Expert: Daniel Humphrey - 5/25/2010

Question
QUESTION: Hi,

I am building an art studio and using a/c plywood walls.  Someone put some non paintable sealant caulk at where the pieces of plywood meet when I wasn't around.  It can't be sanded or painted.  My carpenter suggested using drywall tape and compound and then sanding.  He's made some questionable judgements in the past so I decided that I had better check this out with an expert.  Can this method be used and will it be very smooth, like drywall?  Will the tape show or will it crack over time?  Do you have any other suggestions?  I am also trying to build as green as possible.  Thanks in advance.

ANSWER: Dear Shelley,

I think the silicone caulk might repel any tape, but hopefully the tape will stick at its edges and span the crack. I believe taping and painting is worth a try. Keep in mind that drywall does not hold up on plywood over the long run. If it does get unsightly in future years, you can always add another layer of plywood.

Daniel

---------- FOLLOW-UP ----------

QUESTION: Hi,

I'm confused by the answer, probably because I am so unfamiliar with building materials.

I have had all the silicone caulk removed.  Now I need to know the best way to fill the space between the pieces of plywood wall?  They are 4x8 a/c sheets that I intend to prime and paint.  I want them to look like a sheetrock wall. What should I use to make the cracks between the plywood nice and smooth and not subject to cracking?  Please can you be very specific because when it comes to building materials I'm a bit retarded.

Thank you.

ANSWER: Dear Shelly,

I'll summarize here in steps.

Step 1: Sand where the silicone was around the edges to remove any silicone film.

Step 2: Prime the plywood with an oil base wood primer. This will be a bit smelly but will dry quickly and air out.

Step 3: Caulk the seams with one of the caulking products I linked. I recommend Alex Plus from DAP, or acoustical sealant from Sheetrock Brand.

Step 4. Have a buider tape and sand the joints and do a drywall skim float over any uneven areas on the sheetrock. This will be a minimum of two coats, but request three.

Step 5: Sand any uneven edges. Use white spackle to fill any low spots your drywall taper may have missed.

Step 6: Caulk and smooth any nail holes or tiny spots you notice with white Alex Plus or white Polyseamseal.

Step 7: Paint with a water based, low VOC white paint that is easily matched.


Hope this helps. I've enjoyed the challenge of your requests!

Daniel



---------- FOLLOW-UP ----------

QUESTION: Hi Daniel,

Now I'm really confused!  I am not talking about sheetrock.  I'm talking about a/c plywood.  What do you mean that sheetrock doesn't hold up over time on plywood?  Please advise on this as now with all the confusion I'm considering going the extra money and putting sheetrock over plywood to save myself grief.  Now after reading your email...I may be asking for expensive grief!

I've removed the silicone from the a/c plywood seams (walls) and want to know what do I put into and on the seams that will be water base and breath with the wood.  Thank you.

Answer
Dear Shelley,

I'm totally with you. You have some A/C plywood that you want to look like sheetrock and hang pictures on in a studio. You also want to be able to move pictures around and fill nail holes. The seven steps above will give you that surface.

OK.

Sheetrock is a panel made from gypsum and paper. You don't have that.

I said, "drywall does not hold up on plywood over the long run." Drywall is not sheetrock.

Drywall is what you make from tape and drywall compound. Drywall is the coating you are after with tape and mud. "Drywall" is also used as a verb: to make a drywall surface from tape and gypsum compound. There are two kinds of drywall compound--setting and drying, as I explained in my earlier post. A skim coat of mud is very similar to gesso on a canvas.

Please go back and read everything I wrote in this light. All the steps are very well explained for what you need to do to get the plywood wall to look like sheetrock.

All the products I mentioned are water based except for the plywood primer. You may substitute a water based primer if you can find it.

One option you mention (which I mentioned in one of my posts) is to cover the plywood with sheetrock. Sheetrock is cheap. In the long run, it may save you labor and give you a better wall. You can drive nails through it and repair it easily. But let's dont' talk about that yet, until you understand the steps in the post immediately preceding this one.

Daniel