Suggestions for porch furniture finish

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Dorm

New User
Dorm
First off ... I am an experienced woodworker, but my knowledge when it comes to finishing is scant. Most of the work I've done in years past involved painted surfaces, and I struggle with staining, clear surfaces. I'm fairly ignorant of the good practices or processes involved to get hi-quality finishes with urethane or especially lacquer.

And so, I need some help with some items I built last year for our screened porch. This week I looked a bit closer at them ... mainly the finish. The items were natural finished using BLO and a clear, oil based finish - likely it was a Min-Wax or similar urethane. And with this, there were a couple of issues I'm concerned about.


  1. Some black spots appeared beneath the urethane a few weeks after completion (see below)
  2. Longevity ... I can start to 'feel' the grain, which was no so much the case when the stuff was first finished.

The process I used was to finish these was wet-sand the wood with BLO and 180g paper and finish off with urethane. The BLO wet-sanding did a great job to smooth out any raised grain; the oil soaked into the wood and gave it a really nice tint. I wiped on the oil-based poly; let it dry; light sanded and applied one more coat. I'm wondering if the black spots could be mold ... could this have formed and grown after I applied the urethane? If so, this leads to - should I nix using the BLO to wet-sand the material with? Is there a good substitute that doesn't promote mold or mildew? If not - what's the cause for the black spots? Any other suggestions or ideas on what the spots might be?

Lastly, for furniture that's going to live in this type environment - what is the best finish process to do? What finish will have some longevity to it? And to clarify "environment" - I mean a screen porch, under a roof where the stuff is not exposed to full-on rain, but totally subject to cold, moisture in the air, humidity, heat, dust, wind, et al.

Thanks in advance for your input.

Ciao ... Dorm

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chris_goris

Chris
Senior User
First off, was this wood kiln dried?. It looks like red oak?. r]Red oak is very open grained and it sounds like maybe it is mold, possibly wasn't dry when it was top coated?. For me, I would use white oak for outdoor furniture (think whiskey barrels!). As for something new, I would probably use Spar varnish Or Sikkens Cetol as a top coat over the white oak.
 

Brantnative

Jeff
Corporate Member
What did you use to wet sand? If it was steel wool the black spots could be small particles of iron interacting with the tannins in red oak.

I've recently finished some outdoor furniture mad of cypress using the Waterlox marine sealer and satin finish. It's only been a few months but it's holding up out in the rain. I've no experience yet with the hot summer. My only concern was that it yellowed the wood quite a bit. Still looks good but yellow. I used a sponge backed sandpaper between coats.
 

Skymaster

New User
Jack
Sorry but +1 on mold. Since blo is organic it might be the cause. First exterior finish that is tuff and long lasting the one we hate; Paint. UV is the killer for exterior finishes.
+1 on white oak Red oak is a no no for exterior. Sikkens are the best finishes money can buy and bring plenty with you :}:} Marine Varnish has special UV inhibitors in it. Your best option is to;Sand down to raw wood, find a fungicide that will kill that mold, you are seeing only a tiny bit of it on surface, quite a bit more internally. Cypress is a fantastic exterior wood most just let it age on its lonesome, it turns light grayish. Any exterior finish you put over wood begins a maintenance program,tho high dollar, marine finishes will give the most time between re coating, I include sikkens in that.
Sikkens is the common finish on million dollar log homes for that very reason.

https://www.homedepot.com/b/Paint-Exterior-Stain-Waterproofing-Wood-Deck-Stain/Sikkens-ProLuxe/Semi-Transparent/N-5yc1vZbbbmZewdZ1z10m0l

[url]http://www.wood-deck-stain-finishes.com/Exterior-Wood-Finishes.php

[/URL]
 
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Jeff

New User
Jeff
My only concern was that it yellowed the wood quite a bit. Still looks good but yellow. I used a sponge backed sandpaper between coats.

Tung oil and BLO is naturally yellow in color and cypress is a light colored wood so that yellow color is typical. I've used Waterlox Original Sealer/Finish but not their Marine products.
 

Jeff

New User
Jeff
+1 to Jack's comments.

Also, Epifanes Marine Spar Varnish is excellent. It won't crack or peel because it's flexible and allows the wood to expand/contract with changes in the humidity and temperature. Polyurethane is a very poor choice for an exterior wood finish because it's hard and brittle so it'll crack and peel; also offers little protection to exterior furniture even though sheltered in a screened porch.

Here are some cypress planters about 7 years ago and they were left unfinished intentionally and now they're a weathered pewter gray color.

P5070121.jpg

 

Dorm

New User
Dorm
Great info and thanks. Is there a good oil or other to wet sand the wood with? I know BLO sort of encourages mold growth so what other oil could I use to sand with ? I’d rather not use water or water based finishes. However, if there are good water based products for this application let me know please.

Ciao ... Dorm
 

Jeff

New User
Jeff
Great info and thanks. Is there a good oil or other to wet sand the wood with? I know BLO sort of encourages mold growth so what other oil could I use to sand with ? I’d rather not use water or water based finishes. However, if there are good water based products for this application let me know please.

Ciao ... Dorm

I understand the purpose of wet sanding but most furniture doesn't need it even for interior use and French polishing. So why are you wet sanding porch furniture? I'm just curious why you're persisting with wet sanding anything.

But if you must...... Mineral spirits is fine as a lubricant for wet sanding.
 
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Dorm

New User
Dorm
I understand the purpose of wet sanding but most furniture doesn't need it even for interior use and French polishing. So why are you wet sanding porch furniture? I'm just curious why you're persisting with wet sanding anything.
[/QUOTE

Silly me I guess, but when anything 'wet' is applied to the red oak, the grain is raised and it just doesn't have the waxy smooth finish I'm trying to get. Regardless of whether is porch furniture on interior furniture ... I have my standards of quality. I may not know how to get there, but I know what I want :).
 
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