To calculate the build-up height correctly, you're on the right track by listing out the layers involved. Let's break down each layer, including the adhesives, and check if they are likely to compress or change over time:
Primer (0mm) – The primer doesn’t contribute to the height, so it’s effectively 0mm.
- Substrate adhesive (3mm) – This adhesive layer is generally applied to the substrate (the surface the screed is going over). Typically, adhesives do not compress much once they have cured, so this 3mm is a good estimate for the adhesive thickness.
- Ditra mat (3mm) – The Ditra mat (likely a decoupling membrane) adds around 3mm to the build-up. There is no significant compression of the mat itself once it’s installed.
- Tile adhesive (14mm) – You’ve mentioned this layer consists of 10mm applied on the mat and 10mm for back buttering the tiles. The thickness of the adhesive beneath the tiles could vary, but 14mm (in total) seems reasonable for typical applications. However, be mindful that this layer could be somewhat compressed, especially depending on the type of tiles and the type of adhesive used. In general, this layer might compress slightly (roughly 0.5–1mm), but it's often not a significant amount to impact the overall build-up height.
- Tiles (10mm) – Tiles themselves do not compress, so this is a fixed dimension.
Total Build-Up Height:
- Primer: 0mm
- Substrate adhesive: 3mm
- Ditra mat: 3mm
- Tile adhesive: 14mm (with a slight possibility of compression)
- Tiles: 10mm
Total = 30mm, with a small potential for compression of the tile adhesive layer (around 0.5–1mm, depending on factors like tile size and adhesive type). So the final build-up height would be around
29–30mm, assuming typical conditions.
This should provide your builder with a close estimate for where the front door needs to be installed. It’s always a good idea to discuss this directly with the builder in case they expect further variations depending on specific materials or installation conditions.
