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Old 04-11-2010, 11:11 PM  
slootwater
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Default problem painting porch

Hi,

I am about to repaint my (non-enclosed) porch. The top coat is latex floor paint right now (did not do this myself, done by previous owners). It flakes kind a bit, since the porch is open on 3 sides and exposed to rain.

I am debating what the best way is to paint the porch. My original plan was to sand it down completely, and put an oil based floor paint on it.

However, the house is from 1910 and there are 4--5 layers of paint on the
porch already. Although the lead paint test kit was negative, I don't trust it. The bottom 2 layers are so hard to remove, I'm kind of convinced it is lead paint anyway.

So, sanding won't work. I scraped the worst loose paint this afternoon, wondering what to do next.

I want to avoid just putting another layer of latex floor paint on it: it will
flake within 2 years and 3 years from now I'll be painting it again.

The hardware store advised me to put deck stain over the paint. I don't
believe this can work though. Paint covers wood and stain penetrates it, right? If it has been covered already, how can the stain still do anything?
Any thoughts on this?

Alternative: put oil-based primer on it, then oil-based floor paint? Or even just oil-based floor paint and no primer?

Thanks for any input!



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Old 04-12-2010, 06:07 PM  
Cork-Guy
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You "can" stain a painted deck, just it takes a lot of preparation and won't look anything like it would if it was bare wood. You can use a chemical stripper to remove all the old paint, plus this gives you a lot more control and prevents you from breathing in lead particles. Even with a chemical stripper you should wear safety goggles and some sort of respirator.



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Old 04-12-2010, 06:18 PM  
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Originally Posted by slootwater View Post
I am debating what the best way is to paint the porch. My original plan was to sand it down completely, and put an oil based floor paint on it.
No, to provide good durability on a floor, every paint company will use it's hardest drying paint as it's floor paint. The problem is that wood outdoors swells and shrinks with seasonal changes in temperature and relative humidity, and the harder a paint is the less elasticity it has to accomodate dimensional changes in wood. Thus, using an interior alkyd floor paint on wood outdoors is sure to result in the paint cracking and peeling as the substrate swells and shrinks. You want to use an EXTERIOR ALKYD paint, which will dry to a harder film than a latex floor paint, but still have enough elasticity to accomodate the range of dimensional change exhibited by wood outdoors.

Quote:
However, the house is from 1910 and there are 4--5 layers of paint on the porch already. Although the lead paint test kit was negative, I don't trust it. The bottom 2 layers are so hard to remove, I'm kind of convinced it is lead paint anyway.

So, sanding won't work. I scraped the worst loose paint this afternoon, wondering what to do next.
What I would do is:

1. Buy a few gallons of xylene, which will dissolve the latex paint, but not the old oil based paint, which is probably an exterior oil based paint anyhow. Use the xylene and some rags or paper towels to remove the top layer(s) of latex paint(s).

2. Now, clean the remaining paint use a fairly strong solution of TSP in water. You should be aware that the primary purpose of cleaning walls with TSP prior to painting is the etch the gloss of the existing paint, thereby roughening the surface of the existing paint, thereby increasing the surface area of contact, and thereby improving the adhesion of the new paint to the old. TSP works well in this regard on the old linseed oil based paints, not as well on modern alkyd paints, and doesn't do squat to latex paints. So, if cleaning with TSP doesn't etch the gloss of your porch floor paint, it's likely to be a modern alkyd, in which case you want to avoid inhaling lead paint dust, so that means sand the surface of the old paint down while it's wet and vaccuuming up the dirty water with a wet/dry vaccuum cleaner or allowing the floor to dry and painting over it with an exterior alkyd primer. (alkyd doesn't actually mean "oil based", but I'm saying to use a modern oil based primer if you have to prime)

3. There is absolutely no point in priming after sanding since primer increases paint adhesion by providing a rough surface, and that you already have. You might want to prime with a tinted primer only if you intend to change the colour of the porch floor.

4. Now paint with an EXTERIOR ALKYD paint.

That will give you the most durable paint you can use on wood outdoors because it'll be as hard a you can tolerate without being so hard that it cracks and peels instead of stretching.

Quote:
I want to avoid just putting another layer of latex floor paint on it: it will
flake within 2 years and 3 years from now I'll be painting it again.
Latex paints (even cross linking acrylics as are used for latex floor paints) simply aren't durable enough to stand up well on a floor.

Quote:
The hardware store advised me to put deck stain over the paint. I don't believe this can work though. Paint covers wood and stain penetrates it, right? If it has been covered already, how can the stain still do anything?
He probably meant to strip the paint off and use a deck stain on your porch. Paint is the most misunderstood or poorly understood technology in the entire home center. If you want to learn more about latex paints, then spend some time at the Paint Quality Institute's web site. Unfortunately, there is no comparable web site for oil based, alkyd or alkyd based polyurethane paints.

http://www.paintquality.com
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Old 04-14-2010, 08:02 AM  
slootwater
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Thanks for the advice!

I'll give the xylene a go over the weekend. I think there are only 2 layers
of latex on there, so that shouldn't be too bad (I hope).

The Ace sells an exterior alkyd floor paint, that was the paint I wanted
to try.

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Old 04-17-2010, 12:06 PM  
slootwater
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An update on the porch:

I tried the xylene this morning. After scrubbing for an hour or so, I stripped about 10 square inches. Yeah, ehm, I do understand it will take time, but with a 400 sq ft
porch this will take forever. . .

I was wondering if I'm doing something wrong. How does one use xylene? I just put it on the porch and scrubbed with a rag and a putty knife.

I `soaked' a small piece of the porch with xylene now and I'll try again in a few hours. Perhaps it needs some time to do its thing.

Any advice?

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Old 04-17-2010, 01:52 PM  
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Quote:
Originally Posted by slootwater View Post
An update on the porch:
I tried the xylene this morning. After scrubbing for an hour or so, I stripped about 10 square inches. Yeah, ehm, I do understand it will take time, but with a 400 sq ft porch this will take forever. . .
Well, you've just proven that you no longer have any remaining latex paint on your porch. Xylene will remove latex paint quickly. I think what you're doing is removing oil based paint with the xylene.

Quote:
I was wondering if I'm doing something wrong. How does one use xylene? I just put it on the porch and scrubbed with a rag and a putty knife.
When I use xylene to remove latex paint from kitchen cupboards that were previously painted with oil based paint I:
1. pour a bit of xylene on the cupboard with a squirt bottle
2. rub the xylene with my hand for less than a minute until the latex paint dissolves in the xylene, and
3. wipe up the dissolved latex paint with paper towels.


Quote:
I `soaked' a small piece of the porch with xylene now and I'll try again in a few hours. Perhaps it needs some time to do its thing.
My question is: Are you sure the paint you are trying to remove with the xylene is latex paint? If you just want to get whatever it is off your porch, you can always use a paint stripper, but you don't need to remove the old exterior oil based paint.

I think you're trying to remove old exterior oil based paint with the xylene, and that's why it's not working.

I regularily use xylene to remove latex paint from oil based paint. The latex paints used for floor are a bit different; they crosslink to form a harder and more durable paint than a wall paint. I didn't think that would matter as my understanding is that xylene dissolves the plastic the paint is made of, so it wouldn't matter whether it was crosslinked or not.

Please advise me if you are SURE the paint you are trying to remove is a latex paint. You can also test for paint chemistry with acetone. Acetone dissolves latex paints much faster than oil based paints. Acetone is typically the principle ingredient in nail polish removers. If you find that nail polish remover is slow to remove the paint you're trying to remove with xylene, then I think you're trying to remove oil based paint.
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Old 04-17-2010, 03:11 PM  
slootwater
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> Well, you've just proven that you no longer have any remaining latex
> paint on your porch. Xylene will remove latex paint quickly. I think what
> you're doing is removing oil based paint with the xylene.

You could be right. Even after a few hours, the xylene didn't do that much.
Acetone didn't do much on the paint in 5 minutes, so that would lead you
to think that it is oil-based after all.

My reasons for thinking it was latex was the flaking in spots where it got
really wet (not much flaking where it remained dry-ish) and the way I
could peel off a few pieces. Perhaps I was completely wrong, should have
thought of the acetone myself!

The status of the porch is as follows at the moment: the worst flaky parts
have been scraped with a putty knife. There are a few areas that look like
`scabs'. I couldn't do much with a putty there, but the xylene has some
effect there. If I put some on it, then I can do a lot with a putty
knife.

Would my best plan be to try and smoothen the scabby parts with the
xylene/putty knife, clean everything thoroughly and just paint with
exterior alkyd paint?

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Old 04-17-2010, 03:43 PM  
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Quote:
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You could be right. Even after a few hours, the xylene didn't do that much. Acetone didn't do much on the paint in 5 minutes, so that would lead you to think that it is oil-based after all.
If xylene didn't cut through it in a few seconds, it's an oil based paint. Acetone is used as nail polish remover because the better quality nail polishes are acrylic formulations similar to good quality latex paints. Acetone will cut through any latex paint in a few seconds, and will also cut through oil based paints.

Quote:
My reasons for thinking it was latex was the flaking in spots where it got really wet (not much flaking where it remained dry-ish) and the way I
could peel off a few pieces.
ANY paint will peel off a substrate that gets wet. The pressure created by the evaporating water will even cause epoxy paints applied to concrete floors to crack and peel. The way to tell if peeling paint is latex or oil based is that latex paints remain flexible, so you'll be able to bend and twist the flakes of latex paint that peel off. Oil based paints dry to a harder and more rigid film that will normally break before it bends very far.

Quote:
Would my best plan be to try and smoothen the scabby parts with the xylene/putty knife, clean everything thoroughly and just paint with
exterior alkyd paint?
I would apply the xylene to the rough spots and SCRAPE them smooth with a SHARP paint scraper. I would use one of those paint scrapers with the replaceable tungsten carbide blades because the xylene would probably dissolve the paint on a less expensive paint scraper. I believe that would work better than trying to smooth those areas with a putty knife. Then, I'd clean up with xylene and give the xylene 24 hours to evaporate. Xylene evaporates completely without leaving any residue, so you won't have to remove the xylene.

If what you have left is oil based paint, my next step would be to clean the paint ONLY with a strong solution of TSP to etch the paint. You should see a dulling of the gloss fairly quickly, so if the TSP isn't doing much good in dulling the gloss, the alternative would be to sand the paint to roughen it. Since there may be lead in this paint, you'd want to wet-sand to prevent the formation of airborne dust.

Once you have roughened the surface of the paint, I'd prime the bare wood areas only with an exterior alkyd primer. Then paint over everything with an exterior alkyd paint. Give the primer several hours to dry before painting over it, and give the paint a day or two to dry before walking on it. Both the primer and paint will continue to harden with time, but they effectively be fully cured within 30 days.

For a smoother finish, you might want to add some mineral spirits to your primer and your paint. By adding mineral spirits, you slow the drying time of the paint, but that also allows more time for the paint to self level better. This is important when you're painting with a brush, but is of less importance when painting with a roller because rollers tend to apply the paint smoother to begin with.

I'll check this thread every couple of hours so that if you run into problems I can respond.
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Old 04-24-2010, 10:13 AM  
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I cleaned with TSP last night, the porch is drying now. I hope to prime to bare wood tomorrow.

It will probably be next weekend before I can paint. [ This is a project for the weekends! ] I have one question left I guess: the paint. The Ace sells an interior/exterior alkyd floor paint. Would that be better/worse than a regular exterior alkyd paint? The fact that it is `interior/exterior' worries be a bit. Usually, is a product is marketed to `do both well', it actually does neither. . .

Again thanks for all the help and advice!

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Old 04-24-2010, 11:44 AM  
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Did cleaning with TSP result in the floor looking duller (less glossy) in the non-traffic areas?

Also, you need to rinse off that TSP well before painting.

Regarding the choice of paint...

I would check with Ace that this product is intended for use over WOOD floors outdoors.

As explained previously, you need a hard paint to provide good service on a working surface like a floor. However, the harder the paint, the less elasticity it has, and that's critically important for wood outdoors.

Wood located outdoors expands and contracts due the changes in it's moisture content arising from seasonal changes in temperature and relative humidity. Consequently, to paint a wood floor on an outdoor porch, you can't use an interior floor paint or a hardwood polyurethane. Both would dry too hard to stretch to accomodate wood movement. (You COULD use an interior oil based floor paint or a hardwood floor polyurethane on a concrete or steel floor outdoors because neither will expand or contract sufficiently due to temperature changes for even these hard paints to crack and peel.) However, wood swells and shrinks WAY WAY WAY more from changes in it's moisture content than it (or anything else) does due to thermal expansion. For a wood floor outdoors, you need the hardest paint you can get that will still be soft and elastic enough to stretch to accomodate the swelling and shrinking of the wood.

So, I agree with your assessment and resulting confusion. Indoors, you don't want to use an exterior oil based paint cuz an interior oil based paint will dry harder and provide better service. Outdoors you don't want to use an interior oil based paint because it will crack and peel off because it can't stretch with the wood.

I would phone ACE customer service 1-800 phone number, explain the problem and ask if this interior/exterior alkyd floor paint is intended for WOOD floors OUTDOORS. If you get any hemming and hawing, the person at the other end probably simply doesn't know enough about paint to understand the issue, and in that case they're libel to tell you anything just to get rid of you. (They're not getting paid enough to deal with the stress of important questions.) If that happens, I'd just go with any exterior alkyd paint to play it safe.

You might want to consider adding traction grit to your paint to make it less slippery when wet.



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