What happened to my park bench?

[Don Farr]

I completely reworked this park bench last winter. All new Cyprus slats and stainless hardware with a least four coats of Poly. I bet Jim Becker remembers seeing the post when I finsihed it.
It was a gift from my mother in law and the LOML is really upset. This is not just on the surface, it's down in the finish.
what do you guys think?

[Dave Dionne]

Hi Don

This is only a guess but did you seal the ends of the slats also? Looks like a chemical reaction, And I bet the ends of the bench are cast metal. Could be that when it rained the metal leached and mixed with the tanins (sp) in the Cypress.

Just a guess though I am not an expert, but I am married to a chemist.

Dave Dionne

[Carl Eyman]

I believe that poly's lack of resistance to sunlight is the problem. Even the cans that say they contain ultra-violet blockers don't work in my experience. After you have removed all those slats, sanded or planed them down, try spar varnish. Also, in my expereience, cypress seems to be more prone to this sort of problem than some other woods - mahogany, for instance.

[Don Farr]

Hi Don

This is only a guess but did you seal the ends of the slats also? Looks like a chemical reaction, And I bet the ends of the bench are cast metal. Could be that when it rained the metal leached and mixed with the tanins (sp) in the Cypress.

Just a guess though I am not an expert, but I am married to a chemist.

Dave Dionne

Yes Dave I did. In fact I dipped the ends of the slats into the can of Poly and let them dry before I assembled the bench.

[Don Farr]

I believe that poly's lack of resistance to sunlight is the problem. Even the cans that say they contain ultra-violet blockers don't work in my experience. After you have removed all those slats, sanded or planed them down, try spar varnish. Also, in my expereience, cypress seems to be more prone to this sort of problem than some other woods - mahogany, for instance.

Never thought of UV damage. The bench was facing west, so it got a lot of afternoon sun.
That makes good sense because when we first noticed it, the bench was under a oak tree. I moved it out in full sun thinking that maybe the tree was causing it. It got worse.

[Glenn Clabo]

Don,
I agree with Carl. Spar varnish is the only thing that really works up here by the ocean. I finished the cedar slats on the old bbq 4 years ago and they still look like new. Poly can't take the sun and water near as well.

[Jim Becker]

What happened is you used a film finish...and water got under it. The comments about UV are very important. Poly is actually not a good choice for outdoor projects. If you want a clear coat, some of the experts on another forum dedicated to finishing report that exterior oil tint base has all the additives but dried clear. Personally, I don't put anyting on cypress and just let it grey naturally.

[Lynn Sonier]

There's some stuff called Cetol thats really weather resistant. You can find it at marine supply stores. If none in your area, try:
westmarine.com
Good luck!

[David Blangger]

Don, You have some good answers to your post. In this case I think chemical reaction is the closest to right. You will notice the part of the bench that is the most contaminated would be where your trousers were touching the varnish. The other side was contaminated by probably someone wearing shorts. The top rail was probably an arm rest...again in contact with clothing.

So my guess would be something in the laundry detergents absorbed into the poly finish.

[Rob Glynn]

To add another option.

It has the appearance of mould to me.

If mould had attacked the timber prior to its installation then sanding it for finishing and sealing it with a film type finish may not have eliminated the spores. There is enough moisture in timber for mould to grow under a finish.

Just a thought. If it is correct, you may have to treat the timber (bleach of some sort) before trying again.

[Don Farr]

Thanks to everyone for the input. I guess at this stage of the game I need to do some checking and see how deep the stains are. I learned something today. I really hate to admit it but I thought poly was a good choice for outside. If it looks like it will be to difficult to get off then I will just rebuild it again.
I would rather do that than spend two weeks sanding on it.

I hate sanding by hand Is there possibly a new tool called for here?

[Jim Becker]

I really hate to admit it but I thought poly was a good choice for outside.

The marketing on the "evil poly" is so pervasive, there are way too many folks think it's the answer to anything. I avoid it like the plague...'don't like the look, the smell, or the drying time. I only use it when it's clearly indicated, such as the eating surface on our kitchen table...the only project in 5 years I've used the stuff!

There are so many great finishes available today. Not as many for outdoors, but there are choices. Like I said, before, I don't put anything on cypress at all.

I hate sanding by hand Is there possibly a new tool called for here?

Yes, a nice Festool sander...and the special deal is only for a few more days.

[Alan Turner]

Try Epiphane (sp?), from Jamestwon distributors. Holds up well to the weather, although I have not used your wood so have no comment there.
Alan

[Don Farr]

. Like I said, before, I don't put anything on cypress at all.



Yes, a nice Festool sander...and the special deal is only for a few more days.

I am going to run that by the better half tonight. (no finish) I guess if we go that route then I will have to remove every spec of existing finish?

And the sander also

[Glenn Clabo]

This is soooo easy. Get her to agree that it should be no finish...then burn your old sander up in the first few minutes. Festool sander here you come...
Evil ain't I?