Need an opinion, don't know what happened

[richard b miller]

i built my wife a potting bench about 18 mos ago. it sat outside on our back deck. when we restained the deck last week, i moved the potting bench and noticed the top coat (GF Exterior 450 top coat) had flaked in one area. i had originally used Behr semi-transparent weather proofing, all in one stain and sealer, then top coat on top of that (all water based). i also noticed the top of the boards were slightly uneven, as in some a little higher than others. when i built it, i ripped pine boards into 2" strips and glued all, using Tightbond lll. i removed top and sanded/planed top so it was flat again. i restained yesterday (2 coats ) and top was left outside to dry. when i brought it in last night, i noticed it had a slight bow from front to back. this morning, i put a level across from front to back and the top had bowed so much, the gap in the center was 5/16" !!

where did i go wrong, as this is VERY discouraging! should i turn it upside down and weight it, to see if it will flatten out or should i just rip the boards again and start all over?

Thanks all !
Rich

[Mikail Khan]

Did you seal top bottom and sides?

MK

[Randy Heinemann]

My experience has showed me that it's virtually impossible to weather proof any wood that will sit outside unless you use a good exterior paint. I believe this would be especially true of pine. Any wood that sits outside in all types of weather will eventually deteriorate when finished with any stain or finish unless the finish is maintained regularly. With pine, which really isn't resistant on its own, that's even more important; annual restaining or refinishing.

Plus, I assume that you used lumber from a local lumber store or place like Home Depot. That wood may not be dried to the correct moisture content and, when used in constructing something like the potting bench will continue to change shape as it finally dries out in place.

For a potting bench that will sit outside all the time I'd use something like cedar or cypress that has been kiln dried properly to start with. The wood will cost significantly more, but I doubt you'll have the warping problems. Then, since this wood is, to some degree, weather resistant, don't finish it and let it weather over time.

[richard b miller]

i did seal all sides and faces

[Frank Pratt]

The most important thing here is to avoid the use of Behr products. They sell tons of product because of good marketing, but the quality is very poor.

[Jon Grider]

Just a thought, when you left it outside overnight did you lay it flat on an outdoor table or bench so one side was exposed to air and the other was not? If so perhaps the exposed side had more humidity change than the protected side resulting in the bowing action.

[Don Jarvie]

As Randy mentioned pine is not a great wood for outdoor use. Cedar, team and mahogany will do better outside.

[Malcolm McLeod]

As Randy mentioned pine is not a great wood for outdoor use. Cedar, team and mahogany will do better outside.

Or in AL, cypress should be readily available.

[Joe Jensen]

wood moves with changes in humidity, sealing all sides doesn't stop it. If you look at the grain pattern on an edge I am fairly certain you will see that the growth rings do not run parallel to the face or perpendicular to the face but they run at an angle, probably in a curved pattern. If you had a board with the grain running parallel to the face and another with the grain running perpendicular you would see that the one parallel to the face moves a lot more with changes in humidity. In fact for pine it would move about 3X as much. Because of this when the grain is not parallel or perpendicular to the face it will cup when the humidity changes. If you built it in a climate controlled space and always had it in the same temp and humidity it would not warp. The book "Understanding Wood" is fantastic if you want to learn and understand how and why wood moves.

[Mel Fulks]

I would use a plywood top. Glue light canvas to that with Titebond 2. Paint with acrylic . Trim the legs on one side to give
slight slope. Will last many years.

[Art Mann]

My experience has been quite the opposite. I get better results with Behr than I get with Scherwin Williams premium paint. Consumer Reports did a long term durability on various house paints that verified my experience.

The most important thing here is to avoid the use of Behr products. They sell tons of product because of good marketing, but the quality is very poor.

[Peter Kuhlman]

My guess is the top was left at ground level or not much above it causing it to warp. Will be very difficult to impossible to fix that most likely. I would elevate it, flip it, leave it I protected spot outdoors for a couple days and see if it straightened out any. I have used treated pine lumber for outdoor tables that I let dry for a week or so prior to assembly. After painting with a decent outdoor big box oil based paint they held up for about 10 years before needing repairs. I disassembled and ran thru planer before reassembly and painting again. Was in use for over 20 years total before wood deteriorated too much. This was in Louisiana.

[Randy Heinemann]

If you used pine from the lumber store, I the most likely problem was it wasn't completely dry and the subsequent evaporation of moisture from the wood through the end grain changed the wood significantly.

Re-making the top with a wood made for outdoor use would be the best solution - cedar, cypress, treated lumber, or even composite decking (which is a great choice because it would last a long time without any maintenance).

[richard b miller]

To all that responded - Thank you!
today i took the top (which was the TOP of the potting bench) and sawed the planks apart and i noticed an interesting thing. several of the board had 25-50% moisture content!! i won't point fingers, but i said i used GF Exterior 450 top coat, two coats. so my intent is to let them dry to ~12%, trim edges smooth and reglue. i might use a marine varnish as a top coat - thoughts on that? i just can't help believing that with the proper top coat, pine can be used.
thanks again
Rich

[Mel Fulks]

I used to think good paint would protect low quality wood. It will not. No experience with marine stuff.

[Randy Heinemann]

Over time everything will require refinishing if it is exposed to the weather continuously or even for seasonal periods.

We built our house with an oak door which I finished with marine varnish. It required light sanding and refinishing every year to maintain it. If I left it for 2 years between refinishes, it required heavier sanding and possibly 2 coats of finish. Once I left it 3 years because I didn't have the time in summer. The door never completely recovered and eventually we replaced it with a woodgrain fiberglass door which obviously isn't the same but never needs maintenance.

Good luck but I would say it's likely you will need to sand and refinish at least every 2 years; maybe every year to keep it maintained.

I would replace the top with composite decking with a wood grain pattern and the color that makes the potting bench look good. That material will give you the longest life without annual or semi-annual refinishing.