How do I prepare or paint over old timber?

[keterlich]

We have an old stone cottage that was built in 1830. The architraves and skirtings are the beautiful large, old style timber mouldings however they have been stained with a mixture of kerosene and bitumen/asphalt oil (that's what I've been told). In some spots there is a sheen and I'm not sure if someone has varnished it at some stage as well.  The doorways and windowsills are very deep due to the thickness of the stone walls so there is a lot of area to cover. 

What is the best product to undercoat or seal them with before painting them? Should I sand them lightly or try to sand back to bare timber? The timber itself is in very good condition so not much sanding is needed to bring them back to good condition from a surface damage perspective.  I want to paint them with Dulux Aquanamel for the top coats.

Thanks for any help!

[MitchellMc · Accepted solution]

Hi @keterlich,

Painting over old timber coated could be challenging, especially given the possibility that the coating has penetrated deeply into the wood. This situation becomes more complicated when there's a chance the timber has also been varnished, which may create a shiny surface that hinders paint adhesion. When working with such old, complex coatings, fully removing the layers may not be feasible, as the substances likely seeped into the grain over time. Over-sanding to remove the coating could alter the profile of the original mouldings, which is not ideal when trying to preserve the character of a heritage property.

To ensure any new paint bonds well, a test section is important. Preparing a small area and painting it with your chosen products will help you see how well the paint adheres without committing to the entire surface. Once dry, check if the paint bonds strongly by gently scratching or pressing it; this test will reveal how well the coating is likely to perform on a larger scale. Given the potential for the old coating to release oils that could interfere with paint, using an oil-based primer may provide a better foundation than a water-based one. Oil-based primers are designed to block stains and can seal in underlying oils, creating a stable base for water-based topcoats like Dulux Aquanamel.

For surface preparation, begin with light sanding to remove any sheen and create a rougher texture for better adhesion. Avoid heavy sanding to maintain the integrity of the mouldings, then thoroughly clean the area with Sugar Soap or a similar degreaser to ensure that any remaining residue is removed. After this preparation, apply an oil-based primer to the test section and let it dry before covering with Aquanamel. If the test shows strong adhesion, proceed with this approach across the entire area. 

Please let me know if you have any questions.

Mitchell

[keterlich]

Thanks so much for the detailed reply Mitchell!

I'll send some before and after photos.

Kathy