Sealing MDF

[Eric The Viking]

This isn't really finishing, but it seemed like the most appropriate place to ask:

I'm doing a few melamine-faced MDF jig projects at the moment, including a pillar drill table, and have had some issues with MDF sagging and swelling at the edges as it absorbs moisture. These are workshop items only, so I need durability over looks (it's the story of my life really, well, looks would've been useful too, I guess... ).

Anyway, enough of dimly-remembered teenage angst! I could do iron-on edge banding, but I'd prefer to round-over the edges for practicality, as in my experience the banding doesn't take knocks very well, and rounded corners are less likely to damage workpieces.

So, for coatings, I've got:

-- one-part polyurethane yacht varnish,
-- water-based and traditional glosses,
-- "MDF primer/undercoat" (B+Q's finest--don't ask!),
-- loadsa-PVA, of the standard sort (could thin it),

and probably a few other unlikely alternatives like cellulose spray paint and Hammerite 8). I could go shopping too, but the budget for this is really what's on the shelf, unless there's a huge reason to spend money.

I almost forgot - it's got to stick reasonably well too. The MDF primer doesn't seem to adhere at all well, so that won't really do for things that will get knocked all the time (yes I can gloss over it, but if the foundation doesn't stick, that probably won't help!).

So, what's the best sealer to use, that will keep moisture out and won't swell the fibres as it's applied? And anyone who's got an elixir-of-life-and-eternal-youth that works, please send me a PM...

 

[Paul Chapman]

I've made a lot of MDF jigs and workbenches. I always lip the edges with softwood (fitted with biscuits). For something like a shooting board, I just wax it

If it's going to get wet or get any oil on it, I varnish it (NOT water-based varnish).

This way I've never had any problems with moisture or swelling and the items last for years

Cheers :wink:

Paul

 

[Eric The Viking]

I've made a lot of MDF jigs and workbenches. I always lip the edges with softwood (fitted with biscuits). For something like a shooting board, I just wax it...
... If it's going to get wet or get any oil on it, I varnish it (NOT water-based varnish).

This way I've never had any problems with moisture or swelling and the items last for years.

Thanks Paul.

It makes a lot of sense. I think Polyurethane's the way to go for the small/light use stuff, and edge lipping for the more used items. I can do biscuits, so that should do it. I'll experiment with the Poly, to see if it causes swelling.

Many thanks for the advice.