What is rising damp in a concrete floor?

What is rising damp in a concrete floor?

Do you have water coming up through the floor after rain and you don’t know what is going on and should you be worried? Or maybe you have water seeping through the slab foundation and don’t know what to do about it?

For a homeowner, both are something that would make you worry. I’ve also experienced it myself with my garage so I decided to do a little write-up about the problem.

If you have water coming up through the basement floor after heavy rain you might want to read about this article about pool waterproofing. It has a little bit written about negative pressure.

In pools, there might be two kinds of forces present. The one that’s made by water and the pool is containing it in, and then there is the outside pressure from land and water in it.

Sometimes the water that is saturated in the land has so much pressure that it gets in the pool outside the pool walls and it’s called negative pressure. The same can basically happen to your basement if the exterior waterproof is not OK.

Water coming up through the concrete floor in the garage can be caused by cracks in the concrete slab. It doesn’t have to be even very wide for the moisture to get in.

So what can we do to moisture coming up through the concrete floor? And what are the acceptable moisture levels in concrete floors?

How to stop water from coming through concrete floor

So there were already 2 different cases of water coming through the floor or walls. I think it’s a pretty good presentation of the two major problems so let’s go with those.

Basements and ground water

The basement is probably the harder one as it might take more effort to fix. If the water is coming from the ground outside, sealing from the inside of the basement might not work as you hope.

It might just push the waterproof off the walls and floor. If you try to paint the walls, you might soon notice little water pockets like balloons on the walls. That’s how latex paint will turn out when it’s introduced moisture beneath it in some cases.

So when you have moisture coming from the outside, you need to check if the waterproof on the exterior basement wall is whole. If there is none, you should waterproof it.

Also, making some sort of water drainage like french drain would be worth it. You could control the moisture surrounding your house and have a controlled exit for it.

If there are cracks on the wall, you should fix them properly. It will help to stop the water and also stop the cracks from getting any worse.

As always, it’s always to consult some professionals about it. Remember to consult more than 1 if you choose to, it will help you to have more neutral opinions.

Concrete slab and water

This should be the easier one to fix if the concrete slab has only little cracks and you know there is no such thing as water or sewer pipes under it. If you know there are, you should take action and call a professional.

If the concrete slab is something like the garage I mentioned I had, I know 100% there is nothing under it as I know from where my water and sewer come and where they go.

I know it’s the groundwater that’s causing me the trouble and I’ve got multiple ways to deal with it. The first thing would be the french drain I mentioned and also proper water drainage for the water that comes from the roof.

When those are taken care of and I know water coming up through the concrete floor will be minimal from then on, I’ll fix the cracks that are possibly on the concrete surface.

How do I seal a damp concrete floor

How to install damp proof membrane on concrete floor

There should be a damp proof membrane under the concrete slab already, but it might be damaged if there is moisture on the slab. Fixing it is very expensive and would need professionals to do it.

If the moisture problem isn’t that bad, you could use a liquid membrane and see if it will fix the problem with the combination of the following measures.

After that, I’d use a liquid damp proof membrane concrete floor sealer or something else that works like it and seals the concrete pores properly.

It should hold small levels of moisture off. When you look for the proper sealer, you should ask around your local hardware stores and see what they sell in your country. There should be multiple products as this is a common problem.

So how do I seal a damp concrete floor? The concrete slab needs to be clean, cracks should be fixed, and then it’s a paintbrush and paint roller job. You need to look at what the sealer manufacturer says about what products should be used on the concrete.

There can be primers for the coatings and sealers or it can be just one sealer job.

How to stop rising damp in concrete

So if you have damp concrete-like previously mentioned, the reasons for it can be many. If you have drainage around the slab installed, it could be damaged. Maybe you have removed trees around the building so there is more moisture.

Those are the first things I’d look for. If there is no proper drainage, I’d make it a weekend project and make one, it’s not hard.

If that won’t work I’d look at how to treat damp concrete floors like previously described. If the damp floor treatment doesn’t work for some reason, the problem is more serious and needs bigger intervention.

Still, if the amount of moisture is only a little, a damp proofing floor should work. There are all kinds of concrete floor problems that could be the cause, it’s best to start troubleshooting from the cheap end.

How to prevent moisture problems on concrete floor

If you want to avoid fixing moisture problems in your concrete slab, it’s best to try to avoid them by preventing them.

If you start to see some water, it’s good to locate the cause immediately. If there are no proper water control systems installed, maybe it’s time to do so.

No big trees should be growing near the slab, roots can cause trouble for the concrete easily.

The concrete floors should be sealed. It’s porous by nature so sealing them will help you to stop the water.

If cracks form, it’s good to repair them as soon as possible. Usually, these will only spread with time so if you stop them early you will save yourself from some trouble.


I hope you got an answer for what is rising damp in a concrete floor. I might have gotten a little carried away with solutions, but it’s basically uncontrolled water.

If you live in a country where it rains, be it all the time or seasonally, there are always times when the ground is saturated with water. Now if the foundation is in a puddle, lower than the ground around it, it’s natural the water will find the way up to your slab.

For that kind of reason when we build, the structures are placed on higher ground. If the slab sinks or the land around it transforms so that the water cannot flow in proper drainages, it’s trouble.

French drainages and such can help a little, but these kinds of problems should be handled as a whole entity I think. No use placing a small fix when the bigger problem remains.

It’s also the reason why I like to repeat the professional consultation. A lot of product reviews and such tell how awesome it is for fixing damp concrete floors etc., but sometimes they forget to mention probable causes.

Anyway, If you know your concrete work and have some common sense, some of the problems can be handled with research and work.