I installed an 18' x 23' uncovered mahogany deck last summer. The deck is attached to the house with a ledger board and sits on posts on concrete piers. Frame work is PT; the decking is tongue-and-groove mahogany. My problem is that some of the decking is buckling significantly (>1"). The first 4 courses of mahogany are screwed down with SS deck screws. The rest of the mahogany is blind-nailed with port-a-nail, SS, serrated flooring nails. The last course of mahogany is screwed. The mahogany was sanded and treated with clear Behr Premium Deck Sealer which seemed to function well for about 2 months then started fading badly. I suspect that the sealant faded and the wood is getting wet, swelling, and since the last course is fixed, it can only buckle to relieve stress. Comments, suggestions on how to fix this?

PS - I live in Massachusetts and the deck exposure is northwest. The reason for mahogany is someone gave it to me.

A tongue-and-groove deck fully exposed to the weather is always going to buckle. Wood expands and contracts, and there is nowhere for it to go when it expands except to buckle. That is one reason why most decks are built with spaced deck boards.

Thanks for the feedback. My hope was that with the deck sealed well the wood wouldn't swell too much. I'm planning on treating the wood again but with Woodzotic from Restore-a-Deck. I'm hoping this will minimize expansion in the future. I've resigned myself to the fact that I may have to re-lay the deck but with some spacing, say, every 4 courses or so. Does this sound like a reasonable plan? I'm tied into the mahogany since I can't afford to buy new material.

Many factors
1st Richard is correct wood will grow and shrink with weather.
It was inportant when installing the deck that the contractor check the moisture level of the wood to be sure that the wood was not to dry when installed. Not to wet either.
2nd fastening of the deck is critical. New pressure treated lumber requires nais or screws that will not corroid because of the chemicals used in the treated lumber. This will cause poor fastening and allow the wood to cup and lift.
In order to prevent this from happening the contractor should have routed out grooves on the backside of the boards to prevent them from cupping.

You now need to remove the deck material and start again. As sanding the top smooth will not do any good as once the wood dries up, it will crack.

All of the wood should have been treated with at least two coats of waterproofing on all sides and ends before it ever got installed. Treating just the top side is going to buckle because of one side being dry and the other being wet.
If the deck had of been built without the tongue and groving using tiger claws to hold in place, and the wood was sealed on all sides it would have held up.

This story proves why it's important to get a contract with warranty in writing from your contractor so you know 1 year from now the Tiger Claw fasteners he used on your premium deck will not have to be ripped up and start your deck building process all over again. What a waste. Thanks for sharing your story so we don't make the same mistake.

Speaking of mahagony T & G, we are restoring a covered porch on a house built in 1924, in the suburbs of Phila (GO PHILLIES!!!). The original wood porch was ripped off and replaced with concrete, which has cracked and broken off. We have installed pt 2x6 sleepers w/ 10 in centers anchored to the concrete. The flooring is 1x4 Meranti. Our question is this, what is the BEST treatment for the wood. RAD is out of Woodzotic, which after some research we had determined would be the best. We are not adverse to a tinted treatment if that is best? We are DIYers with years of experience on old houses but this is our first time using mahogony. What do you pros think out there?

Despite my problems with the deck, I found a stain that works very well. Here's the link:
http://www.woodrich-brand.com/category_s/2.htm. I used the Woodrich wiping stain. It looks beautiful and lasts a long time. This is the company that supplied Woodzotic to RAD. BTW, I would avoid RAD at all costs. I had to file a complaint with the BBB and the PA Attorney General after they failed/refused to deliver. I was only able to recoup my money after disputing the charge on my credit card.

Maybe that's why Woodzotic is not available. HMMMMMM!!!! Thanks for the advice. I will definitely look into that. Have you heard about Penofin?

I have heard of Penofin but I don't know anything about it. Unfortunately, you could probably research wood treatments forever...

Yes, you're right there!!! But we have come down to Messmers UV for Hardwoods, Penofin Brazilian Rosewood Oil or your recommendation. we'll probably have to buy a gallon of each and test it on a scrap. The finish will make this porch and all our work will be for naught if we don't nail the right finish!!!

Thanks for your advice. I'll let you know which one we go with.

All T&G decking has to be covered [as is roofed over the entire area] to prevent buckling. Treatments will not prevent the problem, even if you coat all four sides. Routing the bottoms will not prevent cupping.

Best thing you can do is pull up the decking, rip the tongues off and put it back down with at least 3/16" spacing between boards.

If you used Micro ACQ, most any coated, zinc, or ACQ-rated deck screw will work without corrosion problems. If you used ANY version of regular ACQ, you will be better off with stainless screws.

Kelly, based on my experience with my deck, I can't agree more. The portion of the deck that is somewhat sheltered from the elements is fine. The rest is in varying degrees of distress. I do plan on re-laying the deck as you and others have suggested but I'm still trying to gird myself for the work.

At least the pulling up won't be too bad, but I do understand the reluctance to want to do it so soon. I hate doing anything twice when it comes to projects like that.

You're correct that the pulling up won't be bad; it's removing all the nails I'm dreading! Oh well, as they say, "a mistake is an opportunity to learn."

If you nailed through the tongues you're home free. Flip the decking over and run it through a table saw...you have to cut the decking anyway. Get a Freud Diablo 10" blade, they can cut right through those nails with ease.

Be sure to wear eye protection though.

Kelly, thanks for the great suggestion! I will definitely buy a Diablo (they always seem to be on sale somewhere.) I guess I always worry about damaging my blade but, even if it did, it's worth the time savings. Kudos!

Your welcome....and don't worry....Diablos eat framing nails for breakfast and your nails are much smaller. I have only dislodged ONE carbide tip in the last 12 years!