Gaps appear in large gate when wood dries in summer.

[23790954]

Hello to all you good forum members.
Although I am in my 70's, I still like to maintain my property in good repair, and would like some advice on the following problem.
About 2 years ago, I made a very large wooden arched gate, which is erected at the end of my driveway. It measures about 10 feet wide by 8 feet high.
When I made this gate, the frame of which is made with 3 x 2 wood, I made the main part using dressed 7" sheets of wood. After finishing making and fitting the gates, I painted them Oxford Blue. However I now find that whenever the wood dries out in summer, the sheets of wood, part from each other, leaving long fine gaps between the sheets, which look very untidy. I attempted to fill some of these gaps in, last summer, with some wood filler, but to my disappointment, the gaps have appeared again, this year.
Can anyone, preferably a joiner, advise me of any material with which I can fill these gaps, to stop them appearing again in the future.
Thanks for all advice given.

 

[gregers]

try an exterior painters mate filler,thats if they do it?you need something thats flexable,my driveway gates do the same but i just put up with it,there is a lot of expansion/contraction going on,and there not exactly small.