4 Reasons Your Paint Separates When Applied (& How to Fix It)


I know how exasperating it can be when your paintwork is full of imperfections and you’re not sure why. Fortunately, the remedy is usually pretty straightforward.

Problems while painting are mostly caused by a failure to properly prepare the surface. If your paint is separating while it’s being applied, it’ll be due to a lack of silica, lack of adhesion, over-thinning or using the wrong type of thinner, or a lack of primer.

This article is going to take a closer look at the 4 reasons for paint separation before showing you exactly how to fix the problem at the end.

4 Reasons Your Paint Is Separating

Paint should not separate after an application if you have prepared the surface, used the right paint, and applied the paint correctly. Here are some reasons why your paint is separating on your surface.

1. Lack of Silica

Another name for paints containing silica is mineral paint. Mineral paint includes pure silicate, dispersion silicate, and sol-silicate paints. Silica is common in many types of construction materials, including sandpapers, concrete, and paint.

Paint manufacturers and professional painters prefer silica-based products. Silica helps with the structural integrity of the material and enables it to last longer in harsh environments. You also find silica in caulk since it is weather and corrosion-resistant.

Silica offers significant textural properties to oil-based paints without affecting the color. Silica helps oil paint to dry harder, making the texture waterproof while still letting the walls of your property breathe. The silica also helps the paint to bind better when dry – since the paint can bond directly with solid silica particles.

2. Lack of Adhesion

You want your surface to have no contaminants and to offer the best possible conditions for your paint to stick. Painting water-based paint on an old-based painted surface is one of the biggest mistakes. Oil will reject any water in paint and cause it to pool together in droplets, and the same applies to primers.

Even without the surface being painted, dirt and oils condensing out from the pollution in the air will have the same effect as an oil-based paint. Oil-based paints should stick to most surfaces, but they will struggle to cling to latex paints. Latex paints will expand and contract in the heat, oil-based paints will not, and this will cause separation and alligatoring.

3. Over-Thinning

The paint manufacturer will specify the type and percentage of thinner to mix into your paint. Adding the wrong thinner, such as water, into an oil-based paint will destroy the mixture and form large patches as the paint tries to dry on your surface.

Even if you use the correct thinner, you need to stay within the recommended proportions. Too little thinner and the final mix will be difficult to apply, and it will struggle to sink into the material you are painting. Too much thinner, the paint will take a long time to dry, it will drip more, and reduce the paint’s adhesive powers.

4. Lack of Primer

Primer helps to create a clean and sticky surface for your paint. Materials like metal and plastics resist the attempts of paint trying to sink into their surfaces, but a primer sets up a new surface. Primers seal in the material you are painting, giving it greater protection from moisture and general damage.

A primer prevents the paint from separating as it dries and should also prevent the paint from cracking and peeling. When using a primer, ensure that you do not mix primers for oil-based and water-based paints, and check that you are using the correct primer for your paint.

If you leave the primer on too long, the primer will lose its tackiness, and the adhesion of the paint will be poor. Painting on top of the primer before it dries will lead to your paint and primer mixing, which will spoil the color and the finish.

How to Fix

Check the base of the paint that you are using (whether it is an oil- or water-based paint) and buy the appropriate primer. Wait for the surface to dry between coats and, if possible, use a roller rather than a paintbrush.

Follow this step-by-step guide if you are having trouble with your paint separating:

Tools and Materials

  • Primer
  • Paint
  • Roller
  • Paintbrush
  • Sandpaper: 60-grit and 220-grit
  • Sanding block
  • Filler
  • Scraper
  • Drill
  • Paint mixing attachment

Guide

  1. Sand and Scrape – Use a scraper for leveling out large sections of paint bubbles and flakes. Use 60-grit sandpaper on a sanding block and rough up everything that you are going to paint. 60-grit should leave deep scratches for your new paint to stick to and help to level out bubbles and loose flakes, which will also expose any cracks. Steel wool is good on metal surfaces and concrete walls for giving you a starting surface for paint.
  2. Clean – Clean off the surface and removes loose paint with a scraper. If the remaining old paint is well stuck, you may be able to paint over it with the following steps. If you are painting an outside wall, you may want to blast it clean with a pressure washer.
  3. Dry – While you have a clean surface, look for damp areas around the corners of your ceilings or walls and see if there is moisture leaching through. Water rising in the wall from the floor can be a sign of a plumbing issue or the lack of a damp course. Both should be fixed before painting.
  4. Repair – If your wall or ceiling is full of cracks and holes, these need to be repaired. Any break in the surface is a place for water to enter. Use a filler compound to patch up and smooth over the damage, and level it off with 60-grit sandpaper when dry.
  5. Primer – Oil-based and latex-based primers are better on wooden surfaces. These primers provide a better seal from moisture, which causes wood to swell and push out the paint. Oil-based primers are also better on metal surfaces. Water-based and latex primers are easy to apply onto concrete, fiberboard, and plaster. If you need to mix the primer with a mineral spirit or water, use a paint mixing attachment on a drill to ensure thorough mixing.
  6. Wait – Let the primer dry to the surface. With oil-based primers, the drying time is around 24 hours. When dry, the primer should still be tacky but should not leave paint on your fingers when you touch it. Water-based primers take between 4 to 24 hours to dry. The manufacturer will specify the ideal drying time.
  7. Paint – Mix your paint with the correct base and pour it into a roller tray. Paint rollers are a faster way of applying paint to a smooth wall than a brush, and they apply the paint more consistently.
  8. Second Coat – After painting, wait another 24 hours before trying to apply a second coat. Applying the second coat too soon will lift your first coat up and off the surface.

Note: When painting any surface, make sure that it is dry and stays dry while the paint cures. Check the weather before starting, and do not paint in rain or when the humidity is over 75%.

Graham Walsh

I want to share everything I know about home improvement in order to help you. Whether you're a home enthusiast or an industry professional, I have the information that you need.

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