Best MDF edge sealer?

[mrgazer]

Hello all.

Just wondering what you guys do to seal up the edges on mdf?

So far, I have seen:

-Undercoat primer
-wood filler
-PVA with water

THere are a lot more but I forgot what they are now..

Also, found this vid on youtube, looking at 4:31 - that stuff looks pretty amazing. What's everyones video on this?

I have to say that my MDF's edge are very rough. Unlike what he was holding at 4:31

If everyone could shed some lights. then that would be great.

 

[nickjb]

Liberon sanding sealer is very good. Or just use valchromat instead of traditional mdf.

 

[foxhole]

I have used danish oil, seals without making the edge fluffy and then takes paint well.

 

[Deleted member 174758]

I have to say that my MDF's edge are very rough. Unlike what he was holding at 4:31

You need to get a good edge before doing anything else and for an edge with a profile (e.g. round-over, cove, ovolo, ogee, etc) I'd recommend MR-MDF (green core) over ordinary MDF any day. To start off getting a good edge finish you need a smooth cut- so your saw needs to be either a table saw or a portable saw running on a guide (this can be home made). Next you need a finer tooth blade than the one hich came with your saw - so for a 190mm saw that would mean a 48 to 60 tooth blade (160mm requires 48 teeth, 250mm 60 to 72 teeth and so on). The teeth of your blade msut be sharp; you'd be surprised at how quickly a blade can go off, but a sharp blade with the right number of teeth gives a far better finish than a blunt, low tooth count rip blade. Having dust extraction on the saw (a vacuum cleaner) will also improve the quality of the cut a bit. Lastly, before sealing, the edges need to be sanded - start at 100 grit (if you've made a decent quality cut) and work up through P120 - P180 - P240 - P320. vacuum (or at least dust off) the edge then wipe off with a clean, soft cotton rag (well washed old T-shirt) dampened (not soaked) with white spirits and leave to dry for 10 to 20 minutes until all the white spirits have evaporated. As you are then starting from an excellent surface rather than a very rough one it will be far easier to seal and finish the edges properly with almost anything from Zinsser BIN to thinned dewaxed white (blonde) French polish. The real key isn't a magic formula to apply to a crap surface - it's a decent surface to start with. So as they say in the military, PPPPPP (or Perfect Preparation Prevents **** Poor Performance)

BTW as others have intimated, water based sealants tend to raise the grain and require more work than solvent based ones. Either way the best surfaces are always going to come from several (3 to 5) coats of sealer which as denibbed and flatted back between coats with a fine sanding paper (P240 - P320). This is how furniture manufacturers can get excellent finishing on such a manky material as MDF.

Your finish can only ever be as good as the underlying surface quality and the preparation work you do - and nobody ever got a good finish without a bit of work

 

[mrgazer]

Many many thanks for the advice!

Am I correct in saying that my edges are too badly cut?

And what am I best off to do? Get them cut again? It is a good 4 metres of mdf I will need if this is the case

Is there any way round this?

 

[mrgazer]

 

[Deleted member 174758]

Am I correct in saying that my edges are too badly cut
And what am I best off to do? Get them cut again? It is a good 4 metres of mdf I will need if this is the case

Probably. The outside edges as they come from the mill are sometimes shocking and it can be necessary to make what is called a "dust cut" to start with before doing any dimension sawing - not that the average muppet in a DIY warehouse would understand this

Is there any way round this?

Actually yes. You can sand the rough edges, starting with a P80 grit or even a P60 grit sanding board. Basically a sanding board is a piece pf 12 to 18mm thick MDF or plywood which has aluminium oxide sand paper attached to one side using spray contact adhesive. I used to keep a selection by my bench in the days when I worked on the bench regularly, from P80 up to P320, typically 200 to 250mm long x 70 to 100mm wide (and made from scrap offcuts). If I needed to ensure that I sanded edges bang on square and without dubbing over I'd sometimes add a "squaring fence" - or simply a piece of planed, square edged timber, 2 x 1in or 2 x 2in. The result looked something like this:



The red bit (meant to represent sanding paper) runs against the edge, the block against the top face of the material. Simples!