Garage Floor Damp Problem and Ideas

[brightblue]

Hi all,

I’ve lived in our house with a double garage for about 9 years. The garage is single skinned, has a concrete floor is heated with a small rad and I’ve had a dehumidifier in it for most of the time I’ve owned it. Soon after moving I installed an interlocking vinyl floor which had held up well but I’ve always suspected was getting damp underneath. Today after noticing some moisture and white staining around the tile joints I finally got around to lifting a centre section of tiles and found them all to be wet on the underside (see pics). The garage has generally never been overly damp and maintains a sub 60% humidity level most of the year (with the help of the dehumidifier and radiator).

Does anyone have experience with this sort of problem? Do you think the concrete floor is the problem or are the floor tiles just stopping it “breathing”, causing condensation to form underneath. Could vented floor tiles solve the problem or do I need seal the floor with some form of epoxy first?

Just throwing the questions out there but not sure they are the right ones, just hoping there are some experts or experiences out there to point me in the right direction!

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Whatever type of tile you fit to the surface and how well they ventilate, the problem of moisture rising through the concrete slab will remain.

My advice would be to install a inexpensive moisture resistant barrier directly on top of the concrete and relay your existing tiles on top.

You might want to try using standard grade roofing felt rolled out and weighted along the edges of the garage. It tends to want to curl up when first laid but soon goes flat.

I appreciate this isn’t going to be the best look, but it is effective.

 

[James3200GTA]

Just my 5 cents worth: If the concrete is sealed off by non-venting tiles any moisture trapped will collect there as the space underneath the tiles does exchange air when it is not airtight due to gaps, expansion and contraction etc.

Warm air contains more moisture and when the garage concrete cools or its temp is under the dew point, it condenses. The air exchange is enough to bring moisture in over a period of time, but not enough the evaporate and dissipate it. This is not helped by the fact that some of the moisture may penetrate the concrete top layer acting as a sponge retaining the water.

Most extreme example are insultated aircon piping. It is recommended to use 1 size smaller ID insulation and glue it to prevent the exchange of air inbetween the insulation and the pipe and prevent condensation. I've seen bad excuted instals with water runnning out like it's the Niagra falls. Other examples is a doormat out in the rain. Even when it has not been raining for days, the mat will still be wet underneath.

Coating (sealing) the concrete will prevent moisture coming up from the ground but does not help to the air exchange. Solution would be to use the vented tiles or glue the non vented ones in place stopping any air exchange (which the negates the removable part of the tiles).
Also recommend to seal the first few layers of brick above the floor as moisture may also travel through the walls.

Other option would be underfloor heating, where the temperature of the air space between the floor and the tiles is kept above dew point. A lot of work, but is nice in winter when working on the cars.
Ventilation however will remain key for any applied solution to expel any moisture.

 

[Zep]

All the conversations with our garage build have led to the fact that getting the floor right is key and that starts at the foundation stage. Concrete acts like a sponge it will soak up and pass through moisture which is fine if its not covered and has decent airflow over the surface but if you build an air tight box on top of it or seal the surface the moisture has nowhere to go. As Phil did we will be putting a membrane down under the main concrete slab which will also rise up the sides to minimise the amount of moisture absorbed, that an a polished concrete surface should allow any moisture to escape naturally.

The next step is keep ing the garage vented, if its used naturally and doors are opened on a regular basis this is all that is required but if you don't open the garage for a month of so then the moisture will build unless you have additional ventilation a bit like the condensation that can build up in an old fridge. Heat and Dehumidifiers can help but airflow is the best natural solution.

The key is not trying to stop moisture, more to manage it so it doesn't become an issue.

This is kind of true, but there are challenges with the natural vent route.

A well sealed and insulated space, with no route of ingress for moisture - I.e. DPCs and well sealed doors) is unlikely to suffer from the build up of moisture and so will remain generally dry if undisturbed.

An unsealed, but not well ventilated space will suffer from a build up of moisture from external sources.

Allowing airflow will, under most circumstances, allow moisture to escape regulating the humidity. The main point here is that for external air to help humidity, it needs to be less humid than the space you are looking to control. Otherwise your external air will increase the humidity.

Circumstances when this can happen are when it is raining, or has recently rained and when there is a drop in temperature overnight (both summer and winter). If you go from 15 C and 50% RH to 5 C, the humidity will be 100% (and so condensation will form on cool surfaces)

I’ve had to deal with some equipment failing of late in a ventilated space. It’s designed to work with RH between 30% and 90% and most of the year the open vent space is perfectly fine. But as winter comes in we see regular failures because the RH spikes as the temp drops, condensation forms on the PCBs and the magic smoke escapes.

The moral is, if you really want to control humidity, it needs to be sealed.

 

[c4sman]

Whatever type of tile you fit to the surface and how well they ventilate, the problem of moisture rising through the concrete slab will remain.

My advice would be to install a inexpensive moisture resistant barrier directly on top of the concrete and relay your existing tiles on top.

You might want to try using standard grade roofing felt rolled out and weighted along the edges of the garage. It tends to want to curl up when first laid but soon goes flat.

I appreciate this isn’t going to be the best look, but it is effective.

I think a painted on seal is more likely to be the solution I opt for due to the factor of the cars coming in and out. I suspect a roofing type covering won’t cope with a 1.7tn GT sitting on it for long periods so will try to find a paint on solution and cover with vented tiles. The brick walls have a damp proof layer that I can see two bricks off the ground BTW so no sure if I should paint all the way up to that layer?

 

[TimR]

If you need to control what’s called “ bridging” , ( although the brick courses don’t strictly need it to pass moisture above your floor to the interior air mass in your case )then you probably should also seal the bricks up to the DPC level. Depends whether the moisture wicked from this small area of brick is significant enough to warrant the effort & expense. And this will vary on the type of brick used to some degree, as far as I understand it…

 

[Zep]

I think a painted on seal is more likely to be the solution I opt for due to the factor of the cars coming in and out. I suspect a roofing type covering won’t cope with a 1.7tn GT sitting on it for long periods so will try to find a paint on solution and cover with vented tiles. The brick walls have a damp proof layer that I can see two bricks off the ground BTW so no sure if I should paint all the way up to that layer?

Seriously - don't use the vented tiles. If air cannot pass over it, condensation will not form. Vented tiles will allow air to move over the cold surface, promoting condensation as Allan saw above.

Think about it in these terms. When it is below freezing overnight, ice forms on cars that were parked before the temperature drops below zero, because it freezes condensation which has formed as the temperature drops. If you park a car with a clear screen after it has dropped below zero, no ice forms, because there is no moisture to condenser.

Providing the concrete surface is sealed to prevent moisture rising up and has a barrier to prevent airflow / vapour from penetrating from above (the non-vented tiles) - no condensation will form, because what little air is between the tile and the floor will not contain a lot of water and that water will not be replenished from external sources.

And yes, paint up to (or a bit past) the DPC.

 

[c4sman]

Seriously - don't use the vented tiles. If air cannot pass over it, condensation will not form. Vented tiles will allow air to move over the cold surface, promoting condensation as Allan saw above.

Think about it in these terms. When it is below freezing overnight, ice forms on cars that were parked before the temperature drops below zero, because it freezes condensation which has formed as the temperature drops. If you park a car with a clear screen after it has dropped below zero, no ice forms, because there is no moisture to condenser.

Providing the concrete surface is sealed to prevent moisture rising up and has a barrier to prevent airflow / vapour from penetrating from above (the non-vented tiles) - no condensation will form, because what little air is between the tile and the floor will not contain a lot of water and that water will not be replenished from external sources.

And yes, paint up to (or a bit past) the DPC.

I guess I can go without vented tiles and see how things perform as there is zero cost (I already have the tiles). I can then try an alternative if I’m still suffering with condensation under the tiles.

 

[c4sman]

So… today I started the first stage of getting ready to deploy the liquid damp proof membrane on the floor by removing all the tiles. I’ve had a wobble however as I found some parts of the concrete under the tiles completely dry, whilst other areas effectively were soaking wet (2-3mm of water in the “grooves” of the concrete). Noticed that the water was slippery and potentially soapy! My worry now is the whether the source of my damp is the concrete OR is a wet car from rain and or washing is dripping onto my tiles, and the interlocking tiles let water through the interlock, and then trap it there. With no airflow it builds up and a small amount makes it way back out of the interlocks. This makes me think that investing in vented tiles after I seal the floor might be the only solution as the water would settle on the DPM but be able to evaporate off rather than remaining trapped?

I defo need to seal the floor either way.

Let me know your thoughts!

 

[midlifecrisis]

It's been very dry weather for the past week or so. I reckon you should lift all the tiles and see what's what. Give the garage a good airing whilst it's relatively warm and dry. The concrete should be dry as the water table should have dropped a bit.
It'll rain next week and you'll see quite clearly whether it's damp seeping through or wet car water finding the low point.

 

[James3200GTA]

It's been very dry weather for the past week or so. I reckon you should lift all the tiles and see what's what. Give the garage a good airing whilst it's relatively warm and dry. The concrete should be dry as the water table should have dropped a bit.
It'll rain next week and you'll see quite clearly whether it's damp seeping through or wet car water finding the low point.

Good point. Returning back to my earlier comment, imo you need to take into account that moisture may get into your garage, especially if you park a wet car.

Venting the garage is the only way of getting rid of that. It can be aided if you can get heating in the garage. I've got mine at 7dgr C in winter (anti freeze setting of the central heating radiator thermostat)

When i park the car wet, it'll stay wet for a few days, but it is dry after that. If it freezes outside the vent air will have low RH to start with, get heated in the garage lowering the RH even more, then it's dry within a day.

If you trap the moisture in the garage, temp drops, eveything gets wet from condensation and mould will start to grow (health hazard).

So my advice:
1. Prevent moisture entering via the construction
2. Add venting, also under the tiles
3. If possible add heating, a few degrees above outside ambient temp should do it. 17drgC + in the garage if you want to be absolutely sure.

As for Zep's fried electronics: when there's a risk of condensation, standstill heating is to be installed in the electronics cabinet.
Even if you where to seal it to IP68, you'll probably do that in a 20dgrC workshop. So unless the workshop temp is at -20dgr when you seal it or purge it with dried air, when put outside the moisture still condense and fubars the pcbs.
Of course you can mess about with silicone moisture absorbers, these have their own challenges. Ask me how I know.
Conformal on the pcbs will add some extra redundance
Anyway on topic, preventing moisture from entering a garage is impossible if you actually use the car and garage and thus should be accounted for

Some background reading:

The Importance of Good Ventilation | EnviroVent

Improving the ventilation in your home can help alleviate condensation, damp, and improve air quality.

www.envirovent.com

Moisture control and ventilation - WHO Guidelines for Indoor Air Quality - NCBI Bookshelf

 

[c4sman]

Thanks all. A couple of bits of info. The garage is heated and has a dehumidifier that operates all year. I’ve now removed all the tiles and it hasn’t rained for a week or so so everything around us is very dry so I’ll be able to see if the concrete drys out and what it does when it rains. I think vented tiles will be necessary as I can’t avoid putting a wet car away. I have 4 double glazed windows at the end of the garage so can ventilate easily if necessary. Will report back when I learn more, thanks as always!

 

[James3200GTA]

Thanks all. A couple of bits of info. The garage is heated and has a dehumidifier that operates all year. I’ve now removed all the tiles and it hasn’t rained for a week or so so everything around us is very dry so I’ll be able to see if the concrete drys out and what it does when it rains. I think vented tiles will be necessary as I can’t avoid putting a wet car away. I have 4 double glazed windows at the end of the garage so can ventilate easily if necessary. Will report back when I learn more, thanks as always!

That's almost the ideal set-up.
Might I suggest adding a movable fan blowing air on the wet patch to aid the drying of the concrete for the time being. Once it starts raining again it'll be easier to see where the water comes from if everything is bone dry.

If you can get hold of a flir, you'll be able to detect damp patches earlier as these tend to be a few degrees colder than dry patches, even before it is visually noticable. It'll also make defects in the insulation more clear. These also tend to be colder and following the RH theory tend to be locations of local condensation.

 

[Bebs]

Thanks all. A couple of bits of info. The garage is heated and has a dehumidifier that operates all year. I’ve now removed all the tiles and it hasn’t rained for a week or so so everything around us is very dry so I’ll be able to see if the concrete drys out and what it does when it rains. I think vented tiles will be necessary as I can’t avoid putting a wet car away. I have 4 double glazed windows at the end of the garage so can ventilate easily if necessary. Will report back when I learn more, thanks as always!

Maybe consider tilling the entire floor with porcelain tiles after sealing it?
I did that to my 60 square meter garage floor and it makes it very easy to spot any standing water, leaks, cleaning/wiping the floor etc.

 

[RoaryRati]

We put down some left over vinyl so as to spot what's happening - but as our garage doors for so badly our garage is like a 'closed' car port which works fine, unless it is really cold and damp (that happens a couple of days a year)

 

[midlifecrisis]

Maybe consider tilling the entire floor with porcelain tiles after sealing it?
I did that to my 60 square meter garage floor and it makes it very easy to spot any standing water, leaks, cleaning/wiping the floor etc.


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That's on my list of things to do. After, ASHP, Solar/battery, new kitchen tops, etc, etc, blah blah blah

 

[Bebs]

That's on my list of things to do. After, new kitchen tops

Let the missus wait

 

[James3200GTA]

That's on my list of things to do. After, ASHP, Solar/battery, new kitchen tops, etc, etc, blah blah blah

Did most of those, tiling is also on the wish list as one of the last remaining items, but don't know where to leave all my cr@p.
A garage like Bebs' would be a dream, unfortunately no space here to extend here.

 

[c4sman]

Maybe consider tilling the entire floor with porcelain tiles after sealing it?
I did that to my 60 square meter garage floor and it makes it very easy to spot any standing water, leaks, cleaning/wiping the floor etc.


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That looks lovely but I cannot justify the cost. My tilling sucks which means bringing in a trade….

 

[c4sman]

I jet washed all the crud out that was underneath the tiles today in prep for DPM to make sure it adheres. So the garage is now damper than ever

 

[Bebs]

That looks lovely but I cannot justify the cost. My tilling sucks which means bringing in a trade….

It’s really not that expensive. Tiler day rate of say £180-200. Think it was 5 days for my 3 door garage.
Tiles were just cheapie B&Q porcelain jobbies at around £600-700. (Must be porcelain as they don’t crack under the weight)