Wall Materials: CoolBlock vs Q-CON

Carlos's recommendation for Soluna exterior + interior walls

Context: Carlos recommends these as the only two worthy alternatives for our walls. The assembly method matters as much as the material — he's pushing for double-skin cavity walls on all perimeter/exterior walls, and thicker single blocks for interior walls.

The Two Products

CoolBlock

Concrete + EPS foam core

Portland cement block with expanded polystyrene (EPS) insulation sandwiched in the middle. Austrian technology, made in Thailand by Polyfoam Group.

  • MaterialCement + EPS foam core
  • Thermal conductivity0.089 W/m.K BETTER
  • Water absorption< 9.3%
  • WeightMedium
  • WorkabilitySaw, nail, groove
  • Fire ratingGood (FR-EPS)
  • CostLower CHEAPER
  • MarketGrowing / newer

Q-CON (AAC)

Autoclaved Aerated Concrete

Sand, cement, lime + aluminium powder, steam-cured under pressure. Millions of tiny air cells throughout the block. SET-listed manufacturer — the industry standard in Thailand.

  • MaterialAerated concrete (air cells)
  • Thermal conductivity~0.11 W/m.K
  • Water absorptionModerate
  • WeightVery light LIGHTER
  • WorkabilityHand-saw, easy
  • Fire ratingExcellent NO COMBUSTIBLES
  • CostPremium
  • MarketEstablished / everywhere
Property CoolBlock Q-CON (AAC)
Thermal conductivity 0.089 W/m.K ~0.11 W/m.K
Block sizes (thickness) Standard options 75mm–375mm (25mm steps)
Weight Medium Very light
Fire resistance Good (FR-grade EPS) Excellent (inorganic)
Installation speed Fast ~60% faster than masonry
Cost More affordable Premium
Availability (Thailand) Growing Widely available
Track record Newer alternative Stock-listed, decades

Carlos's Recommendation: Cavity Wall

The key insight: the assembly method matters as much as the block choice. Carlos recommends a double-skin cavity wall for all exterior (perimeter) walls, and single thick blocks for interior walls.

Exterior Wall — Double Skin Cavity Wall

OUTSIDE (rain, heat, humidity) INSIDE (cool, dry, comfortable) Render + limewash Outer leaf block layer Cavity 50–80mm air gap Inner leaf block layer Plaster Paint limewash DPC (Damp Proof Course) — waterproof membrane ~15cm below ground ground level ~255mm total Why cavity walls? Moisture barrier Rain can't travel through — the air gap stops it completely Thermal insulation ~48% better than single wall R = 3.48 vs 2.34 (w/ insulation) Sound insulation Better than thick solid walls No condensation Air circulates in cavity, prevents mold + paint peeling Needs skilled labor Wall ties must be precise; mortar can't fall into cavity

Cross-section: Exterior double-skin cavity wall (Carlos's recommendation for all perimeter walls)

Interior Wall — Single Thick Block

ROOM A ROOM B Plaster Single thick block 150–200mm Plaster ~200mm total No cavity needed No weather exposure Sound insulation Thicker block = better noise separation Simpler construction Standard masonry, faster

Cross-section: Interior wall — single block with plaster both sides (no cavity needed)

What is DPC (Damp Proof Course)?

A waterproof membrane layer installed at the base of walls, typically ~15cm below ground level. It stops ground moisture from "wicking" up through the blocks into your walls (capillary action).

Each leaf in a cavity wall gets its own DPC layer at the same level. This is standard best practice — especially critical in Koh Phangan's high-humidity, heavy-rain climate. Carlos is confirming Eliya will spec this for all perimeter walls.

Without DPC: rising damp, mold, paint peeling, structural weakening over time.

Carlos's Full Recommendation

Health & Safety: Indoor Air Quality

With three kids and a wellbeing-focused home, this matters. Are these materials safe to live with long-term?

Q-CON (AAC)

100% Clean — Zero Concerns

AAC is fully inorganic — sand, cement, lime, water. The aluminium powder used in manufacturing reacts completely during production (creates the air bubbles, then it's gone).

  • No VOCs, no off-gassing, no toxic fumes — ever
  • Hypoallergenic — used in homes for people with chemical sensitivities
  • No combustible materials whatsoever
  • Won't burn or produce toxic smoke in a fire
  • FDA-style safe — it's essentially minerite with trapped air

Only hazard: Silica dust when cutting blocks on-site (standard for any concrete product — workers wear masks during installation only).

CoolBlock (EPS Core)

Mostly Safe — Some Caveats

The EPS (expanded polystyrene) foam sandwiched inside is the component to scrutinize. It's a plastic/organic material encased in concrete.

  • Once cured/aged, EPS is ~98% air — considered chemically inert
  • No formaldehyde, no CFCs or HCFCs
  • FDA-approved for food contact (used in food packaging)
  • Concrete encasement seals it from living space + protects from fire/UV
  • Uses flame-retardant (FR) grade EPS specifically
  • Contains residual styrene — classified as "probable human carcinogen" (IARC). Very low levels in finished products, but it exists
  • EPS max operating temp is ~80°C — west-facing walls in KPG afternoon sun can get very hot
  • If exposed to fire, EPS produces 57 chemical byproducts including styrene monomer and toxic smoke
  • Long-term heat degradation can release small amounts of styrene over decades

Bottom line: The concrete encasement mitigates most risks significantly. It's widely used and considered safe for residential construction. But it's not as "clean" as pure AAC — there is an organic/plastic component in the wall.

Safety Factor Q-CON (AAC) CoolBlock (EPS Core)
VOC off-gassing None — fully inorganic Very low — trace styrene possible
Indoor air quality Hypoallergenic, zero emissions Good (sealed by concrete)
Fire toxicity Non-combustible, no toxic fumes EPS produces toxic smoke if exposed
Heat degradation Stable at any building temp EPS max ~80°C (encased = mitigated)
Chemical composition 100% mineral Mineral + EPS plastic core
Mold / biological Mold-resistant, non-allergenic Good (EPS doesn't support mold)
Long-term (30+ years) No degradation concerns EPS may degrade slowly under heat

Our Take: Q-CON is the Safer Choice for This Home

Given our wellbeing-focused design (circadian lighting, sleep optimization, grounding) and three young kids, Q-CON's zero-emission, fully inorganic composition is the healthier long-term choice.

The thermal performance difference vs CoolBlock can be made up by the cavity wall assembly itself — the air gap plus optional polystyrene insulation sheet in the cavity (which is at least ventilated, unlike CoolBlock's permanently sealed EPS core).

CoolBlock is not dangerous — it's widely used and considered safe. But when you have a cleaner option available at a similar price point, there's no reason to introduce an organic/plastic component into the wall structure of a health-conscious home.