Need some finish advice on a desk
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- This topic has 21 replies, 5 voices, and was last updated 8 years, 7 months ago by Salko Safic.
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15 September 2015 at 6:30 am #130499
Hey everybody 🙂 I figured I’d ask some questions this time BEFORE I get myself into trouble. 🙂 I’m about to refinish a computer desk for my girlfriend and was wondering what the best finish choice would be for the desktop itself. She wants a good durable finish that will protect from water rings, permanent marker, etc. (basically, a kid-proof finish)
I was thinking about using polyurethane over BLO, but I’m not sure if it would be durable enough to be “kid-proof”.
I’ve got it sanded down to 120-grit for the moment, because she was talking about painting it at first until I showed her what the underside of the top looked like with a little BLO rubbed in; she loves it. The main desktop and hutch are made from solid wood (although, not just one species. It looks like they made it from several scraps of different light-colored woods and press fit them all together) and the cabinets underneath are hardwood-veneered plywood.
Any and all suggestions and recommendations would be greatly appreciated 🙂
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You must be logged in to view attached files.15 September 2015 at 6:31 am #130504Hey everybody 🙂 I figured I’d ask some questions this time BEFORE I get myself into trouble. 🙂 I’m about to refinish a computer desk for my girlfriend and was wondering what the best finish choice would be for the desktop itself. She wants a good durable finish that will protect from water rings, permanent marker, etc. (basically, a kid-proof finish)
I was thinking about using polyurethane over BLO, but I’m not sure if it would be durable enough to be “kid-proof”. I was also thinking about shellac, but I’ve never used it at all before, and I don’t know if this would be the best project to try it out on.
I’ve got it sanded down to 120-grit for the moment, because she was talking about painting it at first until I showed her what the underside of the top looked like with a little BLO rubbed in; she loves it. The main desktop and hutch are made from solid wood (although, not just one species. It looks like they made it from several scraps of different light-colored woods and press fit them all together) and the cabinets underneath are hardwood-veneered plywood.
Any and all suggestions and recommendations would be greatly appreciated 🙂
- This reply was modified 8 years, 7 months ago by George Fulford.
15 September 2015 at 7:35 am #130506If you like to use BLO you can and then add some poly over the top but you must allow the BLO to cure before adding poly. The curing rate is 4 weeks. Here is the run down on poly choices. Water based poly will not darken the timber it will retain it’s natural colour however oil based poly will add a yellow/orange colour and will darken over time, so you could consider that before you apply BLO. Poly is plenty strong enough to with stain against moisture, scratch, heat, water stains etc and is easy to apply with a brush because it’s slow drying. You can thin it and make it into a wipe on poly which will give you excellent results but you will need to apply several coats to build it up. Always remember because it’s slow drying dust will settle on it and create little nibs so you have to sand in between coats and not sand the final coat. This is regardless whether you use a wipe on or brush.
The other thing you have to keep in mind if your using an oil based poly is that it can take on a plastic look if you apply too many coats and don’t forget about the colour change as well. None the less it is a very durable finish.
If you choose to brush it on using full strength poly will leave brush marks but that’s ok in the beginning because you probably want to built up the coats quicker you want to sand the last coat and then apply a couple of coats of thinned poly because thinned poly will give you a brush free mark results. Lastly on oil based polys if the temp is low it will dry very slowly, you could turn the heater on to heat your room or place heat lamps on it. The drying process can take upto a week.
Water based finishes are not as solvent resistant nor are they scratch resistant nor heat resistant like oil based poly. They dry fast so yo have to work fast and you should wait several hours of drying time before applying the next coat. You could on a pleasant day finish it one day. Because of the fast drying action if you use a brush I think you will find great difficulty in using it mainly because you are using it on large surfaces. However again because of the fast drying action dust nibs are greatly reduced. It’s easy to clean up your brushes using water which is also a nice advantage over oil based poly.
To finish this off without turning it into a book you could opt out on brushing altogether by using an aerosol spray and avoid brush marks. They work like any professional spray gun but without the equipment the only downside is they are expensive. I did try out an aerosol spray called cabothane clear by cabots and also clear gloss by dulux and I found cabots to give a beautiful finish the best I have ever seen but the drying time was 24 hours as opposed with dulux touch dry within 10 mins but the results are no way near as good.
You have a lot to think about but your best bet after everything I said if you want to avoid brush marks and runs is to use a wipe on poly, you can buy the minwax version and apply 6-8 coats or at least until you think it’s enough.
I personally use shellac but I make clocks so i don’t worry about water stains or beverage spills but there is a new product out by ubeaut in Australia he’s a genius and a character. He developed a new type of shellac it has all the fast drying properties of shellac but with the durability of poly. Now you can’t get any better than that.
Happy painting whatever you choose.
Hope this helped.
15 September 2015 at 4:01 pm #130511Maybe something like a wiping varnish that Bob Flexner talks about. His books are very good in regards to finishing. His book Wood finishing 101 is nice.
16 September 2015 at 2:47 pm #130546Thanks for the replies 🙂 I put the first coat of BLO on the desktop yesterday.
Salko, Thanks for the tips. One question though. What will happen if you put the poly on before the BLO cures? I knew you had to wait for the BLO to dry for a day or so before you coated it, but never heard about a 4 week cure time. I’ve done this on smaller projects and didn’t seem to have a problem.
David, thanks for the lead on Bob Flexner. Never heard of him before. You’ve given me some good late night reading 🙂
Dan, much like my own childhood, coasters soon become ninja stars or frisbees. lol
16 September 2015 at 3:07 pm #130547All oils take 4 weeks to cure they seem dry on top but internally it isn’t much like shellac you’d think it dries very rapidly surface wise and that’s true but internally it hasn’t cured. The correct drying times between coats with shellac is 7-10 days sounds a lot but that’s how it is. So to answer your initial question your poly will either cure very slowly or not at all. Some people said nasties can happen just what nasties not a words been mentioned so I take it they’re parroting someone else without questioning. I have many of times applied 100% tung oil left to dry overnight and then applied shellac over it, nothing happened even though the consensus is tung oil should be left 3 days to dry before coating with more oil or some other type of finish. Who knows maybe in 10 years something will happen till then I honestly don’t know.
Just to leave you with a thought, so called danish oil where they got that name from beats me is nothing more than BLO, denatured alcohol and poly. The poly serves as a drying agent and adds a small amount of sheen. If the poly that is mixed in with BLO can cure then why can’t it cure with BLO that has dried overnight. I reckon and I would bet either way it would still take 4 weeks to cure even though it’s touch dry on the surface.
Hope this helps.
Salko,
Just a couple of points.
The BLO cures by reacting with the Oxygen in the air, ditto Alkyd varnishes.
The Poly cures by reacting with the moisture in the air.
Both are diffusion limited reactions.
I agree that once the carrier solvent has evaporated the two should be compatible.
Danish oils do not contain denatured alcohol(not compatible with either the BLO or Poly) but use an Aliphatic solvent like Mineral Spirits as the carrier/viscosity reducer. This allow the “resins” to be carried into the wood pores where it cures.
Some formulas use the BLO with a solvent Alkyd varnish instead of the Polyurethane.
There are quite a lot of commercial variations available and it’s not hard to mix up your own combination if you wish.
Because of the VOC restrictions it’s becoming harder to find the solvent borne Alkyds and Polyurethanes since most manufacturers are switching to waterborne formulations.
Best,
Craig16 September 2015 at 10:16 pm #130560So I should be ok if I left it to cure for a week, then put the poly on? If anything goes wrong in 6 months or a year ( or 10 years) I can always blame it on the kids again 😀 lol
16 September 2015 at 11:02 pm #130565Thanks Craig for those points when I typed denatured alcohol I was at the time thinking about shellac it was an error on my part ad why I do that beats me so yes it’s true mineral spirits is what I should of said. I normally use citric solvent in my batch because it’s natural and has a pleasant smell.
I still stand on my point that it does take 4 weeks to fully cure which you can research if you like and find this to be the case. You have made though very valid points and I agree with what you have written besides the curing rate.
17 September 2015 at 2:12 pm #130593Craig I think working till midnight is starting to take a toll on me having reread what you have written I cannot find that you disputed the curing rate, what made me think you did bewilders me. I think I need to step down a bit I’m starting to hallucinate words that do not exist.
17 September 2015 at 2:37 pm #130594Well, I’m really confused now. I did some more research and I’m getting conflicting advice. Some say to wait the 4 weeks for the BLO to cure, others say that it’s ok to wait 3-4 days until the BLO is surface dry, sand lightly, then go over with a 50/50 thinned oil-based poly. Still others say wipe on a 1/3-1/3-1/3 mix of oil-based poly, mineral spirits and BLO (from what I’ve read, also, the proportions aren’t critical). The only thing I’ve read so far that is a big no-no is to use water-based poly over the BLO.
17 September 2015 at 2:45 pm #130595In my opinion….I would never use straight oil. It doesn’t dry. I can’t wait weeks. A straight oil finish has no scratch resistance properties, and I think the original object was a desk . The blend of poly/mineral is a wiping varnish that works well. The poly/mineral/blo is just making your own “danish oil”. Straight blo, or tung oil wont dry or if it does it takes week. I highly recommend Flexner’s small book finishing 101.
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