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can you apply min-wax polyurethane over behr premium weather proofing wood stain?

I  have put several coats of Behr Premium Weather proofing wood stain on 2" x 8" pressure treated boards. My question is:  Can you apply min-wax polyurethane over behr premium weather proofing wood stain?  Will they bond together.  What preparations should I use?  Should I use a water based poly or oil base poly?

 

Thanx,

John Garden

 

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Posted 2013-09-03T20:08:32+0000  by garden48 garden48
 

Hello garden48!

 

No John, neither manufacturer recommends the combination of these products.

 

Let's break it down:

 

1) Minwax polyurethanes are, for the most part, interior only product ... their poly with exterior rating is Spar Urethane.

 

On their label, Minwax suggests Spar (and their other oil-based polys) for application only over another oil-based product.

 

2) Behr premium weather proofing wood stain is a water-based penetrating sealer that contains both stain and waterproofing.

 

On their label, Behr suggests that two coats are sufficient to protect wood and as such additional topcoats are not needed.

 

MAINTENANCE NOTE:

 

If you chose to apply a clear coat after Behr PWPWS, it would have to be a water-based clear coat rated for exterior application ... containing ultra violet light inhibitors.

 

And once the clear coat starts to fail, in a year or two, you would have to sand off the entire surface to add another coat of Behr ... penetrating sealers simply cannot absorb into the wood if you seal the surface with a clear coat.

 

TECHNICAL SERVICES SAID ...

One of my contractors inquired if we had any more cans of a particular color Minwax stain in stock.

 

When I looked, he had thirteen quarts in his cart.

 

This seemed like a lot for any stain project, so I asked and he said he had, "only finished one-third of his customer's deck and needed more than we had to complete the project."

 

Imagine the look on his face when I showed him the "Interior Only" statement on the Minwax label.

 

I called technical support and they encouraged him to finish the project but to expect that the product would wear off in less than one year ... at which time he would simply need to restain the deck with an appropriate exterior rated product.

Posted 2013-09-03T20:46:12+0000  by Pat_HD_ATL

 

Every once in awhile, I have a customer who says he wants to varnish his deck. After cringing, I advise him that it will look beautiful this year, and I will guaranttee that ti will begin peeling in the spring!

 

Stains and varnishes are two different concepts. Stains  breathe, allowing moisture which has accumulated in the deck boards to respire outward without causing the finish to fail. Unfortunately, the way decks are constructed, it is impossible to totally keep moisture from getting into the wood. There are too many lapped joints and  butt joints that can never again be sealed once the deck is put together. Further, hardly anyone seals the bottoms of the decking boards or tops of the joists before the initial assembly ( ideally, they should be)! Subsequently, water wicks up from the bottom into the wood. As decks age, deap cracks form allowing moisture DEEP into the wood. Most decks are held down with screws which have been over torqued and sit in little craters that hold water and allow it to slowly seep laterally into the grain of the wood. Suffice it to say, by springtime, in a wet climate, you will have 20% or more moisture in the decking.

 

If you now put an moisture impermeable oil or urethane varnish on the typical deck, you have trapped that moisture in the wood. Oil finishes and urethanes for all practical purposes, do not breathe! That trapped moisture WILL GET OUT. Lacking another way out, it will push the finish right off the surface of the wood, regardless of how good the initial bond was.

 

My rule of thumb is, if you can keep the wood totally dry, fine, varnish it. If you cannot keep moisture out of the wood, for goodness sake, don't put a varnish or other non- permeable finish on it!  Here the permeable, breathing exterior finishes are superior choices.

 

Most of Behr's exterior stains are acrylic base. Acrylics breathe. Tranparent and semi-tranparent oil stains also breathe. They do not form a solid, impermeable film on top of the wood, as do varnishes.

Posted 2013-09-04T01:12:11+0000  by ordjen
 
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