Painting MDF

[Tim Watts]

Sorry for the thicko question:

If emulsioning bare MDF, is it necessary to prime - and if so, just regular primer/undercoat?

Just made some boxing in and it needs to become wall coloured...

Cheers

Tim

[Andy Dingley]

It's a good idea to keep the amount of water down in the first coat, otherwise you get fibres lifting on the surface. You can use MDF primer (cheap enough), or I often use cheap shellac.

[Tim Watts]

Andy Dingley ( [e-mail]) wibbled on Wednesday 19 January 2011

00:09:

"MDF primer" - ah, not come across that before.

Will use that - many thanks Andy.

[Tim Watts]

harry ( [e-mail]) wibbled on Wednesday 19 January 2011 09:29:

Thanks Harry - that makes sense. The edges willl be super sucky, but the almost polished surface I can see behaving like the shiney sie of hardboard.

[sm_jamieson]

A trick mentioned here before is to rub filler into the cut edges of the MDF, else you can get a fibrous sort of effect, especially if MDF has been routed. Simon.

[Andy Dingley]

I often don't care about this, because if I'm making something "MDF like" and I'm going to care about the finish on the edges (esp. if moulded), then I use Valchromat instead of MDF. Valchromat is much the same as MDF, but with a higher resin content and a colour. You get ready-finished coloured surfaces from it (wax polish is useful, but they don't need much else), better moisture resistance, and also a much cleaner edge surface from a router cut.

[Skipweasel]

Depends how sharp your router is! Routed edges paint up nicely provided you rub down between coats, and apply at least three coats - the first two will do a lot of work.

[Mark]

Is it really moisture resistant? I had thought it was just "pimped-up" MDF.

[Skipweasel]

Their website says not.

[Andy Dingley]

No, but it does have better moisture resistance.

You can make wall-hung bathroom cabinets from Valchromat and they'll last. Make them from plain MDF though and they start bulging and flaring at the edges, owing to airborne moisture. Neither stands up to spilled liquid or really high sustained humidity.