Surface regularity, and the wall behind a covering

Surface regularity is stated as a class, and a class states one figure: the deviation permitted under a 2 m straightedge. It says nothing about level, and it says nothing about fall.

Classes, and the finish each one is set for

Class	Deviation permitted under a 2 m straightedge	Set where the finish is
SR1	3 mm	Thin sheet, resin, and any covering laid without a bed
SR2	5 mm	Tile to a bed, and thicker sheet and plank coverings
SR3	10 mm	Bases carrying a further build-up, or a raised floor above

A class is a maximum, not a target. A base brought to SR1 satisfies a specification written to SR2; a base at SR2 does not satisfy one written to SR1, and it is not brought into class by laying a thicker bed.

Level and regularity are recorded apart on the survey sheet. A floor can be flat and out of level, and it can be level and out of class, and the two are prepared for in different ways.

The straightedge is laid on the base, not held against it. It is laid in two directions at every station, and it is moved by half its length between readings so that no gap is stepped over.

Deviation is read with a slip gauge or a graduated wedge under the edge. The figure written down is the largest gap found under that placing, and it is written against the station it was found at.

An abrupt change is recorded separately from a gradual one. A lipped joint and a gentle dish can give the same figure under the edge, and only one of the two reads through a thin sheet.

Curled edges are read along the joint rather than across it. A slab edge that has curled will give its worst figure within 300 mm of the joint, and that is where the straightedge is placed.

Readings are taken again after preparation, and before the finish is ordered. A base is not accepted into class on the strength of the survey reading alone.

Wall coverings are surveyed on the same principle as floors: the substrate is measured first, and the covering is specified against what the measurement shows.

Flatness is proved with a straightedge held vertically and diagonally across the face. Bulges and hollows are recorded to the nearest millimetre, with the height they were found at.

Background is recorded by type. Plaster, plasterboard, render, masonry and tile-on-tile each carry a different preparation, and each carries a different weight limit for the covering laid on it.

Soundness is tested by tapping. A hollow area of plaster or render is cut out and made good prior to any covering, and the made-good area is brought back to the flatness the covering requires.

Setting out starts from a datum line struck at the survey. Tiling is set out from that line, not from a floor or a ceiling, because neither can be assumed level.

Movement joints in the background are carried through the covering. A joint that is bridged will telegraph through the face, and the covering will then fail along the line of it.

Three routes are open where the measured deviation exceeds the class the finish demands, and the survey report states which of the three is specified.

The base is corrected. Levelling compound is laid to the mean thickness read off the grid, or high points are ground back, and the base is read again afterwards.

The finish is changed. A covering with a higher permitted deviation is specified, and the class on the report is rewritten to match it.

The base is replaced. Where deviation runs through the whole area, or where the base is unsound under it, a new screed is specified and the drying programme begins again from the day it is laid.

The route is decided against the figures on the grid, and it is decided before anything is ordered. A base that is out of class is recorded as out of class, and it is brought in before the finish arrives on site.

Where correspondence about a floor is needed, quote the reference the report was issued against and write to the surveys mailbox.

SEALUS LTD
C/O Taxassist Accountants
35 Bartholomew Street
Newbury
RG14 5LL
United Kingdom
surveys@sealus.work