Garage Floor Damp Issue... Any suggestions please?

[Richard77]

Hi All...

Currently renovating (very slowly!) the garage to house inverter, batteries, panels on roof, etc. Might put some gym stuff in there when finished too. Probably won't have any heating in there, but the walls will eventually be studded and insulated (50mm foil PIR).

It was built on an old concrete slab that had probably been there for 50+ years, it originally housed an old timber/asbestos garage (glorified shed). We had a double solid bricked wall behind it and stupidly I thought it was a good idea to use the bricked wall as the back of the garage and just add concrete block at the sides, front and top to complete the garage structure. In hindsight should have just knocked the wall down and built the whole thing from scratch. The walls are rendered (k-rend) with a silicone top coat. Damp course one block up at the sides, non on back old wall (I don't think). But back to the important bit...

When it rains heavy outside I get a bit of water ingress at the bottom of the external walls on the floor. See pics below:




The garage floor is between 100mm and 50mm below ground level along the sides. At least 100mm at the back. The front of the garage floor though is basically level with ground level. The outside slopes towards the front, the garage floor inside is roughly level from front to back, even though it is a bit up and down in places and definitely needs a thin screed or self levelling compound to smooth it out. Pics below:






So I'm a bit stuck!

I want:
1. Floor to be level and smooth.
2. No damp issues.
Issues:
1. Don't want to dig out the concrete floor.
2. Garage floor is level with the outside at the front entrance to garage, so can't just raise internal floor with insulation, dpm, screed, etc. as the garage floor would be about 150mm above ground at entrance.

Is the only way to just to liquid dpm it and then lash a load of self levelling compound down and hope for the best?

Any suggestions, ideas would be a massive help. Thanks.

Richard

[spread-tee]

Sounds like the floor is too low in relation to the ground, and maybe no DPM below? If you can't raise the floor can you lower the ground around the perimeter a bit? and maybe back fill with course shingle? Acco channel? Then as you say liquid DPM and self level (get yourself a spiked roller, makes self level much easier)

Desp

PS

From those piccys it does look like surface run off from those paviours is penetrating the bed joint under the first course, if you can get the paviours out without too much damage you could try a couple of coats of black jack on the first course to as low as you can get, might help a bit.

[Stinsy]

How is the drainage around the perimeter of the outbuilding? Can you dig a trench and fill it with a land drain and some pea gravel?

[Richard77]

Sounds like the floor is too low in relation to the ground, and maybe no DPM below? If you can't raise the floor can you lower the ground around the perimeter a bit? and maybe back fill with course shingle? Acco channel? Then as you say liquid DPM and self level (get yourself a spiked roller, makes self level much easier)

Desp

Thanks Desp.

I've added some pics above.

Unsure if there is a dpm under the concrete, it might have been there originally and have been there for over a 100 years as far I know. House is pre 1900.

The water only comes in from the sides, the middle of the floor is always bone dry. It seeps under the bottom of the first block on the side walls. When the guy built the side walls, the trench/foundation was below ground level so the first block was below ground level. I assume water just pours in from outside and sits against the bottom blocks and seeps through gently.

There are blocks and tarmac on the sides so didn't really want to disturb any of that.

[Richard77]

How is the drainage around the perimeter of the outbuilding? Can you dig a trench and fill it with a land drain and some pea gravel?

Thanks Stinsy...

There is no drainage...

Blocks on the floor to the outside of garage wall and tarmac. (See pic above).

I don't really want to disturb any of it.

I simulated heavy rain by leaving the hose on the outside at the bottom of the walls and it slowly sleeps through.

[spread-tee]

How is the drainage around the perimeter of the outbuilding? Can you dig a trench and fill it with a land drain and some pea gravel?

Thanks Stinsy...

There is no drainage...

Blocks on the floor to the outside of garage wall and tarmac. (See pic above).

I don't really want to disturb any of it.

I simulated heavy rain by leaving the hose on the outside at the bottom of the walls and it slowly sleeps through.

I can understand not wanting to disturb the outside, but honestly you can only do a proper job from outside. Coating the inside will make a difference but you are keeping the first course wetter by restricting any escape of damp to the inside, which TBH wont cause heavy concrete blocks too much distress but it's not ideal.

What about a fillet along the bottom of the first course and a coat of blackjack on the outside? that would at least throw the water away from the joint.

[Richard77]

Thanks Desp...

Could I ask what a fillet is? Only ones I know of are in my fridge!


Any recommendations for any brands of liquid dpm?

[jonc_uk]

Stinsy is right in that the correct solution really is to drain the water away outside the walls with a perimeter drain.

Essentially it looks like your bottom course of blocks is sitting in a puddle. I don't think an injected DPM in that course would make much difference here as the water is not wicking up the blocks much.

I think the correct solution would be as if you were converting a leaky basement - a delta system with a gutter in the slab which round around the inside to collect the water and direct it away, either via a suitable drain or a sump with a pump in it. Possibly overkill here?

Maybe some sort of waterproof render up the block before a liquid DPM?

[Richard77]

Stinsy is right in that the correct solution really is to drain the water away outside the walls with a perimeter drain.

Essentially it looks like your bottom course of blocks is sitting in a puddle. I don't think an injected DPM in that course would make much difference here as the water is not wicking up the blocks much.

I think the correct solution would be as if you were converting a leaky basement - a delta system with a gutter in the slab which round around the inside to collect the water and direct it away, either via a suitable drain or a sump with a pump in it. Possibly overkill here?

Maybe some sort of waterproof render up the block before a liquid DPM?

Thanks jonc_uk

I'm looking at doing this as cheap as possible with as little disruption as possible. It's only going to be a plant room, with occasional gym use.

I know I should do it the proper way, but I have only basic DIY skills, not much cash and want it finished years ago!

I'm just after a quick, easy, not completely botch-job (semi-botch is ok).

[Fintray]

I'm looking at doing this as cheap as possible with as little disruption as possible. It's only going to be a plant room, with occasional gym use.

If it is only going to be a plant room/gym where is the problem with raising the floor level?