Heritage Conservator's Guide to Dry Ice Cleaning
A plain-English guide for heritage architects, conservators and council asset managers: where dry ice cleaning can suit heritage fabric, where it doesn't, how sample testing works, and how we fit in as a subcontractor under your conservator.
This guide is for heritage architects, conservators, council asset managers and principal contractors weighing up dry ice cleaning on heritage fabric. It is deliberately cautious. Dry ice cleaning is useful on some heritage surfaces and the wrong choice on others, and on heritage work the cost of getting that wrong is permanent.
Where we stand, plainly: Dry Ice Blasters is a young Central Coast NSW business. We have not yet completed a heritage-listed project. On heritage work we operate as a subcontractor under a principal contractor or conservator, who sets the scope, the method limits and the sign-off. We don’t pitch dry ice as a heritage-approved method, because there is no such blanket approval.
Why conservators look at dry ice at all
Every common cleaning method has a known cost on historic fabric:
- Abrasive blasting removes surface material and can erase tooling marks and carved detail. It is widely avoided on significant stone.
- Acid and alkaline cleaners can etch stone and leave residues and salts in porous substrates.
- Pressure washing drives water into joints and substrate and can mobilise salts.
- Chemical poultices work well on specific stains but introduce moisture and chemistry.
- Hand cleaning is slow, and for high-value sculpture it often remains the right choice.
Dry ice cleaning is of interest because it introduces no water and no chemical residue — the pellets sublimate to gas. That makes it worth testing where moisture or residue is the specific concern.
Where it can suit heritage fabric
Dry ice is most likely to be a reasonable option, subject to testing, for:
- Soot, grime and biological growth on harder substrates such as granite and hard-fired brick
- Paint and graffiti on non-porous or low-porosity surfaces
- Timber, metalwork and interior fabric where water would cause damage
- Plant, machinery and fittings within heritage sites (engines, switchgear, industrial heritage)
Where we are cautious — or say no
- Soft and significant sandstone. NSW heritage guidance treats abrasive cleaning as damaging, and the case for dry ice on soft sandstone rests mostly on vendor material. We don’t recommend it on significant sandstone unless the conservator has specified it after a sample test, and we’ll recommend a different method where we think it’s better.
- Friable, delaminating or salt-damaged surfaces. Any physical cleaning can dislodge loose material.
- Historic paint and patina you want to keep. Selective removal is possible but must be proven on a test area first.
- Highly porous stone with graffiti. Some ghosting may remain. A poultice may suit better.
Pressure: the conservator sets the limit
Blast pressure is the dominant variable. On heritage fabric we work to the lower of the conservator’s specified limit and the NSW heritage guidance ceiling of 500 kPa (about 72 PSI). We start well below that and only step up on the test area with the conservator’s agreement.
We don’t publish a pressure-per-substrate table. The right setting depends on the specific stone, its condition and the contamination, and the sample test establishes it.
How a heritage job runs with us
- Brief from the principal or conservator. Substrate, contamination, significance, desired outcome, constraints.
- Site inspection. We assess access, containment, ventilation (CO₂ is an asphyxiation risk in enclosed spaces) and protection of adjacent fabric.
- Sample-area test. On an inconspicuous area agreed with the conservator, at the lowest effective pressure, with before, during and after photography.
- Method statement and SWMS. Covering pressure, pellet size, sequence, masking, ventilation and the documentation record. The conservator reviews it and signs it off.
- Consent. If consent is required, the conservator or principal makes the submission. We supply the method statement and test record.
- Works and record. Carried out to the agreed method, with a photo log and conservator hold points.
What we can provide for a tender or submission
- Method statement and SWMS specific to the scope
- Sample-test photographic record
- Public liability certificate of currency (insured to $20m)
- Our two documented jobs so far (both non-heritage, so you can see how we record work): a commercial fryer at Shelly Beach Golf Club and a Porsche 996 underbody
We will not supply heritage references we don’t have.
Pricing
Heritage work is quoted per scope after inspection and sample testing. Access, scaffolding, containment, conservator hold points and documentation usually outweigh blasting time. We don’t publish heritage price ranges, because we haven’t done enough heritage work to make ranges honest.
Common questions
Can you work with our existing conservator? Yes. That’s the only way we take on heritage work.
Do you hold council preferred-supplier status? Not yet. We’re happy to go through a council’s supplier or prequalification process.
What about graffiti on heritage assets? Test first. Low-porosity surfaces usually clean well. Porous stone may ghost, and the conservator decides whether that’s acceptable.
Is it safe to work inside heritage interiors? With ventilation and CO₂ monitoring, yes. Dry ice introduces no water, which is often the reason it’s considered for interiors.
How to engage
Send the scope through the quote tool — substrate, location, heritage status and your conservator’s details — or email office@dryiceblasters.com.au. We’ll arrange an inspection and, if the fabric suits, a sample-area test before anything else.