Finish coating bubbles on linseed oiled siding
Over fifty years ago when we applied cedar siding to the exterior walls, the only way we were told to treat it then was with linseed oil.
Now, as we paint the surface, blisters still appear on the shadier side of the house where the sun apparently hasn't completely dried out the old oil.
Rather than sand all these bubbles off and start again, and which still would not remove the oil, could we inject a little glue or some kind of adhesive into the bubble then press it flat allowing the air to escape through the needle hole?
I have never seen (or heard of) linseed oil bubbling. With that said, I have seen other coatings bubble once applied over linseed oil. Spar varnish for example will bubble and tends to take a good amount of time to dry out. Paint will also bubble if the surface hasn't been first cleaned or primed (with the proper primer) prior to painting.
I'm thinking that you have a few choices. It does depend on the type of coating/s that your dealing with though.
1.) Strip the bubble (or siding) with a chemical stripper, re-oil (or prime) the repaired area, then coat the entire length (board) of siding (or the whole wall surface if yo prefer) with your chosen coating.
2.) Use a curved or flexible syringe, (found on-line) filled with an exterior, low viscosity, glue, to glue under the bubble. Be sure to poke a hole on the opposite side of the bubble to where your inserting the syringe. Having an exit hole, for air and the glue to seep out, will insure all of the bubble sticks to the surface after the bubble is pressed down. Be sure to immediately wipe excess glue from the surface before it dries. Reapply your coating.
4.) Use a rented sand blaster, filled with soda (or other recommended blasting material) to blast off the old coating and replace it with a new coating.
5.) My final solution (and the most expensive) would be the best option, which is to replace the bubbled boards with new boards then re-coat them.
Number 5.) is the best solution, only because it's the one that guarantees a good quality in the finished coating. Even so, matching the new siding color to the existing siding could be a problem if your applying a clear coating.
All the other solutions could still end up with a finish that's discolored, or has noticeable splotchyness, along with the surface being rough, bumppy or rippled. Also, your bubble gluing may not work because of contamination under the bubble itself. In which case the bubble must be removed (by scraping or cutting). Once removed fill the area with exterior filler, let dry, sand flush, dust, prime the repair, then paint or re-paint (with solid exterior stain or siding paint).
Unfortunately, you might have to try each solutions (easiest to hardest) until you find what works best for your situation.