Why does filler keep showing through paint?

Question

I've patched a hairline crack in the wall twice and it keeps coming through the paint even after two full coats. Is this a priming issue or am I using the wrong filler?

James · Accepted Answer

It could be down to a few reasons.
1. Poor quality paint.
2. Some Fillers are highly absorbent so the paint soaks in more making the filler stand out.
3. If the area is not sanded completely flat with the surface then the light will hit it differently and make it more noticeable.
4. Filler has not been primed prior to painting. ( although some fillers say they won’t ‘flash’ they usually still do. So a spot primer will help and create a more uniformed look.

Hope this helps

Abdallah · Answer

It is an annoying problem.
Perhaps you didn't let the filler dry completely, or you didn't sand it down fully.

Saer · Answer

If the filler is still showing after two coats, it's usually because the repair has shrunk or flashed. Lightly sand the area, apply a quality primer/sealer, then repaint. If the crack is reopening, use a flexible filler and reinforce with scrim tape before repainting.

Izmir · Answer

It generally needs two to three coats of painter before the filling vanishes

Clifford · Answer

Hi ideally use a filler that doesn’t flash, also when you have prepared the cracks, filled them etc give them a good rub down and blot them out with the colour you are using allow to dry, then apply two coats.
Regards
Cliff

Wayne · Answer

I am assuming you are using a cheaper brand of paint? Trade paint or better would be a good starting point or is it something bleeding through? Nicotine r damp? Efflorescence?etc

Ankit · Answer

It's usually a priming issue. Many fillers are porous and absorb paint differently, causing the patched area to "flash" or show through even after two coats.
What to do:
Sand the filler smooth.
Apply a mist coat or a stain-blocking primer to the filled area first.
Then apply your top coats.
If the crack itself is reappearing (not just the patch showing), use a flexible decorator's filler/caulk instead of a standard filler, as the wall may have slight movement.

Paul · Answer

For best results run a Stanley knife into the hairline cracks so you open it up then fill it then sand it flush after then apply paint

Keith · Answer

If it’s a plaster wall it could be many reasons movement in the wall 
If the crack becomes larger over time a structural engineer would be adviseable
If it is a minor crack it may be worth scraping both side and fill, put some plasterers tape over the crack and skim over

Stephen · Answer

It only shows through on the first coat. If its dry give it a 2nd coat. All fullers need at least 2 coats.

Why does filler keep showing through paint?

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