Mortar Floors - David Sleight Conservation

The Manor Gatehouse, Wormleighton, Warwickshire

The four storied tower of the gatehouse dates from 1613 and is Grade II*

Mortar floor repairs

The floors within the tower are the original lime mortar floors.

All first and second floor suspended floors in The Tower Gatehouse are formed from a thin layer of mortar (approx. 45mm) laid over riven lath. These type of floors, commonly termed lime ash floors are common in the Midlands as an alternative to timber flooring. Lime ash is misleading as very few that have been tested contain lime. Of the floors tested the vast majority contained gypsum as the binder, Gypsum doesn’t shrink on drying and can be polished.

As with lime mortars for repointing tests were carried out to ascertain the best match for the existing mortar floors in The Gatehouse.

Please click on each photograph for more information

Due to a period in the buildings history when the building was roofless rain had eroded areas of the second floor lime mortar flooring. The areas adjacent to the voids maybe weakened. To minimise loss of the original floor the areas were repaired from beneath

Cracks emanated from some of the larger voids.

The ceiling beneath was rotten due to water ingress so was to be replaced. Looking upwards through the rotten ceiling laths the original laths that supported the mortar floor can be seen. Although some are still in place, they were rotten and provided no support.

Again looking upwards from the floor beneath in between the floor joists. There is an obvious hole in the floor, but here the original laths that supported the floor had rotted and were missing. The floor is only 45mm thick.

To repair the hole in the floor a lath frame was made, placed beneath the void and screwed to the joists either side.

The lath frame was then plastered which gave a base for the hole above and supported the adjacent cracks in the floor.

In some areas the laths that had supported the floor originally had rotted and were missing. The arrows points to the gap left by the laths. This gap between the timber and the floor was not supported and left the floor hanging and was liable to further cracking and long term failure.

To provide that missing support more lath frames were fixed in place.

These lath frames were then plastered with a stiff plaster to provide support for the mortar floor above.

This photo shows the various stages of support and repair. The lath frame supports screwed to the insides of the joists; the laths then plastered over to consolidate that support. Lastly the new oak ceiling laths fixed to the floor joists. This ceiling was then plastered with lime plaster.

The completed repair. The repairs to the floor above are concealed by the new lath and plaster ceiling.

Matching the flooring mortar.

The original flooring mortar had to be matched for colour, texture and strength.

The main binder of the original floor was a type of gypsum, but the gypsum binders of today are very different from those used in the past; the main form of gypsum used in the past is no longer available. Used in isolation other forms of gypsum such as Plaster of Paris set too quickly. Some hard modified casting plasters were considered together with combining hydraulic lime and casting plaster as suitable binders. Coal ash together with graded crushed stone and brick were considered for matching aggregates.

Please click on each photograph for more information