druderman

I have some fungus between sistered joists under my deck.
It is white and looks like spray-foam insulation.
Unfortunately, it isn't.

It seems like an important joist, since it was sistered and it supports the top of the stair.
It is about 7 feet off the ground and I can walk underneath.
This is a very very damp part of my house, since I am adjacent to wetlands.

I'd hate to pull up the decking and replace this joist, since it probably means I have to take lots of the deck apart.

There is also one other joist with similar issues.

Any advice on what to do next?

Roque Valente

hello, I am not sure if this is available in your country but here for damped surrounding coming from the floor we use simple Styrofoam and/ or ventilation of the room of course. Please note that with dry air the moist itself disappears if it has not been there for too long time.
Fungi is caused my too much moisture in the air. If the cold and wet comes up from the walls, then there is a oil based product that you need to cover the walls with, for your local brand you should ask your dealer. For much more information on fungi and moist, please visit www.roquevalente.com/deckstain.htm .

aron searle

Firstly check the condition of the beam with a screwdriver or 1mm drill bit. If the screwdriver can be driven into the timber, or the drill offers no resistance, it's knackered.

Assuming it's still solid, then remember that brush on treatment does not really penetrate into the timber. The joists should be held away from the wall or on joist hangers (so that moisture does not transfer), and it may be that water is being held between the two sisted joists, work out if/where moisture is being trapped and eliminate it.

Possibly the timber is just inadequately treated, in which case just go nuts with any treatment, but remember it's not the same as pre-pressure treatment and will only prolong their life a bit.