What product can I use myself on a flat concrete roof?

dpm_dpmartin · 16 Nov 2015

My flat concrete roof has been redone at the cost of £10K, but the parapets weren't part of the deal. Dumb. So I have these two foot wide bits sticking out all around the house, and they're flat. They'll just hold water. I'm supposing I should get them slightly angled? Although they've been how they are since before 1900. Yet budget doesn't really allow a professional to come back, just yet.

Thinking that I should do something to cover these flat concrete areas (there's previous signs of something black and something grey) what product could anyone recommend I can apply with a brush to give me some peace of mind over the winter?

Black Jack DPM? Thompsons Water Seal? Watco products? Flexacryl? Isoflex? I could really do with a guiding hand as to what works and what I can apply at this time of year, mindful of cost but willing to spend to get good stuff.

When it's all dry next year I'll get the professionals in, if the house is still standing.

cAtLeYx · 17 Nov 2015

Hi
Was the parapet up-stand treated when you had the roofing works carried out. If so was is dressed into the underside of the coping stone. What condition are the joint is? Are there any gaps between the underside of the coping stone and the bed joint?
Out of interest what covering was used on the roof?

dpm_dpmartin · 17 Nov 2015

cAtLeYx said:
Out of interest what covering was used on the roof?

I do not know the answer to all your questions... but I think for this one the answer is "Firestone"? Also the roof is now a metallic colour as it was painted with some aluminium(?) injected paint to reflect heat from the sun?

The roof itself looks the business and I have no issues with it... it is slightly sloped now so all water runs off into 2 downpipes. I just don't know what I might be able to use on the parapets myself.

I believe the flat part of the parapet and the vertical part were not done. Your other questions (coping stones and bed joints) I just don't understand, sorry.

cAtLeYx · 17 Nov 2015

Do you have any signs of water ingress?

^woody^ · 17 Nov 2015

I'm confused by "flat parapets holding water".

What does that mean?

dpm_dpmartin · 17 Nov 2015

^woody^ said:
I'm confused by "flat parapets holding water".

What does that mean?

The parapet, I'd figured, was the bit sticking out from the roof and this is shaped like an L... so there's a vertical bit and a horizontal bit - the horizontal bit is, well, horizontal and appears to have no incline, however shallow, therefore water landing on it can just sit there... doing naughty stuff.

cAtLeYx · 17 Nov 2015

Assumed coping stones

ree · 17 Nov 2015

Why dont you post pics of your situation? Pics from inside the parapet and from outside.

FWIW: the drawing above is wrong:

1. what are called "flashings" are actually DPC's and:

2. the copings dont protrude beyond the face of the brickwork and:

3. the copings need throatings.

dpm_dpmartin · 17 Nov 2015

I didn't want to go out on the roof, just yet, but I've just taken this picture... does it help?

ree · 17 Nov 2015

Thanks for the pic but its difficult to give much of any advice on the strength of it.

If you stand further back away from the house and take some pics it might help a bit but, as above, pics at parapet and roof height are needed to give more informed suggestions.

"This black bit is vertical" area seems to show a coping stone with a good projection beyond the render - but i'm only guessing

dpm_dpmartin · 17 Nov 2015

P.S. - I can happily, and safely, lean over the top wall when on the roof to reach the horizontal top of the big sticky-out bit below.

ree · 17 Nov 2015

Fine but like you say, do it safely, at the end of the day its only bricks and mortar. I drum into apprentices: "You are in the building trade/construction not the circus"

dpm_dpmartin · 17 Nov 2015

Well, yes, I guess I can get up on the roof later on... I'm just working from home at the moment, so I don't want to skive for too long.

But, I guess my question is simply this... let's take it that I have a parapet thing going all around my house and there is a flat horizontal bit that sticks out about 2 feet or so... it's all made of concrete... what product would be good to use, that I can apply with a brush, to give it a bit of winter protection until sometime in 2016 when I can get the professionals back in?

dpm_dpmartin · 17 Nov 2015

ree said:
Fine but like you say, do it safely, at the end of the day its only bricks and mortar. I drum into apprentices: "You are in the building trade/construction not the circus"

I will. I will be safe because the roof has a ridge about thigh-high running all the way around, I can get on my knees, lean over that and reach the flat horizontal bit no problem...no unnatural stretching or anything like that.

ree · 17 Nov 2015

You dont have any ongoing difficulties with damp so if i were you i should leave well alone until if and when the parapet needs attention.
Pics would enable a judgement to be made about the current condition and any future possibilities of water penetration.

To really answer your question - my answer is that i have no faith in water sealers or water proofing liquids, and think that they might muddy the waters in the long run. If your parapet is rendered both sides then i think sealers are useless on render.

Thompsons water sealer seems to be the most referred to on here.

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What product can I use myself on a flat concrete roof?

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