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How to paint a wooden house that has stained boards?

I am painting our entire wooden house (about 40 years old). Some is painted and some is stained. I have already started some sections and have some questions/concerns. Where I have painted the stained section, the undercoat has started to yellow/discolour. What am I meant to put on there before the undercoat?

The painted section is also not adhering, I think it is oil based and I asked the bunnings paint section man and he said the undercoat I bought would be fine to go straight on and I didn't need to sand the wood. I have spent a lot of effort painting this section and the paint just scratches straight off, it's not sticking to the wall at all. Is this normal? was I meant to stain?

Please help! Pictures attached. stained wooden wall.jpg Painted wall.jpg painted wall 2.jpg

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MitchellMc

Hi @indiaww,

It sounds like the stain is bleeding through your undercoat, which can happen if the original stain isn’t properly sealed. If you're seeing discolouration, you'll need a stain-blocking primer like Zinsser CoverStain Primer Sealer to prevent bleed-through before applying your topcoat.

For the painted section, when you say it's not adhering, are you referring to the undercoat or the final topcoat? Provided it was just a stain on the area and not a stain and varnish, then you should be able to apply an undercoat directly over it. It's varnishes that require sanding.

Could you let us know what undercoat you used? That will help determine if it’s the right product for the job.

Please let me know if you have any questions.

Mitchell

indiaww

https://www.workshop.bunnings.com.au/discussion/comment/49905#Comment_49905

Thanks Mitchell. For the undercoat I am using British Paints White water based 4 in 1 prep primer sealer undercoat. When I use the sealer how many coats do I need to do? do I do the undercoat on top of that?

With the painted section, I have done 2 coats of the undercoat but if I scratch the wall it comes straight off. As I was painting the second layer of undercoat where the roller bumped the wall the paint came straight off.

Thank you 🙂

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/87053#Comment_87053

Hi @indiaww,

Was it raw timber that you've painted the undercoat over, or did it have a shiny surface? Would you be able to take higher-quality photos of the same timber elsewhere so I can try to ascertain whether it is coated? If the undercoat hasn't adhered correctly, it's likely that the surface wasn't compatible with being coated with a standard paint. We really need to work out why it isn't bonding before we apply any other layers.

The sealer would likely require two coats to block the stain out fully. However, first, we need to identify why the undercoat didn't bond, and secondarily, we need to decide whether this coat needs to be sanded off and the underlying timber prepared to accept a coating. It sounds like the timber needed to be sanded first to remove a coating on it that prevented the undercoat from soaking in.

Mitchell

indiaww

https://www.workshop.bunnings.com.au/discussion/comment/108977#Comment_108977

The section where I don't think the undercoat is adhering to was painted. So one side is painted and now has 2 coats of undercoat which isn't sticking. The other wall where it's 'bleeding' was stained but the undercoat is sticking to the wall properly, just discoloured. So for those areas I will use the stain blocker and then do the undercoat. Photos below. The right hand wall is the painted wall.

Thank you!

House 1.jpg House 2.png House 3.png

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/121814#Comment_121814

The stain blocker is an undercoat, so there is no need to double up @indiaww. It's good that the undercoat is sticking there, and you can overcoat it with the stain blocker and then paint.

So, the section where the undercoat isn't sticking is likely due to being unable to bind to the previously painted surface. That would be due to an incompatibility between oil and water-based paint or the previous paint was glossy. In either case, that would mean the wall needed to be sanded and/or a specialised primer applied. For hard-to-paint surfaces, or if you're switching from oil-based to water-based, I'd typically lightly sand the wall to scuff up the surface to remove any gloss and then undercoat with Dulux Precision Max Adhesion primer.

To fix the issue, start by removing the undercoat, as it’s not adhering properly. You’ll need to sand or scrape it off completely. Once the surface is clean, use a medium-grit sandpaper (120-180 grit) to roughen up the existing oil-based paint, which will help new coatings adhere better. Next, apply a bonding primer such as the Precision primer mentioned above. These primers are specifically designed to bond to glossy, oil-based surfaces and provide a strong base for water-based topcoats. Over oil-based paints it's best to let the Max Adhesion cure for 5-7 days before topcoating. This allows it to fully cure and achieve its full strength.

I apologise for the effort that you've already put in. If you can let me know the store where you purchased the products, I'd be happy to put you in touch with a team member there who can help resolve the issue.

Mitchell

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