mickchipp

Hi. I'm kinda new to decking and looking for opinions on a new red cedar deck I laid two months ago. The customer wanted something different, 'rustic' looking, so I ordered mid-grade lumber (not heartwood) and let the deck weather a month or so before sealing with a clear acrylic polymer. It was just perfect by then, greyed slightly, very happy customer. I'd noticed a few tiny black specks had appeared during that few weeks, thought nothing of it but it did look like mold.. sanded off the parts I could see before sealing but two months further on there are black spots everywhere and the customer is not as happy as she was!

It did get really wet during a rainstorm while it was untreated, which I would have thought would just help the weathering process. It was two weeks drying again before treating. I wonder if anyone has any idea (a) what it might be (b) if it will get any worse, and (c) what to do about it?

Thanks.

troubleseeker

You already have your own answer, mold, or mildew, call it what you want. Two weeks was not enough time for "really wet" wood to dry before trapping the dampness under the sealer. It will continue to get worse until the sealer is removed and the wood is cleaned and allowed to thoroughly dry. Ask the paint store that supplied the sealer what you can use to remove it.

Squrtgun

And for crying out loud stop using acrylic on decks.It will look like poo in a few months and a deck restoration contractor will be cursing you and your family when he tries to remove it.
Strip the deck,neutralize with oxalic or citric acid and recoat with a clear oil basesealer(if they insist,a semi is a better choice sice it gives UV protection) when the moisture content is at or below 12%.It will gray naturally even with the clear oil based.
I will walk from a deck job if the customer tries to tell me what they want instead of trusting my knowledge on the subject.
Paint,solids acrylic,semi-acrylic and clear acrylic suck on decks.

Some of the best deck stains out there can not be bought in SW,ICI or Porter.
Look into Bakers grey away or Ready seal.Both have great color selections and are long lasting.

mickchipp

Thanks for the replies.

The acrylic was *almost* what I wanted, i.e. a non-glossy, transparent, water-based, non-toxic, odorless treatment which I thought I was a penetrating seal, rather than a varnish-type surface finish. I'm in Spain and there's precious little to choose from along these lines. I was concerned enough, once I'd started to apply it, to leave it at one coat and see what happened. It's supposed to allow the wood to 'breathe', which made me less concerned than I would have been otherwise, but I'll definitely scrape it off and start over with oil.

Do the acrylics you get there in the States claim to allow the passage of moisture? Only this is a big, exposed deck which will wash/dry much better once the winter's through and *maybe* this stuff hasn't totally sealed the wet in. I'm thinking leaving it until the Spring would make a proper restoration more feasible. Bad idea?

mickchipp

Up until now I've been taking the customer at her word that there is a worsening mold problem with the deck. I've finally been allowed to go and have a look and it's exactly the same as it was when I last saw it!

What IS different is the finish on the sun loungers I built her, the bill for which she still hasn't paid. I didn't prime these but recommended she did so. I think she used oil, but whatever it was, it has allowed a rash of black spots to develop on the upper side. Underneath and sides are clean. These are stored outside in full sun - seems strange (to me) as I'd expect mildew in shaded, damp conditions.

Anyway, it seems the real problem is she has issues with one of my outstanding bills, which is much easier to fix than stripping the whole deck! I'm obviously quite relieved but still a little concerned as to why this wood should be allowing the development of such ugly marks.

Is it ok to post some pics here? If it would help, I have some good close-ups of the problem.

PressurePros

The key to any coatings job is prep. Allowing wood to gray before you seal it is a bad idea in general. Cedar is a particularly tough one because of its soft nature it holds moisture as well as has high level of extractive bleed in the sapwood varieties.

I agree with Scott on the acrylics. You are going to have a Behr of a time getting that off. (Sorry, couldn't resist)

In my signature is a link to products I sell to DIY'ers for wood prep. I detailed proper prep, pH balancing and sealings chemistry in there. Make sure you read the FAQ and Newsletters sections. The verbage is broken down into homeonwer terminology but it will give you a stronger understanding of how to make an exterior finish last.

__________________
Ken Fenner
Pressure Washing PA
Ipe Deck Cleaning
Cleaning Contractors