Beam Restoration reveals a lot of woodworm decay

[Mulder]

Hi

We've just had our internal beams cleaned to remove a thick coating of black paint. Now they have been revealed, I can see why they were covered in the first place. They have a lot of woodworm damage and decay. 25mm deep in some places!

Keen to hear people's thoughts, good and bad and any recommendations for how best to go about making them more presentable. Is abrasive sanding back to the hardwood a good course of action?

Worst case, I was considering filling in the cracks (not sure how) and painting white with lime wash.

 

[Cubist]

Don't be too quick to judge. The thick paint may have been the real culprit and cause of much of that decay and could very easily have prevented previous owners detecting that a moisture build up behind the paint is what attracted the woodworm - no one gets a perfect finish with paint and a couple of pin holes or access through those shakes (the cracks) for the beetles would have been very possible, Before discussing remediation can you tell us please What are the Width and Depth dimensions of those timbers and how was the old paint cleaned away?

 

[Mulder]

They were blasted, from what I can tell, to a good standard as I was expecting all of the soft rot to have been blasted away, alas no.
I would estimate the beams to be 300-400mm each way. I'll have to get in the loft to measure exactly.

The beam on the other side has actually been reinforced with a newer one, probably 100 years ago.

 

[Cubist]

Media blasting can produce considerable collateral damage to surrounding surfaces/materials and whoever did this work was very good given they've even managed to leave that woodchip paper intact. I asked about the dimensions of the timbers because sometimes purlins, joists and the like in old timber frames were formed using circa 100x100mm timbers. At 300-400mm they are pretty massive, particularly in what I suspect is a gambrel or mansard roof, but such dimensions do reduce one of my key concerns insofar that removing any material from them can obviously weaken them. However, my primary concern at the present is that the worms, and the media blasting, will have stripped away the softer tissues of the wood leaving behind the much harder indigestible timber behind - and if that's ancient oak then you will find that they will resist, and can even destroy, the strongest electrical sander or multi-tool. The latter also poses an additional danger insofar that the blades used to cut and sculpt the timber can produce enough friction to set the timbers alight.

Frankly I think your best options would be to consider and decide upon what your preferred final appearance of the timbers would be in terms of a gloss or matte finish and colour and then pursue a strategy of filling the holes and gaps with a suitable material and using camouflage paint techniques to hide the results. I've had some success here using this approach and can suggest some materials, tools and techniques if you're interested.

 

[Mulder]

Thanks for the reassurance cubist.
I've had a go at sanding a small section with a 60 grit flap disc on a grinder. It removed the loose rot and did improve the appearance significantly but still not completely.

I just wanted to check I wasn't committing some carnal sin by removing so much material.

I'm not sure if the finish will be quite what we hoping for, especially given the size of those cracks. We may end up doing as you say, fill the holes and gaps then paint. At least the paint will be more subtle (and breathable) than the previous mess.