Fixing paint bubbles in weatherboard cladding

Forums › Home Workshop DIY › Fixing paint bubbles in weatherboard cladding

chonk

13 posts

Geek

#269855 11-Apr-2020 16:14

Hi folks,

Complete noob here when it comes to home DIY.. but hoping to change that starting with fixing up the paint on my house!

Looking for some tips and tricks with the prep work please.

I have a 1960’s weatherboard house that was painted by the previous owner in 2015. The paint has bubbled up on the north facing walls.

So I have started the prep work on a small section of the house just to try and figure out what I am doing and could use some tips when it comes to feathering in the paint around where the bubbles were.

The problem I have is that, after scraping off the blistered paint, I try to use the orbital sander to smooth out / feather the paint and basically if I spend more than a few seconds in the same spot, the heat off the sander ends up ‘melting’ the old paint making it sticky and rough..

There is at least three old coats of paint here so I am not sure if it is due to different types of paint being applied over each other or whether I am just doing it wrong.

I found that if I am more aggressive with the scraper before sanding, that helps but its slow going and risks gouging the cladding. It took me about 3 hours just to clean up one 4 mtr long board.. and its still nowhere ready for paint..

So any tips or advise wold be appreciated.. :)

1 | 2

29755 posts

Uber Geek

Trusted

Lifetime subscriber

#2459452 11-Apr-2020 16:51

Ive never ever seen paint melt when sanding. Id do a test by using scraper, one with a razor blade. If the boards have cupped a little, you can scrape up, not sideways. No need to press hard, let the scraper do the work. Hand sand the edges to remove a sharp edge, hand sand under the bubble to help the paint stick. (Bubbles usually caused by moisture) Making sure its dry, seal with undercoat. From what you say its probably easier to use an exterior filler. When dry, san with 220 sandpaper, just by hand Small sanding wood with paper wrapped around it), you just want to smooth it off. Undercoat and paint.

Do this when the humidity is low.

ObidiahSlope

260 posts

Ultimate Geek

#2459463 11-Apr-2020 17:14

I had a situation where ordinary acrylic exterior paint did not bind to the weatherboards and subsequently bubbled.

It was a north facing wall in a Central Otago type climate, extremes of heat and cold.

I found this Resene product to be effective as an undercoat;

Resene Aluminium Wood Primer.

Obsequious hypocrite

timmmay

20591 posts

Uber Geek

Trusted

Lifetime subscriber

#2459465 11-Apr-2020 17:19

I had a similar situation. Paint bubbling, with water inside that ran out if punctured. I tried all kinds of things, spot work, area work, etc, nothing worked. Doing part of a board doesn't work as water creeps along. Turns out I have cedar weatherboards, which is really resistant to paint.

The key for me was stripping the entire house back to bare wood, priming with Dulux one step oil base primer / sealer, then two top coats. Did that last year, cost about $16K for the house, other than a few minor spots things are good now.

So my recommendation is to do the job right, first time, rather than mess about for years with half measures. Strip to wood, oil based primer / sealer, paint.

mdf

3523 posts

Uber Geek

Trusted

#2459512 11-Apr-2020 19:43

timmmay:
The key for me was stripping the entire house back to bare wood, priming with Dulux one step oil base primer / sealer, then two top coats.

You need to use the right type of primer *for the wood*. Cedar is an oily wood and you must use an oil based primer for that. But other wood (especially some nz natives - e.g. totara and matai) will react badly to oil based primer and acrylic must be used for that. Read the can and follow the instructions. If the instructions don't help, google the data sheet for the product. If that still doesn't help, look for specialist advice.

To the OP, a linbide scraper works best for rapid stripping. Once you get the angle right, you can get a lot off quite easy. Don't worry too much about scraping the wood a little, it is easy enough to backfill.

If you're paint is melting then it is too hot. Some things to check:

Have you got the right discs for your sander? If you have holes, are the discs lined up? Can you add a vacuum/better dust extraction? How fast are you moving? What grit are you using?

You will never get the edges feathered perfectly on weatherboards. By the time you prime and undercoat you will add back a bit of a layer and if it is bad, a little but of bog or permafiller will smooth things out.

Bubbling might be due to UV. But if it is relatively new paint, you might need to investigate further. Could be moisture, incorrect paint or something else. But overpainting without fixing the issue may well just lead to bubbling again.

timmmay

20591 posts

Uber Geek

Trusted

Lifetime subscriber

#2459513 11-Apr-2020 19:45

Agree that you need to use the right product for the wood. It took us quite a white to find the right one. Generally oil based primers stick better than others, is my undersatnding.

chonk

13 posts

Geek

#2459678 12-Apr-2020 09:37

tdgeek:

Ive never ever seen paint melt when sanding. Id do a test by using scraper, one with a razor blade. If the boards have cupped a little, you can scrape up, not sideways. No need to press hard, let the scraper do the work. Hand sand the edges to remove a sharp edge, hand sand under the bubble to help the paint stick. (Bubbles usually caused by moisture) Making sure its dry, seal with undercoat. From what you say its probably easier to use an exterior filler. When dry, san with 220 sandpaper, just by hand Small sanding wood with paper wrapped around it), you just want to smooth it off. Undercoat and paint.

Do this when the humidity is low.

Thanks tdgeek, I will try this today and see how it goes. I have lots of small bubbles all over the place so will be fun :)

chonk

13 posts

Geek

#2459679 12-Apr-2020 09:38

ObidiahSlope:

I had a situation where ordinary acrylic exterior paint did not bind to the weatherboards and subsequently bubbled.

It was a north facing wall in a Central Otago type climate, extremes of heat and cold.

I found this Resene product to be effective as an undercoat;

Resene Aluminium Wood Primer.

Thanks ObidiahSlope, I will look into this product! Appreciate your reply.

Sharesies

Trade NZ and US shares and funds with Sharesies (affiliate link).

chonk

13 posts

Geek

#2459681 12-Apr-2020 09:41

timmmay:

So my recommendation is to do the job right, first time, rather than mess about for years with half measures. Strip to wood, oil based primer / sealer, paint.

Thanks timmmay, totally agree on doing the job right first time! Its great to be able to get advise from the kind folk on here to help that happen :)

Lastman

306 posts

Ultimate Geek

#2459685 12-Apr-2020 09:48

Perhaps if you posted a pic we might get a better idea.

chonk

13 posts

Geek

#2459690 12-Apr-2020 09:59

mdf:

To the OP, a linbide scraper works best for rapid stripping. Once you get the angle right, you can get a lot off quite easy. Don't worry too much about scraping the wood a little, it is easy enough to backfill.

If you're paint is melting then it is too hot. Some things to check:

Have you got the right discs for your sander? If you have holes, are the discs lined up? Can you add a vacuum/better dust extraction? How fast are you moving? What grit are you using?

You will never get the edges feathered perfectly on weatherboards. By the time you prime and undercoat you will add back a bit of a layer and if it is bad, a little but of bog or permafiller will smooth things out.

Bubbling might be due to UV. But if it is relatively new paint, you might need to investigate further. Could be moisture, incorrect paint or something else. But overpainting without fixing the issue may well just lead to bubbling again.

Thanks mdf,

Yes I have been using the linbide and its great! I have been working the angles and it is effective but still leaves edges to the areas scraped (where the bubbles were) that need to be sanded out.

I have been using a 125mm orbital sander with correct sanding disks (holes lined up) and also a 1/2 sheet orbital sander without the correct sanding pads (ive just been using normal sandpaper, no holes).. I was getting the same result with both sanders but I have been using the sheet sander most of the time.. Im using between 60 and 80 grit to start.. mainly 80 grit..

So I will ditch the sheet sander and try and use the 125mm orbital today.. see if that makes much of a difference in general..

if I put some pressure on the sander and focus on one spot to smooth out the bubble hole i.e. moving the sander back and forth at a moderate pace but in the same general 4-5cm radius, after a few seconds or so the heat generated off the sander starts to make the paint tacky and then it will set like that when it cools off.. making it more of a job to sand out.. its hard to describe..

I also tried using the heat gun to remove the paint, same thing happens.. the paint just goes tacky then when you try and scrape it off, it is like trying to scrape off gum..

Anyway, thanks for your help.. ill be trying a few things again today and see if I can find the trick to making this less of a painful job :)

chonk

13 posts

Geek

#2459691 12-Apr-2020 10:00

Lastman:

Perhaps if you posted a pic we might get a better idea.

Will do, ill grab some pics of the process today and post later :) cheers

timmmay

20591 posts

Uber Geek

Trusted

Lifetime subscriber

#2459707 12-Apr-2020 10:19

The professionals tend to use chemical paint stripper, or sometimes burn it off. Either is about ten or twenty times faster than manual methods.

Batman

Mad Scientist
29771 posts

Uber Geek

Trusted

Lifetime subscriber

#2459717 12-Apr-2020 10:54

mdf:
timmmay:

The key for me was stripping the entire house back to bare wood, priming with Dulux one step oil base primer / sealer, then two top coats.

You need to use the right type of primer *for the wood*. Cedar is an oily wood and you must use an oil based primer for that. But other wood (especially some nz natives - e.g. totara and matai) will react badly to oil based primer and acrylic must be used for that. Read the can and follow the instructions. If the instructions don't help, google the data sheet for the product. If that still doesn't help, look for specialist advice.

To the OP, a linbide scraper works best for rapid stripping. Once you get the angle right, you can get a lot off quite easy. Don't worry too much about scraping the wood a little, it is easy enough to backfill.

If you're paint is melting then it is too hot. Some things to check:

Have you got the right discs for your sander? If you have holes, are the discs lined up? Can you add a vacuum/better dust extraction? How fast are you moving? What grit are you using?

You will never get the edges feathered perfectly on weatherboards. By the time you prime and undercoat you will add back a bit of a layer and if it is bad, a little but of bog or permafiller will smooth things out.

Bubbling might be due to UV. But if it is relatively new paint, you might need to investigate further. Could be moisture, incorrect paint or something else. But overpainting without fixing the issue may well just lead to bubbling again.

wow you learn something everyday

mdf

3523 posts

Uber Geek

Trusted

#2459745 12-Apr-2020 12:15

Hmmm, interesting. Well, not really for you!

A picture will help. If you can manage to scrape off a solid flake of paint, can you post a picture of the back of that flake?

Are the bubbles solid, or have they split? If you poke it with a finger or finger nail, is it flexible or brittle? Any sign of "elephant wrinkles" in the paint? When you heat it with your heat gun, does it bubble solidly for a bit then burst, or just go straight to a mess?

I think you mentioned that the north face of the house is having the issues. Is it just this side of the house? Is the only difference between this face and the others the fact it is north facing/most UV? Is there a chance that either the weatherboards or the previous layers of paint are different on this side from the rest of the house?

More info would be good, but based on the "gooeyness" you've described, I'm worried that a previous layer of paint has broken down or reacted chemically to something. It might even be as simple as a previous layer of paint being applied in direct sun and drying too quickly to form a good bond. I've dealt with this once myself and it is a right PITA.

*If* that is the case, unfortunately patch repairs will likely not be enough and you will just end up with further issues later. Bare wood and start again will be the only way to ensure that you get decent results.

When I had to deal with something similar, the best solution I was able to figure out was heat gunning a small hand's width section every half meter or so. Scrape this "normally" as best you can. Then flip your linbide scraper over in your hand so the blade is at the back of your hand (little finger end). Then you can sort of use a punching type of movement that you can step into along the weatherboards. Feels to me like you get a lot more leverage this way (using chest and leg rather than arm muscles?). Once you get the knack of it, you can sort of go from heat gunned section to heat gun section pretty quickly.

But maybe post some more info first.

chonk

13 posts

Geek

#2460084 12-Apr-2020 18:15

mdf:

Hmmm, interesting. Well, not really for you!

A picture will help. If you can manage to scrape off a solid flake of paint, can you post a picture of the back of that flake?

Are the bubbles solid, or have they split? If you poke it with a finger or finger nail, is it flexible or brittle? Any sign of "elephant wrinkles" in the paint? When you heat it with your heat gun, does it bubble solidly for a bit then burst, or just go straight to a mess?

I think you mentioned that the north face of the house is having the issues. Is it just this side of the house? Is the only difference between this face and the others the fact it is north facing/most UV? Is there a chance that either the weatherboards or the previous layers of paint are different on this side from the rest of the house?

More info would be good, but based on the "gooeyness" you've described, I'm worried that a previous layer of paint has broken down or reacted chemically to something. It might even be as simple as a previous layer of paint being applied in direct sun and drying too quickly to form a good bond. I've dealt with this once myself and it is a right PITA.

*If* that is the case, unfortunately patch repairs will likely not be enough and you will just end up with further issues later. Bare wood and start again will be the only way to ensure that you get decent results.

When I had to deal with something similar, the best solution I was able to figure out was heat gunning a small hand's width section every half meter or so. Scrape this "normally" as best you can. Then flip your linbide scraper over in your hand so the blade is at the back of your hand (little finger end). Then you can sort of use a punching type of movement that you can step into along the weatherboards. Feels to me like you get a lot more leverage this way (using chest and leg rather than arm muscles?). Once you get the knack of it, you can sort of go from heat gunned section to heat gun section pretty quickly.

But maybe post some more info first.

Thanks mdf,

Firstly, an update on the sanding issue I had.. so I went back to the 125mm orbital sander that I initially was using and had ditched due to the initial “heat melting paint” problem.. what I found was that due to the cupping of the boards I was having to angle the sander to get to the bubbles and I think what was happening was that I was touching the side of the sanding disk (the disk the sanding pads attach to) to the wood and this was rubbing the paint and making the tacky mess. So a bit of practice and I was able to avoid doing that and its helped speed up the process a lot!

So, now that I am feeling better about moving forward with the sanding process, it’s good to address the cause of the bubbles. My assumption (based on some random YouTube videos etc.) was that it was due the paint being applied in direct sun. The previous owner may have painted the house herself (well, her son) as they did all the “renovations” themselves and to be blunt, they were pretty below average renovations (i.e. looked good for 5 minutes).

Some of the bubbles have split but most are still solid.. they are small, typically 5-8mm in diameter and fairly solid when touched (they don’t break easily). If I apply the heat gun, the paint does not really bubble (very faintly bubbles) then I apply the scraper (not the linbide but just a normal scraper) and it just glugs down like gummy mess).

Was hard to get a clear pic of the backside of the paint as they are small pieces but ill upload a few other pics that I did take.

The bubbles are mostly on the north side and less so but also on the west side, the other sides have no bubbling paint at all. I really don’t think that the weatherboards and paint are different on these sides of the house but not impossible.

My plan is to fix the small section that I am working on now ahead of winter and then in the spring / when weather is warmer I would continue with the rest of the walls. So I am thinking that it would be a good test to see if in time the bubbles re-appear in the part that I fixed and also a good way to learn along the way.. which at the end of the day is really why I am doing it myself :)

1 | 2