Walls and paint: filling, preparing and painting

A coat of paint is the job most people try first, and it's the one that shows every shortcut. A filled hole that wasn't sanded, a new wall painted before it dried, a stain painted over without asking what made it: each comes back through the new paint within weeks. And two things about a wall decide whether it is safe to prepare at all, before the question of how it will look: what's in the old paint, and what made the mark you want to cover. This lesson puts the work in order, from reading the wall to the last coat, with a maker's methods labelled as a maker's, and it sends you to lessons 18 and 19 at the two points where the job may have to stop.

Painting a room opens nothing up, but it does bring you close to the switches and sockets, which the preparation section comes back to. The box stays shut, as in lessons 5 and 6: CPSC, the US Consumer Product Safety Commission, says panel boxes "are usually electrically live, even with the main circuit breakers turned off",¹² and HSE's guidance for people who work on electrical systems does not recommend "non-contact devices such as 'volt sticks'" for proving anything dead.¹³

Two parts of this lesson state law: the rules on what a UK paint tin's label must say, and the US rules on one paint stripper. This is general information, not legal advice. The rules differ between England, Wales, Scotland and Northern Ireland, and between US states and cities, and they change.

Most of the method here comes from Dulux, a paint maker, on its own website, writing about painting with its own products and a filler range its page promotes. This course names none of those products. It uses the pages because they were the most specific method it read, and labels each step as Dulux's. Where a tin or a filler you are using says something different, its own instructions decide.

First, read the wall

Before a filler or a brush, the wall gets two questions. Neither is about paint.

What made the mark? A brown ring on a ceiling, a grey bloom in a corner, a patch that bubbles every winter: these are marks made by water, and paint doesn't fix water. For the US, Purdue University's extension bulletin on paint failure, written in 1988 about paint on the outside of wooden houses, says "The most common cause of premature paint failure on wood is moisture", lists "Plumbing leaks, overflow of sinks, bathtubs or shower spray and improperly sealed walls" among the sources of water from inside, and puts the rule plainly: "If a new paint coat is to be successful over a problem area, any moisture problems must be eliminated."⁶ It is old and about outside woodwork, but it is the only painting source this course read that says what to do about a wet patch, and its rule matches the order lesson 18, "Damp inside: condensation, mould, ventilation and rising damp", teaches for the inside of a house: find and fix the cause first. That lesson also has EPA's line on mould, "Do not paint or caulk moldy surfaces."⁷ So a stain goes to lesson 18 before it goes anywhere near a tin, and a stain in a rented home goes to the landlord.

What is in the old paint, and what's on the ceiling? Filling and preparing a wall means sanding, and sometimes scraping. In an older house, the layers underneath may contain lead, and a textured ceiling or wall coating may contain asbestos. Lesson 19, "Asbestos, lead paint and radon: what not to disturb", teaches both: how to tell whether your home is old enough to matter, what the law and the advice say, and what to do instead. This lesson does not reteach any of it. What it does is mark the points where you stop and go there: before you sand or scrape any paintwork that might be old enough, and before you fill, sand or scrape a textured coating at all. For the US, EPA's page for people doing their own renovation puts the first of those in one sentence: "If your home was built before 1978, it may have lead-based paint; the older your home, the more likely it has lead-based paint."¹⁰

Finishes, and the two countries' names

Dulux describes the finishes by how much light they reflect: "To hide imperfections, use velvety matt emulsion. Satin and silk are mid-sheen finishes that look slightly polished and reflect some light. Eggshell sits somewhere between the two, with a surface that looks as its name suggests. Choose a gloss finish for a shiny look that reflects lots of light."¹ Dulux's reason for the choice, as far as it gives one, is that matt hides imperfections. That a shinier finish shows them more is this course's reading of "reflects lots of light", not Dulux's words.

"Emulsion" is the British name for ordinary wall paint thinned with water. In American shops the name you will see for water-based wall paint is "latex", and Purdue's bulletin uses it ("acrylic latex").⁶ This course read no source that defines either word against the other. Treating them as the two countries' names for the same kind of paint is this course's reading, and the tin decides what's in it. Dulux also says synthetic brushes suit water-based paints, because the bristles "don't swell up and cause tramlines to appear in the paint".¹

Where you see "solvent-based" or "oil-based", the paint is thinned with a solvent instead of water. The UK law in the section on labels below calls them "water-borne" and "solvent-borne", and defines them by how the paint's thickness is adjusted: with water, or with an organic solvent.³ Both kinds give off some VOCs (the limits in the table below are above zero for both, and EPA says paints contain organic solvents). What you breathe while it dries is the section after that.

Filling holes and cracks

Dulux's preparation page tells you to buy "a filler that’s up to the task", and describes fillers made for particular jobs: hairline cracks, screw holes, deeper holes, and a flexible filler for "around the tops of skirtings, windows and door frames".¹ (A skirting is the board along the foot of a wall; in the US it is a baseboard.) Dulux gives no reason why those gaps want a flexible filler, and this course supplies none. Its method, for filling:¹

1. Clean and check. Wipe the wall down, wash it with sugar soap and rinse it (more on that below), then look it over for cracks and holes.
2. Fill with a filling knife, using the filler for that surface.
3. Deep holes in layers: "For any holes that are more than 10mm-deep, build up the filler in layers." (10 mm is about 3/8 inch.)
4. Dry, sand, dust: "Allow to dry for one to two hours, sand until smooth, and give the wall a final once-over with a duster."

The drying time is for the fillers Dulux sells; the filler's own instructions give yours. Dulux says sanding is needed because it "ensures your fresh, new paint will adhere to the surface properly".¹

Filling screw holes and small cracks in a plain plastered wall is Yours. Two things change that. The first is step 4, which sands. On a newer wall that makes plaster and filler dust. Lesson 13, "Tools, dust and fumes: a small kit used safely", gave HSE's kinds of dust (gypsum, in plasterboard or drywall, among the "general" ones), and its advice on masks and clean-up applies. On old paintwork it's lesson 19's question, and on a textured coating the answer is no. The second is the crack itself. This course read no source on reading cracks: which are shrinkage, which are movement, which mean the building is moving. Structural work is one of the jobs lesson 1 named as needing a professional, and a crack you can't account for, or one that comes back wider, is a question for a surveyor or builder, not for a filler. That is this course's line, not a source's.

Sticking doors, sealant round a bath and wallpaper are left out: this course read no maker's or official method for any of them, and it does not teach from general knowledge.

Preparing the room, in Dulux's order

Dulux's advice is to "Set aside half a day to complete all your prep", and its warning is that skipping it can leave "an uneven finish, unsightly paint bubbles and obvious imperfections, such as holes and cracks".¹ Its steps, in its order:¹

1. Clear the room. Furniture, pictures, curtains and blinds out; a dust sheet over the floor and whatever can't move.
2. Switches and sockets. Dulux says: "Loosen or tape around electrical cover plates on switches and outlets." This course teaches the second half only. Tape around the plate. Loosening the plate is the first step of opening a fitting, and this course teaches no work on fittings, anywhere (lesson 5 set out where the householder's hands stop). That is this course's scope decision, not a claim about the law.
3. Hardware. Unscrew, or tape over, handles and locks on doors and windows.
4. Clean. "Wash the walls thoroughly with sugar soap and rinse them with clean water to remove any residue." Sugar soap is a British name for a wall-cleaning compound; this course read no US source that names an equivalent, so in a US home the cleaner's own label is the guide.
5. Fill, then sand the filled spots and any woodwork you will paint, and wipe the dust off.
6. Mask the edges you want sharp, such as the tops of skirtings, with masking tape.
7. Prime a surface that has never been painted. (New plaster has its own section, next.)
8. Paint from the top down. Dulux: "start at the top of the room and work your way down". Ceiling first, "Apply two coats and move onto the walls, working away from natural light." Then: "Paint your windows in the morning so they have a full day to dry before you close them at night. Lastly, finish off with doors, door frames and skirting."

Two of those steps have a stop in them. Step 5 sands, which in an older house is the point to check with lesson 19 first. And step 8 starts on the ceiling, which means a stepladder. Lesson 16, "Stepladders, and what the ladder injury figures count", worked through painting a hall ceiling from a stepladder, with HSE's rules and the choice of a roller on a long handle from the floor, and it applies here unchanged.

New plaster

A wall that has just been plastered, or skimmed (a thin new coat over an old one), is the one wall where waiting is part of the job. Dulux, answering a reader in its "Dr Dulux" column, gives the reason in one line: "Plaster is extremely permeable, which means it’ll soak up any moisture quick."² Its steps:²

1. Let it dry. "As a rule of thumb, plaster takes up to 4 weeks to dry completely." What sets the time: "There are different factors that influence how soon can you paint on new plaster, such as the type of material and weather." Dulux adds: "You can speed things up with a heater or by opening a window." And the cost of hurrying: "If you don’t let the plaster dry and apply emulsion paint to wet plaster, it’s likely to crack and peel off."
2. Mist coat. "Mist coat paint is simply watered-down emulsion paint, which acts as your primer." White emulsion, thinned: "Ten parts paint to one part water should work."
3. Why it works, in Dulux's words: "The mixture will soak into the wall and seal the plaster." Dulux says this is what helps the top coat stick. Any flaws can be sanded or filled once it is dry.
4. Top coat as normal.

Dulux's "up to 4 weeks" is a rule of thumb from one maker. So: drying time depends on the plaster, the thickness and the weather, and the plasterer who did the wall and the maker of the paint you are using are the people to ask. Dulux's ratio is for its emulsions; another maker's tin may give its own. And its method is written for British plastered walls. Nothing this course read covers a new plaster skim in an American house, or drywall, so applying Dulux's wait and mist coat there is this course's reading, and the paint maker's own instructions come first.

The label on the tin

This section states law. This is general information, not legal advice.

In the UK, paints and varnishes for the walls, woodwork and fittings of buildings (aerosols excepted) come under the Volatile Organic Compounds in Paints, Varnishes and Vehicle Refinishing Products Regulations 2012. A volatile organic compound, or VOC, is defined there as an organic compound with an initial boiling point at or below 250°C (482°F).³ The Regulations apply to products that "are to be used in any part of the United Kingdom" (with a further condition for products in Northern Ireland that refers to the EU's customs territory).³ This course read the revised text on legislation.gov.uk, which shows the 2020 change to that scope and says there are "no known outstanding effects" for the Regulations.

What they do: under regulation 4, a person "must not place on the market" a paint covered by them unless its VOC content is within the limit for its kind, and it carries the label regulation 5 requires. That label must show "the sub-category of the product and the relevant VOC limit values, measured in g/l", and "the maximum content of VOC in g/l of the product in a ready to use condition".³ "Ready to use" matters: the Regulations define VOC content as the mass of VOCs "in the formulation of the product in its ready to use condition", and regulation 4 applies the limits to a product that has to have solvent added before use in its ready-to-use state.

Notice who the law binds. It's the person placing the tin on the market. Nothing in it tells you how to use the paint, and nothing in it binds a householder. What it gives you is a number to read.

A few of the limits in Schedule 2, for the kinds of paint in this lesson:³

The table is this course's selection; the Schedule has twelve sub-categories for paints and varnishes. Read across the trim row and you see the difference the last section described: the law sets a solvent-based trim paint's limit more than twice as high as a water-based one's. The figure on your tin is the product's own maximum, which may sit well under its limit.

In the US, this course read no federal rule on labelling a consumer paint's VOC content, so it says nothing about what an American tin must show. What it read is EPA's advice, in the next section. Its list of steps opens: "Increase ventilation when using products that emit VOCs." "Meet or exceed any label precautions."⁴

Air, leftovers and strippers

Part of this section states law. This is general information, not legal advice.

EPA, the US Environmental Protection Agency, says "Paints, varnishes and wax all contain organic solvents", and lesson 13 gave its figures for how far indoor levels rise, especially while stripping paint. EPA is also frank about how much is not known: "At present, not much is known about what health effects occur from the levels of organics usually found in homes."⁴ Its advice doesn't wait on that. Its general step is "Increase ventilation when using products that emit VOCs", and among its steps against benzene, which it says comes partly from paint supplies, it lists "providing for maximum ventilation during painting". Where a label says to use a product in a well-ventilated area, lesson 13 gave EPA's order: outdoors or with an exhaust fan, otherwise open windows.⁴

A dust mask is no help with any of this. Lesson 13 showed why: the masks this course read about filter particles, and a solvent vapour is not one.

Then the leftovers. EPA:⁴

• Buy small. For paints and strippers used now and then, "buy only as much as you will use right away".
• Don't keep what you won't use. "Because gases can leak even from closed containers, this single step could help lower concentrations of organic chemicals in your home." What you do keep, EPA says, goes somewhere well ventilated and out of children's reach.
• Don't put it in the bin (trash). "Do not simply toss these unwanted products in the garbage can." EPA sends you to a local collection day for toxic household wastes, where one exists.

That is US advice. In England, Thames Water, a water company, says: "Take chemicals, solvents, engine oil and paint to your local refuse or recycling site", the same line lesson 4, "Water out: traps, vents and blocked drains", gave for keeping them out of the drain.⁵ Thames Water's page is about its own area; this course read no other UK body on leftover paint, so your council's waste service is the one to ask.

Strippers. Lesson 13 covered methylene chloride, a solvent some old paint strippers contain, which EPA says "is converted to carbon monoxide in the body".⁴ In the US, EPA's rules since 2019 have prohibited making and distributing it for consumer paint removal, and for a tin someone already has, "EPA is encouraging all consumers to stop using methylene chloride products that they may have already purchased for paint and coating removal."⁸ EPA's indoor air page still says to "Use products that contain methylene chloride outdoors when possible; use indoors only if the area is well ventilated."⁴ Lesson 13 set the two pages side by side; for paint removal, this course follows the one about the rules. This course read no UK rule on it. Any other stripper, in either country, is used by its own label.

Old paint: overcoat or strip?

This is lesson 19's decision, and this lesson only marks where it comes. If the paintwork you are preparing is old enough to fall inside lesson 19's dates, the question isn't how to sand it but whether to disturb it at all. The two countries' advice differs, so here it is one country at a time.

In the UK, the British Coatings Federation says in its guidance for the public not to remove lead paint that is in sound condition, especially if the lead paint is not the top layer: "overcoating is the safest option to prevent exposure".⁹ Where sound paint needs preparing for the new coat, it says to rub it down wet, so no dust is made. Lesson 19 labels that Yours, on conditions: the paint is sound, and any rubbing down is wet.

In the US, EPA's page for do-it-yourselfers says: "DIY projects can easily create dangerous lead dust, so EPA recommends homeowners hire lead-safe certified contractors for all RRP projects in pre-1978 homes." (RRP is renovation, repair and painting.) If you can't find out the home's age, it says "it’s safest to assume the area you are renovating has lead-based paint and use the DIY lead-safe work practices described below".¹⁰ Those are seven practices, which lesson 19 sets out, and doing the job yourself on those terms is lesson 19's Yours, on conditions.

Everything after that, the methods that are allowed, the ones that are not, the heat limits and the law, is in lesson 19.

So, for this lesson's purposes: in the UK, sound old paint that only needs a fresh colour is painted over without disturbing it, which the BCF calls the safest option, and any rubbing down is done wet. In the US, EPA's first advice for any renovation, repair or painting job in a pre-1978 home is a lead-safe certified contractor, and doing it yourself means EPA's seven practices in lesson 19. In either country, anything that needs stripping, or flaking paint in an older home, is a lesson 19 question before it's a painting one.

A living room in the Forest of Dean

Take the simple case first. In a house in the Forest of Dean built in 2006, the owner wants to repaint the living room walls. There are six screw holes where a shelf came down, a hairline crack over the door, and the walls are the original matt emulsion, a bit grubby near the light switch.

1. Read the wall. No stains, no mould, no bubbling paint. Built after 2000, so on HSE's line "Buildings constructed after 2000 are unlikely to contain asbestos", and well after the dates the UK sources give for lead paint (the British Coatings Federation's cut-off for testing is "Pre-1995").¹¹⁹ No textured coating. Nothing sends this job to lesson 18 or 19.
2. Choose. Matt emulsion again, since Dulux says matt hides imperfections, and the filled spots are imperfections.¹ A filler for screw holes and fine cracks, used by its own instructions.
3. Clear, protect, tape. Furniture out, dust sheet down, masking tape round the switch and socket plates (not loosened, the course's line).¹
4. Clean. Sugar soap, then clean water, and let it dry.¹
5. Fill and sand. Fill the holes with a filling knife; none is deeper than 10 mm, so one layer. Let it dry for the time the filler gives, then sand smooth and dust off.¹ It is plaster and filler dust from a newer wall; lesson 13's clean-up advice (no dry sweeping) applies.
6. Paint. Window open while painting and afterwards: EPA's "Increase ventilation when using products that emit VOCs", applied in England as this course's reading, plus whatever the tin adds.⁴ The walls in two coats, working away from the window, then the woodwork if it's being done.¹

This is Yours. What made it simple is step 1: a house new enough that neither lesson 18 nor lesson 19 had anything to say.

A renovation in Youngstown

Now one with a wrinkle, and a gap for you.

In a 1920s house in Youngstown, the owners have had a back bedroom's walls skimmed with a thin coat of new plaster. It has been ten days, the walls look dry to them, and they want to paint this weekend, full-strength, because their guests arrive in two weeks. The same room has the original door, with thick layers of paint that have begun to crack. They want to strip it back to the wood and varnish it, and one of them has already bought a tin of paint stripper.

Two questions sit in this room, and they go to different places.

The walls. Dulux's rule of thumb is "up to 4 weeks", and ten days is inside it.² Dulux gives no way of telling by eye that a wall is dry, and says the time depends on the material and the weather. This is a US wall, and nothing this course read covers a US skim coat, so Dulux's wait and mist coat are one British maker's method, not the answer here. The people who know are the plasterer who did the skim (what was used, how thick) and the maker of the paint they plan to use, and the question to ask both is when it can be painted and what goes on first. What Dulux does say about rushing, for its own paint: emulsion on wet plaster is "likely to crack and peel off". Yours, on conditions: the plasterer's and the paint maker's say-so on timing and first coat.

The two questions in that house look alike, since both are about waiting, but they're different kinds of answer. The plaster wait is a maker's rule of thumb about how paint sticks: get it wrong and you repaint. The door is about what is in the paint, and that's the one lesson 19 was written for.

What people get wrong

"Paint over the stain and it's gone." A mark made by water comes back until the water's fixed (Purdue; lesson 18), and EPA says not to paint mouldy surfaces.⁶⁷

"New plaster that looks dry is ready." Dulux's rule of thumb is up to four weeks, and it depends on the plaster and the weather; paint on wet plaster is "likely to crack and peel off".²

"The mist coat is optional if you use more coats." Dulux gives the sealing job to the thinned coat.²

"A low VOC number means no need to open a window." The label is a legal requirement on whoever puts the tin on the market, about what is in the tin; EPA's advice, to increase ventilation when using products that emit VOCs, makes no exception for a low number.³⁴

"Leftover paint is fine in the cupboard with the lid on." EPA: gases can leak even from closed containers.⁴

"Sanding old paintwork is just preparation." In an older home, it's lesson 19's question first. (And for the stripper: lesson 13.)

Practice

For your plan

To the stop list: sanding or scraping any paintwork old enough for lesson 19, and filling, sanding or scraping a textured coating; painting over a stain whose cause isn't fixed; loosening switch or socket plates. To the calendar: nothing seasonal of its own, but a note to paint in weather that lets you keep the windows open. And for the repair write-up: if your one repair is a patch and a repaint, this lesson's order, from reading the wall to the last coat, is its plan.

Connections

Lesson 13, "Tools, dust and fumes: a small kit used safely", gave the masks and why they do not touch solvent vapour, EPA's ventilation advice, and methylene chloride. Lesson 16, "Stepladders, and what the ladder injury figures count", took a stepladder to a ceiling. Lesson 18, "Damp inside: condensation, mould, ventilation and rising damp", is where a stain goes first. Lesson 19, "Asbestos, lead paint and radon: what not to disturb", owns old paint and textured coatings. Lesson 4, "Water out: traps, vents and blocked drains", is why paint doesn't go down the sink.

Next, lesson 21, "Pests: find the cause, then control it", uses the same habit of fixing the cause first. Lesson 22, "Who may do what: reserved work, and the argument about licensing", is where the rules on who may do which job are gathered, and lesson 23, "Hiring a tradesperson, and when to stop", covers hiring a decorator, including, in the US, a lead-safe certified one.

Go deeper

• Dulux, "Dr Dulux: How to paint new plaster". Read here in full. A maker's page that promotes its products: the wait and the mist coat, with the reason it gives.
• Legislation.gov.uk, the VOC Regulations 2012. Read here: regulations 2 to 5 and Schedules 1 and 2, revised text. Short, and Schedule 2 is the whole table your tin's label comes from.
• EPA, "Volatile Organic Compounds' Impact on Indoor Air Quality". Read here in full. The US government's page on solvents and paints at home.
• Purdue Extension, "Paint Failure Problems and Their Cure". Read here in full. From 1988 and about outside woodwork: why paint fails where water gets in.

Sources

1. Dulux, "Painting Tips: Preparing Walls for Painting". Read: full text, re-read 26 September 2026. A paint maker's page about its own products, with product promotion.
2. Dulux, "Dr Dulux: How to paint new plaster". Read: full text, re-read 26 September 2026. A paint maker's page about its own products, with product promotion.
3. The Volatile Organic Compounds in Paints, Varnishes and Vehicle Refinishing Products Regulations 2012 (SI 2012/1715), on legislation.gov.uk. Read: regulations 2 to 5 and Schedules 1 and 2, in the revised ("latest available") text and as made, 26 September 2026.
4. US Environmental Protection Agency, "Volatile Organic Compounds' Impact on Indoor Air Quality", last updated 23 June 2026. Read: full text, re-read 26 September 2026.
5. Thames Water, "Blockages and blocked drains". Read: full text, 25 September 2026. A water company, about its own area in England.
6. Daniel L. Cassens and William C. Feist, "Paint Failure Problems and Their Cure", NCR-133, Purdue University Cooperative Extension Service, revised March 1988. Read: full text, 26 September 2026. About paint on the outside of wooden buildings.
7. US Environmental Protection Agency, A Brief Guide to Mold, Moisture and Your Home. Read: full text, as recorded for lesson 18.
8. US Environmental Protection Agency, "Risk Management for Methylene Chloride", last updated 6 March 2026. Read: full text, 25 September 2026; the key line re-checked 26 September 2026. EPA's summary of its 2019 and 2024 rules; the rules' own text was not read.
9. British Coatings Federation, "Lead in painted surfaces: Repainting and removal. Guidance for the general public", HS032, version 2.2, October 2025. Read: full document.
10. US Environmental Protection Agency, "Lead-Safe Renovations for DIYers", last updated 20 August 2026. Read: full text, re-read 26 September 2026.
11. Health and Safety Executive, "Introduction to asbestos safety", parts 1 and 2. Read: full text of parts 1 and 2, re-read 25 September 2026. Written for people at work.
12. US Consumer Product Safety Commission, Publication 5133, "Preventing Home Fires: Arc Fault Circuit Interrupters (AFCIs)", dated R042012. Read: full text.
13. Health and Safety Executive, Electricity at work: Safe working practices, HSG85, third edition, 2013. Read: the whole PDF extracted; "Proving dead" paragraphs 53 to 55 read. Workplace guidance, used here only for what it says about non-contact testers.
14. Health and Safety Executive, "Asbestos: FAQs", updated 4 September 2025. Read: full text, re-read 26 September 2026. Great Britain.