# Bubbling on Cedar (lap) siding



## EvansAndEvans (Jun 23, 2013)

Hey guys (and gals) I have a question for you that is sure to bring out many theories and opinions.
What is the cause of latex "bubbling" on old cedar siding?

I am painting in the Northwest and have found old houses build between 1890's and 1940's that have horizontal cedar overlapping siding, to be prone to bubbling when painted over with latex.

Obviously I am not applying the first coat of paint as these are old structures and all i have been able to do, short of heat-gun scraping, is to scrape off old and peeling paint, sand down the edges, apply a coat of oil-based primer, then a coat, or even two coats of Peel Stop or similar product, and paint. But The bubbles come back, just in a different area.

I tell the client that it is moisture vapor leaving the structure, finding the path of least resistance, but they want to pin it on the painter. I just cannot find an answer that satisfies peoples frustration that seems to plague painters here in the Northwest. Any ideas? And thanks if you got this far.


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## NCPaint1 (Aug 6, 2009)

You answered it. If the HO's don't like the answer, well that's too bad....its reality. Most of the newer cedar sided jobs around here have vents. They can still peel even when properly installed. Cedar doesn't like to be painted.


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## DeanV (Apr 18, 2007)

We have some rough side out cedar siding that we have done since the mid 90's and the base primer is finally letting loose. Started with a little bubbling a couple years ago and now it is starting to let loose all over.


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## 6126 (May 9, 2010)

EvansAndEvans said:


> Hey guys (and gals) I have a question for you that is sure to bring out many theories and opinions.
> What is the cause of latex "bubbling" on old cedar siding?
> 
> I am painting in the Northwest and have found old houses build between 1890's and 1940's that have horizontal cedar overlapping siding, to be prone to bubbling when painted over with latex.
> ...


I am also in the NW, and I no longer do the "Peelers". Its just not worth it. I stay plenty busy repainting the newer homes with Hardi-Plank siding.


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## y.painting (Jul 19, 2009)

Somewhat common here on old cedar clapboard. Usually moisture (no/little venting on those older homes).

Although I've seen it happen in places like barge boards or window trim where moisture wasn't the issue. Two homes last year - the HOs both cut down very large trees that fully shaded the west side of the homes. Painted the homes after cutting down the trees and a few weeks of intense sun on those sides produced new bubbling (down to bare wood) which never happened before even though the homes have been painted plenty prior to the trees coming down.


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## TJ Paint (Jun 18, 2009)

Got this house right now. No peeling. Love those.

One time right after painting it started bubbling. The house was old and not wrapped. I told him beforehand it might do that. I felt bad but not enough to duck when he paid me.


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## Epoxy Pro (Oct 7, 2012)

We are having this issue on only one side of a small addition, this is the only part of the house that was not ripped apart since it was a recent addition, it is only bubbling on one wall and not the rest of the house, the contractor and i had talked, they found a roof leak above that wall after tearing into it they found it has a vapor barrier on the inside and outside of the framing, this is a bad no no for old homes, it has only a ridge vent and soffit vent the new contractor added, the peeling side has a smaller roof with no peak or vents. It is cedar siding, I paint these all the time and over all my years I have only seen this 3 times, the house being sealed up way to tight was the issue on 2 the 3rd I have no idea they never called the guy I worked for back after we repainted it.


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## Carl (Jun 18, 2011)

Maybe scrap the oil based primer since water vapor cannot pass through that and use an acrylic primer that breathes. Also, make sure the gap under each board is clear.


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## Gough (Nov 24, 2010)

EvansAndEvans said:


> Hey guys (and gals) I have a question for you that is sure to bring out many theories and opinions.
> What is the cause of latex "bubbling" on old cedar siding?
> 
> I am painting in the Northwest and have found old houses build between 1890's and 1940's that have horizontal cedar overlapping siding, to be prone to bubbling when painted over with latex.
> ...


First of all, what's under the bubbles? The general rule of thumb is that, if it's bare wood, moisture is the culprit; if it's other paint, it's either solvent bubbling or interlayer failure.

We've been painting cedar-sided homes of this vintage for 40 years in this area (Inland Northwest). The only time we've had a problem with blisters has been with solvent blisters from dark colors getting in the sun too soon.

I'm curious about oil primer, then Peel Stop. Why both? We normally just use a long-oil primer with good results.

I've also been the contrarian here on PT about paint on cedar. Probably 95% of the houses here that were built before 1970 are sided with cedar claps. We paint them with oil primer and acrylic latex and often see 12-15 years out of a paint job.

I can think of one job where we had widespread paint peeling, and the owners had had a huge ice dam the previous winter, completely saturating the wall cavity and causing a large amount of plaster damage as well.


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## Damon T (Nov 22, 2008)

I'm with you Gough. Been painting older homes in the NW for the last 20+ years and cedar is great. Especially the old quarter sawn boards. Beautiful stuff. The newer flat grain boards that occasionally pop up in remodel stuff is pretty bad, but mostly because of the way the grain pops up. 
Once an older home starts blistering I tell owners unless we strip it all to bare wood you WILL get bubbles again. Impossible to say where or how much, but it will come back. Typically peels at the edges where it has previously been scraped down to bare wood. 
We used the long oil primers with success for years, I think it was called Moorwhite? Nowadays mostly just peel bond, permanizer plus, etc as a tie coat to help stabilize things, and if there's any concern about tannin bleed spot hit just the areas that went to bare with Smart Prime, 123+ etc. usually the extra step isn't needed. A lot of times the old cedar isn't as "bleedy" as new stuff IMO.


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## Gough (Nov 24, 2010)

Damon T said:


> I'm with you Gough. Been painting older homes in the NW for the last 20+ years and cedar is great. Especially the old quarter sawn boards. Beautiful stuff. The newer flat grain boards that occasionally pop up in remodel stuff is pretty bad, but mostly because of the way the grain pops up.
> Once an older home starts blistering I tell owners unless we strip it all to bare wood you WILL get bubbles again. Impossible to say where or how much, but it will come back. Typically peels at the edges where it has previously been scraped down to bare wood.
> We used the long oil primers with success for years, I think it was called Moorwhite? Nowadays mostly just peel bond, permanizer plus, etc as a tie coat to help stabilize things, and if there's any concern about tannin bleed spot hit just the areas that went to bare with Smart Prime, 123+ etc. usually the extra step isn't needed. A lot of times the old cedar isn't as "bleedy" as new stuff IMO.


We've seen that same blistering at the edges of scraped areas when we've come on some jobs. I've wondered if it's due to the previous guys trying to feather the edges with power sanders and heating up those thick areas of old paint to the point where they're prone to failure.

I'm amazed how the quarter-sawn stuff still looks like new when we remove all those layers of paint. And it certainly does hold paint a lot better than the flat sawn claps.

When you have to strip it, what do you use? We've used both the PaintShaver and the Metabo, but keep coming back to heat plates and scrapers. It can be tedious, but we can do it with minimal damage to the old surfaces.

We've generally used either PPG #1-70 or the BM primer, which they now call Fresh Start Moorwhite.


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## Damon T (Nov 22, 2008)

If I get another strip job I'll buy the paint shaver pro. I've used the Metabo primarily, which I think is a good tool, but the videos of the new paint shaver head look like they have better dust control than the Metabo. The little doors on the sides of the Metabo break off pretty quickly. I've taped stir sticks etc around the side to help with containment.


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## EvansAndEvans (Jun 23, 2013)

I really want to thank everyone on here for all the pro advice. It has helped a lot.


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## plainpainter (Nov 6, 2007)

I don't necessarily believe moisture is the culprit - there may be actual vapor causing the bubble, but I think the interpretation is backwards. There is always moisture in wood - the problem comes when the primer deteriorates, whether it be crumbly or didn't stick because wood had mill glaze. It's when the sun heats the surface, similar to using a heat gun that makes the paint expand and comes off the surface and form a bubble.

You can do this experiment - take a piece of wood measure it's moisture content - preferably kiln dried or really seasoned anything - and prime and paint. Wait a month or two and then stick a heat gun on it - it will bubble. Now it won't bubble under ordinary circumstances, but a surface can get as hot as 170-200 degrees in the direct sunlight - so if this wood had more than normal moisture, improperly prepared surface - then something might let go.


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## Mustache Paul (Jan 11, 2015)

Depends on when it bubbles, prior to painting or in the course of it. A lot of the older cedar homes had solid body stains applied which at the time of use were open architectured coatings that could breathe and allow moisture to move in and more importantly out of a surface. The newer products are "weather resistant" read as more like paint than stain. So what I have had happen is a surface that looked solid and tight to the siding all of a sudden balloons out on the second coat (which I spray). 

For other blistering problems if it's widespread I just re plane all the siding in place and dress sand it out. Regards Mustache Paul


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## daArch (Mar 15, 2008)

DAMN, got sucked into another necro. 

Read like the first seven posts before realizing it was over a year and a half old. I GOTTA look at the dates before reading.


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