MDF sunken joints

[tedtargett]

I'm having some urgent issues with the MDF walls for my gallery. Once painted 5 times, the wood filler join lines are appearing on some walls and not in others. I'm going to eventually plasterboard them, but want a quick fix to conceal the lines for two months. Will poly filler or wood filler do then sanded, painted?

 

[opps]

Which filler did you use previously?

The gap only looks to be 0.5mm deep. I would recommend either Toupret Redlite or Red Devil OneTime.

Flush fill and then give it a light sand using 120-180 grit Mirka Abranet paper using a sanding block. Tap the abrasive from time to time to dislodge the dust.

The filler is very soft, and shouldn't be difficult to sand. If you sand carefully, you shouldn't cut through the existing paint. Unlike powder based fillers it will be slightly flexible and should cope with the expansion/contraction of the MDF in the short term.

 

[tedtargett]

Thank you so much! This is super helpful

 

[opps]

Thank you so much! This is super helpful

We are here to help people- and other members help us when we ask questions.. Looking at the shrinkage in your photo, it looks like someone used caulk as the filler, which would explain why it shrunk back.

The recommended fillers, as I mentioned earlier, will tolerate a very slight degree of movement. I don't see why you think you need to apply plasterboard over the top. You risk very tiny hairline cracks (that can be filled with emulsion paint as and when they present).

1000/1200 grade lining paper over the MDF will deal with tiny cracks and is much, much cheaper than plasterboard and a skim coat.