I have used this product a number of times with the same problem. it doesn't dry. last application decking cleaned and coated in October. it's now mid February, hot hot summer no rain during this period. just five mm of rain boards have turned soft and milky. nopoint contacting haymes as they will pretend to test the product and say it's fine. and yes i'm speaking from experience. i havehad other issues with haymes paint. do yourself a favour...use another brand.

Doesn't dry! still goes soft and cloudy from moisture after four months curing in summer with no rain

After using the oxalic acid (woodclean) sold to me, I did a water bead test, with this showing the water was being absorbed the guys at Bristol Erina sold me dexspress merbau for my merbau deck.
They told me I would get 1 or 2 years out of this product 3 years later in half undercover half exposed to the weather I have put a coat of natural back over the whole deck for maintenance as I was happy with the darkness of the original coats.
more expensive but coating less often
Could only do 2 boards the whole length of deck at one time

I've been using this product for six years and I would recommend it to anyone who is in the market to paint/seal/stain a new timber deck (mine is merbau). It needs to be re-coated every 2-3 years if in direct sunlight. If the area is totally undercover you could probably stretch it out to 4 years providing the original preparation and application are as directed by manufacturer.
Cost effective and plenty of advice from retailer.
You should not apply this product unless you have a good three to four days of decent weather during and after application as moisture or cooler weather causes the fresh coating to become cloudy in appearance.