Ammonia/water wash before varnish ? WHY

Welcome to the new Bear Mountain Builders Forum - an interactive internet service we provide to encourage communication between canoe and kayak builders
Post Reply
User avatar
HighPlainsDrifter
Posts: 70
Joined: Tue Mar 22, 2011 9:30 pm
Location: Brookings, SD USA

Ammonia/water wash before varnish ? WHY

Post by HighPlainsDrifter » Wed Apr 27, 2011 9:14 pm

I have my can of Z-Spar Flagship before me, and the instructions for bare wood that has been epoxied read:

"must be throughly scrubbed with an ammonia/water solution then sanded with 120 grit and solvent cleaned prior to varnishing".

Obviously I am near ready to varnish. I have used Systems III SilverTip laminating resin. I have epoxied my bare wood components. The instructions say nothing about prep of epoxy fiberglass, but make a point about wood covered in epoxy.

So the questions:
1) what function does ammonia play in surface prep?
2) why is bare wood with epoxy singled out for special attention with ammonia wash?
3) instructions say nothing about concentration of ammonia wash ! What mix do I use?

User avatar
Glen Smith
Posts: 3719
Joined: Sat May 08, 2004 9:08 am
Location: Baie-St-Paul, Quebec, Canada

Re: Ammonia/water wash before varnish ? WHY

Post by Glen Smith » Wed Apr 27, 2011 9:40 pm

Some companies recommend an ammonia wash to eliminate any "blush" on the epoxy surface. Silvertip does not blush so you should skip this step.

Between final sanding and varnishing I clean with shop-vac then warm water and a cloth. Final cleaning is done with a tack cloth.

User avatar
HighPlainsDrifter
Posts: 70
Joined: Tue Mar 22, 2011 9:30 pm
Location: Brookings, SD USA

Re: Ammonia/water wash before varnish ? WHY

Post by HighPlainsDrifter » Wed Apr 27, 2011 10:48 pm

Thank you

That makes perfect sense...... I think. The Systems III Epoxy Book, briefly said that some alkyd one part varnishes may not properly dry on resin coatings. (Z-SPAR is an alkyd polymer) They indicated that free unreacted amine in the epoxy coating interferes with the action of the driers.....

So it is the amines that cause blush (I think). SilverTip is blush free. That is good :wink

User avatar
Glen Smith
Posts: 3719
Joined: Sat May 08, 2004 9:08 am
Location: Baie-St-Paul, Quebec, Canada

Re: Ammonia/water wash before varnish ? WHY

Post by Glen Smith » Wed Apr 27, 2011 10:55 pm

Right on! The real name of "blush" is "amine blush". Actually it is water soluble and ammonia is not necessary. just warm water and a clean rag. Then the surface should be wiped dry using paper towels to remove any blush that resisted the washing.

AlanWS
Posts: 209
Joined: Thu Mar 17, 2005 4:30 pm
Location: Shorewood, WI

Re: Ammonia/water wash before varnish ? WHY

Post by AlanWS » Thu Apr 28, 2011 9:33 am

The ammonia wash is a good idea if you have blush. The reason is that epoxy hardeners are amines, which are basic. Exposure to water and CO2 can convert them to their bicarbonate salts, which are water soluble if small enough molecules. This part you can wash away with plain water. But some of the amines could be incorporated into the cured resin and still be partly protonated. Exposure to ammonia converts these back into the basic amine form, negating the need to wash them away, though you do need to rinse to get rid of the protonated ammonia.
Alan

sedges
Posts: 291
Joined: Fri Jul 09, 2004 5:37 pm
Location: georgia

careful about ammonia used

Post by sedges » Thu Apr 28, 2011 11:51 pm

I have used an ammonia wash for decades-long before "blush-free" epoxies. I still do it. I believe it chemically improves the surface for other finishes.

Be careful to use a pure ammonia in your solution. There are many cleaning ammonia products that have detergents in the mix and you do not want to use those.

Post Reply