Sealing a desk made of MDF with decking oil?

[Mattyess]

Ok. I've had a bit of a look around the net and this forum trying to find an answer to this question, but couldn't find a straight one. So maybe its a stupid question with an obvious answer. But knowing basically nothing about the topic I thought I'd ask you bunch of wise gents.

Can I seal a desk I have built out of MDF with decking oil? i.e Cabots 4L Natural Decking Oil I/N 1523576 | Bunnings Warehouse (http://www.bunnings.com.au/cabots-4l-natural-decking-oil_p1523576)

I really like the plain wood particle finish. I don't want to put a laminate down, I don't want to paint it. I just want it to be reasonably well sealed so that if I spill a beer on it I'm not going to stain it or end up with bumps or just plain ruin it.

After reading some stuff on the forum I think the idea of using a PVA & water mix (1:10ish) to seal the edges is a good idea (after staining it) but I was hoping that maybe 5-10 coats of decking oil would do the job.

Also if this is a suitable(ish) way to seal the MDF, do I need to seal the non-exposed non-visible sides also?

[rod1949]

Yes of course you can.

But if its not moisture resistant MDF then your wasting your money as the standard MDF is like a sheet of cardboard and no matter how well you think you've sealed it moisture including atmospheric moisture will be absorbed swelling the board. This can even happen to moisture resistant MDF. Then you have the structural properties of MDF to consider.

[Master Splinter]

Yes, you can paint a desk with decking oil, but it may not give you your desired performance characteristics (keeping water out). Decking oil is mostly for colour and UV protection of external timber, not waterproofing (it's a water repellent).

I'd suggest either many coats of Minwax Wipe-on poly or a few coats of varnish of the paint or spray on variety. If you are keen for a spray on solution, the cheap clear spray enamel is also a possibility. The original bunnings cafe tables with the hammer icon on them were MDF sprayed with polyurethane varnish.

If you really want to keep moisture out (to the extent you could leave it sitting in a bucket of water for weeks on end) then marine epoxy is the only way to go.

[snowyskiesau]

I built a big desk out of MDF and used a Wattyl polyurethance on it, many coatswith sanding between each.
After 2 years, it'sstill looking good and I live near the water - about 50 metres away.

[Mattyess]

Yes, you can paint a desk with decking oil, but it may not give you your desired performance characteristics (keeping water out). Decking oil is mostly for colour and UV protection of external timber, not waterproofing (it's a water repellent).

I'd suggest either many coats of Minwax Wipe-on poly or a few coats of varnish of the paint or spray on variety. If you are keen for a spray on solution, the cheap clear spray enamel is also a possibility. The original bunnings cafe tables with the hammer icon on them were MDF sprayed with polyurethane varnish.

If you really want to keep moisture out (to the extent you could leave it sitting in a bucket of water for weeks on end) then marine epoxy is the only way to go.

Great, not looking to use this desk in any underwater conditions, so I think water resistant (i.e not harmed by limited exposure to liquid) would do me. So would a varnish like this do me? British Paints 1L Satin Clear Polyurethane I/N 1409647 | Bunnings Warehouse (http://www.bunnings.com.au/british-paints-1l-satin-clear-polyurethane_p1409647)

Is it ok to apply after oiling? As I kinda thought I'd give it a whirl today and put about 5 coats on (looks good).

[Mattyess]

BUMP. Would really like an answer to this from someone who knows about such things. Is it ok to use an oil based clear varnish after decking oil?

[rod1949]

Yes of course you can.

But if its not moisture resistant MDF then your wasting your money as the standard MDF is like a sheet of cardboard and no matter how well you think you've sealed it moisture including atmospheric moisture will be absorbed swelling the board. This can even happen to moisture resistant MDF. Then you have the structural properties of MDF to consider.

I've just realised its a DESK you wanted to seal. My initial read I thought it was a DECK relating it the the use of decking oil:doh:

[Mattyess]

I've just realised its a DESK you wanted to seal. My initial read I thought it was a DECK relating it the the use of decking oil:doh:

Ha! No, If I was going to build a deck, I wouldn't do it out of MDF!

Still need to know if I can apply an oil based polyurethane varnish to seal it properly on top of the decking oil I've used on it now. I suppose I could always ask someone at Bunnings, but its rare for me to actually find someone there who knows anything they're actually selling.

[david.elliott]

for a graphic design studio from MDF and coated with an oil based varnish. Three coats, sand between each. Started showing wear after about 2 years. That's 2 years of use 5 days per week. Quick sand, recoat, all good...You must use an oil based coating though, the water based ones will swell the open cut edges.

Whoops! missed the part about after oiling, I have no idea but I'd suggest not...the whole idea of oil is to protect, so...
Why not have a go on a scrap!

[Mattyess]

Don't really want to buy a bunch of varnish only to find it reacts badly with the oil. Thought someone here would know so I don't have to experiment.

[Master Splinter]

The question is why do you want to oil under polyurethane?

The oil is neither going to improve the appearance or offer any added protection, and there's a chance that it might create problems for polyurethane adhesion. The only thing I'd put under poly is shellac, and even that would be as a sanding sealer.

If you're doing poly, just use poly. Anything additional is a waste of money!

If you want really hard wearing, use a floor polyurethane, but that one from bunnies should be fine (never used that brand, but poly is pretty much poly).

A little scrap bin stool I made from MDF/poly varnish to assist the kids get to bathroom basin height lasted at least six years plus in the bathroom before being retired from use; the only failure point was water absorption where the nails for the rubber feet pierced the varnish.

If you want really, really hard wearing, the two pack 'pour on gloss' type stuff is good (it's epoxy).

EDIT: Ahh, you've already used the decking oil. Personally, I'd leave it at that and call it an experiment. If it turns out that it doesn't do what you want, just chuck the top (it's only MDF, so the top is probably worth less than the finish) and make a new one.

[Mattyess]

Hmm, looks like I should have held off on the oil stain. But just wanted to get the job done before the heat wave set in.

After a bit of a spot test, water does seem to bead rather well on the surface, but after it dries it leaves a bit of a stain. And now after doing some more googlin it seems that poly varnish after oil stainer is a bad idea as it will probably separate after it dries.

About to throw in the towel, put a couple more coats of decking oil on and just accept its going to get messed up and at some point maybe put a laminate on. That is unless some bright spark has a suggestion for something that'll seal it a bit better and stick to decking oil.

[david.elliott]

Hmm, looks like I should have held off on the oil stain. But just wanted to get the job done before the heat wave set in.

After a bit of a spot test, water does seem to bead rather well on the surface, but after it dries it leaves a bit of a stain. And now after doing some more googlin it seems that poly varnish after oil stainer is a bad idea as it will probably separate after it dries.

About to throw in the towel, put a couple more coats of decking oil on and just accept its going to get messed up and at some point maybe put a laminate on, That is unless some bright spark has a suggestion for something that'll seal it a bit better and stick to decking oil.

I reckon you're buggered there too. I'd think that contact adhesive will not stick to the oil stain either....

[Mattyess]

I reckon you're buggered there too. I'd think that contact adhesive will not stick to the oil stain either....

Bugger.

:banghead:

Guess I really stuffed up.


Well I'm NOT going to replace the top. Its 3m long, I've routed the edges, countersinked all the screws and filled them and made the joins almost invisible. It looks fantastic. Just hope it'll stay that way.

I'm super surprised that there is nothing that would stick to it. It feels dry and like it would absorb another 20 coats of oil or anything else.

[Master Splinter]

The problem is you can never really tell what 'out of recommended use' things are compatible till you try 'em.

You could just throw a clear vinyl tablecover over it; it's about $10 a meter off the roll.

[Mattyess]

The problem is you can never really tell what 'out of recommended use' things are compatible till you try 'em.

So you're saying that the poly might stick?

[Master Splinter]

It might stick permanently and very well and you'll never have any problems with it; it might stick initially but start delaminating after a week/month/year, or it might - after a week or two of looking perfect - suddenly revert to being a gluggy, sticky mess which has to be removed with a scraper and the sort of effort only justified by a substrate as expensive as a granite top.

There's no way of knowing - short of immediate and calamitous failure - how the chemistry of the two finishes will react over time.

Even well researched, designed-to-be-compatible paint systems can have problems - just look at your nearest car park and count the number of cars where the clear coat has broken down and is flaking off.

[Mattyess]

It might stick permanently and very well and you'll never have any problems with it; it might stick initially but start delaminating after a week/month/year, or it might - after a week or two of looking perfect - suddenly revert to being a gluggy, sticky mess which has to be removed with a scraper and the sort of effort only justified by a substrate as expensive as a granite top.

There's no way of knowing - short of immediate and calamitous failure - how the chemistry of the two finishes will react over time.

Even well researched, designed-to-be-compatible paint systems can have problems - just look at your nearest car park and count the number of cars where the clear coat has broken down and is flaking off.

Fair point.

Well I decided that a calamitous failure was a risk I was willing to take, as the oil had left the MDF feeling a little fuzzy, only slightly water resistant and any liquid that touched it would stain it. I went to my local paint store and the guy adivsed me that if it can still absorb water, then it should be able to absorb water based poly.

I've just chucked the third coat on it and it looks good. I just have to cross my fingers now and hope that it doesn't do as you mentioned and turn into some sort of hideous mess a day after I install it my studio and rest 5 grand worth of equipment on its surface.