What is this growing on my garage floor?

[mypinkmonkey]

We have some kind of fluffy growth on our garage floor - photo attached. We have brushed it off but it comes back. Any ideas what it may be and how I can get rid if it please! Looks a bit like fake snow!

[charlestonchaplin]

Yup, efflorescence. I take it the floor has suffered repeated flooding of some sort, which moves soluble salts through building materials to the surface. When the floor dries out you see the salts.

[mypinkmonkey]

Ah that's interesting thank you. It hasn't suffered any flooding at all so that isn't the cause. Will it keep coming back?

[PigletJohn]

it may also happen if the floor is damp for some other reason, such as newly poured, rainwater running under the door, plumbing or roof leak, no DPM under the slab. You only see it as the concrete dries out.

If you are in a chalky area you may also see it coming out of the lowest two courses of bricks in your walls. Sweep a bit up and drip vinegar on it, it will probably fizz. Don't try to wash it away with water, it will soak back in and then appear again, worse.

If the concrete has a DPM and is protected from damp, it will eventually stop, but this may take years.

[mypinkmonkey]

Ok thanks PigletJohn the garage was built 3 years ago and does have a DPM. Apologies if this is a stupid question - would I have seen the water on the surface of the floor or can it be coming from under the floor? As the floor has never been soaked- rain water doesn't come in and there are no water pipes under the garage floor I'm at a loss as to the cause of the efflorescence. I guess we will just have to keep an eye on it.

[PigletJohn]

garage floors are cold and not usually exposed to warmth or sunlight, so they are slow to dry. If it is not part of the house, there is a chance rainwater could penetrate the walls, especially if there is a leaking gutter or downpipe. Integral garages usually have cavity walls and are built on the house slab to a higher standard.

If you tape clear sheets of plastic tightly to the floor, you may see damp or water appear under the plastic as it rises through the concrete and cannot evaporate. If there are particular patches that are especially damp there might be a leak. For example my incoming water main is under the garage floor (but the dpm should stop damp rising) and the soil pipe and water pipes run in a plumbing duct in the corner.

If you drive the car in on a rainy or snowy day, water will drip off it.