Garage Floor Damp Problem and Ideas

[c4sman]

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!

 

[c4sman]

Considering switching to this type of vented tile

 

[SE_123]

I'm not expert, but I would suspect it is almost certainly the concrete getting cold, moisture forms in the small air gap above, but there is not enough air flow for it to dry.

Those vented tiles look like they should be worth a try

 

[Scaf]

Are you sure the garage floor has a damp proof membrane?

When my sister converted a garage from a 1980’s house into living accommodation she discovered there was no damp proof membrane in the floor, so that was job nos 1.

 

[c4sman]

Are you sure the garage floor has a damp proof membrane?

When my Wooster converted a garage from a 1980’s house into living accommodation she discovered there was no damp proof membrane in the floor, so that was job nos 1.

I’m not 100% sure. It would have been laid in the late 70s or early 80s when it would have been standard practice but not guaranteed. Not sure how I check?

 

[DLax69]

My guess is also no vapo(u)r barrier...and you can't really check for that in a non-destructive manner. Concrete can be permeable if the pores are interconnected. Easiest first step is to eliminate the vinyl altogether...

 

[philw696]

That was my thoughts too.
When I was renovating my workshop putting in a good concrete floor it was essential for a decent membrane to be put down.
Cost a lot but then it's 225 square meters.
4 years on and the the two Renault 16 projects have not deteriorated further in the back corner.

 

[allandwf]

Tiles are stopping it breathing. I painted mine nice shiny and red. Worst thing I ever did, bad condensation problems in the winter as the concrete holds the cold and then warmer damp air condenses.

 

[mjheathcote]

I've got thick ecotile PVC flooring and don't have issues, as I've mentioned before elsewhere my humidity is just over 40% with no dehumidifier.
Infact every few years I scrub and pressure wash the floor, and it quickly dries out underneath naturally.
So i don't think it is the flooring, although it is trapping what is constantly rising so never drys out.
If you are getting salty deposits it's definitely rising damp from the concrete.

 

[Zep]

It is the time of year where this sort of thing happens. That you need dehum and heat to keep it sub 60% means you have a source of damp.

My money is on a small amount of water coming through the concrete - the tiles mean that the floor is effectively insulated from the internal space, and no air flows over the cold floor. If you use ventilated tiles, you will run your dehum more as more of that moisture will make it into the occupied space.

 

[mjheathcote]

The salty deposits:

Concrete efflorescence is a white or grayish deposit of mineral salts that forms on the surface of concrete when moisture evaporates:

• What it is
  Efflorescence is a natural process that occurs when water migrates through concrete and dissolves soluble salts within the material. The salts are then left behind on the surface as the water evaporates.
  
  
• Where it occurs
  Efflorescence is most often found in underground car parks and other subfloor areas.
  
  
• How to remove it
  You can remove efflorescence by:
  • • Scrubbing with a dry brush
    • Scrubbing with water
    • Light waterblasting
    • Using a product designed to remove mineral buildup
    • Using an acidic solution of one part hydrochloric acid in 50 or 100 parts of water
• • How to prevent it
    You can prevent efflorescence by applying a waterproofing sealant to concrete surfaces. You'll need to reapply the sealant every three to 10 years.

Efflorescence is unsightly but generally harmless. However, it can indicate damp or moisture problems in your property. You should also remove efflorescence before painting because it can prevent paint from adhering effectively.

 

[c4sman]

Thanks for all the feedback. The consensus seems to be that there’s no vapour barrier underneath the concrete then. Assuming that’s the case a quick google suggests there are “paint on” damp proof sealants that I can put on the concrete before adding vented tiles on top. Has anyone had success with one of these products?

Liquid Epoxy Damp Proof Membrane For Concrete Floors | Liquid DPM

Need a fast curing & easy to install damp proofing liquid? RFC liquid DPM puts a waterproof barrier between your floor & the surface below.

www.resinfloorcoatingsuk.com

https://www.screwfix.com/p/bostik-aquaprufe-flexible-damp-proofer-waterproofer-black-5ltr/36405

 

[c4sman]

I’m thinking I lift the remaining tiles. Paint on one of these finishes and then replace the tiles with a vented type to avoid condensation issues.

 

[Zep]

These types of coatings work very well.

Years ago I was involved in testing a lab which had an issue with tiny amounts of air passing through a brick wall. It was painted and the problem was solved.

 

[Zep]

You won’t have condensation under the tiles, you need airflow for significant condensation, and you won’t have that.

 

[c4sman]

You won’t have condensation under the tiles, you need airflow for significant condensation, and you won’t have that.

that would be even better as I can then reuse the existing tiles

 

[c4sman]

It is the time of year where this sort of thing happens. That you need dehum and heat to keep it sub 60% means you have a source of damp.

My money is on a small amount of water coming through the concrete - the tiles mean that the floor is effectively insulated from the internal space, and no air flows over the cold floor. If you use ventilated tiles, you will run your dehum more as more of that moisture will make it into the occupied space.

This seems spot on BTW as this morning the garage is showing higher humidity than I’ve seen for a long time (my gauge logs all time highs and lows). This is after I removed the central strip of tiles. I’ve just put them back down to keep moisture down until I do the damp proofing (probably in the spring when I can more easily empty the garage).

 

[zagatoes30]

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.

 

[c4sman]

Agreed, I can’t justify the cost and disruption of removing and reinstalling the concrete so will try the surface sealant route. I also think I may still opt to switch to vented tiles to minimise the chance of capillary action drawing moisture in under the tiles (hopefully much reduced so not resulting in the dehumidifier having to work much harder).

I have 4 double glazed windows in the garage so ventilation is easy enough as they can be locked in vent mode.

 

[philw696]

@zagatoes30
On the money there Andy.
I used a contactor that only does commercial floors and many far bigger than mine.
It wasn't cheap but it's too ensure I don't have problems with my lifts and damp.
One window I've left it short of a row of glass blocks purely for ventilation.