How to dry old, damp concrete & penetrating or film-forming sealer?

[BobLoblaw]

Hello workshop community,

Hoping you can help! I'm in the process of reducing moisture in a small shed (about 2.65m x 1.8m). It's attached directly to the concrete path, which is very old, and has gotten a lot of water running through it, causing it to get damp and dirty. I've pressure cleaned it and sealed where the walls meet the floor. Next step, sealing the concrete. This is a temporary fix that just needs to tide me over for a couple of years. 

Qu. 1. The middle of the "floor" is damp. Is there a way of quickly drying it enough to seal? E.g. some sort of heater (hired) that is ok in the small space, or an absorbent material?

Q2. Penetrating or film-forming sealant? I got Crommelin Paving and Concrete sealer, which is penetrating and allows the concrete to breathe. Thought this might be good to let deeper moisture out during summer while still repelling moisture, but I realise there's a good chance my logic is wrong.

Thank you in advance for any help or thoughts!

BLL

[Jason]

Sorry that the community missed this one @BobLoblaw. How's it going? Is the middle of the floor still damp?

Jason

[Mathy]

Hi @BobLoblaw - Things can take a long while to dry out. I wouldn’t use a “film forming” sealer, it will just come off where the damp is. The Crommelin product looks suitable. I haven’t used it, but they make good products and the “How to Guide” suggests that it would work in your situation.

How does the concrete look now you’ve pressure cleaned it? I’m asking because, if it’s a temporary fix and the concrete is serviceable “as is”, I’d just leave it be and use the money saved on something else, cheers Deb

[BobLoblaw]

Hi @Mathy 

thanks for your answer, sorry I didn’t see it till now. Funnily enough it’s still relevant as i had to go away for a few months just when the floor was dry enough. I came back during winter and am only now getting back to thinking of this. 

my cleaning and taping managed to allow more dampness in and then locked it in during winter. More mould and rust. Oops. So I will have to just do things properly! Funny how that happens!

[MitchellMc]

Hi @BobLoblaw,

Many thanks for updating us on the project.

Just to clarify, this moisture is coming from the ground/pathway and rising through the concrete? If a builders underlay was not used when constructing the slab it is unlikely that it will ever fully dry out. Each time it rains the concrete will just soak in more moisture from the surrounding area. If you feel the pathway is transferring most of the moisture into the sheds slab then you might like to look at de-coupling it. You could cut a groove where the path meets the slab and insert some type of water-impermeable membrane or plastic damp coarse.

You might like to look at installing some drainage around the perimeter of the sheds slab to stop groundwater penetrating the sides of it. This would involve digging a channel down slightly deeper than the sheds slab, installing Draincoil at the bottom and filling with Bastion 10mm Blue Metal - 20kg. The Draincoil would then be run to another location or a stormwater outlet. 

Please let us know if you need further information or had questions.

Mitchell

[BobLoblaw]

Hi @MitchellMc ,

Thanks for your advice on this. 

The damp is coming up through the concrete and the cement-backed tape didn’t form a complete seal either unfortunately. The shed was just bolted directly to an existing part of a pathway which was not in great shape to begin with. All before my time!

It’s just a small shed so it won’t be too much trouble to remove it and get it right (I think). I’ll plan something out and come back to the brains trust if needed. 

Thanks again

B