I've never had an outside rug, but I have seen many comments on them. People in the southwestern states generally comment that the rug fades quickly, but none of those mentioned the surface below. In wet climates the rugs can get mossy, but the wood below them also isn't mentioned. It could be that all these people were concerned only with the rugs, and just didn't think to add any other concerns. Hopefully, others will respond with more complete answers.

We have had outdoor rugs on an exposed deck. The rugs dry quickly after rain and there is no ill effect to the deck. There are a few different kinds of outdoor rugs, though. The ones we have used outside have come from Lowe’s, Home Depot or Pottery Barn, and they’re woven polypropylene. I have also had an indoor/outdoor rug that is what feels/looks like looped carpet fiber. The one has worked fine at our front door, but I am not sure it would dry quickly enough not to have an impact on an exposed deck - but I’m not really sure.

What is the finish on your mahogany deck?

What climate zone are you in?

Do you use the deck 12 months of the year?

So nice of you all to reply. To the pro, it's treated only with that Australia oil. I don't stain it. I'm in NY, long island to be exact. Fairly harsh climate in the winter. Deck is used May-October.

I like the look of an outdoor rug but not the mildew/mold/surface concerns so I like the idea of just putting it down when guests come over.

Many thanks for these helpful replies. I never wrote comments/questions on Houzz before but will definitely do so again! I'll probably forego the rug. Not worth the risk to the deck. Thanks again!

sounds like you already made up your mind, but here is my 2 cents: i just had my mahogany deck re-stained & sealed last year, the pro painter told me NOT to use a rug, he said they traps moisture & will eventually rot the wood. they do look really nice, but as someone else said above, they fade fast, you really only get 1 or 2 seasons out of one.

Sorry ...don't see the point of an outside rug !

It depends on the rug that you choose ,nothing with a backing for sure, roll it up if rain is in the forecast and bring it in.

We have a nylon rug with rubber backing laid over our covered paver patio and it's lasted 4 years now. It's protected from the elements and is a nice touch (I think) under the dining area. Living in AZ it's nice to have a cool soft surface when we're outside dining. Easy on the tootsies.

This definitely depends the type of rug you are looking to put in the space. Kilim rugs have the ability to be used both inside and outside, these are typically used as long as they are not 100% wool. They tend to do alright outside, and wouldn't cause damage to the deck.