# Damp in garage workshop



## fingerless (4 Jan 2013)

Hello all,

I'm after some tips on what to do with my garage to overcome a major damp problem. I had it extended in length last year, and a new roof put on. The roof is ply on joists, then covered with felt, then roofing felt. This seems to be watertight. The extension consisted of pouring a concrete base which butted up to the previous concrete base. The walls are brick. During construction, after the concrete was poured and semi-set, but before the roof was put on, it snowed. After construction the builder painted the concrete floor with garage paint. This has lifted over the new patch of concrete, but not on the old concrete. The major problem is that the underside of the ply panels are now covered in mould, and the damp is unlikely to be doing my tools any good either. I'm guessing the moisture is mainly coming from the concrete floor, but maybe also from the generally humid air due to the terrible weather this year. We did try to air it as much as possible through the summer. The windows and doors are double glazed UPVC.

So, what do you advise? I can try heating it (oil radiator or convection heater?) or I can try a dehumidifier, although they seem to be extortionately expensive. I'm open to any advice, as I don't want a new roof destroyed by damp...

Thanks for any input.

Colin


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## DIY Stew (4 Jan 2013)

I am not a builder but I believe you have to put down a damp proof membrane before you pour the concrete, did the builder do this?

Stew


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## undergroundhunter (4 Jan 2013)

I would 2nd the damp proof, if the paint is peeling on the new section and not the old it would suggest that there is no damp proofing under the concrete. Give the builder a ring and get him to come and have a look to see what he thinks.

Matt


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## Harbo (4 Jan 2013)

Lack of DPM I think - lots of buildings are constructed during bad weather and once weather tight dry out without any problems?

Go back to the builder.

Rod


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## Pond (4 Jan 2013)

It certainly sounds like you have a damp membrane problem; either you haven't got one, or it has failed under the floor somewhere.

If there is a DPM (Damp Proof Membrane) it is most likely there is a gap between the old and new.

You need to install a damp barrier somehow. The easiest way is to lay a dpm, either liquid or polythene sheet on top of the concrete floor, making sure it is cut into the lowest brickwork mortar course or the damp will creep up the walls. A floating overfloor, T&G is the easiest, can then be laid on top of the DPM. Floating is best as you cannot put fixings into the concrete or you will puncture the DPM and it won't work. The hardest part is damproofing where the walls meet the floor!

Heating will make the problem worse, as the moisture will evaporate and rise, condensing on the coldest and highest part, ie the roof! A dehum won't really help if you have constant moisture entering, as it will just be condensing a never ending amount of moisture.

Personally I would confirm the problem by having a report done by a surveyor or similar, then get the person who did the job round and ask him what HE proposes to do about it.

HTH


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## Fromey (4 Jan 2013)

I have a shed with a poured concrete floor. I didn't do it, the numpty who built the whole shed many years ago did. I suspect it doesn't have any damp proof membrane underneath it (I can't know for certain). When it pours I get water actually rising up through it and the lower bricks of the shed along two edges.

Similarly, I have a roof made of external grade plywood laid on joists with two layers of felt. It seems quite water tight. I should have put a breathable membrane up there when I did this, but at the time I didn't have sufficient knowledge and I was racing against time to get it done before it rained (plus I had a broken wrist, don't ask, and a friend was finishing the job for me).

Almost immediately I also got mould forming on the ceiling plywood. In addition, in the winter, in one corner (the last bit of the shed to be hit by the sun) I got so much condensation forming it actually ran down and dripped off significantly.

Gaaa! If I knew then what I know now, I would have demolished the shed when we bought the house and built a proper timber job. Anyway, we live and learn.

My first update, other than the roof, was to completely pain the exterior concrete walls with sandtex paint.

Next, I decided to insulate the roof with some foil backed bubble plastic they sell in B&Q and such places. It provided a bit of insulation but the glue I used wouldn't stick to the plywood so the insulation kept pealing off.

Eventually I got around to buying some fairly thick celotex rigid foam insulation (double foil backed), cut it to shape and rammed it up between the joists on top of the previous insulation. I then battened it in so it's a tight fit. Now that fixed it! Of course I don't know if there is insidious water collecting immediately under the plywood, but so far there's been no mildew or leakage anywhere.

I still have the rising water occasionally, but I don't think there's anything I can do about that other than laying down a water proof membrane and pouring another layer of concrete on top.

I have a humidity monitor in the shed at all times and habitually look at it. It never gets above 75% relative humidity and normally it's down in the low 60% range. I periodically take out our household dehumidifyier and give it a couple of days of treatment. That can lower the humidity down to 50% but it soon rises back up to 60%. I figure that's going to be the general background level simply coming in from the British air and rising from the floor.

From what I understand of rust on tools, the main culprit is letting the tools get too cold and then warming them up. I now have an oil heater in the shed on at all times to maintain a temperature of about 10 degC (stops the glue and paint going off as well) and it rises to 15 - 17 degC when I work in there. To date I've had no rust problems other than a bit in the early pre-insulation days.


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## pip1954 (4 Jan 2013)

is the garage insulated? is it boarded out on ceiling? is it double or single skin brick work or block work? all these things can have an effect on the situation, if you say it is condensation you can use dehumidifier .
pip


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## fingerless (4 Jan 2013)

Thanks for all the replies. Just to confirm, this is a slab of concrete that forms the foundation for the walls and the floor of the garage. Are you saying there should be DPM under this concrete (it would probably then be below ground level outside)? There is DPM in the walls, but not under the concrete as far as I'm aware (although I wasn't there when the concrete was poured, so I don't know). The garage isn't insulated, is single brick walls, and the roof isn't boarded out.
The builder is coming around next week to "have a look".
Thanks,
Colin


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## Lons (4 Jan 2013)

Hi Colin

I'm a builder and I can't add much to the advice you've already been given.

A properly laid concrete floor with the correct thickness DPM does not allow moisture to ingress from below. (If a membrane has been installed, it is possible the sub base hasn't been consolodated and blinded sufficiently and has punctured the membrane.) the DPM must be fully lapped under the DPC of the walls to be effective.

Having said that, it is also possible that the floor paint has lifted because the builder didn't allow the concrete to cure fully before painting. To be on the safe side, 1 month is recommended.

As an aside, I always take WIP photos when doing groundworks and foundations so I can prove compliance. Have never needed to but better safe etc.  

cheers

Bob


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## Pond (4 Jan 2013)

Yes there should be a damp barrier under the concrete. It doesn't matter what the floor level is outside. The idea is to prevent moisture rising through the concrete from the ground below it. This is then 'tied in' to a DPC in the brick mortar which should be approx 2 courses (6") above the highest ground level outside. The 6" rule of thumb is to stop large amounts of rain splashing above the dpc level on a regular basis, or vegetation growing above this height and bridging the dpc.

If installed correctly, you would have a 'tray' like shape, ie the DPM is laid under the concrete, then laps up the walls to be buried in the brickwork at DPC level, creating a single barrier.

sorry to repeat Lons but the posts overlapped (same as a DPM should  )


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## Lons (4 Jan 2013)

fingerless":18zl9z2c said:


> Thanks for all the replies. Just to confirm, this is a slab of concrete that forms the foundation for the walls and the floor of the garage. Are you saying there should be DPM under this concrete (it would probably then be below ground level outside)? There is DPM in the walls, but not under the concrete as far as I'm aware (although I wasn't there when the concrete was poured, so I don't know). The garage isn't insulated, is single brick walls, and the roof isn't boarded out.
> The builder is coming around next week to "have a look".
> Thanks,
> Colin



OK, it's in effect a "raft" foundation. It should actually be deepend all the way around to carry the weight of the walls and is usually reinforced as well to prevent possibility of ground shrinkage breaking its back.

The concrete should very definately have a DPM of something like 1200g and should be lapped and protected at the edges. Exposed DPM should be covered and protected from UV.
I assume you mean DPC in the walls, so where is that? Is it under the bottom brick course or 1 or 2 bricks further up. Wherever it is, if it isn't lapped into the DPM, you will get water through, if not the floor then under or through the bricks.
Looking outside, is top of concrete above, level or below ground level?

Single brick walls if not rendered or treated will always allow driving rain through btw. Can you be sure your moisture is not from the walls rather than the floor?

Bob


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## kostello (4 Jan 2013)

The peeling floor paint is due to the damp being trapped in the concrete.
Dtdt

The cheapest way to dry it out is to keep circulating fresh air..

Keep the doors or windows open and maybe a fan on..

A dehumidifier will only work if the ambient temperature is above a certain point as it works by cooling the air to dry it.


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## graduate_owner (4 Jan 2013)

I'm not a builder but I believe oil heaters (also gas and LPG) produce moisture as a by-product of combustion, so if you intend to heat your workshop then electricity may be the best option - although probably the most expensive to run.

As a matter of interest, I'm working on damp-proofing and insulating my workshop too. Polystyrene, glass fibre matting and urethane foam all being collected ready for the job.

K


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## Dusty (4 Jan 2013)

Evening Fingerless 
One thing you have to remember is that when a garage is built , it was never really deemed to be important to have the same level of damp proofing as a house , hence why yours hasnt either . If it is a raft footing as was cast as one and normaly above ground level to prevent water running in ,and as Lons said there is still ways to prevent damp and protect the Membrane overlapping the base from damage and UV light , but they woudl never have bothered with a garage plus the footings / raft would of been higher than the ground . 

I have had to deal with a few garage conversions over the years in the same situation as you have got , both masonary and pre-fab ie woolaway concrete . The only way I would say to be 100% if you have the head height is to lay a 1200 gauge membrane or use a liquid membrane like synthaproof or similar ( bitumen ) and then lay a 50mm screed over the whole floor , the membrane will need to continue up the wall and sealed up to the damp course or above . 

If you lay a floating floor , the floor will either have to be very very level / flat or protected with Kingspan or similar to prevent the floor moving ( expansion ) and damaging the membrane or bitumen . you could lay a screed floor down to about 35 mm if you use a liquid poor screed but the cost of that system is big compared to traditional screed . 

And as for the paint peeling on the floor , if you pour a 100mm concrete floor , once it is protected from the weather ie an extension , it will take in the region of 4 to 6 months to fully dry out , if your floor has no membrane then it will suffer from rising moisture and never fully dry , causing the floor to sweat and push the floor paint off . This can work but it is necessary to use good quality paint and to prime the floor first , not DIY products like wickes . 

Hope this helps 

Dusty


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## fingerless (8 Jan 2013)

Thanks again for the extensive responses, especially from the builders (are any of you in the essex area?)!
I've had a closer look and in the extended section there is DPC in the wall two bricks above ground level. In the old section, the DPC is at the same level as (or maybe just below) the concrete floor. There is no damp proof membrane from the floor joining to the DPC in the extended section. It looks like the builder painted black rubbery paint on the floor, followed by the garage floor paint. This was done within a week of the roof going on, so probably 1-2 weeks after the snow was gone. It sounds like this was far too soon.
I'm fairly sure the damp is coming in through the floor as if I leave something on the floor the underside gets wet.
I agree that garages may not be done to the same level of damp proofness as houses, but the builder did know this was going to be a workshop, so it is annoying. In addition, I don't see the roof lasting very long with the amount of mould that's growing on it. Given the drying times mentioned in your posts, and the fact that the floor was painted, I could believe that the concrete just hasn't dried out yet, but if there's no DPM then it sounds like there will always be a damp problem, unless I do something extra.

I do have the headroom for a screed, so that is definitely an option, although the doorways / thresholds may be a bit awkward. I'm guessing the peeling paint is not a good surface for applying any form of damp proofing paint, and it needs to take wear from foot traffic, wheelbarrows etc. so maybe screed is the only option. Roughly how much is a 50mm screed / m^2?

I will see what the builder says when he visits on Thursday, but I have a feeling a real solution is going to be expensive.

Cheers,
Fingerless


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## Dibs-h (9 Jan 2013)

By 50mm screed, I am assuming folk are talking about anhydrite screeds. These aren't cheap and must be professionally laid and are laid via pump. I entertained it when building my shed, but gave it a miss due to the additional cost of the pump, etc. (when I say - I mean a lorry pump).

I don't think a traditional sand\cement\concrete\etc screed at 50mm will last - but folks mileage may vary.

Regards

Dibs


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## Peter Sefton (9 Jan 2013)

I have pumped free flowing screeds in our barn conversion over underfloor heating - these screeds are excellent for that but I would say OTT for a workshop. Our furniture workshops have some old concrete floors which never had a DPM as they were agricultural in a former life. We do have a DPC 150mm above outside ground level and have layed a new DPM and wrapped it up the walls 300mm before laying a floating floor of Kingspan covered with 18mm chip board as a glued floating floor, which we painted with Koovar floor paint and have a very warm and dry workshop now. The walls and ceiling may take more work to sort out the problems of condensation and water ingress. If you are in the Worcester area come and see us and I can show you how we overcame similar issues.

Cheers Peter


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## simocco (11 Jan 2013)

Try this site for all things damp...

http://www.heritage-house.org/pages/dam ... -damp.html


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## vinnie_chip (2 Feb 2013)

If the builder missed out the DPM he should do whatever is necessary to fix it.. at his expense


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## fingerless (3 Feb 2013)

So, the builder came around and admitted there was a problem, saying the concrete and mortar had not had a chance to dry out properly.

He left a dehumidifier with me for 2 weeks, which I ran along with heating (he'd hired the dehumidifier at his own cost). He has also offered to lay a wooden floor over a damp proof membrane, where I pay for materials, and he covers the labour. His plan is to lay the DPM on the existing concrete floor, lay 2x2 joists on that, and then fix ply to those. I'm aware of the issue of breaching the DPM when fixing the joists to the floor from Dusty's response. Can the breaches be sealed, or should the joists not be fixed to the floor?
I was also wondering if it is worth putting insulation under the boards to warm the place up, and I'm planning on boarding up the ceiling as well, potentially with insulation between the rafters. Do you think this makes sense?

Overall I'm happy with the response from the builder, and hopefully the workshop will be a cosier more pleasant place to do stuff at the end of all of this.

Cheers,
Fingerless


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## Peter Sefton (3 Feb 2013)

It’s good news you and the builder are moving on, you could deal with the floor as I previously mentioned which has worked for us.

Cheers Peter


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## Dibs-h (6 Feb 2013)

fingerless":1c3hdkhy said:


> So, the builder came around and admitted there was a problem, saying the concrete and mortar had not had a chance to dry out properly.
> 
> He left a dehumidifier with me for 2 weeks, which I ran along with heating (he'd hired the dehumidifier at his own cost). He has also offered to lay a wooden floor over a damp proof membrane, where I pay for materials, and he covers the labour. His plan is to lay the DPM on the existing concrete floor, lay 2x2 joists on that, and then fix ply to those. I'm aware of the issue of breaching the DPM when fixing the joists to the floor from Dusty's response. Can the breaches be sealed, or should the joists not be fixed to the floor?
> I was also wondering if it is worth putting insulation under the boards to warm the place up, and I'm planning on boarding up the ceiling as well, potentially with insulation between the rafters. Do you think this makes sense?
> ...



FingerLess

I did something similar for my shed. Lay the DPM down (be nice if you could lap it to the DPC in the walls) and you lay 3"x2" down around the perimter and then lay 2"x2" down in between. Making sure things are a tight fit. Almost like making a timber framed wall but dropping it onto the floor. No reason to screw thru the DPM into the floor - so no breaches to deal with. Just "toe screw" the end of the 2"x2" into the 3"x2" (which is laid sideways)

Ply straight onto the 2"x2" - filling the gaps between the 2"x2" 1st. 16" centres should be ok and "noggins" where boards meet the other way.

Assuming your concrete is actually level.

HIH

Dibs

p.s. Obviously my floor has 4"x4" going round the perimeter and 4"x2" across.


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## RogerBoyle (6 Feb 2013)

Please tell me I have got this wrong

Mr Builder lays a new floor on a new bit of an extension Knowing what it is to be used for and fails to fit a DPM.. His solution is to now lay a DPM on the new floor and raise the level by a minimum of 3 inches and wants you to pay for it I.E. the materials..Has he said who is paying for the electric on the dehumidifer as they can be expensive to run Depending on model 

Am I the only one that thinks this is unacceptable


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## Lons (6 Feb 2013)

RogerBoyle":262ww2lp said:


> Please tell me I have got this wrong
> 
> Mr Builder lays a new floor on a new bit of an extension Knowing what it is to be used for and fails to fit a DPM.. His solution is to now lay a DPM on the new floor and raise the level by a minimum of 3 inches and wants you to pay for it I.E. the materials..Has he said who is paying for the electric on the dehumidifer as they can be expensive to run Depending on model
> 
> Am I the only one that thinks this is unacceptable



As a builder, I agree with Rogers comments.............. However, getting him to rip up the floor and do it properly is another matter. Unless the construction of the floor was specifically detailed in his quote and/or drawings, which you should have approved prior to awarding the job, you don't have a leg to stand on. Remember that it's not a dwelling which would have been subject to building regs. and inspection.

The builder knows damn well that the problem isn't "hasn't had time to dry out" and the reason for the dehumidifier is to get the surface of the floor as dry as possible before laying a DPM. A waste of time if the damp is coming up through the floor.

His solution will work ok but the labour will be a small part of the cost and he's getting off lightly. Better than nothing if no other way but I wouldn't be happy.

If you're putting in heavy machinery, make sure there's plenty of support in those areas btw and possibly consider some electrics? Insulation well worth it 'cos impossible later.

Bob


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## Peter Sefton (6 Feb 2013)

Lons":3np8kyue said:


> RogerBoyle":3np8kyue said:
> 
> 
> > Please tell me I have got this wrong
> ...



I agree, I am not saying the builder is correct just sometimes you have to move forward with a problem and I am not commenting on who should pay.


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## RogerBoyle (6 Feb 2013)

Sorry guys I thought i was cracking up when i read this as it seemed that nobody was saying the builder was just wrong to do this and now he wants the customer to pay for it to be fixed.

Fingerless

Did you have any plans drawn up for the builder specifiyng the layout and what materials to be used ???
If as Lons has suggested see if they mention a DPM on them either written on the plan or in the notes .
As a matter of interest how big an area are we talking Because if its not to big I really would be pressing him to dig it up and redo it .
Its not that hard a job to do just very noisy and extremley dirty/dusty.

Roger


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## Lons (6 Feb 2013)

> I agree, I am not saying the builder is correct just sometimes you have to move forward with a problem and I am not commenting on who should pay.
> _________________
> Peter Sefton



That's the way I read your post Peter. Sometimes you just have to bite the bullet and accept or decline the offer. If it were me however I would be pushing a bit harder until that point was reached. A reputable builder would put it right even if it wasn't specified. As a professional, he should have suggested that a DPM was at least desirable if not essential. I would!

Bob


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## RogerBoyle (6 Feb 2013)

Lons":3eeu2imw said:


> > I agree, I am not saying the builder is correct just sometimes you have to move forward with a problem and I am not commenting on who should pay.
> > _________________
> > Peter Sefton
> 
> ...



I totally agree 100% with that 

Roger


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## adzeman (6 Feb 2013)

> The major problem is that the underside of the ply panels are now covered in mould,



This is a clue, The mould is a type of mushroom who's spores are ever present in the air. They float around looking for the right conditions so they can set their seed.
The conditions are three in number which are:- 
1 Darkness. Cant do much about this as we have night time and cupboards etc up against walls.
2.Moisture. Cant do much about this either as we have humidity in the air and condensation.
3.Still Air. This we can do something about. Ventilation (also cures condensation)

Take away any one and you cure mold growth Ventilation is the easiest solution.

One other thing If it catches hold it needs none of the three things as it sends out Micella (fine fibres) and infects any surface.

Oh another thing, it takes three weeks to kill it. Keep applying the treatment till its dead. How do you know its dead? Rub your hand over it and look at your palm. If its black its still alive. If its silver its dead.


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## adzeman (6 Feb 2013)

Sorry bad spelling again! Mycelia


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## MARK.B. (6 Feb 2013)

I would reccomend that when dealing with the mould that you wear a suitable respirator as the spores of some moulds can be nasty and you dont want something that likes warm damp places getting into your lungs.


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## adzeman (7 Feb 2013)

If the mold has caught hold it would be better to bring in the proffessionals as they have some pretty leathal stuff. At the council I had a dediated team of two blokes booted and suited. You coud contact the council and they would do it for a charge. Less than a private company.

If it is of manageble proportions you can buy mold removal from B & Q but I found you can use ordinary household bleach a lot cheaper which comes with free elbow grease to treat every day for three weeks.


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## adzeman (7 Feb 2013)

Most important, have you a couple of these? Are they clear? best opposite each other.







How about a picture of your mold growth to show extent.


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## fingerless (7 Feb 2013)

Hi All,
Thanks for the opinions and suggestions. Apologies to Peter, I missed your post about how your floor was done. I think I will follow that advice as it was in line with what I was thinking and has worked for you, and then I need to get the ventilation sorted out.
Cheers,
Fingerless


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## Peter Sefton (7 Feb 2013)

No problem, I hope it all gets sorted out and you can get on with woodworking.

Cheers Peter


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## Phil Pascoe (7 Feb 2013)

Mike B. Are your air bricks better opposite each other? I'd have thought the opposite - that anywhere but would be better. I know from keeping aquaria that if the filter inlet and outlet are opposite each other you get "dead" areas where there is no circulation - I'd have thought the same would happen with air?
phil.


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## adzeman (8 Feb 2013)

No they are not due to it being a terrace of garages and I have the middle one so I have to depend on the drauaght under the up and over door.

As a matter of interest in a previous post in general woodworking I mentioned my own workshop is condensation free and I put this down to when I work in the shop I have my dust exctraction working. This keeps the air moving and stops the dust settling. Well I am making some alterations at present and the some of the tubes altered which means its switched off. I have had 100mmm of snow on the roof, freezing temperatures and an electric heater on and I HAVD CONDENSATION! The snows gone, but its still very cold (as we speak) I am still working in the shop with the heater on and the Vac system sort of running in an incomplete state. No condensation.


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## pip1954 (8 Feb 2013)

hi all as an ex builder i think some are missing the point first what was asked for, you should not have to second guess what the customers want, the other thing people are saying take it up but by the sound of it it is a raft ie under the walls not inside the walls what if there is no dpm under the exsisting garage why would you put it under the new bit ,yes it would be best practice but the place will be damp because of the old part, it will also always be damp because single skin brick.
my answer would be to strike best deal with the builder and bite the bullet i think the way forward would be to think what would be the best out come,
i would dpm then insulate the floor with one of the 8x4 sheets types maybe with ply bonded to it then put 3/4 ply over the floor as discribbed with timber around it and between sheets to leave a very good finish just fix ply to timber not to concrete leave dpm long enough to go up the walls above dpm in walls then if you board walls you can put it behind timber battens for wall boarding 
i would think it would be about best of a bad job . if mine i would insulate walls and ceiling and floor that would mean minimal heating in future 
ok i'm going to hide now (hammer) 
pip


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## buffalobill (9 Feb 2013)

Maybe this could be an easy solution 
http://www.atechtt.com/tech/index.php?o ... &Itemid=53


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## adzeman (9 Feb 2013)

> “I think some are missing the point first what was asked for, you should not have to second guess what the customers want,”



You are quite right in your assessment and without more detailed information one can only give advice as to how you see it or have experience. Also it is always easy to blame the builder. There are cowboy builders out there but not as many as the media like us to believe.

We are only guessing at the construction and remember the Victorians did not use Lead core D.P.C’s, membranes under slabs, insulation, cavity walls.

What do we know?
The roof is 3 layer felt on ply. No mention of insulation.
The ply is covered with mould growth. Cause, lack of ventilation, no mention of insulation?
Windows double glazed. Are they vented? Again possible lack of ventilation.
The walls are brick, Are the H.B. single skin? 1B single skin? Or HB facing on 100 insulated blocks? No mention of air bricks. Relationship of damp course with external ground level, concrete slab or existing garage.
Bad weather conditions are mentioned but the initial set in concrete is within approx 20mins from then on its in curing mode. (if on a rising thermometer)
Therefore, as Pip1954 states how can we help? The only definite cause we know until further info givenis is a lack of ventilation.


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