Wall-to-wall desk with battens

Question

I'm planning to build a wall-to-wall desk in a brick alcove using wooden battens to hold the desk up. I'm doing this post to find out what size screws and plugs I need and if I'm using the correct materials -- I don't want the desk to collapse.

ALCOVE

Here are the alcove with a temporary desk showing the dimensions. All 3 walls are brick. Unfortunately, neither of the corners are exactly 90 degrees.

DESK TOP

25mm MDF Board, Medium Density Fibre Board: 1200 x 600mm. https://www.amazon.co.uk/gp/product/B07YM5JZX4/ref=ppx_yo_dt_b_asin_title_o09_s00

BATTENS

Planed softwood: 1800 x 34 x 34mm. Is this ok? If not, I can get another piece.

SCREWS AND WALLPLUGS

What type and length of screws and wall plugs should I use? How many should I put in?

EDIT: Weight: the desk will only be a workstation, so it will only have keyboard, mouse, someone's elbows...etc

UPDATE #1

Thanks for the advice. I have decided to use 2x4 as the baton and attach with the 85mm fittings in the photo. Like this desk. Still need to get brackets or a metal stiffener.

QUESTION: Do I need a table leg under the right baton that sticks out past the wall or can it just float out past the wall?

Answer 1

Given the lengthwise span and the truncated support at the right end, I'd use cleats on the ends and two brackets across the back. 25mm MDF won't handle that load without a lot of bounce and some chance of collapse.

On the left, I'd use four 3/16" x 2-3/4" concrete screws with hex heads. Phillips heads are fine also, but they're difficult to keep from stripping, in my experience.

On the right, two or three such screws.

Across the back, either use screws every 20cm or so, or use two large steel brackets mounted with 3/16" x 1-3/4" concrete screws. Such brackets are unobtrusive to the user and don't catch the eye from across the room. The stability is well worth their use.

If you choose not to use brackets, you may find that you need a stiffener running lengthwise to support the front edge of the desk. It wouldn't need to be at the front edge--it could be back 1/3 or so. An aluminum angle or a tall wooden rail might do well.

Notes about concrete screws

I'm not familiar with what metric screw sizes are available, so I listed fractional sizes. The key is to get at least 30mm of penetration into the masonry.

With concrete screws it's critical to pilot properly. These don't grab like wood screws, where almost anything goes. If your pilot is too small they won't go in or they'll break off. If too large they'll immediately strip.

If you need to remove a screw, drill a new hole. As the threads cut they disintegrate the surrounding material, and a second run-in isn't likely to hold as well.

Answer 2

I think you should be fine with a couple of tapcon screws. How much weight you put on it will determine whether it collapses or not. Not because the tapcons will fail but because I wouldn't trust a lot of weight on a 4' MDF board without center support.

Tapcon = concrete screws. I'd say at least a 60mm length and 6 or 7mm diameter should work. Yes tapcon is a brand and I can't suggest a specific product as I don't know where you live (guessing outside the states since you use metric). I would put 2 screws into the side batons and 3 or 4 into the longer back side. I'd still have concern over using MDF however.

Answer 3

The corners are almost never exactly 90 degrees - welcome to real houses, as opposed to fictional constructs.

Fastening to the walls has been hashed over rather well. It's not the difficult part of this job - for brick walls, I'd probably use lead anchors in 10-12 mm holes 35-60mm deep.

Structurally, a "taller or deeper" baton (batten) on the right hand side would provide some support to the floating corner - i.e. that might be 34x68x600mm (guessing at likely available size from the size you have shown) with 3 or 4 screws into the brick, running all the way to the front edge. If you are not willing to go to plywood (and perhaps even if you are) some additional support in the 1040mm-1120mm direction is required - the relatively easy one would be at the face of the "nook" (310mm) with again, a deeper baton than you have started with. Assuming you have a baton along the back wall, the secton between the two would be well supported, but you'll likely have sag in the portion that extends out into the room - there, your baton depth may be limited by leg clearance, and it would be supported by the projecting part of the right hand baton and the left hand wall.

Another possibility would be to make the desk surface into a "torsion box" construction to make the whole thing more rigid - just look that up (it would then be thicker as a whole, but also much less prone to sag, so needing much less external support.)