plus friction is going to add up.

I have some 6' blinds and haven't measured it, but it takes a lot of force to raise them. I normally lift them with my free hand as I pull the string, but my wife isn't that "nice". There's also some lateral force if you're not pulling straight down and when you have to pull sideways to unlatch the mechanism.

Any pull force listed on the magnet is in a purely perpendicular force performed in a lab. They are very, very strong, but I wouldn't trust a "working load" with that listed weight. You're going to get a stronger hold from a mechanical fastener like a screw or bolt.