19th Century fireproof cast in-situ floors.

Over the past few years I have come across different types of solid early concrete floors, these were developed to be fireproof. When I’ve come across these in the past, there was never the opportunity for any investigation to confirm the construction of the floor.

Photo of the top of a cast in-situ 19^th century concrete floor at first floor, this was in a poor condition, where the boarding, skirting and floor battens had been previously removed, damaging the top of the concrete slab.

 

Recently I worked on a structure where these early fireproof floors existed in varying states of decay, in places the condition of the floor structure enabled one to understand the layers and materials used. This was interesting and the extent of the eroded floor enabled me to identify it as a ‘Fox & Barrett’s patented fireproof floor’. The conservation engineer I was discussing this with referred to these floors as a beam-and-fill floors; a common term relating to many of the variations of the 19^th Century fireproof floors.

The Fox & Barrett floor was laid with hot rolled steel beams which would span the floor, 25x25mm timber battens would then be laid between the web of the steel beams with spaces between them, as can be seen in the photos, once in place these battens provided the function of laths for the lime plaster ceiling, it also provided shuttering for the impending concrete (for those of you who have not read my previous blogs about lime, 19^th Century concrete would be more comparable to a NHL5 strength lime-crete floor today); this looks like it was made with a fairly lean mix, with large aggregate, it can be assumed that this was to prevent it from just pouring between the laths and for its setting time to be reasonably quick. As soon as this lime mix had been poured, timber floor battens would be laid into, and semi-recessed into the wet slab. The timber floor boards were then able to be nailed to these timbers battens.

Useful drawing of the Fox and Barrett’s floor, image taken from the Practical Building Conservation, Mortars, Renders & Plasters, published by English Heritage.

In the 19^th Century there were many different types of variations of fireproof floor, there was the ‘Dawnay’s Fireproof Floor’, ‘Dannetts’s Fireproof Floor’, Evans Fireproof Floor’, Fawcett’s Fireproof Floor’ and the ‘Doulton-Peto Fireproof Floor’ to name but a few.

Useful drawings of other types of fireproof floor of the 19^th and early 20^th Century, image taken from Adams Building Construction, Henry Adams, first published 1906.

Useful drawings of other types of fireproof floor of the 19^th and early 20^th Century, image taken from Adams Building Construction, Henry Adams, first published 1906.

So next time you are in a 19^th or early 20^th Century building with ‘concrete floors’ there is good chance that they could be one of the many patented floors above!

Some of these types of floor can be a challenge to repair due to the reliance of the floor on each of the component parts of the floor.  The removal or decay of any of the elements of the floor can have a detrimental effect on the structural performance of the floor.

 

Marked up photo of the top and underside of the floors.

Photo of an area where all the battens and ceilings have been previously removed, note the steel beams with the concrete laid over.

The building which I came across these floors, had areas where the underside, plaster and battens were missing, there were also areas where the top boards, battens and some of the slab was missing. The really concerning areas were where both the top and the underside were missing!

 

Photo of an area where all the battens and ceilings have been previously removed and the timber work at the top, due to prolong water ingress the concrete has failed, note the decayed steel beams.

This was combined with an unknown level of decay in the steels at the perimeter of the building due to long term water ingress, the best advice which can be given is to employ a conservation engineer, the other is to not assume anything about the floor, investigation of the different areas is the key to finding the right repair solutions for each scenario.