Before choosing your lime mortar or plaster, you need to understand your substrate.

In this bonus episode of Talking Conservation, Stephen and Rich explore the importance of knowing what's behind or beneath your mortar; from soft handmade bricks and old stone to chalk walls and cob.

Whether you're repointing, plastering, or rendering, understanding the substrate is critical to choosing the right mix and achieving long-lasting results.

We cover:

- What a “substrate” actually means in traditional buildings

- Common types found in historic homes (brick, stone, cob, timber)

- How substrate affects your lime choice and application

- Assessing problems and indicators of hidden issues

- Mistakes to avoid when applying lime to inappropriate surfaces

- Decision making, such as when to strip inappropriate materials

- Key questions to ask before starting any conservation work When to call in the professionals

- Keeping a record

▶️ Whether you're a homeowner or a professional working with heritage buildings, this video helps you avoid common issues and build with confidence.

👉 New to the Lime Series? Start here:

Ep.1: The Lime Cycle Explained – How lime is made and reabsorbs CO₂

Ep.2: Lime Mortar Types Explained – Key differences between air lime, NHL, pozzolans & more

Ep.3 Part.1: Which Lime to Use? – Mortars for pointing & bedding in older buildings

Ep.3 Part 2: Which Lime to Use? - Plasters and Renders

Ep.3 Part.3: High Exposure Areas & Floors – Using lime in chimneys, ridges, parapets, and floors

🔔 Subscribe for upcoming episodes on more specialist areas

📞 For 1-to-1 advice or a consultation, visit: www.expertible.com

💼 Professionals: Training & mentoring available at www.beconservation.com

#TalkingConservation #SubstratesExplained #LimeMortar #BuildingConservation #OldHouseDIY #HistoricHomes #TraditionalMaterials #LimePlaster #problemsolving #decisionmaking #professional help #heritageskills #limerender #lathandplaster #historictimberframes

Chapters00:00:00 – 00:00:50

Introduction00:00:50 - 00:02:23

What is a substrate?00:02:23 - 00:03:33

Flint00:03:33 - 00:05:22

Stone00:05:22 - 00:05:31

Cob and earth00:05:31 - 00:06:12

Wattle and Daub, lath and plaster00:06:12 - 00:06:56

Multiple substrates00:06:56 - 00:08:24

Behaviour of substrates (the science bit!)00:08:24 - 00:09:43

Timber00:09:43 - 00:10:57

Absorbency and moisture performance00:10:57 - 00:14:25

Cement render on timber frame (case study)00:14:25 - 00:16:34

Assessing problems and key indicators00:16:34 – 00:19:48

Delamination and hammer testing00:19:48 – 00:23:02

Decision making00:23:02 – 00:24:43

Should I remove cement render/pointing?00:24:43 – 00:26:36

Have I got layers of material?00:26:36 – 00:27:46

A judgement call and bringing in professionals00:27:46 – 00:28:52

Substrate preparation00:28:52 - 00:30:43

Wetting down surfaces 00:30:43 – 00:32:05

Plaster coats00:32:05 – 00:34:56

Use of hair in mixes00:34:56 – 00:39:25

Controlling the ‘set’00:39:25 – 00:40:14

Lath and plaster00:40:14 – 00:41:33

Dealing with modern interventions00:41:33 – 00:46:37

Removing modern material00:46:37 – 00:49:30

Surface finishes00:49:30 – 00:55:58

Changing aesthetics and appearance00:55:58 – 00:56:56

Key message – understand the building00:56:56 – 00:58:27

The importance of keeping a record00:58:27 – 00:59:11

Future episodes00:59:11 – 00:59:48

Expertible00:59:48 – 01:00:05

Close01:00:05 – 01:00:28

Outro