Retrofitting a damp proof layer?

Have a look at chemical damp proof layer and damp proof layer injection - probably the easiest method - way back in time I did an installation of a slate damp proof layer into the front wall of some old house.

The garage I’ve just fitted a new roof to has no membrane under the slab. It has no damp proof under the blocks ( the blocks are laid straight on the mud - no foundations. The outside walls are only painted and the ground level outside is level with the slab. It is dry inside now it has a new roof. Are you sure the water isn’t getting in elsewhere. Ground above floor level, gutters or roof leaking? I’m sure rising damp shouldn’t go above 1.2m.

Unless there is some outstanding reason to buy this property, walk away whilst you can. The situation you have outlined is going to be a huge money-pit to achieve anything like a suitable solution.

One option would be making an offer on the property, less the cost of dmolishing and rebuilding a properly constructed garage/workshop. Ask the seller if the work to build the present workshop was built in accordance to both planning and building regulations? Going by your description of the structure I would surmise that it has not.

'Caveat emptor' OR 'Buyer beware' as the saying goes.

Thanks for the replies guys, doesn't look so promising :/

jonsey, it's actually a mixture of condensation off the roof and rising from the floor I think. There's one corner inside which is especially damp, there's a big patch on the floor which also goes about 50-60cm up the wall.

Does anyone have any experience with tanking? Seems like it's the only option which may solve the issue without breaking the bank.

Unfortunately I'd already made an offer and had it accepted before I saw all this and asked the pertinent questions - the viewings before were in the dry. Paid the solicitors their first fee, but not 100% committed yet, trying to figure this out before going any further!

Tanking can be done - there are a couple of systems - one is chemical where you apply a paint substance then a membrane that ideally terminates in to a brickwork / blockwork course - I have only ever used this system once on a new build - below ground retaining wall which then had a cavity wall built forward of it hence it went unseen - I doubt if this would work in your case - there is a liquid water proofer that can be added to a cement render and this is probably your best option - you could get a local plasterer to do this for you and if you came up the wall for say the first metre to a stop bead that's probably going to be your best cost effective solution and it does work I had a contact of mine with a block work inspection pit that filled with water via the walls and was cured utilising this method - other things that may help if you are going replace the roof is to use a pre insulated roofing sheet and ensure a decent overhang from the external blockwork - addition of a gutter will very much help has will ensuring that the slab is free draining around its perimeter by reducing the ground level and infilling with a loose pea gravel

Hi Badger,

I have a bit of experience in this sort of thing as part of my job involves inspecting churches (different scale but same principles!) so I would suggest you take a look at the following:

1. Is the ground level higher than the floor of the garage particularly in the spot which is damp?
2. Are the gutters (if it has any) leaking, and is any water dripping from them in the damp area?
3. If it has gutters, is there a downpipe in the damp area and is it leaking or does it direct water against the wall rather than into a drain?
4. Is the garage in an exposed spot (on a hill, or with open ground to the south west) where rain could be blown against the walls or up under the eaves, under doors etc?
5. Is the condensation on the roof dripping particularly in the damp spot?

The damp you are describing doesn't sound like rising damp and I would be looking for the source elsewhere rather than spending money on treating the symptoms.

Tanking, which you mention, is only really needed if the ground level is above the floor level and you are holding back water under a bit of pressure - it doesn't sound like that is the case with this garage. To keep the floor dry, the simplest method would probably be to lay a thick polythene DPM (Damp Proof Membrane) over the concrete slab and then cast a new concrete slab or lay a screed over that. I would suggest an injected DPC is your best choice for the walls, and involves drilling holes at intervals and injecting a waterproofing liquid - it has been around for years and there are plenty of companies who do it, but the kit can be bought quite easily.

Just a thought on the planning permission side of things, while you are getting the searches done, I would suggest looking on the local authority's web-site as they will have all recent planning applications on line, so you would be able to see if planning permission was sought for the garage. It might have been done under permitted development in which case I would be asking the vendor for a Certificate of Lawfulness for the garage.

Hope that helps a bit, and good luck.

My downstairs bathroom has no damp proof layer, [old coalhouse] the quarry tiles were laid over whatever compacted aggregate stuff they thought was useful in 1903. I used an epoxy floor resin that was 2 pack and around £50, then tiled directly over the top and it's never shown any evidence of damp in the last 10 years, however, i did lower the ground level as far as reasonable. 

Thanks for all the replies guys - I've decided to go ahead with the survey (a full building survey) and we'll see what it turns up. I'm not massively happy with the garage revelations, and came to the same conclusions regarding the implications for the rest of the property, but I'm going to proceed with caution.
I already knocked 2 grand off the asking price on my initial offer, but I'm tempted to lower it a bit more - especially if there's more wrong with the house. We'll see what transpires I guess!

My house has a single skin brick utility room built on the back.

It had horrific damp when I moved in. Brick onto slab no dpc.

I bought a load of hydrophobic injectable damp proofing and put it it.

It worked brilliantly and theres been no damp since.

It was only cheap stuff so I was surprised how well it worked. May be an option for you.