# Applying Polyurethane to Hard Maple



## billjam (Jul 20, 2009)

I have a hard maple highchair that I've almost completed. The plans say to use 3 or 4 coats of polyurethane for the finish. On the polyurethane can it says to use a bristle brush or foam applicator. I had bought an HVLP sprayer from HF for $50. I know that's not going to be a great HVLP as most of the moderately good ones cost $300 and up but I thought I might give it a shot.

My question is, would I be better of just using a bristle brush?

Bill


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## Plastyk (Jul 9, 2009)

I have the touch up gun from HF and use it often. Works just fine so you should be alright. It will still need a sanding before the final coat.


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## Wood4Fun (Aug 29, 2008)

being that varnish is being used, I'm pretty sure sanding is required between all coats, not just the final.... I'm not knowledgeable about spraying at all, but varnish is varnish, no?

Also, taking above disclaimer into consideration, I think you will need to thin before spraying. How much, and if at all, I really don't know


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## billjam (Jul 20, 2009)

Wood4Fun said:


> being that varnish is being used, I'm pretty sure sanding is required between all coats, not just the final.... I'm not knowledgeable about spraying at all, but varnish is varnish, no?
> 
> Also, taking above disclaimer into consideration, I think you will need to thin before spraying. How much, and if at all, I really don't know


The can said to apply at least 3 coats four hours apart and if a coat happens to dry over 12 hours, to sand lightly before applying the next. I wondered about those instructions too. I thought you should always sand between coats.


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## Jim Tank (Apr 28, 2009)

A high chair would be a difficult spray til you get some experience spraying. practice on flat pieces til you feel comfortable with the gun then try some freeform spraying ( like a chair). You will have fun with runs and thick overlaps, but experience will come and you'll never look back and wonder what to do with those brushes. A quality bristle brush will work better on curved surfaces than foam. Some folks love foam, but as it forms around a round leg it will leave less product on the part the foam puts the most pressure on. A bristle will give you a more even coat. Sanding between coats lets you sand down any runs or nits before you have two coats of finish on them. Thinning 3-5% will allow drying sooner, but you still want it hard enough to sand and not be roll boogers of varnish because the finish is still soft. The more articles you read or advice you get, the more confused you'll get cuz methods of applying the same products differ in every shop. Practice alot trying different methods and you will figure what works for you in your shop.


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## frankp (Oct 29, 2007)

Varnish doesn't have to be sanded between coats if you get them on before the layer hardens too much. 

I have no experience with sprayers but people always seem to require thinning agents to get good performance.


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## jerry (Nov 1, 2006)

Any varnish is a mess to spray- it stays in the air quite a while and since it takes some time before it dries it sticks to everything and everything sticks to it. When polyurethane resin is added to the varnish another set of conditions is introduced. Polyurethane varnish has adhesion problems (even sticking to itself) and as the directions on the cans state need to be sanded between coats to give it "tooth" for the next coat to adhere to.

Jerry


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## cabinetman (Jul 5, 2007)

Jim Tank said:


> A high chair would be a difficult spray til you get some experience spraying. practice on flat pieces til you feel comfortable with the gun then try some freeform spraying ( like a chair). You will have fun with runs and thick overlaps, but experience will come and you'll never look back and wonder what to do with those brushes. A quality bristle brush will work better on curved surfaces than foam. Some folks love foam, but as it forms around a round leg it will leave less product on the part the foam puts the most pressure on. A bristle will give you a more even coat. Sanding between coats lets you sand down any runs or nits before you have two coats of finish on them. Thinning 3-5% will allow drying sooner, but you still want it hard enough to sand and not be roll boogers of varnish because the finish is still soft. The more articles you read or advice you get, the more confused you'll get cuz methods of applying the same products differ in every shop. Practice alot trying different methods and you will figure what works for you in your shop.





jerry said:


> Any varnish is a mess to spray- it stays in the air quite a while and since it takes some time before it dries it sticks to everything and everything sticks to it. When polyurethane resin is added to the varnish another set of conditions is introduced. Polyurethane varnish has adhesion problems (even sticking to itself) and as the directions on the cans state need to be sanded between coats to give it "tooth" for the next coat to adhere to.
> 
> Jerry



I agree with Jim and Jerry. Spraying an oil base finish successfully isn't easy. It's heavy and stays wet too long. If you want to use an oil base you could just use an interior varnish. But, for a straight oil base varnish or oil base polyurethane, I would use a good natural hair bristle brush, like Badger hair. 

Practice on a sample that's not flat to get the feel of how wet the brush can be and how to draw out and feather with the bristle tips.


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## Plastyk (Jul 9, 2009)

With polyurethane, brands may vary slightly, there is no need to thin for spraying, no need to wait four hours between coats, and unnecessary to sand between coats.
When spraying, the coat only needs to tack before another coat is applied, so there is a chemical bond instead of a mechanical bond like with sanding. Once the number of coats are applied, let set overnight and give it a light sanding with 400 grit to knock down the dust or whatever has cured in the finish, and spray another coat on.
If you don't start out with runs or sags, this will give a glass finish. As stated already, if you haven't sprayed anything before, practice on some scrap. It will save you a lot of time and aggrivation.


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## billjam (Jul 20, 2009)

Plastyk said:


> With polyurethane, brands may vary slightly, there is no need to thin for spraying, no need to wait four hours between coats, and unnecessary to sand between coats.
> When spraying, the coat only needs to tack before another coat is applied, so there is a chemical bond instead of a mechanical bond like with sanding. Once the number of coats are applied, let set overnight and give it a light sanding with 400 grit to knock down the dust or whatever has cured in the finish, and spray another coat on.
> If you don't start out with runs or sags, this will give a glass finish. As stated already, if you haven't sprayed anything before, practice on some scrap. It will save you a lot of time and aggrivation.


Plastyk: On the can is says to stir and not shake or you will get bubbling. Loosely interpreting what it said on the can to mean the spraying could cause bubbling too (seemed logical at the time), I asked the paint "professional" (??) at HD and she also told me that spraying could cause bubbling so I brushed it on. Sounds like you are having success spraying it on though.

Concurring with you, the can also says no sanding - unless it is left to dry longer the 12 hours. So far, after 3 coats I haven't seen the "no sanding" to be a problem. Tomorrow I will put on the 4th and last coat after sanding with 500 grit.


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## rrobor (Jul 22, 2009)

Learn from my experience on a floor. I went by instructions, 10 hours between coats so did it so that I did a second coat then went to bed, got up and did a third coat. After a few days there were bits I thought needed another coat so did the floor again and it looked great. After a few months the odd bubble appeared and it progressed to a floor that looked like a bad case of sunburn. Do not do as I did


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## billjam (Jul 20, 2009)

*Completed!*

Just to show the "finished" product...

Here's my make shift drying stand










I had conformat screws to put the chair together so I used them to suspend the pieces










As was mentioned to me in this post, corners can be very hard to spray paint. Well, I had goobers just trying to do this piece with a bristle brush! Hard to see in this picture though.









And the final product assembled


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## Jim Tank (Apr 28, 2009)

Looks great ... all you need now is a baby!


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## clarionflyer (Apr 27, 2008)

If it's working good... use it.
There are a gazillion theories and approaches to finishing. Each relys on the conditions.

If you're interested. My favorite, is thinning the poly w/oderless spirits.. add several coats with a good brush. Lightly touch in-between w/fine steelwool. Done in less than a day...


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## frankp (Oct 29, 2007)

BillJam,

Great looking chair. Did you get the plans online or make them yourself? I ask because my son was born 6 days ago and I'd love to build him a high chair that converts into a table, similar to this but a little less "bulky" and more elegant: http://www.healthchecksystems.com/product/?product_id=3611 

Your chair looks like a good start for something like that.


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## billjam (Jul 20, 2009)

No, Woodsmith issue #67. I've had it for years. I think you can order that issue from them but it seems like Woodworkers Supply or Rocker had a highchair plan that looked almost identical.


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## billjam (Jul 20, 2009)

clarionflyer said:


> If it's working good... use it.
> There are a gazillion theories and approaches to finishing. Each relys on the conditions.
> 
> If you're interested. My favorite, is thinning the poly w/oderless spirits.. add several coats with a good brush. Lightly touch in-between w/fine steelwool. Done in less than a day...


How long do you wait between coats?


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