Prep is most of a paint job. In St. Louis that means old plaster, old oil paint on trim, and wood that has been through a hundred humid summers. This page answers the common questions about primer, sanding, stains and peeling.
Do I need to prime before painting?
You need primer on bare wood, bare plaster or drywall, patches, stains, glossy or oil-painted surfaces and any big color change. You do not need to prime sound, clean, flat painted walls that are being repainted a similar color.
Primer does three jobs: it sticks to hard surfaces, it seals porous ones and it blocks stains. A paint and primer in one product does not do all three.
Do I need primer if the old paint is in good shape, and can you paint over old paint?
No primer is needed over old paint that is clean, dull and firmly attached. Yes, you can paint over old paint. That is what most repaints are. Wash it, fix the flaws, scuff any shine and paint.
The exceptions are old oil paint, peeling paint and stains. Those need the right primer first.
Do I need to sand the walls before painting?
Walls need a light sand where they are glossy, rough or patched. A full sanding of every wall is not usually needed on flat paint in good shape. Trim and doors are different: they should always be scuff sanded so the new coat bonds.
In a home built before 1978, sanding old paint can release lead dust. Lead-safe methods apply. Do not dry sand or power sand old paint in an older St. Louis home without them.
Do painters fix nail holes, cracks and dents first?
Yes. Filling nail holes, small cracks and dents is a normal part of prep, and in our quotes patching, sanding, caulking and priming are included. Larger repairs are listed separately so you can see them.
Plaster cracks are the local specialty. Hairline cracks are opened slightly, filled and sanded. Cracks that keep coming back are taped. Plaster that has come loose from the lath needs more than filler, and we say so.
How do I paint over a water stain so it does not bleed through?
Seal the water stain with a stain-blocking primer, then paint. Ordinary wall paint will not hold a water stain back. It bleeds through again within days, however many coats you put on.
Fix the leak first and let the area dry. Stains under bathrooms, around chimneys and below flat roof sections are common in older two story homes here.
Can you paint over smoke stains or pet smells?
Yes, with the right primer. Smoke residue is washed off as far as possible, then the surface is sealed with a stain and odor blocking primer before paint. The same approach works for nicotine and for pet smells in walls and subfloors.
Paint alone will not do it. The yellow comes back through and the smell returns in humid weather.
Mold on the bathroom ceiling: can it just be painted over?
No. Mold has to be killed and cleaned off first, and the surface dried, or it grows back through the new paint. After cleaning, a stain-blocking primer and a moisture-resistant paint help.
Fix the cause as well. Many older St. Louis bathrooms have no exhaust fan, only a window. Long humid summers make that worse. Large areas of mold, or mold that returns, point to a moisture problem that needs more than a painter. The published national figure for small-area mold remediation is $500 to $1,500.
Paint is peeling to bare wood on my old house. What prep does it need?
Loose paint is scraped off down to a firm edge, the edges are feather sanded, the bare wood is primed and the gaps are caulked before painting. Bare wood that has gone grey should be sanded back to bright wood, because paint does not hold on weathered fibers.
On a house built before 1978, this work must follow lead-safe practices: ground cover, no open-flame burning, no dry power sanding without containment and careful clean-up.
Why is my paint peeling?
Paint is peeling because something broke its bond: water, a dirty or glossy surface, or the wrong product. Outdoors the usual cause is moisture getting into the wood from behind or through open joints. Indoors it is steam, a leak, or latex put straight over old oil paint.
Find the cause before repainting. New paint over the same problem peels the same way.
Why is paint bubbling or peeling in my kitchen or bathroom?
Paint bubbles and blisters in kitchens and bathrooms because of moisture and poor bonding. Steam gets behind a weak paint film and lifts it. Grease on kitchen walls stops paint from sticking in the first place.
The fix is to scrape and sand the failed area, clean it, prime it and use a paint made for damp rooms. Running a fan or opening a window after showers protects the new finish.
How do I know if old paint is oil or latex, and can latex go over oil?
Rub a hidden spot with a rag and rubbing alcohol. If paint comes off on the rag, it is latex. If nothing comes off, it is oil-based. Latex can go over oil only after the surface is cleaned, sanded dull and coated with a bonding primer.
Skip that step and the new paint scratches off with a fingernail. Old trim, doors and radiators in St. Louis homes are very often oil.
Do bare drywall patches need primer?
Yes. Drywall patches and joint compound must be primed before paint. Unprimed patches soak up paint differently from the wall around them and show as dull or shiny spots, called flashing.
The same goes for new plaster repairs. Prime the patch, then paint the whole wall from corner to corner for an even look.
Questions about your own walls? Call or text (314) 742-3507 for a free estimate.