Brick, Concrete and Plaster: Wi-Fi in Old, Solid Homes
A brick wall costs 10-16 dB at 5 GHz, and metal-lath plaster far more. How to get Wi-Fi through brick walls: loss figures, doorway routes, wired fallbacks.
The practical answer to wifi through brick walls starts with the path between the router and the room that has to work.
The router sits in the hall. The back bedroom is thirty feet away and has no usable signal. In a modern wood-frame-and-drywall house that would be strange. In a house built before about 1950, with solid internal walls, it is ordinary — because the thing between you and the router is not a partition, it is a nine-inch stack of fired clay.
Solid-wall homes break most extender advice, because most extender advice quietly assumes the walls are hollow. Here is what changes when they are not.
Your signal budget, and how fast masonry spends it#
Think of it as a budget. A phone standing next to the router reads somewhere around -30 dBm. Reliable 5 GHz performance falls apart below about -67 dBm, and 2.4 GHz limps on to roughly -75 dBm before it becomes useless. So you have on the order of 40 dB to spend between the router and the far corner of the house — and free space indoors barely touches it.
Masonry spends it in one or two moves.
| Wall you are shooting through | Typical loss at 2.4 GHz | Typical loss at 5 GHz |
|---|---|---|
| Drywall stud partition (modern) | 2–3 dB | 3–6 dB |
| Lath and plaster over wood lath | 3–4 dB | 5–8 dB |
| Lath and plaster over metal lath | 10–15 dB | 20–30 dB and up |
| Brick or cinder block, single wythe, about 4 in | 6–10 dB | 10–16 dB |
| Brick, double wythe or cavity, 9 in and up | 10–15 dB | 15–25 dB |
| Poured or reinforced concrete | 10–15 dB | 15–25 dB |
| Rubble or fieldstone, 18–24 in | 12–20 dB | 25 dB and up |
| Masonry chimney stack | Count it as two brick walls | Count it as two brick walls |
Lath and plaster is the one that surprises people#
Every owner of an old house knows the brick walls are a problem. Almost nobody suspects the plaster.
Traditional lath and plaster over wood lath is mild — 3 to 8 dB, roughly a dense stud wall. Plaster over expanded metal lath is a different animal. Metal lath was in common use in US construction from the 1920s onward, and it still turns up in patch repairs, curved work and around bathrooms. Some older repairs use plain chicken wire under the skim coat.
A Wi-Fi wavelength is about 4.8 inches at 2.4 GHz and 2.4 inches at 5 GHz. The openings in expanded metal lath are far smaller than that, so the wall behaves like a screen and reflects the signal instead of merely weakening it. Losses of 20 to 30 dB and beyond are normal, and a room with metal lath on all four walls and the ceiling is a shielded box with a doorway as its only opening.
How to tell which one you have:
- Magnet test. Slide a strong magnet across the wall. On metal lath it drags in a regular stripe pattern; on wood lath it finds only the nail heads.
- Look at a cut-out. Pull the cover off an outlet and look at the edge of the hole: wood strips, metal mesh, or a clean gypsum board edge.
- Knock. Masonry gives a dead, painful-knuckle response. Lath gives a hollow drum between studs. Drywall gives a lighter, papery hollow.
Why 5 GHz dies at the first internal wall#
Attenuation through dense material climbs with frequency. The same brick wall that costs about 8 dB at 2.4 GHz costs roughly 14 dB at 5 GHz and more again at 6 GHz. That single fact reorders everything in a solid-wall home:
- 5 GHz becomes a same-room band. Same room or through an open doorway, expect 300–600 Mbps. Through one solid wall it drops to a fraction of that, or vanishes from the network list entirely.
- 2.4 GHz is not the poor relation here. Through two masonry walls it may be the only band still standing, typically delivering 20–60 Mbps in the real world. That is slow, and far better than nothing.
- Band steering works against you. Many routers push devices onto 5 GHz and hold them there — exactly the wrong instinct in a house where 5 GHz collapses at the first wall. This is one of the few cases where splitting the SSIDs earns the hassle; the trade-offs are in choosing between 2.4, 5 and 6 GHz.
- Extender backhaul inherits the problem. A dual-band extender usually wants a 5 GHz link back to the router. Behind two brick walls that link may not exist, so the unit falls back to 2.4 GHz backhaul — and now your whole extended network is capped by a 2.4 GHz hop that is also carrying the client traffic.
Aim through doorways, not through walls#
Here is the move that actually fixes solid-wall homes: stop drawing straight lines.
Radio does not need a straight line. It will happily go down a hallway, through an open door, around a corner and into the room — losing a few dB to each reflection and diffraction along the way. In a stud-wall house that detour is not worth the bother. In a masonry house it is the whole game, because a doorway is a near-lossless hole in a 20 dB wall.
So the question is not router-to-room distance. It is: what is the lowest-loss walking route to the room that matters?
Frequently asked questions#
How much Wi-Fi signal do I lose through a brick wall?
A single-wythe brick wall — one brick thick, about four inches — typically costs 6–10 dB at 2.4 GHz and 10–16 dB at 5 GHz. A double-wythe or cavity wall of nine inches or more costs more again without quite doubling it, so 15–25 dB at 5 GHz is the number to plan around. Those are rules of thumb — damp brick, thick plaster and hitting the wall at a shallow angle all push the loss higher.
Will a Wi-Fi extender work through brick walls?
It works if the extender itself can still hear the router clearly, and it fails if it cannot. Place it so that its link back to the router crosses at most one masonry wall — ideally none, by routing through doorways — and it will do its job. If every reachable outlet shows a weak link to the router, an extender will rebroadcast a poor signal strongly, which is worse than having none.
Why does my 5 GHz Wi-Fi only work in one room?
Because loss through dense material rises with frequency, and a masonry wall that costs 8 dB at 2.4 GHz can cost 14 dB or more at 5 GHz. In solid-wall homes 5 GHz is often a same-room band, with 2.4 GHz doing all the work everywhere else. Keeping 2.4 GHz enabled, and sometimes giving it its own network name, is the practical fix.
Does lath and plaster block Wi-Fi?
Plaster over wood lath is mild, around 3–8 dB at 5 GHz. Plaster over expanded metal lath is severe — 20–30 dB and up — because the metal mesh has openings far smaller than a Wi-Fi wavelength and reflects the signal rather than passing it. Drag a magnet across the wall: if it grabs in a regular striped pattern, you have metal lath.