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Aaron Scurlock
Posted: Aug 18, 2006 11:13 PM
Ok, so here I am, looking to tear out sections of a SPF roof over wet BUR to the roof deck, and installing new to match. Existing is coated with weathered silicone and acrylic (but barely any acrylic left).

The customer wants to get on with applying a new coating over the entire roof. This will be in phases. I want to do polyurea.

Write the spec.
Melvin Chandler
Posted: Aug 19, 2006 07:59 PM
This is what I'd do but I've seen a similar spec written by an architect for a school that is a bit different...

I'd cut the old roof to the deck and build the thickness back to the old bur roof with board stock. I'd then cut the foam back on the bood bur back about 2' and scarify the foam back another 3'. Once I'm back to bur thickness, I'd cold apply mod bit and cut in (2) two way breathers per 10 squares in the wet area. Then I'd make sure everything is really clean. Prime and spray a rigid roof foam (over 2.6#) and then look at spraying the polyurea about 3+ feet beyond the silly-cone.

The arch speced installing one layer of board stock to the deck and then foaming back to foam level. I'm a CYA guy and want to make sure the old roof assembly is watertight in case something goes wrong above it.
Gerry Wagoner
Posted: Aug 20, 2006 11:04 AM
Unfortunately, nothing sticks to silicone except more silicone.
Aaron Scurlock
Posted: Aug 20, 2006 12:08 PM
Several polyu mfgs have told me that isocyanate primer over a cleaned, weathered silicone will work, but not over stuff less than ten years old.

Am I on the right track, Olger?

I understand that silicone will not even stick to newly cured silicone, correct?
Gerry Wagoner
Posted: Aug 23, 2006 10:06 PM
Silicone is an inorganic product and all other coating that we use are organic. Therein is the adhesion problem. Whomever makes a barrier primer that will allow an organic caoting to lock onto silicone will sell truckloads of it.

Techno 199 primer or Aldoprime or equal will stick pretty well to the weathered film on silicone.

Hope that helps,

Aaron Scurlock
Posted: Aug 25, 2006 08:38 AM
Would you warrant a polyurea over weathered silicone with one of those primers?
Gerry Wagoner
Posted: Aug 27, 2006 11:44 AM
Only if it was a hybrid polyurea.
Aaron Scurlock
Posted: Aug 27, 2006 12:19 PM
It is, indeed, a hybrid.

Does the urethane in it pose better adhesive proporties to the film?

Why not a pure polyurea?
Gerry Wagoner
Posted: Aug 28, 2006 05:20 PM
Pure polyurea is an awesome product, but it tends to contract slightly on a roof. This can raise the edges at times.

A hybrid is less prone to that phenomenon.


Aaron Scurlock
Posted: Aug 28, 2006 05:45 PM
Yep, you use it?

What do you think of it?
Gerry Wagoner
Posted: Sep 03, 2006 09:46 AM
Aaron Scurlock
Posted: Sep 03, 2006 10:34 AM
So now my question is...what is it about the pure polyureas that cause them to pull or curl at the edges? Is this occurring in applicatioons other than roofing? If not , then why not, if so, why so? Thanks for your replies.
Aaron Scurlock
Posted: Sep 09, 2006 09:06 AM
Gerry Wagoner
Posted: Sep 10, 2006 12:00 PM
I'm back. As to polyureas you would need to talk to the manufacturers to discover their reasons, since there are many different formulations.

Pure polyureas tend to contract slightly after curing. This is no problem on a dense substrate like concrete. Hybrids do not have this tendency.

All the best,

Aaron Scurlock
Posted: Sep 10, 2006 12:14 PM
Thanks, Olger. THis is exactly what the company told me. The adhesion is great and pure polyurea was so strong that when it cured, it pulled flshings off walls and of course roof failures ocurred. The hybrid does not do this, thus making it perfect for roofing.
Mark Baum
Posted: Sep 16, 2006 11:01 AM
If the silicone is more than 10 yrs. old, Volatile Free's VFI-1007 primer sticks well and VFI-540 aluminum works great over that to make a great system
Mark Baum
Posted: Sep 16, 2006 11:03 AM
Polyurea-Hybrid is a much better choise to pure polyureas. Volatile free's has a 10 yr track record of over 50,000,000 SQ/FT in service and are the orignal mfg of the hybrid roofing elastomer. This will go over the weathered silicone that is 10 yrs old or more with there primer. And the acrylic.
Aaron Scurlock
Posted: Sep 16, 2006 01:58 PM
Thats what I heard also.

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