Damp proofing concrete floors

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Damp proofing concrete floors

This topic has 13 replies, 13 voices, and was last updated 6 April 2025 at 02:52 by Duff Machinist.

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3 April 2025 at 17:32 #791828
Duff Machinist
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@duffmachinist36701
Howdo all,

I’ve googled and checked the forum for relevant topics, but didn’t find anything that helped greatly with how to damp proof a concrete floor.

Situation and problem: I have a garage, abutting the house, that will be converted into a workshop (to house a lathe, mill, etc.). The concrete floor suffers from rising damp in the winter (cos’ no damp proof membrane).

Objective: I wish to damp proof the floor and ensure the damp proofing is also durable.

Potential solutions: Reconstruction of the floor is out of the question, so a more practical solution would be to coat the floor with a polyurea or epoxy, or similar coating/covering.

Problem: It has been difficult to separate the wheat (facts) from the chaff (paid sponsorship and advertising guff) on the interweb, while it has been rather annoying to read several examples of contradiction as to the effectiveness of potential solutions.

The question to the forum: Has anyone had any real-world experience in damp proofing a concrete floor within the parameters given above, and if so, what did you learn? What methods? What materials? What products?

Many thanks,

Duff
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3 April 2025 at 19:02 #791848
duncan webster 1
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@duncanwebster1
I got mastic asphalt laid on mine. Worked fine.
3 April 2025 at 19:09 #791852
DC31k
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@dc31k
Have you considered option (b)? Lay down a damp proof membrane (1200g polythene), put 25mm polystyrene over it and lay T&G chipboard on that?

It makes a warm, comfortable and damp-free floor.

Minor disadvantage is it might need perhaps 100 x 100 x 6mm spreader plates under any concentrated loads (like the feet of your lathe).
3 April 2025 at 19:10 #791856
Martin Connelly
Participant
@martinconnelly55370
I have a concrete floor that was covered with a plastic DPM then 3mm foam insulating boards (to protect the DPM) followed by standard tongue and groove flooring chipboard. Never had a problem with damp. I don’t have anything bolted down through the floor.

Martin C
3 April 2025 at 19:14 #791858
Martin Kyte
Participant
@martinkyte99762
I did that only I used underlay over the membrane with flooring chipboard on top. The lathe has bolts right through into the concrete with steel bushes to protrude through the flooring so the lathe effectively sits on the concrete.

The mill just sits on the floor.
3 April 2025 at 19:40 #791860
John Haine
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@johnhaine32865
Synthaprufe on the concrete, then your choice of build-up for the floor.
3 April 2025 at 20:31 #791871
Sonic Escape
Participant
@sonicescape38234
But can you figure out from where the moisture is coming from? If it is from the ground, and because of the rain this could be solved in other ways. Like digging a trench around the garage and filling it with gravel. This should break the horizontal water flow.

I’m suggesting this because I had a neighbor on the ground floor of my apartment building that had a similar problem. In his case it was due to condensation. He also tried to cover the floor with waterproof materials but the result was bad smell in the house.
4 April 2025 at 06:21 #791913
Neil Lickfold
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@neillickfold44316
I got a company in that prep and then applied their primer and then the seal top coat. 2 top coats and one initial primer. The coating is a 2 part product that is used in commercial buildings that have a sealed concrete floor. Its an epoxy coating and is very hard wearing. Been down for over 5 years now, and apart from where I have dropped a heavy piece of bar stock and made a chip in it, it is still in very god condition. The product is Epotread 1000 Semi Gloss, and we got the standard colour cloud grey, which is lighter than the regular grey.

Our floor needed some high spots to be ground off and corrected, which was 2/3 of the total bill. I knew nothing about concrete grinding, so got the experts in to do it. They also had the very good dust extraction systems as well.

Neil
4 April 2025 at 08:10 #791929
Hollowpoint
Participant
@hollowpoint
You could use tanking slurry.
4 April 2025 at 09:01 #791938
Charles Lamont
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@charleslamont71117
On 4 April 2025 at 06:21 Neil Lickfold Said:

Been down for over 5 years now, and apart from where I have dropped a heavy piece of bar stock and made a chip in it, it is still in very god condition.

That is one reason why I like my chipboard. Things dropped on it tend not to show damage.
4 April 2025 at 09:34 #791942
JohnF
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@johnf59703
Duff, I think most things have been said but a couple of bits !!

As far as bolting down machines this is probably not going to be possible but you can use the machine mounting feet and use “extenders” if needs be to add stability. e.g. Myford lathes on their stands are top heavy and need a wider base.

There are epoxy coatings available that look attractive but I personally have never used them. Neither have I used this company yet but worth a look, my problem is a leaking inspection pit in the garage and they seem confident it can be fixed but need to do a site inspection before committing

Basement Tanking, Structural Waterproofing & Damp Proofing Systems

John
4 April 2025 at 10:57 #791961
rjenkinsgb
Participant
@rjenkinsgb
Sodium Silicate (Water glass) can be used to seal concrete – it soaks in to the pores and as it dries it turns in to a kind of glass within the concrete surface. It can need 2 – 3 applications with full drying in between, but should then block any damp and prevent whatever paint or other coating from being lifted.

Give it a good brushing after the final coat to remove any loose dried residue.

(I got a 25L drum from ebay very cheaply, to do my garage floor once I get it cleared for refinishing).

Concrete and general masonry treatment

Concrete treated with a sodium silicate solution helps to significantly reduce porosity in most masonry products such as concrete, stucco, plasters. A chemical reaction occurs with the excess Ca(OH)2 in the concrete that permanently binds the silicates with the surface making them far more wearable and water repellent. Apply a solution of sodium silicate, diluted 1 part silicate with up to 4 parts water by brush or low pressure sprayer. Depending on porosity of concrete etc 2 or 3 applications may be necessary. Please Note that concrete and masonary surfaces may appear darker after treatment.
4 April 2025 at 19:57 #792029
Bazyle
Participant
@bazyle
Understand the difference between a concrete sealer or floor paint that is really about stopping dust and a real dpc. The sealer expects a dry surface that stays dry. Damp due to no DPC is often under pressure so will just push up and cause the paint to bubble.
Often the only way is a full coverage plastic sheet that guides the moisture to the sides where some kind of ventilation provision is made to allow it to escape. That typically means going a little up the walls to be join up with the wall DPC else the moisture gets into the wall and advances from there.
6 April 2025 at 02:52 #792136
Duff Machinist
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@duffmachinist36701
On 3 April 2025 at 20:31 Sonic Escape Said:

But can you figure out from where the moisture is coming from? If it is from the ground, and because of the rain this could be solved in other ways. Like digging a trench around the garage and filling it with gravel.

Thanks Sonic. Yep, I had a look a couple of days ago. There is a French drain on one side, but not the other two, and more soil (clay) needs to be removed regardless. I will rectify that issue.

On 4 April 2025 at 10:57 rjenkinsgb Said:

Sodium Silicate (Water glass) can be used to seal concrete

Thanks RJ. Hadn’t considered that and it sounds promising. I’ll look into it further.

…and thanks everyone else. I’ll look into the tanking slurry sides of things again (including the link – thanks John), although as I said the floor top coating needs to be durable as a lot of heavy things will be moved around. This also means that chipboard and the likes won’t really work sadly, but thanks for the suggestions. It is appreciated. …and yep, I make the distinction between sealers/paint and DPM.

I’ll see how the French drain goes, although I won’t know how effective it will be until the winter. If there’s still an issue, then I’ll follow up on the above suggestions.

Cheers,

Duff.
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