What to use for outdoor sign?

[msheppard36]

Just looking for some advice. We live in a converted railway station and there is an old running board in the garden with the station name on it. Last year I decided to remove it and renovate it. The board is a timber frame about 2m long, 300mm high and 100mm thick. It has boards butted together and nailed to it to make it smooth on both sides. There are then timber letters spelling the station name. When i remove it, the letters and some boards were so rotten they simply fell off. I decided to replace the boards with marine ply so i had a single smooth surface. I then used the same ply to cut letters and then glued and screwed these to the ply back. Then 3 coats of primer and top coats. That was a year ago and it now looks pretty bad again. Im surprised the marine ply has not lasted longer than a year so this time I want to use something that will last much longer. I have read that MDO is a good outdoor product but Im struggling to find any in my area. Any recommendations? Thanks.

 

[Deleted member 174758]

MDO is commonly used in the USA by the sign trade but almost unknown here. Plywood, even marine grade, will need the edges thoroughly sealing to protect it from the elements, but the end grain is always a problem which is why railway signage was always given several coats of lead-based primer and top coat. There are timbers which will withstand the weather such as pitch pine, oak or western red cedar but they have other problems associated with their use.. What did you use to paint the sign? I'm asking because I suspect that your finishing materials and techniques are the issue, not the plywood

 

[msheppard36]

I used a trade external primer from a local mechant who advised me it would withstand the weather. I put on 3 coats quite liberally, then a light sanding and 2 top coats of a Farrow & Ball gloss. We have used the same gloss elsewhere, such as the soffits and fascias and they are still looking good after 5-6 years. Maybe I didnt treat the edges enough? The letters obviously stand out so water must have found its way through the laminations.

 

[Dave54]

Might be worth contacting one of the heritage / steam railways to see what they do about it.

 

[Deleted member 174758]

For exterior use you need to fill the edge grain of the plywood with 2-pack filler and sand back before priming. It may also be worthwhile treating the edges with wood hardener first.