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anupkat 12-06-2012 08:34 PM

Patching a flat roof with existing coating
I recently purchased a 40 yr old house which has a flat roof. During the last few rainy days I saw some large puddles collected on the roof. I want to fill these puddles so that they dry off quickly.

My roof already has a silver coating but I don't know what kind of coating it is?

Does anyone has any idea if I can add some elastomeric coating on top of the existing silver coating or do I have peel off the existing coating first? Also any suggestion to reduce puddle sizes?


bigfishcatcher3 12-07-2012 06:38 AM

You can go right over that old coating. The only way to eliminate the puddles is to build up the low spots and roof over them. Depending on how bad it is you might be able to get away with some plywood. If need be you can get tapered roof insulation from a local supplier and have them show you how to cut and install a diamond from the insulation board. Hope this helped

jagans 12-07-2012 07:18 AM

Leave it alone
This is not the time to worry about it. The time to address slope is when you are putting a new roof on. The coating you have is probably an aluminum roof coating. This is an asphaltic based product with aluminum flakes in it. You can buy this at any commercial roofing supply outlet. Bulldog has always been a pretty good one. Pressure wash to old coating while soft brooming to remove flaked off stuff. Let dry thoroughly and re-coat If the ponding only amounts to small puddles, it will evaporate, and is not much to worry about. If it is severe, then it could very well be a structural problem, and installing an additional drain might be advised. Send Pictures.

1985gt 12-07-2012 12:14 PM

I wouldn't go over any alumacoat with anything but alumacoat. A number of people make it but they are not all the same, some have more aluminum and there is also fibered and nonfibered. Coating should be reapplied every 5-10 years depending on weather conditions and slope of the roof. If the roof is in good shape re coat it. If it's in poor shape recoating it is a waste of money and it's time to replace. Products in a bucket are not a cure all for roofing. In this case it's for reflectivity but more importantly its so the asphalt doesn't break down

jagans 12-07-2012 12:55 PM

1985 is correct
1985 GT is correct on all counts. A roof coating is to reflect heat and to prevent oxidation of the underling asphalt roof. Believe it or not, there are still fibered aluminum roof coatings that contain asbestos, so be sure to get asbestos free fibered roof coating if you use the fibered type. He is also right about the amount of aluminum flake in the coating. some have a lot, and some have a little. with all of them, constant stirring is necessary during application, and turning the new, sealed cans over for a day or two to loosen the settled aluminum is a good idea prior to use.

anupkat 12-10-2012 02:49 PM

3 Attachment(s)
Thanks Jagans, 1985Gt, Bigfishcatcher3. This weekend I patched the puddles on my roof with Henry web patch (208r) with some recommendations from Home Depot guy. I will see how it holds up in next bout of rain.

I am also posting some pictures with puddles on my roof. The guy at home depot said the existing coating is some elastomeric coating in silver color which has been discontinues since then. Now the coatings only come in white and black color. He suggested to go with elastomeric coatings only.

I personally thing it is not elastomeric coating since it is very thin and it dries off much quicker that the coating on my neighbor's roof which looks like white elatomeric coatings.

Please advise if I can reuse aluminium coating or should I go with elastomeric coating?

Thanks again,

AndyWRS 12-10-2012 05:14 PM

Back in the mid 80's we did a lot of smooth modified and coated it with a product called Silver Karnac or something like that. I am sure its something similar to that and i am sure its still available so the HD guy is full of crap as usual.

While what you did may help a very very small amount, its not the way to fix it. We get a lot of ponding flats in So Cal and HO's wanting something similar and also have leaks...but of course dont want to pay for a repitch or a new roof. Something like this we would just add a few layers to the low spots to build them up...using modified of course. You have a bandaid at best and you have made fixing it with a better solution a mess. Filling low spots with web and henrys is not really anything i would ever sugest. You cant really torch modbit over that mess now to build up the low spots.

jagans 12-10-2012 06:18 PM

Why didnt you listen
Andy is right. And by the way Andy its Karnak 169. There is a very good possibility that the light oils in that crap you put on will turn your roof to sludge. What makes you think a guy from HD knows more than the professionals that took the time to answer you on this forum? I have been in commercial roofing as a contractor and a Registered Roof Consultant for over 35 years. Oh well its your mess to deal with now. Wait till you track that goop in on your feet, you are going to be one sorry dude. Man, I hope you arent married :laughing::laughing::laughing:

AndyWRS 12-10-2012 07:05 PM

HD has the following 3 silver roof coatings available. Maybe that guy you spoke with worked in Garden, either way, you should not trust what they tell you. I gave up asking them anything, i come here and use the search function or post my question.

I am not trying to be an a$$, it comes natural unfortunately. No one here pointed you into the direction you went, best not to rush into things sometimes.

carpdad 12-10-2012 09:05 PM

I think the elastic coating sold in homedepot is worth less than nothing since it actually had damaging effect on my low slope roof (EPDM roll with cold adhesive). It also gets dirty quickly and in shades, gets mildews.

Windows on Wash 12-11-2012 08:01 AM

Be sure to read up what coatings are rated for ponding water. A majority are not rated for that.

jagans 12-11-2012 09:10 AM

The only thing that puts up with ponding for any length of time is Coal Tar Pitch. A 4 or 5 ply built up roof fabricated of tar glass felts is arguably the best low slope roof that can be installed. Coal Tar bitumen is not emulsified by water. All products based on petroleum will break down over time in the presence of water, Thats why its called "The Universal Solvent"

There are clay based emulsions based on coal tar, and these work OK in ponding, but they are no substitute for a slag surfaced, Pitch based BUR.

It is almost impossible to find anyone who will install a pitch roof anymore though, due to its carcinogenic nature.

I did a roof survey on a 5 ply pitch roof that was 50 years old, and it was still going strong, except for the flashings, which were galvanized metal base Flashings. There were no blisters or ridges and the pitch was still very active. This was a big roof, about a million sq. ft. I told the owner to simply replace the flashings, and he was good to go for another 15 years minimum. His response? " I want one of them new rubber roofs " If a man wants a green suit....................................

1985gt 12-11-2012 12:51 PM

Looks like good old fashion Aluma coating from here, I'd be hard pressed to trust anything anyone from HD tells you. Stick with a good brand of Aluma coating, I do not recall off hand if any are rated for ponding water but I doubt it. Henry's if I recall correctly has a low amount of aluminum in it, Karnak I believe has a few grades and I think you can find some with more. If you want it to last longer, you could cold app down a felt in the low areas to try and raise them up but from the few photo's I see it will likely pond some place else. You may consider spending a few extra $ and get fibered aluma coating, it will last longer also.

anupkat 12-12-2012 02:46 PM

Again, thanks for your comments and criticisms :-). Hopefully the tar will stay for this winter and then I can look for more permanent solution and a roofing contractor next year.

BTW, any suggestions for a good roofing contractors in San Francisco bay area?


jagans 12-12-2012 03:55 PM

You never said your roof was leaking, did you? you just asked if you could coat it, and you were concerned about ponding, correct? Re-roofing is an entirely different story.

For the record, in the roofing industry TAR refers to products containing coal tar bitumen. You roof is asphalt based, specifically, it is a plastic modified asphalt bitumen. Atactic Polypropylene (APP)

What I said about the product you applied was accurate. It could soften your roof and turn it to mush. Kind of like spilling fuel oil on your asphalt driveway. Hopefully it does not have too much solvent (Cutback) in it.

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