Unfortunately there is not much you can do. We are tending to use manufactured woods (modwood and the likes) a lot more now for a number of reasons and this is one.
Here is a paste from another site which may give you an explanation
GG
Q. I have a deck that was constructed from pressure
treated wood. The deck is about 8-10 years old. I have
lived in the house for 6-7 years. The former owners
never waterproofed the deck or cleaned it. Since I
have been living here, I have been cleaning the wood
and waterproofing it although I do not use any stain.
I have not waterproofed it every year because I
thought the finish would build up. Each spring I check
to see whether water still beads up and let that be my
guide. For the last couple of years I have noticed a
lot of sap on some of the boards. I try to scrape it
when I clean the deck in the spring, but it continues
to seep out throughout the summer and is rather
sticky. I did not notice this happening the first few
years. Is there anything I can do about this problem?
The sap does limit the use of the deck.
A. The "sap" oozing from your deck boards is a natural
product of the wood, and it’s really pitch, not sap.
Sap runs in the spring. Running pitch has nothing to
do with stains, sealers, or waterproofing the deck. It
resides in "pitch pockets" in wood, and when the wood
gets hot enough, it melts and runs out. This is
especially true of lumber made from conifers, which
have large pitch pockets. Your deck wood is probably
made of a member of this species, perhaps southern
pine.
You’re most likely to notice pitch problems on the
sunny areas of the deck than in shaded sections, as
those are the areas on the deck that absorb the most
heat. Kiln dried lumber that has been heated to more
than 160 degrees usually does not suffer from this
problem. The high kiln temperature solidifies the
pitch and prevents it from turning to liquid again.
Evidently, the pressure treated lumber used on your
deck was either not kiln dried, or wasn’t dried at a
high enough temperature to cause this solidification.
There’s not a lot you can do about the problem at this
point except live with it. As the deck heats up in the
summer, pitch will continue to run from the boards.
There is no sealer made that can contain it under
these conditions. But the news is not all bad. There’s
really no need to let the sticky pitch ruin your
enjoyment of the deck. A bit of turpentine on a rag
will remove it quickly, and you shouldn’t have to wipe
it up more than a couple of times a summer.
Eventually, the pitch pockets will run dry, and you
won’t even have to do this minor maintenance chore.
.
