Part 2: Weatherproofing the Project
As we saw in part 1 the success of any finishing/coating project is very dependent on the preparation of the surface, but just as important is the condition of the surface that is going to be coated. This is particularly the case for projects that are outdoors or often exposed to the elements. If a varnish type finish is expected to hold up well in an exterior environment, the wood must in effect be “weather-proofed”. This is to mitigate the exposure to continual moisture so as to reduce the chance of the coating lifting or separating from the wood. Moisture intrusion is the greatest challenge to any finish.
Joint Integrity and Sealing
All of the joints in the structure must be properly glued and holding together. If there is excessive movement in any joint areas, proper repairs should be made before finishing the project, if not the coating may crack and allow moisture entry. If any joints need repair, clean them out thoroughly with a saw blade or sharp knife then flush away the debris with acetone. Re-glue the pieces with epoxy or a polyurethane adhesive. Exposed end grain areas must be fully sealed with either epoxy or the coating material, or both. Saturate these areas repeatedly until no more material is absorbed.
One way to greatly reduce the chance of moisture intrusion is to seal up a wood project completely with a thin coat of epoxy or penetrating epoxy sealer (PES). If an piece is going to be re-mounted make sure to epoxy over the bungs after mounting. For the prep treat the epoxy the same way as any other existing coating.
Mounted and Bedded
Any wood that is mounted to other structures such as deck areas should be properly bedded in a compound that will keep moisture out of the back side of the piece. This is an area that is often unrecognized as a future problem, but is actually very easy to deal with. If you don’t know or are unsure if there is bedding compound present, you should presume that there isn’t. It’s surprising how often this very important step is overlooked. If there seems to be compound in place, but it has breaks or gaps, these must be caulked. Using a knife blade or piece of paper try to slide these between the wood and the mounting surface. If you are able to do this, there will be a problem with moisture intrusion.
Where a small piece is easily removable, clean the mounting side thoroughly and bed it back in place with Dolphinite™, polysulfide or a non-adhesive bedding compound. Do not use silicone caulks or household caulks for any reason. If the piece cannot be removed clean out the joint and caulk. Scrape clean with a knife or razor blade, and flush away the debris with acetone. Next, caulk the entire edge, forcing the material into the joint as far as possible with a fingertip. Finally, wipe up all excess or visible material with the recommended solvent and plenty of rags and allow it to cure.
Screw holes should be sealed with a removable compound. Don’t use any type of silicone caulk, as it offers no adhesion to wood, and it is not paintable. Use a polysulfide type material.
There is one final step in the sealing process that comes later, but we’ll cover it here. After the other preparation steps are completed, the masking-off process must be done. When applying tape, back the tape away from any joint by 1/32″ to 1/16”, to make sure that no small slivers of wood are left bare. Then the coating is applied over the entire piece and the caulking, and it forms a seal properly onto the mounting surface.
The Project Moves Along
Now you’ve really made some progress. It’s time to start with the coating application. The next article, DIY Guideline Part 3 covers some basic and easy painting technique information
These steps may sound like a lot of work and bother, but trust us- the old saying is completely true – proper and thorough preparation accounts for at least 90% of your success. These prep steps will pay off for many years to come, and make that beautiful finish stay that way for a long time!