How to stop filler showing through paint

Question

I've filled some cracks in the wall and sanded them down but they're still visible through the paint, even after two coats. What am I doing wrong?

Jamie · Accepted Answer

Some fillers will show what’s called ‘flashing’ when painted. This is basically an inconsistency of how the filler accepts the new paint. 
The solution to combat ‘flashing’ is to paint a primer coat over it first and then your finish coats.

Paul · Answer

Seal the filler with a primer or a mist coat and make sure the walls are sanded evenly

Jordan · Answer

Make sure the surface is all sanded down evenly, then I would give it a coat of primer followed by 2 coats of what’s ever paint your using

Benjamin · Answer

Filler shows through because it absorbs paint different or sits uneven

Fix it like this

* Sand it fully flat
* Add a thin second skim if you still see lines
* Prime or use a mist coat over the repair
* Paint the whole wall not just the patch
* Use fine filler or caulk for hairline cracks

Christopher · Answer

Hi there, you need to spot prime the filler before applying your top coats.

Graham · Answer

Generally once you fill and rub down ,Normal procedure is to touch up the filler before you apply your finishing coats . This normally works but you could rubbing it down to the filler again and start again.

Jamie · Answer

Make sure the filler has been sanded nice and evenly to the wall or it may always show but if that has already been done, spot prime the area before painting

Connor · Answer

If filler is still showing through after painting, it’s usually one of a few common issues.

Firstly, filler can “flash” through paint because it absorbs paint differently to the surrounding wall. Even after two coats, the repaired area can still stand out slightly, especially in certain lighting.

A good way to avoid this is to spot-prime the filled areas first before applying your full coats of emulsion. This helps seal the filler and creates a more even finish across the wall.

Another common issue is the repair not being fully flat. Even if it feels smooth by hand, once paint goes on and light hits the wall, slight high spots, edges or dips become much more visible. Using a good filler, sanding thoroughly and checking the wall from different angles before painting makes a big difference.

It can also happen if too much filler has been applied in one go or if the crack hasn’t been opened up properly beforehand. Small cracks often need to be slightly widened first, filled properly and sanded flush once dry.

For the best finish:

* Fill and allow to fully dry
* Sand smooth and feather edges out properly
* Dust off thoroughly
* Spot-prime repairs if needed
* Apply two full coats of quality emulsion

If the repairs are still visible after this, a further light fill and sand may be required before repainting.

Christian · Answer

To prevent this:
Sand the filler completely flush with the wall.
Apply a primer or sealer to the filled area before painting.
Lightly sand again if necessary.
Apply two full coats of paint to the entire wall.
If the repair is still visible, the filler may have shrunk slightly as it dried, leaving a small depression, or the edges may not have been feathered out smoothly enough. Applying a thin coat of finishing filler over a wider area, sanding smooth, and repainting usually solves the problem.

Jason · Answer

Some fillers when painted over take longer to dry. If it's still flashing after the paint as dried then a watered mix of your paint and spot prime the filled areas then a full coat over surface. I usually either spot primer with paint I'm using depending on what it is or I'll use Peel stop to spot primer. 
Sometimes if the filler hasn't been sanded flush and your using a paint with some sheen in it this will highlight the filler as well.

How to stop filler showing through paint

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