Restoring terrazzo in an old building: what has to match?
Reference photographs. They show the material and the finish; they are not photographs of goods we made, and the colour on screen is not a colour-match.
The figures, and where each one comes from
| What has to match | Why |
|---|---|
| Cement batch | the matrix colour comes from the binder |
| Pigment batch and content | 3 to 6 per cent of the cement weight, by clause |
| Aggregate | graded the same way, or the pattern is visibly different |
| Grinding sequence | a different grit leaves a different sheen |
Why the processes are not interchangeable
Terrazzo is normally specified for uniformity, which makes it a poor material for a repair unless the repair is done to the original rather than to a new batch. The clause that governs it is the one that requires a single colour layer to use one factory's pigment in one batch — written for a new floor, and exactly the rule a heritage repair inverts, because there the requirement is that the OLD material be identifiable and the new material be bought to match it. That is usually the hardest part of the job and it is a sourcing question long before it is a craft one.
What these figures are, and what they are not
The same-batch requirement and the 3 to 6 per cent pigment content are GB 50209-2010 clause 5.4.2. ⛔ We have not restored a heritage floor and we do not offer that service; this page explains what governs the specification, not that we perform it.
If you are specifying this
These are the forms we actually supply for this question, with production photographs where we have them: