Applying Clear Finish To An Interior Birch Door


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Old 01-01-15, 09:43 AM
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Applying Clear Finish To An Interior Birch Door

I have a new birch hollow core interior door that I would like to just clear and keep natural looking.

What products should I use and what procedure should I follow to accomplish this?

I've never worked with birch wood and would appreciate any advice.

Thank you
 
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Old 01-01-15, 01:10 PM
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Are you trying to match the finish on any other birch doors?

Basically all you do is make sure the door is clean and lightly sanded then apply 3 coats of poly or varnish [sanding lightly between coats] Oil base varnish/poly will deepen the colors in the wood a little give it an amber tint. Water based varnish/poly goes on a little milky but dries clear. They don't alter the appearance of the wood any other than to give it a sheen.

Always sand with the direction of the grain, same thing for applying the poly.
 
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Old 01-01-15, 02:58 PM
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Are you trying to match the finish on any other birch doors?
No, I'm not trying to match to any other doors. Its just a single bathroom door in the basement.

marksr, thanks for your response.
 
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Old 01-01-15, 03:01 PM
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It would be a good idea to apply a coat of poly to both the top and bottom edge. That makes it harder for the door to absorb moisture - it will last longer and be less likely to stick when the humidity is high.
 
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Old 01-03-15, 03:36 PM
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I need some more advice.

I decided to go with a water based product and purchased Zar's Aqua semi-gloss clear poly and after light sanding with 320 I applied the first coat to one side of the door.

I applied it with the grain as suggested using a 2 1/2" wide polyester brush going from side to side to avoid dry edges and lap marks which seemed to work fine.

However, once it dried, I could still see where each brush stroke started or stopped. I could see it as I applied it but figured those areas would level out as it dried like I've experienced with oil based poly. So I'm wondering if I used the wrong brush, or wrong technique or if this is a characteristic of the first coat of water based poly and will disappear after it is lightly sanded and a second coat is applied?

I would appreciate some professional guidance before I go any further.

Thank you
 
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Old 01-03-15, 06:06 PM
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Poly needed a natural hair brush.
Should have been applied with the grain.
 
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Old 01-04-15, 03:35 AM
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You don't use a natural bristle brush with any water based coating! the water will make the bristles swell and the brush unusable except as a duster. A polyester, nylon or polyester/nylon blend is the type of brush you need to use with a waterbased poly. There is a big difference between the quality brushes and their cheap counterpart.

It should look a lot better after the next coat. It generally takes 3 coats of poly to get a nice finish. 320 grit is too fine. I normally use 150 grit for the initial sanding and 220 for sanding between coats of poly. I've never seen a need to use sandpaper finer than 220 grit on any wood finish.
 
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Old 01-04-15, 04:43 AM
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Is the lower quality brush that I used for the first coat the primary reason the beginning and end of the brush strokes appeared?

I'm going to buy a much higher quality brush for the subsequent coats. Can I presume a polyester, nylon or polyester/nylon blend brush from Purdy or Wooster would be fine?

marksr, thank you for your expert advice which is always spot on.
 
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Old 01-04-15, 05:09 AM
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I've always been partial to Purdy brand brushes While I use Wooster roller covers and have used their natural bristle brushes a lot, I don't recall using their latex brushes .... but would expect them to be good quality.

Without being there to inspect both it would be hard to say if the brush or technique caused your issue.
 
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Old 01-05-15, 09:18 AM
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It's also possible to over brush poly - it doesn't have a workable surface for long - and that can leave brush marks.

Not a real problem until you get to the final coat, though; as long as you're scuff sanding between coats I don't think the brush marks will show through the next layer.
 
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Old 01-05-15, 02:16 PM
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Here's an update.

I bought a new 2 1/2" Purdy medium-stiff polyester brush to apply the second coat of Zar poly on with.

After light sanding with 220 I tried to carefully brush the poly on with the new brush and although it looks better I still have noticeable areas where the brush stroke starts or stops, however there are no brush marks. Perhaps its my technique that's the problem. I'm trying to work fast and not over brush this finish but it seems like every place I put the brush down after dipping the brush in the container for more finish I'm leaving a small buildup which is what is showing up after to dries. So should I being brushing that small build up out more without over brushing the poly?

I must confess, I'm not sure I like this Zar product. I've built hardwood furniture and used General Finishes wipe on Arm-R-Seal poly with impressive and perfect results and probably should have used it on this door.

Is it too late to switch topcoats from the water base Zar to Arm-R-Seal oil? If not, what steps should I follow?

Thank you
 
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Old 01-05-15, 02:56 PM
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I don't know if a wipe on poly will do ok over the waterbased or not
You might thin the poly slightly. That will make it flow a little better and should make it easier for you to keep a wet edge.
 
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Old 01-06-15, 08:11 AM
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No experience with ZAR (I use Minwax) but I agree adding a little water sounds like a good next step.
 
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Old 01-09-15, 11:36 AM
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Targa:

I would go to a Wipe-On oil based polyurethane now, even though the existing top coat is a water based product. The oil will stick well, but it's never a good idea to apply a hard coating (the oil based poly) over a soft one (the water based clear coat). Still bathroom doors don't have to stand up to rough service like shelves do, so I would just switch to an alkyd based wiping polyurethane now to get a smooth coat.


I'd buy new polyurethane if you want good results. My experience has been that old Wiping Poly dries too fast and the result will be that you'll end up with rough areas where wiping on the poly mucked up the poly that was partially dried.

If you opt to sand down the existing water based clear coat, sand very gently if this is a hollow core door. Hollow core doors have a cardboard reinforcing inside them which will result in the water based clear coat being sanded down more wherever the veneer is supported by cardboard, and that could lead to blotchy results when you wipe on the alkyd based poly.
 
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Old 01-09-15, 04:12 PM
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After I wasn't satisfied with the result of the second coat after very carefully applying it with a $18.00 Purdy polyester brush I decided to call customer service at UGL the parent company of Zar brand products.

The rep I spoke with suggested adding a 1/4 cup of water to the remaining 3/4 quart of Aqua poly I had left, sand with 150 the noticeable areas where the brush stroke start and stop buildup appeared and to switch to a foam brush which I did. When I asked, the UGL rep also stated I could not apply an oil based product over their Zar Aqua and expect favorable results. They said I needed to remove all of the Aqua in order to apply any oil based product to the door which of course I decided against.

I applied two additional coats with the thinned poly and a 4" foam brush and the result is noticeably better. Not good enough for me to apply the Aqua to the outside of the door but acceptable enough to leave it on the inside surface.

Now I plan to finish the outside of the door with General Finishes Wipe on Semi-Gloss Arm-R-Seal oil based poly which I've always had great results with.

Thanks everyone for your comments and suggestions.
 
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Old 01-10-15, 03:57 AM
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Just so you know, the oil base finish will likely deepen the colors naturally in the wood which means the exterior side of the door may not look the same as the other side.

I'm a little surprised that they recommended thinning the poly that much. Generally manufactures frown on thinning their coatings more than 10% .. I never cared for foam brushes but if it works for you ...
 
 

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