Wood primer bubbling..?

[AvronW]

I have an external timber balustrade rail on my balcony that seems to have been neglected for many years, then repainted priot to me purchasing. The result is the paint is cracking, flaking and the timber exposed and cracking.

I have sanded down around half the length, down to the timber and then painted it with a white timber primer (thinned with water, for first coat). All seemed fine, but after a day a few large raised bubbles appeared. There are not many of these, but they are large (average around 15mm diameter and about 5mm high).

I am not hesitant to paint the primed wood with this kind of bubbling and am not sure what could be causing this.


Anyone have a good explanation for this and a suggestion on how to deal with this?

Thanks,
Avron

[Harry72]

Could be a air bubble or some oil/wax or other things.

[dr4g0nfly]

Is it just this blister or are their others?

It could be moisture in the wood, evaporating out of a small crack in the sunshine. Have you popped it to see what's underneath? There should be a film of the moisture on the inside of the bubble if it is.

If you can't see anything sand back and try another coat of primer in that area and see it it does it again.

[AvronW]

Thanks for your response.

Opening it up it seems to be moisture from within the timber. I presume this has been moisture that has made it into the wood through cracks and flaked original paintwork.

There are around 6-8 of these large bubbles, so the problem doesn't seem to be across the whole surface, just in a efw spots.

If I sand back and recoat it, will the same just occur again, or is there a way to try avoid this happening again?

Thanks,
Avron

Is it just this blister or are their others?

It could be moisture in the wood, evaporating out of a small crack in the sunshine. Have you popped it to see what's underneath? There should be a film of the moisture on the inside of the bubble if it is.

If you can't see anything sand back and try another coat of primer in that area and see it it does it again.

[dr4g0nfly]

Welcome to the joys of wood, especially outdoors.

Wood will absorb and change it's moisture content all the time. This is a handrail around your balcony and you're just coming out winter/spring so it's had a period of wet or high humidity to absorb all it can.

You need three things now, patience and warmth (the easy 2), thankfully the sun will provide one. The third is a patient SWMBO, our good ladies sometimes expect the impossible now I'm afraid!

Your doing right by using a latex or acrylic paint to protect the remainder of the wood but you may suffer blisters for a few weeks more yet.

[strangerep]

If I sand back and recoat it, will the same just occur again, or is there a way to try avoid this happening again?

As a result of bad experiences, I never use acryllic primers anymore for exterior use. Even Zinsser exterior (turps cleanup) fast-drying primer disappointed me.

If it were my handrail, I'd sand back to bare timber, and coat with a slow-drying oil-based primer/undercoat. Give it an extended drying time of several days, then sand again where necessary and apply 1-2 more coats the same way. Then leave it for a week or more to see if any problems occur before applying 3 coats of Taubman's Endure exterior. (It's ok to use the water-based Endure on top of the oil-based undercoat provided the latter gets a generous curing time first.)

I've found this combination gives the best of both worlds: and oil-based slow-drying primer/undercoat adheres and seals the timber better, while the exterior acryllic topcoat flexes to a reasonable extent under sun and rain.