DPC question

[GJUK]

Hello all,

I'm new here so be gentle!

I've got a bit of damp on an external wall in my living room an after extensive research I have decided to try and deal with this small amount of damp myself, using an injected 'safe' chemical called dryzone.

The damp inquestion is in a solid brick wall which is external and I have taken steps to reduce possible causes such as 're-pointing' a down pipe to be more central to a drain, doing some pointing ont he external wall and removing a lot of debris which was leaning up agains the wall, both externally and under the floor boards.

I have (as you will see in the photo) chopped off a fair bit of plaster and want to fix the problem before I decorate.

As far as I can see there is no DPC sheeting, as the house is from the 1930's. The method used for DPC in this house appears to be a layer of blue bricks which (again after a bit of research) are possibly the type which resist water absorbsion.

Could anyone confirm from the photos that there is no dpc plastic layer in use, as i dont want to drill any holes which might worsen the rising damp problem.

Here are the photos

Any input very welcome. Thank you very much.

 

[hotrod]

It's difficult to follow your post as the photos are too large and messing up the formatting so I keep having to scroll left / right / up / down to try and make sense of it. Anyway a few pointers:-

1. I can't see a PVC DPC - you are correct there does not appear to be one present.

2. That joist(s) in first picture is showing signs of damp ingress where the joist end bears on the sleeper wall. The joist ends need treating and wrapping in DPC where they are in contact with masonry.

3. IIRC remedial chemical DPC manufacturers specify plaster to be be taken back to brickwork to 1100mm above DPC/FL (can't remember which but double check with Dryzone specs you've gone far enough)

4. Ensure adequete subfloor ventilation, check airbricks etc. Run a dehumidifier for a couple of days. You will be amazed at what it brings out.

hth

 

[GJUK]

Hi mate,

Thank you very much for your reply.

I have added smaller versions of the pictures, I thought the large ones might have added some detail, sorry about that.

Could you tell me please, when you say wrap the joist, do you mean with the plastic DPC, just around the end of the joist, 360* all the way around where it touches the brick work?

Thanks again,

Jon

 

[stanna]

Hiya mate

The cause could be simply no form of DPC/DPC failure or a blocked cavity.
Measure your groundlevel outside and see that it is at least 150mm below any DPC. It probably will not be.

In the 30's they used either lengths of slate or hot bitumen poured on the DPC course. you should really be able to see evidence of this but in the 30's it was a bit hit and miss.

The problem doesnt look to bad but as you have the floor up you might as well do it properly.

I would inject the course of brick that your joists are sat on. Sounds difficult but its easy and very effective if done properly - so do it yourself.

My local independant plant hire firm charge £20 per day for damp injection pump and £25 for 25 litres of fluid. You shouldnt need it for more than a day unless you want to do the whole house.

Simple task get a good SDS drill with 10mm masonry bit and drill 2 holes evenly spaced in each brick. In the centre with a slight down angle. You should have at least six probes with the dpc pump connect them up and lock them. Start pump and when the top of the brick starts to sweat with fluid your done.

don't get a firm in they charge a fortune and u will get some clown who makes a balls of it. If you don't get the sweat and its using fluid chances are brick is split or hole to deep. Try and redrill but if it fails you will have to replace the brick.

Once done wrap the ends of your joist's in 150mm damp proof course(about 5 quid a roll) and secure at top edge with galvanised clout nails.

Make sure there is ventilation ie air bricks venting the sub floor and they are clear.

To finish knock plaster off - BS is at least 1 metre above flo0r level but if the damp has not reached that far i really don't see why if its not damp its just belt and braces.

To never see damp again do a scratch coat of sand and cement render mixed with waterproofing fluid. Pick a good name like Sika and nothing will get through.

 

[stanna]

Sorry

I would treat the ends of your joist as well with a quality anti fungal etc.

Your cause is probably no DPC coupled with a blocked cavity due to the chimmney breast. They filled them up with all kinds of crap during construction.

Have to say though timber is in pretty good condition so its not bee a long term problem.

If injecting i would step it up and across that course of brick in the chimmney breast area.

 

[GJUK]

Hi mate thanks.

I've bought some thompsons water seal

http://www.thompsonswaterseal.com/products/product_detail.cfm?prod_id=1

Shoudl that be okay.

When you talk about the "blocked cavity due to the chimmney breast. They filled them up with all kinds of crap during construction. "

Are you talking about the bit directly in front of the fire place, as it seems to be full of coal and rubble and concrete and all sorts just to build it up.

I'm thinking of taking it down a few inches and building it up with concrete, maybe using a DPC membrane under it to stop the damp rising. Good idea?

Thanks again!

Jon

 

[stanna]

Dont use Thompsons for render. Its probably a similar product i.e. silicone particles suspended in a solution but i have never seen it in a render or used it. Sika is my choice.

If its for damp injection fluid then same again really unless it says you can on the tin.

Whenever i have sealed brick work on the outside to protect repointing i just use DPC fluid. Cheaper.

Yes its a good idea to reduce the hearth of the chimmney breast. If your not going to use it take it below joists and replace short joist with new longer one to cover it. Or new section overlapping 2 ends by a metre a side bolted through with M16's and connector plate washers. Definately use a membrane if still wanting to use hearth making sure it laps up and over the edges of chimmney. Before laying membrane blind it with some building sand to stop sharps penetrating when concrete layed.

The cavity im talking about is not the hearth its the main wall. Shouyld be a cavity between in brick leaf and outer. (not always could be solid and if so theres a further cause).

Only way to see is to take out a brick and see if its blocked. The old black mortar will be knackered and cavity will be full of snots from when constructed. plus old mortar and general debris will have fallen down over time or following any work on the house. Take a brick out from the outside if you prefer doesnt matter.

 

[stanna]

Ooppps! By the way if you do inject only drill to centre of brick not all the way through. forgot to mention that and its quite important. ha ha

 

[GJUK]

Hiya mate

The cause could be simply no form of DPC/DPC failure or a blocked cavity.
Measure your groundlevel outside and see that it is at least 150mm below any DPC. It probably will not be.

Te drop next door is above my DPC level (theline of blue bricks) hwoever there is a 1 foot 'trench' before the driveway level hits my house, a photo would show this better than I'll ever be able to descrbe but, yes that is sort of the the problem. I have moved a down pipe and cleared this ditch of crapola to try and reduce teh water down there.

In the 30's they used either lengths of slate or hot bitumen poured on the DPC course. you should really be able to see evidence of this but in the 30's it was a bit hit and miss.

In the mortar above the blue bricks? I can't see any such stuff im afraid.

The problem doesnt look to bad but as you have the floor up you might as well do it properly.

agreed.

I would inject the course of brick that your joists are sat on. Sounds difficult but its easy and very effective if done properly - so do it yourself.

My local independant plant hire firm charge £20 per day for damp injection pump and £25 for 25 litres of fluid. You shouldnt need it for more than a day unless you want to do the whole house.

Simple task get a good SDS drill with 10mm masonry bit and drill 2 holes evenly spaced in each brick. In the centre with a slight down angle. You should have at least six probes with the dpc pump connect them up and lock them. Start pump and when the top of the brick starts to sweat with fluid your done.

don't get a firm in they charge a fortune and u will get some clown who makes a balls of it. If you don't get the sweat and its using fluid chances are brick is split or hole to deep. Try and redrill but if it fails you will have to replace the brick.[/quote]

Thank you. I've decided to so similar just with treating the mortar layer with dryzone, 12mm holes every half brick and inject the stuff in...

Once done wrap the ends of your joist's in 150mm damp proof course(about 5 quid a roll) and secure at top edge with galvanised clout nails.

I've bought a huge sheet of blue DPC, okay to use this I assume?

Make sure there is ventilation ie air bricks venting the sub floor and they are clear.

They are clear on the external wall, I can feel quite a bit of air moving around under the floor boards but I can't see any airbricks.

To finish knock plaster off - BS is at least 1 metre above flo0r level but if the damp has not reached that far i really don't see why if its not damp its just belt and braces.

To never see damp again do a scratch coat of sand and cement render mixed with waterproofing fluid. Pick a good name like Sika and nothing will get through.

Thank you mate.

Jon

 

[GJUK]

Hi mate thanks.

I've bought some thompsons water seal

http://www.thompsonswaterseal.com/products/product_detail.cfm?prod_id=1

Shoudl that be okay.

When you talk about the "blocked cavity due to the chimmney breast. They filled them up with all kinds of crap during construction. "

Are you talking about the bit directly in front of the fire place, as it seems to be full of coal and rubble and concrete and all sorts just to build it up.

I'm thinking of taking it down a few inches and building it up with concrete, maybe using a DPC membrane under it to stop the damp rising. Good idea?

Thanks again!

Jon

Can I check please, is this item i've bought no good then for the wood? Do I need an anti fungal rather than a waterproof liquid?

Thanks

Jon

 

[stanna]

Not really.

Think of Thompsons Water Seal like car wax. you put it on to give a semi waterproof seal on brick etc to enable good water run off. Just like car wax it only lasts so long and needs doing again. Its a bit of a gimmick product really. If your brickwork and pointing are in good nick you shouldnt need it but it looks nice seeing the water beading so people think its doing a great job.

You need to treat your already damp timber to kill any spores that might have started growing.

Ronseal multi purpose wood treatment will do nicely and should be available in most places.

Be warned though this stuff as well as any other has a really powerful odour so keep the room well ventilated and or wear a respirator as you will get a headache. The smell lingers for around 24 hours so keep the windows open.

This will kill the spoars and any insects/worms that might be taking an interest in your joists

 

[stanna]

Sorry mate missed your big post.

Not sure what your saying about the ground level outside but if its above your DPC and joined to the house then all brickwork will get damp. Best solution if possible is to reduce the outside ground level ideally 150mm below your DPC. If you cant then you will have to bring the DPC up to that level by injecting it and waterproof render the inside if your floor height is below the outside.

I'm assuming that when built the courses of blue brick are Staffordshire Blues. A really hard brick that is a bitch to lay when wet. Theses are often used in new construction directly on a DPC membrane for added protection. They are ok unless they get wet regularly but not really a substitute for a proper DPC. If they are getting wet from the outside ground level or standing water then you need to sort that.

Never used Dryzone or heard of it so i'm afraid i cant comment. I would check if it meets British Standard for the treatment of damp. Ring your local building control annonomously and ask them.

Sounds like your blue sheet is Visqueen which is right as long as its 1200 gauge. Just double it up and make sure you cover what you lay it on with 25 mm building sand tamped down to protect it from penetration (blinding).
If you mean can u use it to wrap the joists then i dont see a problem if you double it up so it doesnt rip. Ideally a role of damp (DPC) would be better and its pretty cheap.

You might not be seeing the airbrick from the inside because they might be level with your joists which will be hiding them. Not ideal but then not much was in the 30's. If you can feel air flow then it should be ok.

Good Luck

 

[GJUK]

Thank you very much with your time on this question, you're being very helpful.

Can I ask do you wrap the entire end of the joist? Or perhaps 360* only, or perhaps even just the areas the wood is in contact with brick work?

Thank you.

Jon

 

[GJUK]

Sorry and also, what do you mean about the sand?

Do you wrap the joist in the DPC, then sand on top of it, or cover the joist in sand then DPC over that?

 

[stanna]

Sorry mate crossed wires.

The sand if for where your going to drop the height of the old hearth.
Cut down all the old hearth, cover whats left with sand and compact it a little with your hand or board. Then lay your blue sheet on top lapping the edges up the walls of chimmney breast, then pour your concrete.

As for your joists - then end that will be sat on brick work just wrap 150mm dpc around the end ie all 4 sides and secure it with galvanized clout nails. on the very end you can overlap a little to cover exposed end grain.

I dont mean the entire length just the bit that sits on the brick work. The point being no matter how wet the brick under or around the joist gets it will not get to the wood.