# Redwood substrate



## charleymcdowell (Mar 27, 2010)

Okay this might be a question for a paint chemist. This is an exterior question because it has most prudence in this area of application i think. When preparing a surface to be primed and top coated, does the level of grit affect the adhesion of the paint. I don't know the chemical process that well but I have herd on more than one occasion that sanding "gives the paint something to bite into." So if this is applicable to bare wood application than; Is an even but rough substrate say, 80 grit better than sanding to oh say, 180? Does this not also mean that the rougher the surface the more susceptible it is to harboring small dirt particles that will break down the top coat quicker?


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## Andyman (Feb 21, 2009)

Just a light sand is usually sufficient for bite. Too much could counter act like you say as well as not look smooth finished. I'm not a scientist though.


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## Rcon (Nov 19, 2009)

Sanding to 180 is too much for a painted surface, especially an exterior one. 100 or fine sanding sponge leaves enough of a scratch pattern for paint to grab ahold of. 

The higher grits are used primarily on interior clear wood finishes where recoat windows have passed.


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## BC_Painter (Feb 14, 2010)

Personally I only need to sand something so material "bites" if it's either previously coated, especially in gloss, or EXTREMELY smooth. 

Otherwise it'll bite on it's own just fine :thumbsup:


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## tsunamicontract (May 3, 2008)

Out of curiousity, I saw no mention of redwood in the post, just the title. What is your redwood concern? Redwood is a little tighter grained than cedar but not so much that paint won't stick to it. The strong tannins in redwood is usually the issue.


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## charleymcdowell (Mar 27, 2010)

well I am painting an old redwood three lap home that has been stripped about three years prior and now the owner would like to paint the thing for the last time. I have learned that if bare redwood has been exposed for this long period of time than the surface must be sanded so that a new more reliable substrate is exposed and will take the primer better. My question pertains to the number grit I will be using on my orbital. I have always like a smooth finish but I thought I would ask the question because I would not want to sacrifice looks for integrity.


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## tsunamicontract (May 3, 2008)

Well Mr. McDowell, I would recommend some say of removing the loose wood fibers, as the resins in wood do break down over time, especially when exposed to UV. Sanding the whole thing might be a kind of tedious way to do it. Powerwashing might be much more effective but may raise the grain. You mentioned 3 lap, do you mean 3in overlap? You might be able to get away with power wash on that with redwood because it does have a tighter, tougher grain than cedar. Maybe one of those rotating brush heads would do the trick with a thorough rinse. Otherwise you could throw some 80 grit on a pole sander.


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## NCPaint1 (Aug 6, 2009)

Good good question. These situations all require different responses. How new is the wood? Is it overlapped? Is there spacing between the siding overlaps? Is the previous coating peeling?

This could potentially be a great job for you. You said the homeowner wants to paint this home one more time....to me that means "I want it done right, and I know its not going to be cheap"

Take your time with this one, do all your homework, which so far it looks like you are starting off right.

Post some pics if you can, I'd love to give a proper prep procedure, and it could be good reference for others as well.


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## charleymcdowell (Mar 27, 2010)

Thanks a lot guys. I love this forum. You guys are all serious professionals. I will definitely post some pictures but until then, a thorough description of the project: 
You were right when you said that the homeowner wants to do it right. She is a very funny lady but definitely knows the advantages of doing it right the firsts time. I am excited to do a nice job, one that will end up in my portfolio. A showpiece if you will. The House itself is probably 80-100 years old.

The siding as well was probably Kd old-growth 3 lap. By 3 Lap I mean that there is one piece of siding that looks like three pieces of rounded lap siding so the overall look of the wall is very small rounded laps. I have worked with this stuff and found it to be very delicate. By that I mean very sensitive to a pressure washer. Not to mention these old houses tend to have funny water proofing issue i.e. not like the submersible homes we are building nowadays and I don't want to be surprised with a big puddle of water in her living room. Thanks for the suggestion but I think i will leave the pressure washer at home for this one.

The condition of the siding varies. Some walls have been completely stripped, I think with some sort of abrasive, not a chemical. The Homeowner said she hired he daughters ex husband to do it but we all now what a good idea that usually turns out to be. So the house has been sitting in this state for about 3 years. The siding has no huge gaps it is all in good condition save for the esthetics of it, and the lack of paint there of. Again I will try and post some pics. I have been researching products and primers and anybody with product suggestions would be greatly appreciated.

There is a website that I have found that is called the california redwood association and they have a lot of information about finishing redwood. Their suggestion is to apply an Oil based enamel undercoater than a water based primer and then two coats of finish. They gave no reason for the primers but I am assuming that the oil primer is for tannins and the water based primer is for uv and flexibility. I don't know if tannins will be an issue because the wood is so old and dried out. Also I have heard that oil enamel undercoaters are no that flexible and so being as it is an old house that breathes a lot and that none of siding is probably back primed I am assuming that I should stay away from any rigid paint. 

Also my choice in caulking and filler has yet to be made. I know that I should stay away from any rigid fillers but I have heard a couple people say that bondo would be fine for small nail holes but I would like to be sure that those little things aren't going to pop up in 6 months to bite me in the a**. So I was thinking of using sikkaflex to fill everything. I know that it is kind of overkill but it really rubs me the wrong way when I see caulking fail. I also don't think the HO will mind if there is a tiny divot were the nail holes were if I assured her that it is the best way to fill them. 

Anyways thanks again for all the advice I will be sure to let the HO know that I got a lot of my info from some experienced fellows in the trade.:thumbsup:


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## NCPaint1 (Aug 6, 2009)

Do they want the home completely stripped? Best bet for bare wood is probably Sikkens Rubbol Siding Finish. No primer and the finish is breathable. 2 coats over bare wood.


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## charleymcdowell (Mar 27, 2010)

I think I will probably take it to bare wood in most places. I have never used sikkens before. what is it like?
Thanks for reply


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## NCPaint1 (Aug 6, 2009)

www.nam.sikkens.com/product.cfm?product_id=40&product_category=exterior

There you go


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## NCPaint1 (Aug 6, 2009)

The nice thing about the Sikkens is that you can apply it without priming. Since you dont know if the wood was back primed, sealing the exposed wood is probably not a good idea. Moisture can still get in from the back, and pop the coating off the front. The Sikkens being a breathable finish will help let moisture ass through the film resisting peeling.


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## charleymcdowell (Mar 27, 2010)

can I still caulk the seems if I use sikkens?


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## NCPaint1 (Aug 6, 2009)

Seems yes, if the boards are shimmed no. I dont know if thats the right term, but I know some siding requires spacing on the overlap. If theres a uniform gap between the overlap, dont caulk that.


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## charleymcdowell (Mar 27, 2010)

Thanks for all the info I will try and post some pics as soon a I can


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