Dum Dum Around heater core cover on engine side of firewall

[Joe M.]

I understand that I need to apply black dum dum in the gap between the firewall and the heater core cover. I know where to purchase gray dum dum, but where can I purchase black dum dum?

[Mike M.]

Re: Dum Dum Around heater core cover on engine side of firewall

the original black sealant was of the consistency of common roofing tar and it was very non-maleable as it aged. most restored c-1s i've judged over the years substitute a soft, maleable silicone type sealant substitute . i know of no product that is of the consistency/density of the sealant gm used in the c-1 era. mike

[Joe M.]

Re: Dum Dum Around heater core cover on engine side of firewall

That sounds like the same black tar-like material I see around the steering column gasket on the engine side of the firewall.

[Dan P.]

Re: Dum Dum Around heater core cover on engine side of firewall

3M made black years ago . They may have stoped making it .Check with a paint store

[Ian G.]

Re: Dum Dum Around heater core cover on engine side of firewall

What about roofing sealant for shingles? It's tar-based black and has that gritty consistency....

[Donald H.]

Re: Dum Dum Around heater core cover on engine side of firewall

Joe,

What I thought was typically referred to as dum-dum is the 3M strip caulk and it is still black. I bought a box of it recently from an auto paint supply store. For the thinner stuff that Doc refers to, there was an article in the Spring 2011 Restorer with a formula for making the thinner tar like stuff. I did mix up some and it worked very good. There are two ingredients, DAP Asphalt Sealant (black in the typical tube) and a primarily Naptha based wax and grease remover. I could not find the USC brand of was and grease remover that the author used, so I used PPG DX330 which is also mostly Naptha. I got the PPG DX330 from the same auto paint supply store.

Mixed to a consistency that you can use a plastic squeeze bottle to apply (like a ketchup or mustard condiment bottle). I used it in a couple of areas and it worked very good.

[Donald H.]

Re: Dum Dum Around heater core cover on engine side of firewall

Joe,

By the way, where did you get the input that you needed to use a sealant on the heater housing? I did not on mine since there are no notations in the 60 AIM in the heater sections (101) to indicate that a sealant is to be used.

Thanks,

Don

[Joe M.]

Re: Dum Dum Around heater core cover on engine side of firewall

You are correct about dum dum; either gray rope caulking or the 3M black black, 12" long strips. I have never seen the black strips.

Lone Star Regional last fall - judge stated that the foam gasket was not correct and that it was "missing dum dum." It was on the Chassis judging sheet, No. 19.

Donald, do you think the thinner sealant will hold up and not melt so close to the exhaust manifold and motor in general?

[Joe M.]

Re: Dum Dum Around heater core cover on engine side of firewall

Donald, is the DAP Asphalt Filler & Sealer by itself too thick without mixing it with wax and grease remover? Based on a little research, the wax/grease remover appears to be a mixture of solvents. I will probably transfer the sealant into one of the bags that cake decorators use to apply cake icing so that I can get it into tight places around the heater core cover.

[Donald H.]

Re: Dum Dum Around heater core cover on engine side of firewall

You are correct about dum dum; either gray rope caulking or the 3M black black, 12" long strips. I have never seen the black strips.

Lone Star Regional last fall - judge stated that the foam gasket was not correct and that it was "missing dum dum." It was on the Chassis judging sheet, No. 19.

Donald, do you think the thinner sealant will hold up and not melt so close to the exhaust manifold and motor in general?

I got the Dap stuff at Lowes, Home Depot has a different brand. It is pretty thick, but for what you are doing it should work. The Restorer article was trying to make it run a little after application to replicate what came from the factory around grommets and such on the engine side of the
firewall

[Joe M.]

Re: Dum Dum Around heater core cover on engine side of firewall

Thanks Donald. I will try to use the DAP product as is. If it is too thick to use, I will mix acetone or MEK to thin it a little. I will try to apply it with a caulking gun first, but if I can't get into the crevasses, will use a cake icing bag to squeeze the DAP into the tight places.

[Donald H.]

Re: Dum Dum Around heater core cover on engine side of firewall

How bout posting your results. I guess I need to pull mine back apart and do the same. Every time I think I have something finished I have to redo it. I may just used the strip caulk dum-dum as I got a fairly large box.

Were the judges specific about what they expect to see, or just that it needs to be a black sealer versus the foam gasket?

Don

[Dennis C.]

Re: Dum Dum Around heater core cover on engine side of firewall

Joe,

Use the black 3M strip caulk. It is available from auto body suppliers, Paragon, and I think Corvette Central.

Dennis

[Ian G.]

Re: Dum Dum Around heater core cover on engine side of firewall

I can tell you mine had the gritty tar stuff sealing the heater box area both sides and at the heater hose holes and it was thin enough when applied at the factory, that it dribbled down in a line for a good couple inches...

[Joe M.]

Re: Dum Dum Around heater core cover on engine side of firewall

Judge wrote 2 words on the judging sheet, "Missing dum dum". I purchased a tube of DAP Asphalt Sealant and if it does not firm up so that it can be touches without getting asphalt all over everything, I won't use it. I spread out a test bead on a piece of wood and will leave it out in the sun on Wednesday to see if it hardens up any. If the test remains a sticky mess for days, I will purchase a package of black dum dum for $25. I have never run across it.