These photos were taken through a small hole in the wall of a house. They are of the inside of the cavity. The hole they were taken through is at a height of about 60cm from the internal ground floor level. The left of the photos is the inside of the outer leaf of the external wall of the house.

What kind of construction am I looking at? How was this wall constructed and what materials is in likely to be made from? What features of the wall do these photos show? Is there anything unusual in them?

Looking to the right, along the wall:

looking sideways

Looking up and to the right along the wall:

looking slightly upward

Looking steeply up and a bit to the right:

looking upward

Picture of the inside of the wall in the corner of another room. The bottom 10cm of the plaster has been removed. The left is the external wall and the right is an internal wall (the corner is rounded!):

base of wall

Detail of the internal surface of the base of the external wall. The hole shown in the picture was found when the plaster was removed, metal can be seen in the hole (it is not the same hole that the other photos were taken through, it is in a different room):

base of wall detail

  • Got any pics of the inside and outside surfaces of the wall ? Nov 14, 2012 at 13:37
  • looks like reinforced concrete
    – DA01
    Nov 14, 2012 at 16:12
  • can you tell if it is precast or in-situ? What are those horizontal lines I can see regularly up the wall? Also, what are the round holes for that seem to be along the base of the wall? There seems to be a bunch of rubble and random stuff at the bottom of the wall between the leaves, does that matter in any way? Also, is the bottom of the wall likely to be solid, and if so is it possible to tell where the cavity starts? Nov 14, 2012 at 16:23
  • 1
    The ridges are from gaps in the form boards. The striations are from pouring in shallow lifts, making this cast in place. Depending on the age and location, we can't really say for sure this is reinforced, only that it is concrete. Rubble is just random material that fell or was tossed into the void during construction after the interior lath was placed, it has little consequence. The void, including rubble, probably starts where bottom of the finish plaster starts.
    – bcworkz
    Nov 14, 2012 at 19:21

2 Answers 2


What I think you're looking at is cast, reinforced concrete construction for the external structure, with an airspace and then a cementitious "mud" or adobe with lathe ... and then a final coat of plaster.

The horizontal lines on the inside of the exterior wall comes from the pieces of wood that were used to make the form. It'd be helpful to have a picture of the outside of the house.

On the inside, the metal (or possibly a plastic or fiber lathe -- it is REALLY difficult to tell from the supplied pictures) was attached to the rebar sticking out from the wall, and then the mud or adobe was forced through it into a smooth surface a few inches thick. This could have been done to a smooth finish and stained or painted, or it could have had tile or some other material applied to it, or it could have been finished with plaster or stucco. The plaster/stucco may have been a later addition.

A similar construction today would be applying metal studs to a concrete foundation home and then putting Durock or another cementboard over it, and either finishing over it with tile, stucco, or plaster. However, cementitious mud is still extremely common as a surface to tile over for showers or floors and especially for floors is considered superior to cementboard.

This kind of construction is common in african and middle eastern homes. In fact, these pictures mirror things I've seen it in pictures of home renovations from Morocco. I imagine that any area with a similar climate would have similar construction. In most of Europe and US (or any non-arid climate) this would be very uncommon construction and would be horribly prone to mold, although it's possible that this kind of construction could have been done for a steam bath or shower in a building with foundation walls either partially or fully made out of cast concrete ... I'm thinking sauna in a basement or similar.

  • thanks. what in particular would make it prone to mold? Nov 15, 2012 at 16:08
  • I think it is approximately 1935, but do not have definitive proof. It is in the UK, 2 floors high, and the whole house seems to be constructed the same way as far as I can tell. I'll try to get pictures of the outside, but I think it has been rendered so I'm not sure how much they will help. Nov 15, 2012 at 16:15
  • Penguin: Condensation between the warmer inside surface of the house and the colder outside surface of the house. Concrete's a very porous surface and the bad kinds of mold really love this kind of construction... and are impossible to eradicate without a bulldozer. This is probably why the holes are there; to try to provide some amount of air movement inside the walls. I don't have any good, creative ways to rectify that without tearing the layer of wall that has plaster on it completely down... although that should be safe to do if I'm right about how it's constructed. Nov 15, 2012 at 16:40
  • there are rectangular grills about 20cm above ground level on the outside, that look like they are designed to ventilate the cavity of the wall Nov 15, 2012 at 16:49
  • That only provides a path for moisture to leave, it doesn't do anything about providing enough air movement to pick up the moisture given your climate's average relative humidity. And since there are holes on the inside as well -- that means heating this structure is about as efficient as an outdoor firepit. Nov 15, 2012 at 16:55

After further research this appears to be an example of a Forrester-Marsh house, about 50 of which were built in London. Both leaves of the wall are cast simultaneously in-situ of reinforced concrete using re-usable form-work (metal shutters). The walls ties (one of which can be seen in the pictures) are connected into the reinforcement (cast into the wall along with the formwork spacing blocks). The walls are on top of the reinforced ground slab, which is deepened under load bearing walls.

The construction is detailed in a BRE report - BR155 Forrester-Marsh houses (1989)

An assessment of the structural condition is in BRE report - BR275 The structural condition of early cast-in-situ concrete low-rise dwellings

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