Sand blasting and painting procedure, with a method statement you can copy
A blasting and painting job runs in a fixed order: clean off contamination, check the equipment, blast to the specified grade, check the conditions and the surface, then coat inside the window the paint data sheet allows. This page sets out each step, what gets recorded at it, and what a method statement has to contain.
Flexihose sand blast hose: 175 PSI / 12 BAR working · 700 PSI / 48 BAR burst · 1/2" to 2" bore · DIN abrasion loss below 60 mm³ · Exceeds IS 5894
Key takeaways
- The order is fixed: degrease first, because blasting oily steel drives the contamination into the profile instead of removing it.
- The equipment check belongs in the procedure, not in someone’s head. The hose, the couplings and the deadman are the parts that fail mid-shift.
- ISO 8502-4 says plainly that there is no simple rule for condensation. The familiar 3 C figure is its default, not its whole answer.
- A method statement is scope, sequence, equipment, people, controls and records. If it cannot be audited afterwards, it was not a method statement.
- Every product figure on a job, profile, thickness and overcoating time, comes from the coating data sheet, not from a blasting standard.
The blasting and painting sequence, start to finish
Blasting and painting is one job with two halves, and most of what goes wrong happens in the handover between them. The sequence below is the spine of the method statement further down. It holds whether the work is a fabrication shop floor or a site erection, and whether the abrasive is copper slag, garnet or steel grit. The sand blasting process itself is covered separately; this page is about running it as a controlled procedure with paint on the other end.
- Degrease and pre-clean. Oil, grease and soluble salts come off before any abrasive touches the steel. Blasting a contaminated surface does not remove the contamination, it drives it into the fresh profile where the coating will sit on top of it.
- Check the equipment, and record that you did. Air quality, pot, hose, couplings, deadman and earthing. This is the step that is usually skipped and the one that stops the job at 11am.
- Mask and protect. Anything that must not be blasted or coated: machined faces, name plates, valve stems, adjacent finished work.
- Blast to the specified grade. The grade comes from the coating specification, not from the blaster. How the grades are defined and signed off is set out in our Sa 2.5 surface preparation guide.
- Remove the dust. Blast residue left on the surface is a bond breaker. Vacuum rather than blow down, and never use compressed air on clothing.
- Check the conditions and the surface, together. Relative humidity, air temperature, steel temperature and dew point, then the cleanliness and profile. Both sets of numbers go on the same record, because the coating window depends on both.
- Apply the first coat inside the window. The window is the paint manufacturer’s, taken from the product data sheet for the product actually being used.
- Build the system and verify it. Subsequent coats at the overcoating intervals the data sheet gives, then dry film thickness measured and accepted against the specification.
Flexihose diagram. It shows order and record points only; it carries no time, thickness or pressure figure.
Pre-blast equipment check
Most published blasting and painting procedures jump from “mobilise” to “blast” and never mention the equipment. That is why so many of them are followed once and then abandoned: the procedure does not describe the morning that actually happens on site.
Air. Wet or oily air ruins a blast finish and contaminates the surface you are about to paint. The separator and the receiver drain are a pre-start item, and the compressor has to keep up with the nozzle rather than the other way round, which is covered in our guide to sizing the compressor and nozzle.
The blast line. Hose cover walked for cuts and soft spots, couplings tight and pinned, gaskets sound, whip checks across every joint, earthing continuous, deadman tested by releasing it. Each part and what it does is set out in the parts of a blast line. The full shift checklist, and the factory rules that sit behind it, are in is sand blasting banned in India.
The hose itself. It is the part that wears invisibly, from the inside, and the part a contaminated or under-specified line shows up in first.
Flexihose India (FLEXI HOSE), a brand of Vardhman Hydraulic Hoses Pvt. Ltd., Bhiwadi, Rajasthan, builds its sand blast hose with an extra thick seamless rubber lining free from mineral filler and a cover resistant to abrasion, ozone and weather.
It runs at 175 PSI / 12 BAR working and 700 PSI / 48 BAR burst, in bores from 1/2" to 2" (12.00 to 50.00 mm), from -40 C to +75 C, with DIN abrasion loss below 60 mm³, a copper element that reduces static build-up and a 40 m standard coil. Full sizes are on the sand blasting hose page.
It exceeds IS 5894 and is not BIS licensed to it, which is the distinction to get right when a tender asks for a licence number.
When blasting is not the right preparation method
A method statement has to say what happens when the specified preparation cannot be used, because on site that situation arrives regularly. ISO 8501-1 defines both families of grade, blast cleaning and hand and power tool cleaning, and our Sa 2.5 guide compares them properly. The decision, rather than the grades, is what belongs here.
| Situation | Usual method | Why |
|---|---|---|
| New fabrication, shop conditions | Abrasive blasting | The specified grade is reachable and repeatable |
| Live plant, no containment possible | Power tool cleaning | Dust and abrasive cannot be controlled around running equipment |
| Small welds and touch-up on a coated structure | Hand or power tool cleaning | Masking the surrounding coating would cost more than the repair |
| Confined space, limited extraction | Power tool, or wet methods | Dry blasting loads the air faster than the ventilation clears it |
| Silica sand is the only abrasive available | Change the abrasive, not the method | Free silica abrasive is prohibited in Indian factories |
Method families and their grades are defined in ISO 8501-1:2007. The situations and the reasoning are ours, not the standard’s. The abrasive rule is Schedule VIII of the Factories Rules.
Conditions on the day: humidity, dew point and when to stop
This is the part of the procedure that decides whether the day’s work survives, and it is the part most often reduced to a single number that people then quote wrongly. The standard is ISO 8502-4:2017, and it is worth reading what it actually says.
It opens by stating that relative humidity and steel surface temperature are the basis for estimating the probability of condensation, but there is no simple rule to employ
. It then lists why: heat conductance of the structure, solar radiation, air flow around it and hygroscopic contamination on the surface, all of which can wet a surface locally or stop it drying. Its own instruction is that results should be interpreted with the greatest care
.
The familiar figure is in there, and it is a default rather than a law. The standard says that unless otherwise agreed, the steel surface temperature should generally be at least 3 C above the dew point when paints are used. It immediately notes that for paints tolerant to surface moisture a smaller difference might be acceptable, and that other differences may be specified by the paint manufacturer or agreed between the parties. So “3 C above dew point” is the right starting assumption and the wrong thing to put in a specification without checking the product.
Two of its practical instructions are worth lifting into any procedure. Take at least one surface temperature reading for every 10 m² and use the lowest reading, not an average. And do not use a non-contact infrared thermometer for the steel temperature, because the surrounding air interferes with it.
On when to stop, the standard is graded rather than binary. At 85 percent relative humidity or higher, painting should be judged critically, because the dew point is at most 2.5 C away. At 92 percent it should only be considered if conditions can confidently be expected to stay the same or improve through application and drying, a period it notes is usually about six hours. Even at an apparently comfortable 80 percent, it asks you to look ahead over a similar period before starting.
What this page does not give you. There is no blast-to-prime time here, and no profile or film thickness figure. Those are product and specification numbers: they come from the coating manufacturer’s data sheet for the product being applied, and the priming window is dealt with in the Sa 2.5 guide. A procedure that hard-codes someone else’s paint figures is a procedure that will be wrong on your job.
Painting steel structures after blasting
For structural steel the organising standard is ISO 12944, Paints and varnishes, corrosion protection of steel structures by protective paint systems. Part 4 is the one a blasting contractor meets: ISO 12944-4:2017 covers the types of surface and their preparation, including uncoated steel, thermally sprayed, hot-dip galvanized, zinc-electroplated and sherardized surfaces, and surfaces already carrying a prefabrication primer. It also covers the temporary protection of prepared surfaces, which is the formal name for the problem of clean steel waiting for paint.
One point from it is easy to miss and worth stating: the standard defines preparation grades but sets no requirement for the condition of the steel before preparation starts. That incoming condition is the specification’s job, and it is why the rust grade you started from belongs on the record.
The coats themselves are a system, not a list: a primer chosen for the substrate and the environment, one or more intermediate coats for build, and a finish coat for appearance and weathering. Every number attached to them, the thickness of each coat, the minimum and maximum overcoating intervals, the induction and pot life of a two-pack, belongs to the product and is read off its data sheet.
Verification of the finished system has its own standard. ISO 19840:2012 sets out how dry film thickness is measured on the rough surface that blasting produces, and gives the sampling and acceptance rules that go with it. A single gauge reading is not a result, which is the usual source of an argument at handover.
What a blasting and painting method statement contains
A method statement answers three questions for someone who was not there: what was going to be done, who was going to do it and how, and how anyone would know afterwards whether it was done. The headings below are a working structure. Copy them, delete what does not apply and fill in the rest from your own specification. Nothing in it is standard-mandated, so nothing here has to be paid for or asked for.
Method statement structure
- Scope and references. What structure or area, what coating specification, which standards the specification invokes, and the paint data sheets by product name and revision.
- Sequence of work. The eight steps above, written for this job, with hold points marked where work stops until an inspection is signed.
- Equipment. Compressor and receiver, blast pot, hose size and length, nozzle type and size, abrasive type, extraction and lighting, spray equipment. Include the pre-start check.
- Abrasive. Which one, where it is stored, whether it is recycled and how it is separated if so, and its free silica status.
- Factory work in India rules out sand and any abrasive containing free silica.
- People and competence. Roles on the job, who signs inspections, and what tickets or training each role needs.
- Health and safety. PPE, enclosure and ventilation, medical surveillance where the rules require it, and a job safety analysis. Reference the hazards rather than restating them.
- Environmental controls. Containment, dust and waste abrasive handling, and disposal route.
- Inspection and test plan. Each check, the acceptance criterion, the standard it comes from, who does it and what record it produces.
- Records. The list in the next section, with who holds them and for how long.
- Non-conformance. What happens when a check fails: stop, repair, re-prepare, re-inspect, and who authorises the restart.
The hold points in item 2 are what turns a description into a procedure. A blasting and painting job has at least three: after blasting and before dust removal, after the surface and condition checks and before the first coat, and after the final coat before handover.
The records the job leaves behind
A coating dispute is settled by whichever side kept records. These are the ones worth having, and where each comes from. If you are writing the blasting half of the procedure from scratch, the sand blasting process covers the steps and the equipment those records describe.
| Record | What goes on it | Source |
|---|---|---|
| Equipment pre-start check | Air, pot, hose, couplings, whip checks, earthing, deadman | Site practice |
| Abrasive record | Type, batch, reuse cycle, free silica status | Factories Rules, Schedule VIII |
| Surface preparation record | Area, starting rust grade, grade achieved, profile | ISO 8501-1 and the coating specification |
| Conditions record | Air temperature, relative humidity, dew point, steel temperature, and the difference | ISO 8502-4, clause 6 |
| Coating record | Product, batch, mixing and induction, coat number, time applied | Paint data sheet |
| Film thickness record | Inspection areas, readings, acceptance against the specification | ISO 19840 |
| Non-conformance and repair | What failed, what was done, who authorised the restart | The method statement itself |
The conditions record follows the test report contents listed in ISO 8502-4:2017, clause 6: the reference to the standard, the date and hour, the instruments used, the calculated dew point, the measured steel surface temperature and the difference between them.
Writing the equipment section? Start with the hose
Tell us the nozzle size, the abrasive and the length of run, and we will recommend the bore and send a quote.
FAQ
What is the blasting and painting process?
It runs in a fixed order: degrease and pre-clean the steel, check the blasting equipment, mask what must not be coated, blast to the grade the coating specification calls for, remove the blast dust, check the ambient conditions and the surface, apply the first coat inside the paint manufacturer's window, then build the remaining coats and verify the dry film thickness.
What should a blasting and painting method statement include?
Scope and references, the sequence of work with hold points, equipment, the abrasive and its free silica status, people and competence, health and safety, environmental controls, an inspection and test plan, the records list, and what happens when a check fails. If it cannot be audited after the job, it is a description rather than a method statement.
When should painting stop because of humidity?
ISO 8502-4:2017 grades the decision rather than setting one cut-off. At 85 percent relative humidity or higher, painting should be judged critically because the dew point is at most 2.5 C away. At 92 percent it should only be considered if conditions will hold or improve through application and drying, usually about six hours. The standard also states there is no simple rule, because structure temperature, sunlight, air flow and surface contamination all affect condensation.
Is the steel really meant to be 3 C above the dew point?
That is the default in ISO 8502-4:2017, not an absolute rule. It says that unless otherwise agreed the steel surface temperature should generally be at least 3 C above the dew point when paints are used, then notes that a smaller difference may be acceptable for paints tolerant to surface moisture, and that the paint manufacturer may specify a different figure. Check the product data sheet before writing 3 C into a specification.
What records should be kept for a blasting and painting job?
An equipment pre-start check, the abrasive record, the surface preparation record with the starting rust grade and the grade achieved, the conditions record, the coating record with product and batch, the film thickness record, and any non-conformance and repair. ISO 8502-4 clause 6 sets out what the conditions record contains, including the date and hour, the instruments used, the dew point, the steel temperature and the difference between them.
Does shot blasting need a different painting procedure?
The sequence is the same. What changes is the abrasive and the profile it leaves: angular media cut a sharper profile than round shot at the same pressure, so the profile has to be checked against what the coating data sheet asks for rather than assumed from the blasting grade.
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