Waterproofing a garage

[Electric_Andy]

My tenants are complaining that the garage is damp. The up-and-over door has some gaps at the top and sides but I think the worst problem is that the neighbour's driveway has been built too high so is only 1/2 an inch lower than the damp proof course. I'm thinking of using a waterproof plasticiser to paint on the bottom 6 inches of the garage. Would this do anything? And could I paint it over the DPC at the front (higher end) of the garage base? I'm sure this is where water seeps in during heavy rain, as it pools up initially before it gets chance to drain away. I've seen a tub of Stormdry for £113 which I'm happy to buy but obviously only if it's going to be somewhat effective.

Thoughts please!

 

[MikeG]

Architect here. I get to deal with these sorts of issues all the time. I'm afraid there isn't enough information to even begin to comment. A set of photos would help. At the very least we'll need to know what the construction is, and where the damp is. Obviously the adjacent ground level being so close to the DPC is really poor, but more importantly is the ground level in relation to the slab level, and whether the ground falls away from the building as it should. It should be below the slab ideally. A basic check of the building should include ground levels as I've mentioned, but also gutters, downpipes, and adjacent drains.

Don't go applying any liquid tanking just yet. Applied in the wrong place the stuff can make matters worse, or simply mask the problem for a while.

 

[Electric_Andy]

Don't go applying any liquid tanking just yet.

Thanks for your time. I can't get a photo yet, but I have done a crude Powerpoint slide of the garage. I'm pretty certain that the water gulley is not deep enough to accomodate heavy rainwater, so it pools up and enters through the DPC at the front of the garage before it has chance to run away. The slope is very shallow. It runs in and down behind the plasterboard to the back of the garage, as the slope is approx 10mm lower at the back. It then can't get out, so pools up and has moulded up the plasterboard.

Would cutting the gulley deeper with a large angle grinder do any good? I'm thinking a series of 1/4 inch deep cuts with a fairly wide concrete disc?

 

[MikeG]

The DPC is a red herring. It's there to prevent rising damp getting to the bricks above the DPC. Much more important is the relationship of the external ground level and the floor inside. The latter should be above the former, and if it's not there is a clear route through the wall for moisture. However, none of that may be the problem, or the answer. A splash from a leaking gutter is plenty enough to have damp enter a solid masonry construction. Or a dripping tap. A build up of moss. Without photos or a site visit, I don't think I can say any more.

 

[Electric_Andy]

The DPC is a red herring. It's there to prevent rising damp getting to the bricks above the DPC. Much more important is the relationship of the external ground level and the floor inside. The latter should be above the former, and if it's not there is a clear route through the wall for moisture. However, none of that may be the problem, or the answer. A splash from a leaking gutter is plenty enough to have damp enter a solid masonry construction. Or a dripping tap. A build up of moss. Without photos or a site visit, I don't think I can say any more.

ok thank you