How to dry a hard-to-access space?

Question

I recently found myself having water in a closed space (under a built-in bathtub where the drain cable from the overflow protector on the side of the bath shot loose).

I do not want to cut the bath loose so I basically just have access via the single small hole (bit bigger than a vacuum hose) to access the space. I used a wet vac with a hose to get most of the water out, but then I noticed it stayed humid so I am reluctant to close it up.

I wondered if there was a way to let the space dry quickly as I waited for a few days but did not see notable progress.

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What I thought of:

• the dry vac has a blow function, perhaps I could blow some normal air in but I don't expect to reach the corners well and I am not sure if the device will catch fire if I just run it for a week to see how far we get.
• I have a dehumidifier that can dry a sizeable room, but I don't see a good way to let it interact with the air under the bath
• I could dump a lot of absorbing matter in there (few KG of salt, or cat litter) but not sure if I would regret it in a few years

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Edit: Addressing some comments

What type of flooring is under the tub?: It should be normal tiles like the rest of the bathroom floor. However even with an endoscope I can't get a good view of the entire area so I don't know if they skipped a invisible tile or whether there are other places water might puddle up.

An inspection camera(for smart phone) might help to see if all standing water is removed: After using the wet vac the water level is now almost 0 but not quite. The area seems shiny so I suspect there is perhaps half a millimeter left which is hard to vacuum, but makes me wonder whether attacking the air is sufficient.

Would you consider making a hole in the ceiling beneath the tub: that would be much more invasive than cutting out the bath, but I am starting to think of cutting a hole on the head/foot side of the (half freestanding) bath. If I get desperate I will ask a separate question about that.

Could this happen again? Very unlikely, I would be satisfied with a one off solution

Answer 1

What I would do: first, make another hole in the cavity that you want to ventilate, preferably on the opposite side from the existing hole. I don't know what your bathroom looks like, so I can't tell you where to put it, but you definitely need a second hole for cross-ventilation - you want air to be able to enter through one hole and exit out the other. Then get a cheap inline exhaust fan and set it up to blow into one of the holes. Unlike a shop vac, these fans are actually intended for continuous running.

Setting up a dehumidifier in the bathroom should speed up the drying.

Moisture-absorbing materials won't help. You want to remove the moisture, not soak it up.

Answer 2

You do need both an input and an output path for air, but you don't need 2 holes.

Instead poke a hose through the hole, up to about 1/2 the diameter of the gap. Push it as far into the space as it will go. Blow air down that. A compressor with a low pressure regulator (as used for a blower gun) would be one way; there are also small diaphragm pumps (not as small as fishtank aerators but perhaps something sold for big aquaria).

Then run the dehumidifier in the room. Ideally the air supply would be warm so run the hose through the path of any warm air heating in there, or if you have wet radiators/heated towel rails, use those to warm it. The pump should ideally draw from the dehumidifier exhaust air, because that's dry, but don't block any vents.

Occasionally rearrange the hose to poke into different corners.

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There is also one cheap moisture-absorbing material that could help: silica gel. If reusing it, bake it in the oven, then post it in, not too far. A crucial step is to get it back out again, for which you can use your vacuum cleaner, or as @Huesmann suggests, put it in a sock or similar. Unlike salt, calcium chloride, etc. which end up dissolved in water, you can remove it and remove the moisture once and for all. This may be worth doing as a follow-up step after my main suggestion, which will be more effective

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As a preliminary step, try taping the air hose to the end of your wet vac hose and poking that into places you couldn't otherwise reach

Answer 3

Rather than trying to mechanically dry the space, you might find it easier to buy a bunch of silica gel bags to consume the water. Once you dry out what you can reach, just throw these in, let them there for a couple days, and then extract them. (You can use a vacuum cleaner if you can't reach them directly -- just remember that the silica gel is wet even if it doesn't seem so, so don't let it sit in the vacuum bag.)

You can get 200g worth of the silica gel for about $5, and that should be more than enough. From wikipedia:

Silica gel is able to adsorb up to 37% of its own weight in moisture in high-humidity environments. This moisture can be released upon heating at 120 °C for extended periods of time. This makes it reusable multiple times with very little, if any, loss of efficiency.

Answer 4

A hair dryer / hot air gun at low speed and low temperature for a few hours hours with an exhaust at the other end. Just watch out the electrical equipment stays within a fairly cool range and avoids pvc and wood.

Answer 5

Depending on structure, you might want to avoid positive pressure, as it would push the moist air into the walls through any gaps.

Instead, push a vacuum cleaner hose as far inside the cavity as you can. Leave it running in suction mode. Replacement air will flow in from around the hose and cover the area up to the hose end. Rest of the cavity will dry slower through diffusion and turbulence.

I agree that there are some concerns of the vacuum cleaner overheating over time. If it has a power adjustment, that could work. And in any case I'd only run it when you are close enough to monitor occasionally. Alternatively you could rent a device meant to run continuously, such as a construction dryer with hose attachment.

A dehumidifier in the bathroom will help to make the replacement air more dry and thus capable of carrying more moisture out.

Answer 6

Fan heater will not be coupled to the hole but will work given enough time. You can also add ducting to dehumidifiers.