My paint job is a failure!

Paint doesn't seem to stick to this reader's old house. We examine possible causes, and suggest cures.

I have a house that’s over 100 years old with wood lap siding that can’t seem to hold paint. It was stripped to bare wood and we used a good quality primer and paint. The weather conditions were good. Paint started peeling within a few years. While painting the house we replaced a few pieces of siding that were bad near the bottom of the wall. Those newer pieces have retained the paint just fine. What’s up?

Not to make light of your situation, but what an interesting problem.

It sounds like you did everything right. You stripped the siding down to bare wood, chose a fair weather day to paint and applied a good quality paint and primer.

Yet the paint started sloughing off within a couple of years -- all except for the siding you put at the bottom of the wall.

Moisture will cause paint failure

We may have to delve into building science for clues here, and specifically look at how moisture migrates through a building. Because my first guess is that moisture is causing the problem -- not the siding itself.

It could have been the siding was not thoroughly dry when you painted it. If there had been soaking rains in the not-too-distant past, some moisture might have still been lingering in the wood.

This might also explain why the newer siding held paint. It was dry when it was installed.

Water does like to travel through wood siding. That’s one reason that some builders now advocate building a “rain screen” on the outside of a house.

This amounts to creating an air space between the sheathing and the finish siding to help the siding dry out when it gets wet.

Look for a source of water

But let’s assume the siding was completely dry before you painted it. Water could still be the problem.

Leaks around windows and doors, missing or deteriorated flashing, leaky gutters or roofing all could allow water to seep into the wall. If the siding stayed wet, it could force the paint off the exterior of the house.

This theory has flaws. It seems likely you would also see evidence of leaks on the inside of the house in the form of stained wallpaper or plaster. But it’s still a possibility.

So one step would be to take a very careful look at the building exterior. If there is any potential for this kind of water intrusion you should be able to see it. And repair it.

Water vapor is also a candidate

Water vapor also might be the cause. Warm, humid air wants to escape to the cooler exterior of a house. That process is called vapor diffusion. When the moisture runs into the back of the siding in cold weather, water can condense into a liquid state.

This water will try to push the paint off the siding.

But where is the moisture coming from?

One common source of moisture inside the house is the basement, especially in a century-old house with a stone foundation, no damp-proofing and a dirt floor.

Moisture in the soil around the house migrates upward, then forces its way out through the walls.

The fix here is to cut off the source of the water. If the basement floor is indeed dirt, put a layer of polyethylene plastic over the floor, overlap and tape the seams and seal the edges as best you can. That will cut off a lot of water.

If there’s a lot of bulk water getting into the basement, you might want to install a perimeter drain (on the inside) and connect it to a sump pump. If you don’t have gutters, put them in. That, too, will help keep water out of the basement.

Ventilate the house, too

Finally, a good deal of water vapor can come via respiration, cooking, bathing\-- in other words, day to day living.

Ventilation fans in the kitchen and the bathroom will help. Make sure your clothes dryer is vented directly to the outside and not into the basement or attic.

Be suspicious of anything that produces mist or steam.

I think your answer will be found in identifying the source (or sources) of unwanted moisture inside the house and eliminating them.

Until then, the best paint in the world won’t be good enough.

Scott Gibson is the former editor of Fine Woodworking magazine, and a former editor at Today's Homeowner and Fine Homebuilding magazines. He is an avid and accomplished woodworker and carpenter.